PDA

View Full Version : Battery monitors



Grumpy John
6th November 2014, 01:15 PM
I was told that I MUST fit a battery monitor to my van to keep track of the condition of the batteries. I was looking to fit an eLITE battery monitor (http://enerdrive.com.au/product/epro-elite-battery-monitors/), ~$340 but a real PITA to retro-fit to an existing van. The other day when I was in Carac I saw one of these (https://teambmpro.com/au/shop/battery-check.html), much easier to fit as they use bluetooth to communicate to an iPhone or iPad - no bothersome cables to run.
Has anyone used the BM Pro battery check yet?

Pearo
6th November 2014, 01:44 PM
I was told that I MUST fit a battery monitor to my van to keep track of the condition of the batteries. I was looking to fit an eLITE battery monitor (http://enerdrive.com.au/product/epro-elite-battery-monitors/), ~$340 but a real PITA to retro-fit to an existing van. The other day when I was in Carac I saw one of these (https://teambmpro.com/au/shop/battery-check.html), much easier to fit as they use bluetooth to communicate to an iPhone or iPad - no bothersome cables to run.
Has anyone used the BM Pro battery check yet?

This here will do the same job for a fraction of the price: http://www.ebay.com.au/itm/Analogue-0-30V-DC-Voltage-Needle-Panel-Meter-Voltmeter-/301202722136?pt=AU_B_I_Electrical_Test_Equipment&hash=item462114cd58

The next best thing for checking state of charge is a hydrometer.

The rest is just fluff, but hey, I do like gadgets so I still think you are onto a winner!

Grumpy John
6th November 2014, 05:04 PM
This here will do the same job for a fraction of the price: http://www.ebay.com.au/itm/Analogue-0-30V-DC-Voltage-Needle-Panel-Meter-Voltmeter-/301202722136?pt=AU_B_I_Electrical_Test_Equipment&hash=item462114cd58

The next best thing for checking state of charge is a hydrometer.

The rest is just fluff, but hey, I do like gadgets so I still think you are onto a winner!

Sorry to disagree with you Pearo, but voltage is only part of the story.
It's a bit like your speedo telling you you're going 100 K/Hr, doesn't tell you how far you can go, or how much fuel is in the tank. Also doesn't tell you the condition of your motor.

EDIT: The batteries in the van are sealed AGM deep cycle batteries, hard to use a hydrometer when the batteries are sealed .

Battery Monitoring
Critical loads require constant battery backup power in order to ensure a consistent, uninterrupted power supply. Battery banks are complex systems with many variables contributing to their reliability; by monitoring those variables, problems can be identified before they result in system failure. A battery monitoring system acts as an interface for the operator, communicating critical information on the status of the battery bank. Monitoring systems may also interact automatically with other elements of the energy system, like inverters and generators, to help protect the batteries and other equipment. Battery monitors track a variety of parameters to provide information on the health and status of the battery bank. A battery monitor connects directly with a system's battery bank and inverter/charge controller to obtain data on voltage, current and resistance within the system. Monitoring systems may also be equipped to track specific gravity, electrolyte levels and temperatures within individual cells. Typically, the monitor will display key information such as the state of charge of the battery bank, consumed amp-hours, voltage and remaining battery life. Monitors can also be programmed to issue audible alarms or control other devices automatically when problems occur.
Battery monitoring systems can play an important role in ensuring a robust and sustainable energy system. Battery banks represent a large portion of the investment necessary for solar photovoltaic and battery backup power systems, protecting that investment requires maintenance and monitoring. Institutional support and technician training are two vital aspects of system sustainability, battery monitoring can bolster both. Battery monitors help technicians by providing them critical, real-time information on battery performance. Facility managers benefit from battery monitoring by being able to track energy use more effectively.

Big Shed
6th November 2014, 07:42 PM
How are your batteries charged GJ?

If through a solar panel(s) then most of the solar controllers have battery monitoring built in to them.

That is how I keep track of my batteries even when connected to mains.

Pearo
6th November 2014, 08:05 PM
NOt sure where you are getting your info from Grumpy John, but I have been doing this stuff for a long time. on a commercial basis.

BAttery voltage is the best indication of state of charge short of testing the electrolyte with a hydrometer.

Your anaolgy re speedo is not quite correct either. A volt meter is like your fuel guage. Adding an ammeter tells you how much fuel you are using at a given point in time, think of it as a fuel flow meter similar to what you find in your trip computer. A battery monitor is just that, a trip computer for your battery.

Now I am not sure how your van is set up, or what you are using it for, but in the commercial world we size battery banks according to predictied loads and the time we want that load to run given no power or no solar charge for a set period of time. The gear we use has battery monitors, but they are far more sophisticated than anything you can buy on the consumer market. We also replace batteries on a regular basis to prevent failures.

The biggest killer of batteries is heat, overcharging and excessive discharge.

Grumpy John
6th November 2014, 08:37 PM
How are your batteries charged GJ?

If through a solar panel(s) then most of the solar controllers have battery monitoring built in to them.

That is how I keep track of my batteries even when connected to mains.

Solar, via Anderson plug and mains.

Big Shed
6th November 2014, 09:00 PM
I have a similar system and have a solar controller with battery monitor readout sitting between solar panels on roof and batteries.

Reads things like voltage of battery, %-age charged, voltage going in, temperature of battery etc.

I have seen the BM Pro, in fact saw it on another forum being discussed, and find it hard to see the value in what they want for it.

Looks like an interesting gadget though:;

There are any number of solar controllers available, some costing a small fortune. From memory I paid around the $50 mark for a 30A one and it does the job nicely for my AGM batteries.

Grumpy John
7th November 2014, 07:03 AM
Hi Fred, what brand/model is your battery monitor?

