diy solar

diy solar

LiFePO4 heating pad for cold temperatures

astronom said:
Apart from resistive pads, I have been looking at a heating/cooling system based on Peltier elements, it should hopefully be more efficient than resistive heating (the Peltier element basically acts as a mini heat pump), plus it can do both heating and cooling in one shot to also help keeping the battery fresh during summer. With a well insulated battery case I hope it won't draw too much power. We can start a thread around that if more are interested. Don't have the parts yet but I will try something with some stuff from AliExpress.
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I really like to see a thread on this once you get the parts ..... if you start a new thread please post a link to it on this one.
 
So. I've ordered and received this silicone heating mat from Keenovo a few month ago. It seems decent and relative high quality. It heats up good and has a 3M adhesive backing. I also ordered this Digital Temperature Controller XH-W3001, but haven't tested it yet. Funny enough I haven't got any LFO (or LTO) cells yet so this was just to have the parts available when I'm putting the system together. The plan is to build a relative simple system with relays that switches the heating pad on if the temperature is below say 2-3°C and switches it off again when the batteries are at say 10°C. The tricky part is to have this only being done when the SCC or the alternator (DC-DC charger of some sort) is producing power. Haven't figured that out yet. Someone need to open up a heated battery and figure out what they're using... Hint @Will Prowse ;)IMG_0314.jpg
 
kimsv said:
So. I've ordered and received this silicone heating mat from Keenovo a few month ago. It seems decent and relative high quality. It heats up good and has a 3M adhesive backing. I also ordered this Digital Temperature Controller XH-W3001, but haven't tested it yet. Funny enough I haven't got any LFO (or LTO) cells yet so this was just to have the parts available when I'm putting the system together. The plan is to build a relative simple system with relays that switches the heating pad on if the temperature is below say 2-3°C and switches it off again when the batteries are at say 10°C. The tricky part is to have this only being done when the SCC or the alternator (DC-DC charger of some sort) is producing power. Haven't figured that out yet. Someone need to open up a heated battery and figure out what they're using... Hint @Will Prowse ;)View attachment 4348
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I am going to try to set a thermostat to close a N/O relay at temperature when the temp is above 5 degrees C and when the cooling side reads under 4 degrees C it will allow the N/O to disconnect the relay. The relay will carry current from the solar panels to the SCC only when the temp is above 5 degrees C. Hopefully this will protect my SCC from a low temp disconnect at the battery side that could damage the SCC, and with no charge leaving the SCC this should protect my batteries from low temp charging. I have not done this yet I am going to try to set this up tomorrow. I hope it works, but I would be glad to hear if you have other alternatives. Thanks in advance.
 
Buzzard Bait said:
I am going to try to set a thermostat to close a N/O relay at temperature when the temp is above 5 degrees C and when the cooling side reads under 4 degrees C it will allow the N/O to disconnect the relay. The relay will carry current from the solar panels to the SCC only when the temp is above 5 degrees C. Hopefully this will protect my SCC from a low temp disconnect at the battery side that could damage the SCC, and with no charge leaving the SCC this should protect my batteries from low temp charging. I have not done this yet I am going to try to set this up tomorrow. I hope it works, but I would be glad to hear if you have other alternatives. Thanks in advance.
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Why would a low temp disconnect at the battery side damage the SCC?
 
kimsv said:
Why would a low temp disconnect at the battery side damage the SCC?
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I cannot answer your question, but I am using a epever 60 amp SCC and in the installation instructions it is very clear that the battery must be connected before the panels. This instruction gave me the impression that if the panels remained connected after a BMS disconnected the battery the SCC could be damaged. I could be wrong, maybe someone will give us a better answer to your question. Thank you for asking.
 
Ok, did not know that! It sounds risky. I mean then it would also destroy the SCC if the BMS cut out because of high temp and also high/low SOC?! Lots of variables for destruction that.
 
kimsv said:
Ok, did not know that! It sounds risky. I mean then it would also destroy the SCC if the BMS cut out because of high temp and also high/low SOC?! Lots of variables for destruction that.
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I was unable to set up the thermostat today, but I forgot to add that part of the plan was to supply power to the thermostat down stream from the battery fuse and down stream of the BMS ground. That is to say if the current is interrupted by a blown fuse, or a BMS interruption the lack of current into and out of the thermostat will open a N/O relay and interrupt the current from the panels. Still again I have not applied this idea yet. It is probably someone's go to method, because I rarely have an idea that someone else has not already tried. If anyone has an insight into this method Please comment. Thank You in advance.
 
One thing the companies like Battleborn etc should consider is to have the heater built in, it could be coils around the cells or something, with temp sensor. When the battery is charging, rather than simply cut off, it would just divert the charge current to a separate controller that would put a bit of current through the coils to bring the cells up to temp, since the inside of the cells may still be cold when the surface is not, it would need to be somewhat timed but once it reaches a certain temperature it could then start to slowly ramp up charging. Of course, could do this yourself, but it would be neat if they made this built right into the batteries, given they already have electronics in there anyway. Could even make it part of the BMS. Something worth suggesting to them.

As a side note, having this could also be good for setups that have an alternator. You don't want to run an alternator without a load.
 
I've got for this reptile heater, the silicon RV water tank ones can get to 300 degrees!
Its not thermostatic, so I'll have to wire something....

I also got these for the new water tank of the camper while I was doing cold weather protections....
 
Red Squirrel said:
One thing the companies like Battleborn etc should consider is to have the heater built in, it could be coils around the cells or something, with temp sensor. When the battery is charging, rather than simply cut off, it would just divert the charge current to a separate controller that would put a bit of current through the coils to bring the cells up to temp, since the inside of the cells may still be cold when the surface is not, it would need to be somewhat timed but once it reaches a certain temperature it could then start to slowly ramp up charging. Of course, could do this yourself, but it would be neat if they made this built right into the batteries, given they already have electronics in there anyway. Could even make it part of the BMS. Something worth suggesting to them.

