Thread: Battery monitors

Originally Posted by Grumpy John

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, ~$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, 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-...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!

Originally Posted by Pearo

This here will do the same job for a fraction of the price: http://www.ebay.com.au/itm/Analogue-...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.

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.

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.

Originally Posted by Big Shed

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.

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.

Hi Fred, what brand/model is your battery monitor?

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

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

I got one of these John: http://www.jtsonline.com.au/12-volt-...y-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

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...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...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

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).

Originally Posted by dai sensei

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.

Originally Posted by Pearo

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 . 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

Originally Posted by dai sensei

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