Grumpy John
7th November 2014, 07:57 AM
http://www.fridge-and-solar.net/monitor.htm

http://www.fridge-and-solar.net/monitor-tips.htm

dai sensei
7th November 2014, 12:23 PM
I got one of these John: http://www.jtsonline.com.au/12-volt-products/dual-battery-systems/battery-management/bm-1-compact-battery-monitor.html. The most important thing to monitor is the %charge, but monitoring the charge/discharge rate is very handy, so see what things actually use/charge at. It was easy to install into my existing wiring

soundman
9th November 2014, 10:34 AM
There are a lot of people out there who have very simple beliefs about batteries...for the most part they believe that a battery is like a bucket or a fuel tank......nothing could be futher than the truth.

But there are plenty who will sell to this idea and the desire to know "how much is in the tank".

A battery, in particular a lead acid battery does not carry, store or hold a fixed and consistent amount of energy over its life or on a day to day basis.

There are a great many things that can cause a battery to vary how much energy it is capable of delivering at a particular time.


Most significantly
The amount of energy you can draw from a battery depends on how fast you do it...the more current you draw the less the battery can deliver.

Temperature effects battery perormance dramaticly.....lead acid batteries perform best around 25C, changes in temperature above or below that dramatically effect every factor of battery performance.

All batteries age and dependent on usage patterns.....all factors of performance suffer with age till the battery fails.

It can also be reasonably argued that performance will vary depending on recent charge / discharge patterns...if a battery has been hammered and or not fully recharged in recent cycles or left idle for a period it may not its best.

All these variables make a complex matrix that I do not believe any monitoring system can account for.


SO, the notion that there is a battery monitor that will track remaining capacity or anything other that state of charge and current flowing that a given instant......accurately is nothing more than a salesmans dream.


It is worth measuring battery voltage, because this is all you have as a reasonable indication of battery condition or state of charge.

Some may find it helpfull to know what current is flowing in or out of the battery at a given instant

It is my view that beyond that you are wasting your time.

BUT..there are plenty that will happilly try to sell you fancy battery monitoring systems that cost many hundreds and promise much.

I do not believe they will achive any more than a good accurate voltmeter and maybe an ammeter in line with the main battery cable.

I run one of these in my 4wd http://www.jaycar.com.au/productView.asp?ID=QP5586&CATID=97&form=CAT2&SUBCATID=948#1
Curretly it sits double sided taped to the top of the switch pannel in the back.
I'm realy scratching my head as to there being any benifit to having it in the cab.....I don't think so.

and there is a matching ammeter with a remote shunt.
Altronics also stock these units.

They have recently baught out this..... http://www.jaycar.com.au/productView.asp?ID=QP5582&CATID=97&form=CAT2&SUBCATID=948#1

a similar unit bessel mounted.


Voltage does give as accurate an indication of charge as is reasonable....and you have nothing else if you are running sealed batteries.

Above all you need to know that you are not hammering your battery further and further into discharge every day and that you are bringing it up to a reasonable state of charge.
A simple voltmeter will do this.

We can argue about "fully charged" what that is and how it is determined another time.


NOW one thing you probably should consider is an undervoltage cut out.....so that if you fail to pay attention you can not discharge you battery past the point of permanent damage or no return.


OH..and dont forget the "Grey Nomad Tax", there are plenty out there selling to the 4wd and caravan market and charging well over the odds compared to similar or identical products sold in other sectors......"because the suckers will pay".

Check the marine discounters and the electronics supply stores.

I have seen things selling in the 4wd and caravan market for a great deal more than , what I expect to see in other places.

cheers

dai sensei
9th November 2014, 09:00 PM
I agree with most you say Soundman but a volt meter only measure voltage at the time. A voltage of 12.8 at 90% capacity is Ok as the voltage will drop slowly, but 12.8V at 60% capacity is dangerous for the battery as the voltage will drop far faster (eg overnight when drawing 5.5amp/hour - my fridge and cpap machine).

Pearo
9th November 2014, 09:13 PM
I agree with most you say Soundman but a volt meter only measure voltage at the time. A voltage of 12.8 at 90% capacity is Ok as the voltage will drop slowly, but 12.8V at 60% capacity is dangerous for the battery as the voltage will drop far faster (eg overnight when drawing 5.5amp/hour - my fridge and cpap machine).


You battery monitor will only do the same as a volt meter.


Think of the trip computer in your car. It figures out distance remaining based on average fuel consumption. If you start revving the engine to its redline, then you fuel consumption will detour from the average, so your trip comupter is not accurate. You battery monitor is only guessing based on average current draw.

IF you relly on fridge and CPAP, then you need to size your battery bank accordingly. If you cant carry enough batteries for solar panels to charge, you need to be able to top batteries up with a charger of some type, weather that be an altenator on your car or a battery charger connected to mains in a caravan park or a generator.

dai sensei
9th November 2014, 10:13 PM
You battery monitor will only do the same as a volt meter.


Think of the trip computer in your car. It figures out distance remaining based on average fuel consumption. If you start revving the engine to its redline, then you fuel consumption will detour from the average, so your trip computer is not accurate. You battery monitor is only guessing based on average current draw.

IF you rely on fridge and CPAP, then you need to size your battery bank accordingly. If you cant carry enough batteries for solar panels to charge, you need to be able to top batteries up with a charger of some type, weather that be an alternator on your car or a battery charger connected to mains in a caravan park or a generator.


I have enough batteries/solar/generator etc for what I need, although I would love more :rolleyes:. I have a decent voltage meter as well as the battery monitor (interesting comparing voltages displayed by both) but have the monitor to keep tabs on the battery life (ie current amp hours remaining as % of maximum for battery system). Voltage meters alone can be misleading, especially if you have various things charging/discharging your batteries ( ie you don't get a true at rest voltage reading), it will not give you state of charge.

Check out the links John gave in post 9

soundman
10th November 2014, 12:34 AM
I agree with most you say Soundman but a volt meter only measure voltage at the time. A voltage of 12.8 at 90% capacity is Ok as the voltage will drop slowly, but 12.8V at 60% capacity is dangerous for the battery as the voltage will drop far faster (eg overnight when drawing 5.5amp/hour - my fridge and cpap machine).

