Thread: Electronics O/T

Originally Posted by rodm

I attached a voltmeter to it last night and watched it today to see what is happening. Under 5 volts the flow is not worth worrying about. It stops under 4 volts.
Does that help or is it the same problem with different figures?
Make some suggestions if there is a simpler easier way to do it even if i don't achieve exactly what i am chasing..

Rodney

As I understand it, motors do not actually have a fixed voltage that they work at. If the current drops to small a level then there is not enough power to turn the motor, and if the current rises to too high a level then the motor starts to overheat until eventually it bursts into .... something.

Having said that, just about all motors have a little plate or some sort of indication from the manufacturer as to the conditions under which they believe it will probably survive the longest while still giving good work performance. Did yours come with any such indication?



Bob Willson

Hi Bob,
No spec on the motor. el cheapo through ebay and description was 12 volt submersible pump. The body of the motor looks like a piece of white pvc pipe and no provision for brushes so assuming it is brushless.

I though this would be an easy thing to do but obviously it isn't. It is running OK and the highest voltage I saw yesterday was 15 so might be good to leave as is. It is under water so it gets cooled by conduction and if it blows there is no chance of a fire. I have put a switch in the wiring to turn it off if needs be.

I have a much larger project using solar panels and it would have had the same application as this but I think the best way now for that is to run it through a solar regulator and battery.

To update this here is what I did.
I ended up getting 7.2a/h sealed lead acid batteries and a 12volt solar charger/regualtor. It was much simpler to do it this way and allows for after sunset use.

I have a much larger project on the go with eight 100watt panels powering a air conditioner. It may be cost effective to put that into the power grid but they only give 7cents a kw now and charge up to four times that to take it back.

In any case I am learning a lot like fusing a solar panel at the panel itself as there is no off switch.

been looking at at pelter aircon that transmits cold though a pain of glass , no need to destroy the window frame or security mesh to mount it , heat transfure paste both side of the glass , peltier's are wasteful, but an aircon in 2 parts , cold side hot side ???? swap them over in winter

Hi Ken,
Very similar idea here. The peltiers can be reverse wired to swap hot and cold so a two way switch will take care of that.

I'm using fluid transfer and intercoolers as heat exchangers. A large insulated aquarium on the return side should extend the use after sunset.

I'm using regulators off the panels.

The exchanger will sit on the window and just open the slider to get the benefit.

I am building a frame 8 metres long and over three metres high to hold the panels - tucked behind the shed and out of sight. Didn't want to take up house roof space as I will eventually have a system connected to the grid. The posts are like telegraph poles but angled at the top for our latitude. I'll post some photos as I go along.

Just finshed installing the framework for the solar panels - proper pain as the sloping top sent it off balance so ended up quick set the first post then moved along to next and it held it rigid enough to get around that problem.

The frame is tucked behind the shed and just enough room between the parapet wall and shed for the panels - The panels will be fixed over the beam so a bit closer to the boundary and they will sit over the shed roof.

The structure is 8metres long so room for a little expansion.

See photos and you can see from the yard it will not be that visible. Photo from the yard is the best view of it and normally you won't see it at all unless you move into that position.

Son helped me and he came up with a good idea to build a rack between the wall and posts to store long lengths of steel and such. You know that stuff you hold on to as it might be handy one day.

Once I start building the heat exchangers and control panel the CNC machines will be used so this might become relevant to CNC related topics.

We have earnt a beer so that's it for now.

A little more progress and some bench testing of the peltier cooling method.

I have finshed the framework and installed 12 solar panels. 8 by 80 watt and 4 by 100 watt which is about 1kw so this is a serious attempt to make it work. The larger panels will also run pumps and fans so the extra capaicty will take care of that while still being able to power a peltier. The fallback plan if this doesn't work is to grid connect the panels to the house.

See photo of nearly comlpleted framwork and only the ends to be flashed off to neaten it up. Salon cloth covers the first bay bay so that the neighbors don't have to look at the underside of the panels. A parapet wall hides the rest of the structure. I have used anti glare solar panels on the end so that from the street there is no reflection. There is a growing number of complaints about solar panels and reflected sunlight over here. I have changed to conventional panels once well out of view. The street view is minimal and probably won't be noticed unless you are looking for it.

Bench tests are very promising. See photos of a peltier being driven by one panel. I hope you like the way I have supported the panel - nothing like a sander to hold things up.

The ambient temperature was 34 degrees and as you can see the thermometers are about 20 degrees either side of that. They are measuring the hot and cold side of the heatsinks. Given this setup is not insulated I think it is a good result. It was a very overcast day so on a clear day it might kick up a bit as well. The plan is to mount the peltiers like Ken has for his mister and to insulate the cold side recirculating it through a heat exchanger (to the house) and an insulated storage tank to improve efficiency. If the storage tank works well it should be able to cool for a while after sunset. One advantage of the peltier is that if you reverse the wiring it becomes a heater. If you are wondering what a peltier is then it is what is used on the cheaper car fridges. It is also used for cooling overclocked computer chips and is a semiconductor - I had to look that up. I am not creating anything new and just adapting solar power to a different application.

