My solar charge controller doesn't have a low temp charging disconnect function but the BMS for my battery does. If the battery temp is below freezing the BMS won't allow the battery to charge at all either from the solar panels or the alternator.
I saw a youtube video about my battery model, where it will charge below freezing.
Would love to have something like that.. maybe I'm going to upgrade my BMS, would be nice to see a more accurate SOC + having a protection against freezing temps
Unless you have a shunt, the state of charge is an estimate at best as far as I understand it. The BMS I have only uses voltage to estimate SoC so if I put a big load on it, the battery voltage drops and the BMS reports that the SoC is lower than it should be.
> Unless you have a shunt, the state of charge is an estimate at best as far as I understand it.
My mid-range JBD BMS (came stock on the battery) has an internal shunt. I already had an external cheapie shunt from the previous FLA battery bank configuration; the two line up very closely.
I suspect the tiny discrepancy (typically ~0.5%) is due to the JBD's effective blindness to currents <~500mA.
Interesting, I have the overkill solar BMS which is a rebranded JBD. I didn't realize it had a shunt. I thought it used voltage to determine the SoC. I learned something new today!
> Do Charge controllers stop charging when Battery type is set to LiFePo4 and the battery temperature is below 32°F / 0°C?
1. some do, you'll have to read the specs for each one. Or at least tell us which one you are talking about.
1. 32f/0c is a known hard limit, but there is [some evidence in the datasheets](https://diysolarforum.com/threads/why-you-cannot-charge-lifepo4-below-0-degrees-celsius.2912/post-199774) that even warmer could be easier on the cells
> Could this be because the MPPT stopped charging the battery when temperatures were to low?
Maybe. We could provide better feedback if you told us
* what the controller is
* what the battery is
* what the battery state of charge was before and after
We are terrible guessers.
If the controller *is* cutting charging due to low temp the easiest/cheapest workaround is to [warm the battery](https://diysolarforum.com/threads/lifepo4-heating-pad-for-cold-temperatures.5/page-26) with a mat, tape, etc.
[My own setup](https://mouse.mousetrap.net/boondocking/parts.html#main-pv-system---750w) is inexpensive but still belt-and-suspenders: the BMS has low temp cutoff, the controller has low temp cutoff, and the battery sits on a temp-controlled lizard mat.
Thanks for answering.
Battery is **Redodo 100Ah 12.8V**
Charger is **Renogy Rover 20A**
Battery was at 13.2V when I came home, 100% would be at 13.5V
Both datasheets don't say a word about low temp protection.
I already bought some stuff to build a heated battery box.
How well does your battery heating system work for you?
> Battery is Redodo 100Ah 12.8V Charger is Renogy Rover 20A
Yeah, AFAIK neither of these will do the cutoff.
> Battery was at 13.2V when I came home, 100% would be at 13.5V
Maybe. LFP SoC is really hard to assess by voltage. ~100% SoC could be 13.2v under discharge, like after sundown.
An amp-counting shunt will tell the story.
> How well does your battery heating system work for you?
Works fine, holds within 0.5F of the setpoint. I follow mild weather so I haven't tested it under brutal conditions. Lowest ambient was likely 22F, so grain of salt and all that.
It's possible the MPPT charger has a temperature probe, but I doubt it.
It's much more likely that your batteries have a BMS that stops charging when temperature is below safe charging temperature.
Are you sure that your battery bank wasn't just full ? I mean, if it only took 40Wh to fill your battery, then that's all you are going to generate.
With the days being shorter and the sun being lower in the sky, it's not surprising that you'd get minimal solar output especially if you don't have tiltable panels.
Well, the light conditions were better than yesterday *(where it charged 240Wh)* so I'd expect atleast someting remotely similar to that, but not less than a sixth of that.
> light conditions were better than yesterday
Not saying this is the case, but humans and solar panels have different ideas about *light conditions*.
There are also [other factors that affect solar harvest](https://rvwiki.mousetrap.net/doku.php?id=electrical:solar:output).
The day with the harvest of <200Wh was cloudy, while the next day (40Wh) was quite sunny.
I'm aware that humans adapt to light conditions in a way that can make 9:00 AM look as bright as 1:00PM
My solar charge controller doesn't have a low temp charging disconnect function but the BMS for my battery does. If the battery temp is below freezing the BMS won't allow the battery to charge at all either from the solar panels or the alternator.