Sorry I don't follow

If a rested unloaded battery is reading 12.8 volts it should be 100% charged or there abouts....(agm of calcium modifed)
at 60% the same battery should be reading arround 12.5 volts.

all depending on the battery type, temperature and who's table you are using.

remember state of charge voltage readings are only valid if the battery is unloaded and rested for at least half an hour..if not more....otherwise the voltage readings are more or less meaningless.

ALL the battery monitors have the same problem....contrary to what the salesblurb will tell.....they can not analyse the battery and can only make broad estimates ...at least not those anybody can afford to have in a camper.

I know what the bahaviour of fridges are like..and many under estimate their demand..and from what I hear those cpap machines can suck pretty hard too.

cheers

dai sensei
10th November 2014, 01:28 AM
If a rested unloaded battery is reading 12.8 volts it should be 100% charged or there abouts....(agm of calcium modifed)
at 60% the same battery should be reading arround 12.5 volts...

But there is the problem, neither I nor John are going to disconnect our battery system for half an hour to see what his battery voltages are, it is a working system. There is always something running, charges charging etc, so the voltage meter alone can be misleading. You need something that will tell you at a glance, yes perhaps approximately, what the state of charge is of your system.

The other advantage of the monitoring system is that you can see what the amps charging or discharging are. No point having chargers or solar power systems if they are not working or not working properly. You cannot tell with a voltage meter only. I can also check what various components use that vary due to age/temperature etc. Hence I am able to consider my solar panels perhaps need cleaning, the fridge is getting too old etc etc.

I also look at the state of charge, consider the forecast (cloudy with rain for example so low solar charge probable etc), then decide whether I have enough left in the system (to watch TV because it is raining and I'm bored, with fan because it is hot, and knowing the fridge is working flat out etc etc), and if not enough then run my generator to bring it up.

I will argue you need a monitor to see what your system is doing, not just voltage, when you are relying on that system to provide your daily needs. I used to only have a voltage meter as advised by the manufacturer :~, but I am sure I did damage to my batteries through excessive discharge, as they do not last as long as they used to. With the additional monitor I can check if my charger/solar system is charge/overcharge my system, or if I am excessively discharging my batteries, the 2 biggest killers.

soundman
10th November 2014, 08:51 AM
I understand perfectly well that many people simply can not shut down their systems to make resting voltage measurements to establish state of charge.

And Yes an ammeter is a valuable item in getting some idea of demand and charge progress.

An accurate voltmeter used in combination with an ammeter can give a pretty fair indication of charge progress.

But none of this will achive the function of a simple fuel guage that so many desire and a number of battery monitors purport to provide.

The multitude of variations are just to complex for even sofisticated computer modeling to deal with.

And all this can be done with a simple voltmeter and ammeter and in the reigon of $100 done and dusted.

But still battery monitors promising much and priced in the hundreds of dollars sell like hot cakes.

cheers

dai sensei
10th November 2014, 09:43 AM
I tend to agree battery monitors promise a lot that they cannot provide and cost a heap. But I guess we have to agree to disagree, as I believe a voltmeter and ammeter still can't provide true state of charge easily in a working system, and the monitor is the only way I know how of giving the best estimate.

We will have to get together when I get back to discuss, including the entire rig I have these days, in around a month or so :U when I am due back

Cheers

Pearo
10th November 2014, 10:14 AM
But I guess we have to agree to disagree, as I believe a voltmeter and ammeter still can't provide true state of charge easily in a working system, and the monitor is the only way I know how of giving the best estimate.


You may disagree, but I can assure you that you are wrong. Been working with this stuff for years. Instrument fitter by trade, studied elec engineering at uni, done heaps of industrial remote solar powered instrumentation. Trust me, we know what works and what doesn't. You know what we use? Dataloggers with voltage, current and temp.

Pearo
10th November 2014, 10:28 AM
BTW, the original battery monitor you posted is a rebadged xantrex, so might pay to go price up a xantrex unit before you jump in.

I also had a look at the details of the xantrax, it does not load the battery when measuring, so I would question its usefulness at all. To get an accurate reading of SOC the measuring device needs to temporarily load up the battery.

dai sensei
10th November 2014, 11:48 AM
You may disagree, but I can assure you that you are wrong.

I am a bit confused, you say I am wrong, when what I am saying is that you need more than just a voltmeter (or voltage and ammeter meters alone). You yourself now say you need a datalogger with voltage current and temp, but isn't that what a Battery Monitor is just combined into one unit?

I am no expert and know and respect Soundman's opinion. I have the experience of basically living in my camper for the past 2 years and want to learn and understand more if I am barking up the wrong tree.

Pearo
10th November 2014, 02:00 PM
I am a bit confused, you say I am wrong, when what I am saying is that you need more than just a voltmeter (or voltage and ammeter meters alone). You yourself now say you need a datalogger with voltage current and temp, but isn't that what a Battery Monitor is just combined into one unit?

I am no expert and know and respect Soundman's opinion. I have the experience of basically living in my camper for the past 2 years and want to learn and understand more if I am barking up the wrong tree.

I did not say you need a datalogger, I said thats what we use commercially. Why? So we can track trends and preemtivly diagnose a failing battery. Guess how we determine SOC? Voltage, thats it, nothing more.

Given you use your camper on a regular basis, a simple voltmeter is more than enough. Check voltage when fridge is running or when battery is loaded and you have a good indication of how much power you have left. Once you get below about 11.5V you are damaging your battery.

As for dataloggers, you are it. If you charge your battery each day for 8 hours with a solar panel and the typical battery voltage is 13.8V you can assume the battery is charged. If after a few years, it starts only charging to 13.7V then you know something is not right and it might be time to check the battery with a hydrometer. Getting to understand what voltages to expect after certain conditions is key to understanding you battery, its life and its SoC.

soundman
10th November 2014, 04:21 PM
I know all too well that these battery threads can get a bit out of control.