As a side note, having this could also be good for setups that have an alternator. You don't want to run an alternator without a load.
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BattleBorn are actually releasing a heated battery in March/April 2020 according to Wills interview with BattleBorns CEO Denis Phares.
 
Victron has just released this video:
about a LFP conversion in a sail boat and they solve the heating problem with a silicone heating pad as well. They use the Venus GX to sense the low temp so not really a go to solution for everyone though. The battery install starts around 4:30.
 
If someone is searching for a cheap temperature controller that would handle the heat pads I've found this site with lots of technical specs according to the most common saled controllers on the known china-platforms. There also are informations available about configuration options for any controller.

https://www.smartclima.com/thermostat-mainboard.htm

I personally prefer the model XH-W1304, which is the only one having an acoustical low & high temperature warning which configuration differs from the lowest & highest set working temperature, or lets say, the desired temperature and the allowed backflash. So you can set a temperature range in which the heating pads have to do their job, and if they fail to raise the temperatur or unfortunately do their job better than expected I'll get a beep-beep-beep about it.
 
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In addition to my previous post.

According to the specs of the cells we just need a temperature controlled heating pad when giving load into the battery. Discharging is possible having much lower temps. Doing so we could save much energy.

So, in my opinion it could be an idea to interpose an adjustable undervoltage protection between the temperature controller and the heating pads. Something similar to this (https://www.aliexpress.com/item/-/32857358407.html?spm=a2g0s.8937460.0.0.7e552e0eWAHUrU).

In theory the temperature-controller would only pass current to the undervoltage-controller having the temperature limits valid to go. The undervoltage-controller on the other side has two voltages set, an ON- and an OFF-voltage for the output of the LOAD. If they are independent from each other - like they should be according to this controller (https://www.aliexpress.com/item/4000458589336.html?spm=a2g0s.8937460.0.0.7e552e0eWAHUrU) - one could set the ON-voltage to the lowest charging voltage eg. 13.8V. In this case the controller would only pass the load to the heating pads if the battery is being charged. The OFF-voltage could be set to 12.8V or just lower than ON.

The undervoltage protection below 10V can still be handled by the bms which would simply cut off everything including the temperature-controller with the undervoltage-controller attached to it and the heating pads. This will protect the battery from being discharged by the heating pads comming into critical areas.

Hopefully this would secure everything.

Instead of using the heating pads one could also attach a relay for just cut off everything.

EDIT: Thinking more about it, I'm afraid for security reason this solution necessarily needs to have at least a relay installed or something that will cut off the main power connection as long as the heater pads do their job. The reason is, the battery gets charging load right away but the heating pads have no chance to worm up the frozen cells so fast. Therefore, as long as the heating pads have to work the main power must be cut off, too. The problem is, cutting of the battery also means, no consumers can be served with power. It would only work nicely if the battery would have a separate charging port and only this one would be cut off by the relay. Somehow I still don't really like this solution.

EDIT2: Just had an other idea, what if we just drop the charging voltage so that it won't charge anymore when cells are under 0° C instead of completely cutting off the system? How about a DC-DC-Downward-Inverter? Something similar to this (https://www.aliexpress.com/item/4000498014482.html) but being able to handle much more Amps. By now I don't know if there is something on the market that I could use and at low costs. But I think this might work, even on common battery ports for charging & discharging. I don't really know how the Inverter works, but if there's a resistor inside we have our heating pads for free ;)
 
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Yeah that's my train of thought as well, only have the heating pad work when the battery is actually being charged and if the temp is too low.
 
Red Squirrel said:
Yeah that's my train of thought as well, only have the heating pad work when the battery is actually being charged and if the temp is too low.
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I was thinking about this approach too .... actually use the charge power to warm the battery before allowing it to charge.

A couple potential problems occurred to me. Unless the temperature probe is buried deep in the battery, the internal battery temp could be lower than you think with turning on charging. ( I guess that is a potential problem with any method .... except if the heating pad is always live it is unlikely to occur.) The 2nd issue would be if solar is doing the charging ...... there could be quite a bit of power lost before the battery begins charging ..... and the charge day could be significantly reduced.
 
Yeah there would need to be some smarts to it, like when the sensor detects the temp is right it would still continue to heat for a little while to give time for heat to transfer to the middle of the cell. The timer could be based on the initial temperature. So if you're going from -50C then you know you need to heat them longer before you add charge.

Of course this is also more of a fail safe, as in an off grid application it's probably best to try to just keep the batteries in an area that is actively heated anyway. But at least in situations where they're cold, you can still charge them if it has these heating systems.
 
Ok, what if we put a relay between the PV and the SCC?

Follow my train of thought:
We only use a temperature control relay, not a voltage one, and it senses the battery temp to be under say 5°C.
It triggers the PV relay to switch and instead pass power directly to the heating pad, bypassing the SCC.
I’m really not sure if this works, but it’s a resistive load so I think I should.
When the batteries are warm (above 5°C) the temp relay triggers the PV relay to switch back and feed to SCC.
This way the SCC is never disconnected from the battery which is said to maybe be dangerous for the SCC.
The battery is also always protected IF the battery temp is below 0°C, since it’s not possible for the SCC to charge.
If the battery is cold and there is no sun it doesn’t matter. We can still use power from the battery (unless the BMS says no) and as soon as the sun comes out it heats up the battery first.
The downside with this is that the SCC maybe think that it’s a new day so the statistics may be f*cked up.

What do you think? This way it work a bit like the LFP batteries with built in heating that is said to not use the battery’s own power to heat, only power from a source that try to charge the cold battery.
 
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