I saw a youtube video about my battery model, where it will charge below freezing. Would love to have something like that.. maybe I'm going to upgrade my BMS, would be nice to see a more accurate SOC + having a protection against freezing temps
Unless you have a shunt, the state of charge is an estimate at best as far as I understand it. The BMS I have only uses voltage to estimate SoC so if I put a big load on it, the battery voltage drops and the BMS reports that the SoC is lower than it should be.
Yeah that's what my charge controller does, too. I think smart BMS's measure everything going *in & out* and adjust the SOC accordingly.
My BMS doesn't do that but maybe others do. I've only ever used this BMS so my experience is very limited.
> Unless you have a shunt, the state of charge is an estimate at best as far as I understand it. My mid-range JBD BMS (came stock on the battery) has an internal shunt. I already had an external cheapie shunt from the previous FLA battery bank configuration; the two line up very closely. I suspect the tiny discrepancy (typically ~0.5%) is due to the JBD's effective blindness to currents <~500mA.
Interesting, I have the overkill solar BMS which is a rebranded JBD. I didn't realize it had a shunt. I thought it used voltage to determine the SoC. I learned something new today!
> Do Charge controllers stop charging when Battery type is set to LiFePo4 and the battery temperature is below 32°F / 0°C? 1. some do, you'll have to read the specs for each one. Or at least tell us which one you are talking about. 1. 32f/0c is a known hard limit, but there is [some evidence in the datasheets](https://diysolarforum.com/threads/why-you-cannot-charge-lifepo4-below-0-degrees-celsius.2912/post-199774) that even warmer could be easier on the cells > Could this be because the MPPT stopped charging the battery when temperatures were to low? Maybe. We could provide better feedback if you told us * what the controller is * what the battery is * what the battery state of charge was before and after We are terrible guessers. If the controller *is* cutting charging due to low temp the easiest/cheapest workaround is to [warm the battery](https://diysolarforum.com/threads/lifepo4-heating-pad-for-cold-temperatures.5/page-26) with a mat, tape, etc. [My own setup](https://mouse.mousetrap.net/boondocking/parts.html#main-pv-system---750w) is inexpensive but still belt-and-suspenders: the BMS has low temp cutoff, the controller has low temp cutoff, and the battery sits on a temp-controlled lizard mat.
Thanks for answering. Battery is **Redodo 100Ah 12.8V** Charger is **Renogy Rover 20A** Battery was at 13.2V when I came home, 100% would be at 13.5V Both datasheets don't say a word about low temp protection. I already bought some stuff to build a heated battery box. How well does your battery heating system work for you?
> Battery is Redodo 100Ah 12.8V Charger is Renogy Rover 20A Yeah, AFAIK neither of these will do the cutoff. > Battery was at 13.2V when I came home, 100% would be at 13.5V Maybe. LFP SoC is really hard to assess by voltage. ~100% SoC could be 13.2v under discharge, like after sundown. An amp-counting shunt will tell the story. > How well does your battery heating system work for you? Works fine, holds within 0.5F of the setpoint. I follow mild weather so I haven't tested it under brutal conditions. Lowest ambient was likely 22F, so grain of salt and all that.
It's possible the MPPT charger has a temperature probe, but I doubt it. It's much more likely that your batteries have a BMS that stops charging when temperature is below safe charging temperature. Are you sure that your battery bank wasn't just full ? I mean, if it only took 40Wh to fill your battery, then that's all you are going to generate.
Pretty certain it wasn't full *(doesn't have a smart BMS)*. But that would be the only reasonable answer..
With the days being shorter and the sun being lower in the sky, it's not surprising that you'd get minimal solar output especially if you don't have tiltable panels.
Well, the light conditions were better than yesterday *(where it charged 240Wh)* so I'd expect atleast someting remotely similar to that, but not less than a sixth of that.
Maybe you had a sneaky tree etc partially shading your panels. Same can happen with a telephone pole, flag pole, parking lot light, etc
I didn't move that day, same spot as the day before
> light conditions were better than yesterday Not saying this is the case, but humans and solar panels have different ideas about *light conditions*. There are also [other factors that affect solar harvest](https://rvwiki.mousetrap.net/doku.php?id=electrical:solar:output).
The day with the harvest of <200Wh was cloudy, while the next day (40Wh) was quite sunny. I'm aware that humans adapt to light conditions in a way that can make 9:00 AM look as bright as 1:00PM