On 4wd, boating and camping forums...battery threads are like sharpening threads on woodwork forums....only thing is in sharpening there are a number of different ways that work.

In the case of batteries.....the reality.... while full of uncontrolled variables, is quite simple and the number of actual viable choices is small.


Unless you have access to the electrolite to measure SG ( non sealed batteries)....the only reliable and accurate indication of state of charge is resting unladen terminal voltage....temperature compensated if you want to be fussy.

State of charge is a relativly simple concept.....it is simply an assessment of how a chemical process is proceeding in the battery.

State of charge will actually tell you reasonably little......it will tell you ( for want of a better similie) how full the tank is.

The problem is the capacity of the tank and how much can be put into and drawn from the tank varies...and the tank leaks.

then there is the added complexity that the tank that is full and contains 100 units today ( an leaks) may contain 80 or 120 units tomorrow under different conditions without having any put in or taken away.

to complicate the matter even more.....if I start with a tank that has 100 units...then draw 50 units out realy fast.......it may only have 10 units left.......however if I draw slowly on that 100 unit tank...I may get 130 units out of it .....but If I let it get much below 50% full on a regular basis the tank is damaged .

AND the complications go on.




Unless you put a battery into some sort of controlled environment to reduce the number and effects of the variables....its all beyond modeling.



what a lot of people want to know is beyond "state of charge"......but the problem is..."state of charge" is all that we have that is, at all accurate or reliable.


A simple ammeter is the next most usefull thing to a voltmeter......but again, it tells only a little and can not account for the many variables.

It CAN tell you that ya banging good charge in.....but it cant tell you how much stuck.

It can tell you how much you are drawing out.....but it cant tell you how much is left.

In conjunction with the volt meter it give an impression of how charging is proceeding.....but it is an impression not an accurate or reliable picture.

As has been mentioned there are all sorts of very expensive battery condition gadgets that produce very convincing stories about how much has been used or how much is left.

But they are so inaccurate..due to the many variables....they are near to useless.


In a non attended battery installation..particularly one with a controlled environment...they may give good indications....if the data is correctly interpreted....of the battery condition, capacity and projected life......but they are just that indications.

people so badly want batteries to be predictable and accurately quantifiable....like their petrol tank...but they just aren't and never will be.


cheers

Pearo
10th November 2014, 08:11 PM
Soundman got it.

I disagree about the unloaded measurements, but thats getting academic and probably WAY out of the realm of this topic!!


May I point out one thing. Using the fuel guage example, think about you car. Put a generic fuel guage on your tank, how does it now how full it is? You have to calibrate it to the size of the tank. Do any of these battery monitors allow you to input the battery size?

The best thing you can do to make your battery last is to:


Dont overcharge it. If its a brand name battery, get the datasheet and check the max charge voltage. Check against your various charging mechanisms. Over voltage will boil the electrolyte which is a sure fire way to kill a battery.
Dont let it go to flat. 11.5V should be the lowest you go, but if you can keep above 12V you will ensure your battery remains healthy. Excessive discharge results in sulfate build up on the electrodes which kills batteries.
Keep the electrolyte levels topped up.

dai sensei
10th November 2014, 08:59 PM
Soundman I cannot fault what you are saying, but I am not about to give up and just take the risk, I must try and get the best knowledge I can to make decisions. Hence a battery monitor is better than nothing, certainly better than a voltage meter on it own, even though it may be inaccurate. I do however ignore the hours to charge, discharge etc, only voltage/charge/SOC.

You are right about threads on this though and I feel I am beating my head against a wall :U. I have formed my own opinions through talking to many many actual camper users. Most installers that have great knowledge of installations, and fixing things when they go wrong, give little/misleading/hard to understand/crap guidance for the "working system" to avoid it failing.


I did not say you need a datalogger, I said thats what we use commercially. Why? So we can track trends and preemtivly diagnose a failing battery. ...

So we, the owners aren't allowed to want the same knowledge, ie do I have a failing battery or going to cause it to fail :?


Guess how we determine SOC? Voltage, thats it, nothing more.

Given you use your camper on a regular basis, a simple voltmeter is more than enough. Check voltage when fridge is running or when battery is loaded and you have a good indication of how much power you have left. Once you get below about 11.5V you are damaging your battery.

I am now (compared with last year :-) aware of only using voltages whilst it is under load, but with only voltage, I have no idea of if it is being charged giving a false voltage reading except at night.

Back last year when I had just a volt meter (no generator either) I was reading 12.2V and worried so used my car to charge it till I was reading what I thought was a reasonable 12.6V. I went to bed and woke up to 11.6V and I am sure damaged the battery. It is now my understanding the voltage may have been reading 12.6V but this was probably false and the SOC was probably far less than 60%. I actually have no idea and only guessing, but the voltage dropped far more than it should have overnight. I also know now a quick charge with a car will give a quick drop when under load.

Now, if my monitor says I have 60% SOC in the morning and I know it is going to be a less than perfect solar charging day, I will run the generator all morning (activating the charger in the camper) to bring it up to 90%. If I don't make that decision in the morning, I'm going to p_ss off a lot of fellow campers nearby running the generator at night if I don't get a decent solar charge.



If you charge your battery each day for 8 hours with a solar panel and the typical battery voltage is 13.8V you can assume the battery is charged. If after a few years, it starts only charging to 13.7V then you know something is not right and it might be time to check the battery with a hydrometer. Getting to understand what voltages to expect after certain conditions is key to understanding you battery, its life and its SoC.

All good useful information. I must admit when the voltage shows more than 13V I have been ignoring it as being a charging voltage and not really real, but will now take more notice.

When charging on 240V should it be the same maximums etc?