If your not bored I'll post some more as it develops and pass on what I am learning.

one of the major draw backs with peltier's is the 67c max temp difference between the 2 sides (inside the ceramic , not heat sink temp), once you hit that number it go's down hill real fast

what happens when the hot side cant get rid of its heat is a sort of feed back loop to death

say the cold side is at 10c and hot is at 70 , the pelter will still be pumping all its personal heat into the heat sink , and it cant cool more than 67c on ether side of its self

as the hot side temp go's past 80 , the cold side starts to rise in temp ,staying 67c apart from the hot side , the full wattage of the peltier going to the heat sink

if the heat sink cant get rid of the heat , it will soon go past 120c and the wires will fall out of the peltier's

extra sized cooler on the hot side is a must, dont forget the ?? 60watts from the peltier is added to the heat removed from the cold side

you can double stack the peltier's to double that temp , but then you have 2x the wattage getting turned into heat + the heat removed from the cold side

they also work better when they are squashed between the heat sinks

they use about 2x as much power per watt of heat removed ,compared to a refrigerated type air-conditioner , so 1kw should make a difference to one room

using them to heat in winter ,you will have to watch the cold side doesn't drop below 0c and iceup ??/10c out side temp ??

cheers ken

Originally Posted by rodm

To update this here is what I did.
I ended up getting 7.2a/h sealed lead acid batteries and a 12volt solar charger/regualtor. It was much simpler to do it this way and allows for after sunset use.

I have a much larger project on the go with eight 100watt panels powering a air conditioner. It may be cost effective to put that into the power grid but they only give 7cents a kw now and charge up to four times that to take it back.

In any case I am learning a lot like fusing a solar panel at the panel itself as there is no off switch.

I was going to suggest using something like this
LT3652 - Power Tracking 2A Battery Charger for Solar Power - Linear Technology

but it sounds like you already have

Linear Tech do a pretty good range of power & battery management chips, so you can keep the part count low while getting what you want.

Cheers,
Gordon

Hi Rod,

I had scanned this thread before, and was mildly curious, but now the project suddenly has jumped up several orders of magnitude!... 8x80 watt and 4x100watt panels, now that's a serious amount of power, are you going 12, 24, or 48v, what sort of batteries, I assume it's powering a 240v sine wave inverter.. Selectronic make nice inverters if that's the way you are going..

I've used plasmatronics solar chargers a fair bit, mostly the PL40, but I think you are going to need something a bit bigger...

Regards
Ray

Thanks Ken,
Your input is always appreciated. The heat side I will have recirculating through a large fanned intercooler then through a narrow but long and high glass tank to get as much surface area as possible. Son is a glazier and glass is perfect tank material for this as it is inert so there won't be any galvonic (?) reaction. I will try to create some themal flow by having the tank higher than the peltiers but there will also be a pump circulating the fluid. Still haven't settled on the fluid yet but leaning towards glycol - son tells me bourbon might be a better choice.

Hi Gordon,
I will run these through a regulator as per my photos in previous post. It has a wide input and under and over voltage protection and rated 12 volt, 10 amp.

Hi Ray,
Yes it has scaled up but this was my original intention anyway. I am running 12 volts through a regulator. No batteries as the peltier can handle low voltage up to 15 volts and in my tests the peltier works fine direct wired through a 12 volt regualtor. It will have diodes and fuse protection so should be safe enough. Each panel drives one peltier so with losses probably around 5 to 5.5 amps per peltier. I am using the 4mm cable recommended for solar wiring and the MC4 connectors. All new to me so if I have made a huge mistake point it out.

If this doesn't work I will run the solar through an inverter and grid connect. I will get a sparky to do that if that is the end result.

you loose voltage with every diode , normally 1.2 volts across the diode , the regulator should have one in it ,
another way to diode protect is to wire it up backwards to short out when the power is backwards , and use a beaker , to kill the power when the diode shorts ( rough as guts again ) , the power wont run through the diode when its connected properly so there is no 1.2 volt drop in voltage

see pizza box image bellow , im out of napkins

you also put a diode in that position when there is a large magnetic field in the load , that can put power back into the wire when the magnetic field collapses ( opposite polarity )

Hi Ken,
The peltiers will more than likely try to backfeed as the tanks will have both hot and cold coolant and after sunset the variation in the temperature on both sides of the peltier will produce a current. I measured it on the test bench and it was only about 1.5 volts at that time.

I like pizza box sketches.

Originally Posted by SawDustSniffer

you loose voltage with every diode , normally 1.2 volts across the diode

Hi Ken,
What you say is correct, (Nice Pizza Box Sketch too! ) except the voltage drop across a silicon diode is 0.6V ish not 1.2V it increases a bit with current and temperature.. anyway, what I wanted to say is that power schottky diodes have lower forward voltage drops usually in the range 400-500 milllivolts. Also some solar panels come with reverse polarity protection diodes built in. Might be worth finding out if the panels already have diodes installed.

The problem I see is limiting the voltage to the peltier device when the panel voltage is up around 18-20volts.. and that was discussed at length earlier in this thread. I thought the solar regulator battery charger with SLA battery was a good solution.

The question I've got is how to scale that up for 100 watt panels at reasonable cost.. given that there are 12 panels.

So Rod, are you still looking for a low cost high current solar regulator?

There is this guy who might be worth a look.. Solar Charge Controller items - Get great deals on 10A Charge Regulator, MPPT items on eBay Stores!

It's a very interesting project, must be worth a few carbon credits..

Regards
Ray