Has anyone made a homemade low temperature shutoff for their solar charge controller?
My system:
Batteries: 2 each 200Amp VRLA gel cells in parallel (not in series because my inverter take 12 volts)
Charge Controller: Renogy Rover Elite 20A (input limit of 256 watts solar for 12 volt systems)
Inverter: Renogy 3000 watt Pure Sine Wave (12 volt only input)
Panels: 2 each Harbor Freight 100 watt in series (17VOC/5.56A short circuit)
Notes for (hopefully non-existent) keyboard commandos:
- yes, I know I am using lead acid batteries. You don't know why I chose them, but I need them. And the manufacturer's data sheet puts minimum charge temperature at freezing, so that's why this question.
- yes, I know Renogy isn't the best stuff on the market, but I got stellar deals on all of it, combining Renogy's Black Friday pricing with Home Depot's 10% veterans' discount. (you don't need to thank me for my service, rather I thank you for paying me to live in Europe for 9 years, and having a retirement check and $600/yr healthcare since I was 38 years old).
- yes, I know I could upgrade the charge controller, but not really interested in spending an infinite amount of money for a little system that's basically going to run lights and battery tenders for my tractors inside a shipping container a few hours per week.
- yes, I know I have Harbor freight panels. The pair cost less than $100, and currently charge my Bluetti EB150 at 185 watts in the winter time.
OK, I think I pre-responded to all the potential OT comments, so let's get to my question.
The battery spec sheet says "thou shalt not attempt to charge the battery at below freezing temperatures", so I'm taking this as gospel. Thus, I need a low temperature cutoff on the output of the solar charge controller, and a heater of some sort to keep the batteries from reaching sub-freezing temperatures (the batteries will have a small bit of insulation, probably R1-R2). I also realize that batteries produce heat whether charging or discharging, and that their tremendous thermal mass will take a long time to cool below 32F regardless of ambient temperature.
I've found some 12 volt, stick on RV tank heaters that turn on at 45F and off at 68F (9 degrees cooler than optimal battery operating temperature, but close enough). The tank heaters draw 78watts, so (78*2) /12= 13 amps, which I'll round to 15 amps. I also realize I have 200 usable amp/hrs out of this battery bank, so 200/15=13.3 hours of continuous operation. I don't believe my battery heaters will be cycling very often, but that remains to be seen.
Now the question. Which of the two options do you favor, and why? Or is there a reasonable alternative I missed? Spending more than $50 beyond what I have already is a non-starter.
Option 1: One train of thought is to just wire the heaters up and hope I don't have a week of sub freezing, snowy weather during which my solar panels won't produce enough energy to keep the batteries charged (I'm in a peak 5 hour solar zone).
Option 2: My preferred train of thought is to have a relay inline with solar charge controller to turn its output off when battery temperature is below freezing, using a $5 USD Aliexpress temperature switch with sensor. That handles low temperature charging issue entirely. Along with this solution, I'd set the solar charge controller's load port to be active only when charging current is present, then have that pick a relay to enable my battery heaters. Sure, it might take a couple of hours to heat the batteries, but let us remember that our panels still generate some output outside of the peak hours. I think this will relieve my anxiety of running the batteries down from trying to keep them warm 24/7.
Thanks for the input.
My system:
Batteries: 2 each 200Amp VRLA gel cells in parallel (not in series because my inverter take 12 volts)
Charge Controller: Renogy Rover Elite 20A (input limit of 256 watts solar for 12 volt systems)
Inverter: Renogy 3000 watt Pure Sine Wave (12 volt only input)
Panels: 2 each Harbor Freight 100 watt in series (17VOC/5.56A short circuit)
Notes for (hopefully non-existent) keyboard commandos:
- yes, I know I am using lead acid batteries. You don't know why I chose them, but I need them. And the manufacturer's data sheet puts minimum charge temperature at freezing, so that's why this question.
- yes, I know Renogy isn't the best stuff on the market, but I got stellar deals on all of it, combining Renogy's Black Friday pricing with Home Depot's 10% veterans' discount. (you don't need to thank me for my service, rather I thank you for paying me to live in Europe for 9 years, and having a retirement check and $600/yr healthcare since I was 38 years old).
- yes, I know I could upgrade the charge controller, but not really interested in spending an infinite amount of money for a little system that's basically going to run lights and battery tenders for my tractors inside a shipping container a few hours per week.
- yes, I know I have Harbor freight panels. The pair cost less than $100, and currently charge my Bluetti EB150 at 185 watts in the winter time.
OK, I think I pre-responded to all the potential OT comments, so let's get to my question.
The battery spec sheet says "thou shalt not attempt to charge the battery at below freezing temperatures", so I'm taking this as gospel. Thus, I need a low temperature cutoff on the output of the solar charge controller, and a heater of some sort to keep the batteries from reaching sub-freezing temperatures (the batteries will have a small bit of insulation, probably R1-R2). I also realize that batteries produce heat whether charging or discharging, and that their tremendous thermal mass will take a long time to cool below 32F regardless of ambient temperature.
I've found some 12 volt, stick on RV tank heaters that turn on at 45F and off at 68F (9 degrees cooler than optimal battery operating temperature, but close enough). The tank heaters draw 78watts, so (78*2) /12= 13 amps, which I'll round to 15 amps. I also realize I have 200 usable amp/hrs out of this battery bank, so 200/15=13.3 hours of continuous operation. I don't believe my battery heaters will be cycling very often, but that remains to be seen.
Now the question. Which of the two options do you favor, and why? Or is there a reasonable alternative I missed? Spending more than $50 beyond what I have already is a non-starter.
Option 1: One train of thought is to just wire the heaters up and hope I don't have a week of sub freezing, snowy weather during which my solar panels won't produce enough energy to keep the batteries charged (I'm in a peak 5 hour solar zone).
Option 2: My preferred train of thought is to have a relay inline with solar charge controller to turn its output off when battery temperature is below freezing, using a $5 USD Aliexpress temperature switch with sensor. That handles low temperature charging issue entirely. Along with this solution, I'd set the solar charge controller's load port to be active only when charging current is present, then have that pick a relay to enable my battery heaters. Sure, it might take a couple of hours to heat the batteries, but let us remember that our panels still generate some output outside of the peak hours. I think this will relieve my anxiety of running the batteries down from trying to keep them warm 24/7.
Thanks for the input.
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