Pearo
10th November 2014, 10:00 PM
Soundman I cannot fault what you are saying, but I am not about to give up and just take the risk, I must try and get the best knowledge I can to make decisions. Hence a battery monitor is better than nothing, certainly better than a voltage meter on it own, even though it may be inaccurate. I do however ignore the hours to charge, discharge etc, only voltage/charge/SOC.

You are right about threads on this though and I feel I am beating my head against a wall :U. I have formed my own opinions through talking to many many actual camper users. Most installers that have great knowledge of installations, and fixing things when they go wrong, give little/misleading/hard to understand/crap guidance for the "working system" to avoid it failing.



So we, the owners aren't allowed to want the same knowledge, ie do I have a failing battery or going to cause it to fail :?



I am now (compared with last year :-) aware of only using voltages whilst it is under load, but with only voltage, I have no idea of if it is being charged giving a false voltage reading except at night.

Back last year when I had just a volt meter (no generator either) I was reading 12.2V and worried so used my car to charge it till I was reading what I thought was a reasonable 12.6V. I went to bed and woke up to 11.6V and I am sure damaged the battery. It is now my understanding the voltage may have been reading 12.6V but this was probably false and the SOC was probably far less than 60%. I actually have no idea and only guessing, but the voltage dropped far more than it should have overnight. I also know now a quick charge with a car will give a quick drop when under load.

Now, if my monitor says I have 60% SOC in the morning and I know it is going to be a less than perfect solar charging day, I will run the generator all morning (activating the charger in the camper) to bring it up to 90%. If I don't make that decision in the morning, I'm going to p_ss off a lot of fellow campers nearby running the generator at night if I don't get a decent solar charge.




All good useful information. I must admit when the voltage shows more than 13V I have been ignoring it as being a charging voltage and not really real, but will now take more notice.

When charging on 240V should it be the same maximums etc?

Dont get me wrong, if you want to go down the commercial path and use dataloggers you can. Rest assure, that commercial solutions cost many thousands of dollars. Check out alber or generex gear. I am sure its possible to pick up a cheap voltage and current datalogger that will do the same, and you dont need fancy software to analyse the results, excel will do just as good a job.


Ok, here in lies the big issue with loaded v unloaded voltage measurements (something you battery monitor is incapable of dealing with).

If you stick a charger on a battery and fully charge it, the voltage as measured with a voltmeter (once the charger is removed) will read about the same voltage as your charger which will be about 14V, depending on the battery chemistry and the charger. Let the battery sit for an hour or so, and this voltage will drop to about 2.15V a cell (once again, depending on chemistry), or 12.9V for a 12 volt battery. If you load the battery up straight after you remove the charger, you will read close to that 12.9V give or take a bit. In practice, the most accurate way to measure the SOC is to disconnect the battery and let is rest for an hour, but this is totally impracticable in almost all circumstance other than when you are testing a battery. These measurement will be the same regardless of how you charge it, provided the charger you are using is half decent.


At the end of the day, the battery monitor will not give up much useful info other than voltage and current. You will still need to learn how to interpolate that data and how it applies to your setup.


BTW, the last place you want to gain knowledge is from other camper users. I am not privy to any caravan or camper site, but I can only guess at the pseudoscience that gets circulated in those realms!. I would also question a lot of installers, most are just low level techs and dont have a real understanding of the physics. If you were to chose between the 2 for advice, I would go a tech as they do it every single day, just be warned that a lot of them are salesman too, trying to drive their business.



On a side note, I also test 12V battery chargers out of personal interest. I have done a few now, from supercheap chargers to CTEKS to dispel some myths. I just bought an aldi charger to see how they stack up, but I am yet to put it to the test. I basically load test them, plus check ripple and charge characteristics.

Grumpy John
14th November 2014, 01:02 PM
I've been doing some more research on the subject of battery monitoring, and it seems that a battery should be rested for at least 12 hours after charging to obtain a true reading from a volt meter, totally unacceptable in a motor home/caravan situation.

I find it difficult to believe that many RV manufactures would fit battery monitors if they did not give some sort of reliable information about the state of the house batteries. If these monitors didn't work then we would have many unhappy campers with flat or dead batteries complaining to the RV manufacturers. Furthermore I find it hard to believe that a company like Xantrex would risk their good name on an unreliable product.

More reading:

http://hobohome.com/news/?p=679

http://www.xantrex.com/documents/Accessories/LinkPro-Battery-Monitor/DS20080912_LinkPRO_LinkLITE.pdf

http://www.campertrailers.org/enerdrive_elite.htm

(http://www.campertrailers.org/enerdrive_elite.htm)http://hobohome.com/news/?p=685

soundman
14th November 2014, 02:21 PM
The first and most important thing to get past is that idea that...if someone is selling it or installing it it must be good or usefull.

The fact is that many camper or motorhome manufacturers know squat about electrics and those they have installing know even less.

The fact that many boat, caravan, camper or motorhome manufacturers install barreries in enclosed unventilated places proves that.

The fact that they also install gas bottles, housing generators and petrol containers in poorly ventlated or poorly protected places reinforces the matter.

These manufacturers are not rocket scientists at best they are coach and body builders or panel beaters...at worst they are not even qualified welders.

The majority of the caravan, camper and motorhome manufacturers are consumers and simply rely on what the salesman ( company rep) tells them or what they read on the internet.


AND let me tell you there is some hokum comming out of some of the electronics manufacturers and their representatives...even the better ones.


On the matter of measuring resting voltage......

remember this is all we have, that is realy accurate....AND.... the battery manufacturer documents and the text books will confirm this.

When a few other things are known, resting battery voltage is a pretty accurate indicator of "State Of Charge'.

Remember too that a lot of what is written by the reliable sources is for those in controlled situations looking for accuracy.

The longer the battery is rested the more accurate the state of charge can be assessed using voltage measurement.

BUT

Even after a short period of rest, voltage can be a good indicator of state of charge.
Right from the instant the battery is isolated from charge and load....the error factors begin to rapidly deminish.

After 15 minutes or half an hour of resting, a voltage measurement can give a pretty fair indication of the state of the battery.....the longer the battery is idle the more accurate the indication.

As soon as any load is applied the voltage will drop....and this drop will depend on how heavily the battery is loaded

As soon as a battery is put on charge the voltage will rise...this rise will depend on how high the charger voltage is, how much current it is capable of delivering and the state of charge of the battery.



As far as the viability of battery monitors.

My problem with them is that people take what they indicate as gospel.....and with no further thaught or observation, this leads to problems.

As for capacity settings and other "calibtarions".

Some of the better battery monitors do provide facilities to set the battery capacity and battery type and a very few, quite a bit of profiling.

Some of them may even have a fair go of making an estimate of state of charge while on charge or under load......but don't dream that it will be accurate.


Neil......I know you as an observant man with an engineering background.....I have no doubt that understanding the limitations, you will make good use of whatever instrument is provided.

But you aint the average consumer.

just remember that if the monitor is reading 60%..it may be anywhere between 40% and 80%....of whatever the battery capacity might be.




One thing that concerns me is.

That there is a lot said about batteries in general...and by some reasonable sensible and reliable people.

BUT
There is currently so much variance in batteries available.....the simple stereotypes of the past and the simple assertions are just not reliable.

Many battery chargers and monitors will have a profile for flooded batteries and another for AGM...and maybe a profile for small Sealed batteries.

A flodded battery profile will set the float voltage at arround 13.8V, the AGM float voltage at arround 14.5 volts and the small sealed battery profile will be current limited to a couple of amps.

But we now have flodded batteries that employ most of the technological advances of AGM.

SO do you charge them as an AGM or flooded.

Most of the small sealed batteries are AGM in all but name....and some will cop good hard charge rates...so we do we use the sealed battery programe or the AGM.....or the manufacturer may recommend a 13.8 volt float voltage...do we put it on the flodded cycle.

Then there is such a wide variation appart from that.
If we are to make sensible choices we realy need to know what these over simplistic selections mean, and know the specificaton of the batteries involved.

Of course lots of people simply don't want to know...they just want to know their battery is half full.

Giving them a guage that tells em what they want to know, keeps them happy......regardless if it being at all accurate or the truth.


If concrete was a variable and as vague as the lead acid battery, I don't think we would be building bridges out of it.

cheers

Grumpy John
14th November 2014, 03:47 PM
So, Soundman, are you saying that the elite battery monitor I am thinking of installing is useless? That it is not capable of giving accurate information about the condition of my battery/ies?

Blarney
14th November 2014, 05:45 PM
A flodded battery profile will set the float voltage at arround 13.8V, the AGM float voltage at arround 14.5 volts and the small sealed battery profile will be current limited to a couple of amps.Totally wrong, the float voltage of an AGM is 13.6 V. In float mode the amperage going into all batteries varies between 0.1-2 amps depending on loads at the time.

A battery monitor (the top end ones )monitor more than battery voltage if the parameters are set correctly at installation.

They measure, depending on whether or not you have solar, charging via a battery charger, generator or by vehicle alternator, amperage in and out of the batteries, percentage of amp/hours remaining and also the voltage.

They also factor in Peukerts law to account for appliance usage to give a highly accurate view of the power situation.

Granted that if you had time to sit and watch an ammeter and a volt meter and take in all parameters of a vehicle that may be in Tassy one month, the bogong high plains next month and then Darwin good onya.

Most Rver's don't understand how voltage and amps work let alone how to work it out but they do understand a meter that says you only have 25% power left in your batteries before things die, the beer gets hot and you can't pump water.

I consider them a must in all RV.

Oh yeah, I do low voltage installations and set yachts and caravans and motorhomes up for self sufficiency.

dai sensei
14th November 2014, 10:15 PM
..Most Rver's don't understand how voltage and amps work let alone how to work it out but they do understand a meter that says you only have 25% power left in your batteries before things die, the beer gets hot and you can't pump water


:whs:

Glenn.Visca
14th November 2014, 10:55 PM
On a side note, I also test 12V battery chargers out of personal interest. I have done a few now, from supercheap chargers to CTEKS to dispel some myths. I just bought an aldi charger to see how they stack up, but I am yet to put it to the test. I basically load test them, plus check ripple and charge characteristics.

Pearo,

I am the proud owner of a 1973 Capricorn van, for which I am starting to acquire components so I can install a 12vDC house system. At her age, she only came with 240vAC with a couple of 12v lights running off the car for brief lighting requirements.

Which charger would you recommend ? The common installation chosen by like minded people on the classic caravan forum appears to be CTEK.

Cheers,

Glenn

soundman
14th November 2014, 11:10 PM
Totally wrong, the float voltage of an AGM is 13.6 V. In float mode the amperage going into all batteries varies between 0.1-2 amps depending on loads at the time.

A battery monitor (the top end ones )monitor more than battery voltage if the parameters are set correctly at installation.

They measure, depending on whether or not you have solar, charging via a battery charger, generator or by vehicle alternator, amperage in and out of the batteries, percentage of amp/hours remaining and also the voltage.

They also factor in Peukerts law to account for appliance usage to give a highly accurate view of the power situation.

Granted that if you had time to sit and watch an ammeter and a volt meter and take in all parameters of a vehicle that may be in Tassy one month, the bogong high plains next month and then Darwin good onya.

Most Rver's don't understand how voltage and amps work let alone how to work it out but they do understand a meter that says you only have 25% power left in your batteries before things die, the beer gets hot and you can't pump water.

I consider them a must in all RV.

Oh yeah, I do low voltage installations and set yachts and caravans and motorhomes up for self sufficiency.

So the float voltage of AGM is "13.6 volts".......not on the spec sheets I've looked at...it aint necessarily that clearly defined.

I have probably used the terms a but loosly.

The cycle charge voltage of a non selaed battery in a motor vehicle is generally accpeted to be 13.8 volts..the cycle charge voltage of AGM and many other some other sealed batteries is accepted to be 14.5 ish volts.

as for Float voltage ( term correctly used) its pretty much the same for all lead acid technolgies 13.8 volts give or take a couple of points...
If ya want to argue this one...I'll pull up plenty spec sheets no worries.
Here is one http://www.fullriver.com/products/admin/upfile/DC105-12.pdf

BUT as I said, it is no longer possible to generalise the specifics.....because the specifications and performance of various batteries varies so considerably.



My point being......even though some of the clever battery monitors can do all sorts of modeling....the variation between battery types and brands alone brings their accuracy into question.

That is unless the battery monitor can be specifaiclly be programmed for the paramiters of a specific battery brand, model and capacity.

Charge and discharge behaviour would be very hard to model.......I could easily pull up 5 different batteries, all of similar size and capacity......the discharge behaviour may vary wildly...so these top end battery monitors...do you input battery capacity at 3 or more points on the curve like 20 hour, 10 hour and 5 hour rates.


Yeh I know the claime to factor Peukert's...but how do they account for the differing internal resistance of various batteries and the chenge of internal resistance over the life of the battery.
The internal resistance being a significant factor in the terminal voltage under load.


Then I have not yet heard on a battery monitor that can account for the variation of the battery capacity with age or usage.
such battery capacity that vary in the order of 30 to 50% over the usable life of the battery.

Or do you periodically put the battery on a carbon pile or other tester to establish its remaining AH capacity and on load behaviour.



OH of course...there are battery monitors...and ...battery monitors.

So......whatever battery monitor is being considered.....what facility is available for programming to suit the battery...and how capable is the modeling.

People are paying good money for battery monitors that have limited selection of 2 or 3 battery types, no capacity setting and no temperature probe on the battery

Highly accurate....OK what percentage accuracy do the manufacturers claim......who has confirmed this.


Without
Reasonabley comprehensive selection of battery types
A variable battery capacity setting.
a temperature probe on the battery

A battery monitor has not a hope of being anything like "accurate".

cheers

soundman
14th November 2014, 11:36 PM
So, Soundman, are you saying that the elite battery monitor I am thinking of installing is useless? That it is not capable of giving accurate information about the condition of my battery/ies?

I would not go as far as to say that it is useless.

It all depends on what you are expecting from it.

As far as this sort of thing goes, it looks to be a fair thing.

If you have $400 odd bucks to spare.

Not this little black duck.

cheers

soundman
14th November 2014, 11:50 PM
Pearo,

I am the proud owner of a 1973 Capricorn van, for which I am starting to acquire components so I can install a 12vDC house system. At her age, she only came with 240vAC with a couple of 12v lights running off the car for brief lighting requirements.

Which charger would you recommend ? The common installation chosen by like minded people on the classic caravan forum appears to be CTEK.

Cheers,

Glenn

Ctek, have a big presence in the australian RV market.....there are a lot of people out there who only know two brands..ctek and redarc.

thruth is there are a lot of very good multistange chargers out there a swathe of fair ones and a quite a few cheapies.

If you want a brand name and are not worried about the price....go buy a ctek.

If you don't want to throw you money away that easy..shop around.

here is a place to start
http://www.sidewinder.com.au/product5.html

The important thing is buying one of adequate size.

for charging alone, the typical recomendation is a little above 10% of battery amp hour capacity....if you intend to supply a load as well, that needs to be factored too.

cheers

Pearo
15th November 2014, 10:35 AM
Ctek are not as flash as most think. I am away from home for g20 so will type up a more comprehensive answer when I get home.

Sent from my GT-I9505 using Tapatalk

Pearo
16th November 2014, 01:55 PM
Most Rver's don't understand how voltage and amps work let alone how to work it out but they do understand a meter that says you only have 25% power left in your batteries before things die, the beer gets hot and you can't pump water.


And a simple voltmeter will tell you that you have 25% left.

mike48
17th November 2014, 07:58 AM
Battery State Of Charge for an RV Situation

you need -

an accurate bi-directional ammeter
an accurate voltmeter
a clock
a thermometer
constant monitoring, and,
an ongoing understanding of your particular battery's age, previous usage during lifetime, and manufacturer's charge and discharge characteristics.


You then gain "an indication" of SOC with about 90% accuracy.

From a tech with 40 years experience.

Pearo
17th November 2014, 08:23 AM
Battery State Of Charge for an RV Situation

you need -

an accurate bi-directional ammeter
an accurate voltmeter
a clock
a thermometer
constant monitoring, and,
an ongoing understanding of your particular battery's age, previous usage during lifetime, and manufacturer's charge and discharge characteristics.


You then gain "an indication" of SOC with about 90% accuracy.

From a tech with 40 years experience.

Bullocks.

From an engineer/instrument fitter with 30 years experience, with commercial/industrial where it actually matters.

This debate is circular. I am out. Buy the battery monitor and be done with it.


FWIW, I camp regularly with a 90l primus mammoth dual zone fridge. My battery monitor is a supercheap multimeter.

Pearo
17th November 2014, 08:27 AM
Pearo,

I am the proud owner of a 1973 Capricorn van, for which I am starting to acquire components so I can install a 12vDC house system. At her age, she only came with 240vAC with a couple of 12v lights running off the car for brief lighting requirements.

Which charger would you recommend ? The common installation chosen by like minded people on the classic caravan forum appears to be CTEK.

Cheers,

Glenn

I will put this up in a new thread soon. I will post up some data from the ctek that I have hear. Still a good charger.

Will also post up the aldi charger data.

My personal preference is GSL charger, but its not a smart charger and will still try and attempt to charge a battery with a dead cell(s), where as most smart chargers wont start up.

soundman
17th November 2014, 09:20 AM
Battery State Of Charge for an RV Situation

you need -

an accurate bi-directional ammeter
an accurate voltmeter
a clock
a thermometer
constant monitoring, and,
an ongoing understanding of your particular battery's age, previous usage during lifetime, and manufacturer's charge and discharge characteristics.


You then gain "an indication" of SOC with about 90% accuracy.

From a tech with 40 years experience.

I've no doubt that in theory it should be possible to establish "State Of Charge" well and truly more accuratly than 10% error.

AND in theory it should be possible to estimate capacity consumed and capacity remaining.....AT... the current rate of consumption....at least within a 10% error.

but the hard thing is obtaining the last very large chunk of information with any ease or certainty.

"an ongoing understanding of your particular battery's age, previous usage during lifetime, and manufacturer's charge and discharge characteristics."



One point that has not been raised is the whole notion of needing to know how much is left as a normal operational thing.

What we realy need to know is that we have well and truly sufficinet battery and recharge capacity to supply the load.

because the deeper the batteries are cycled the shorter their life will be.

we need not to be deep cycling batteries on a regular basis and to be recharging to full or nearly full state of charge at the earliest opportunity.

cheers

mike48
17th November 2014, 05:50 PM
Bullocks.



Gee whiz!

Hi Soundman, (inter alia),

you post some good and interesting comment.

I was merely saying that this is not an easy subject to simplify, and that there are a lot of factors involved.

Just using a voltmeter can be confusing to professionals and is definitely mystifying to beginners.
For say if the battery is almost at end of life, a voltmeter could indicate a SOC of 90%, but the actual capacity could be 90% of 30%.
So one needs to know about the previous battery life and usage etc, and its specification.
Professionally, in the aviation industry, batteries are periodically discharge tested to test capacity, even when newly installed, and normally discarded on economic grounds before end of life.

Having said all that, I myself use a voltmeter and ammeter to gauge SOC hour by hour, but I am mindful of all the other factors, day by day.

I'll stick around!

Pearo
17th November 2014, 06:08 PM
Professionally, in the aviation industry, batteries are periodically discharge tested to test capacity, even when newly installed, and normally discarded on economic grounds before end of life.


Battery testing in the aviation world is mostly company specific and is pretty rare. All pilots do is monitor bus voltage and current and look for trend changes. When you fly a type of aircraft you can pick up any subtle changes after just a few hours of flight time. In most GA aircraft, the battery is only crucial for starting and avionics, and most modern avionics have back up batteries that you load test as part of your preflight. Given you can fly a plane without either, batteries are often overlooked. Usually a battery is deemed stuffed when it wont start the aircraft, or when one has an alternator failure in flight.

mike48
17th November 2014, 06:33 PM
Hi Pearo,

I was referring to ground aviation facilities.

soundman
18th November 2014, 10:52 AM
It is interesting to see the differences in how batteries are treated and managed in "serious" applications, like commercial remote power, marine navigational aids, communications, aviation and the military...then compare that to the expactations and inevitable disapointments in the recreational market.

In the commercial and institutional market, wise engineers build certainty, by specifying more than adequate battery and recharge capacity, managing load and replacing batteries before the age related capacity reduction becomes a problem.

There may be low battery alarms and low voltage cut outs, but this whole "wanting to know how much is left" is realy considered a step too far and too late.......AND the accuracy problems are all too well understood.


The whole outlook in the recreational market seems to revolve around the absolute minimum that will do the job..and in the short term.

In general the batteries and recharge capacity is far smaller than it realy should be to guarantee certainty and long life of the batteries.

People don't want to hear that to support a well managed 40 litre compressor fridge ( run as a fridge not freezer) at least 200Ah of battery capacity and at a least 160 watts of solar capacity is required to deliver reliability, certainty and long battery service life.

If I had an extra $400 pluss installation costs to throw arround, I would be throwing it at battery or recharge capacity not an expensive battery monitor.

Only when the installation had reached a significant size and cost would I consider it viable to invest in expensive instrumentation that neither increases my run time or recharge capacity.

By that time I would probably have invested in a " battery managment system" ( battery charger/ voltage regulator) that provided those functions.

Said battery managment system would be maximising my recharge efficiency and would be providing all necessary monitoring at little or no additional cost.

cheers

Grumpy John
9th December 2014, 06:51 PM
I made the plunge and fitted the BM Pro BatteryCheck the other day. I would have preferred using the eLite but it was going to be a PITA to fit.
With apologies to Pearo and Soundman, I accept that I can monitor the battery with a voltmeter and ammeter, but the reality is that in a RV situation it is not practical to:
1. get the required equipment from the toolbox
2. unlock and open the caravan front boot
3. remove the battery covers (which is difficult at the best of times)
4. take readings
5. replace battery covers
6. close and lock boot
7. pack away tools
8. wash up
All in all probably 30 - 40 minutes (longer if it's at night and dark}. After doing this I still wouldn't know how many hours I have left in my batteries.


BatteryCheck connected to batteries.
333714


333717


Initial set up.
333722

Batteries charging via Xantrex charger on 240V.
333715

Xantrex disconnected and solar panels covered with blanket to simulate night time conditions. Current draw is because the iPod was charging through 12v circuit and the solar controller display draws some power obviously.

333727




Fridge running flat chat, 3 x 16 watt flouros, 1 outside light and fan running. After 3 1/2 hours.
333718


333719

Back on the Xantrex with all 12v turned off.
333720

NCArcher
9th December 2014, 10:36 PM
Don't forget to charge your phone GJ. :duck:

Grumpy John
17th January 2015, 12:26 PM
I've yet do do a trip in the van since the battery monitor was fitted, but I do occasionally go out to the van and turn on different appliances and watch the readings change. When charging via the solar panels it's interesting to watch the current draw and available time change as the sun goes behind cloud cover.

A very kind friend has tidied up the 12v wiring in the boot of my van so that it doesn't look a birds nest. I've had to modify the battery box covers to accommodate all the wires.

337148

337149

337150

337151

337152