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Why you cannot charge LiFePO4 below 0 degrees Celsius

Appears charge current control is requested by REC BMS, performed by inverter/charger

Page 15:
"MAXC? or MAXC x.xxx Maximum charge current Returns float current [A] 10.0 to 1000.0 A"
"MAXD? or MAXD x.xxx Maximum discharge current Returns float current [A] 10.0 to 1000.0 A"

Page 18:
"Table 13: CAN message structure description for ID=0x037, dlc=8."
"3 Max charge current high byte Unsigned integer 0-65535, LSB = 0.1 A"

Page 22:
"Battery Pack’s Charging Algorithm: The communication between the REC BMS and the system is established through the CAN bus. All the parameters that control the charging/discharging behavior are calculated by the BMS and transmitted to the system in every measurement cycle. The charging current is controlled by the Maximum charging current parameter. It is calculated as Charge coefficient CHAC x Battery capacity CAPA. The parameter has an upper limit which is defined as Maximum charging current per device MAXC x Charger coefficient CHCU. When the highest cell reaches the Balance start voltage setting, the charging current starts to ramp down to 1.1 A until the last cell rises to the End of charge voltage. At that point the Maximum charging voltage allowed is set to Number of cells x (End of charge voltage per cell – 0.5 x End of charge hysteresis per cell). End of charge SOC hysteresis and End of charge cell voltage hysteresis is set to prevent unwanted switching. SOC is calibrated to 100 % and power LED light is on. Charge optocoupler is turned off."

 
REC isn't just a Smart BMS but a Genius BMS.
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The JBD BMS simply cuts off charge, but then again, it isn't communicating much with upstream charge devices.
 
Yes, REC BMS and AC coupled SMA is by far the best off-grid system i’ve seen for DIY cells.

Best bit is that in Australia you can get second hand gear in great condition for peanuts.
 
I have a bank of 17 280ah LiFE04 cells. Using a Schneider xw6848 and mppt60. I asked the S/E factory about setting(s) to disable charge under a certain temperature. THEY DON'T CARE. To S/E it's the job of the battery system, not at inverter or c/c. Won't be buying any more of their gear. The XW gear already has external temperature sensors so its nothing but programming and CODE to give us a setting to disable charge under a certain temp. Piece of cake but they won't listen. They want to you buy expensive battery apparatus.
 
If BMS can tell inverter/charger what charge voltage and current to use, that should be fine. It would then be the job of BMS to have current vs. temperature profile.
Some BMS use FETs as a diode to allow discharge but not charge below a certain temperature. That may be sufficient (with appropriate charge current limits), but adjustable current as commanded would be better.

But yes, fairly simple firmware to implement either rectangular current/temperature limits or a curve.

"nothing but programming and CODE"

I always say software costs more to design, implement, install, maintain than hardware. And it is less reliable.
 
Just wondering, couldn't I just locate the batteries inside my RV, as in in the cabin area, which is heated/cooled?
 
When I'm actively using my RV in the winter, I turn off the battery warmers. They stay plenty warm because a furnace duct runs through the compartment where the batteries are located.
that might be an option... currently my lead acid batteries are located in the front compartment under the 5th wheel hitch... where both SCCs and the 3000 watt inverter are located.
 
Just set the BMS low-temperature charge cutout to a temperature where maximum available charge current is acceptable. That way, if it does get cold and there is good sun, charging will be prevented until temperature rises enough.
 
that might be an option... currently my lead acid batteries are located in the front compartment under the 5th wheel hitch... where both SCCs and the 3000 watt inverter are located.

A friend recently installed LiFePO4 batteries in the basement of his fifth wheel along with an inverter/charger. This is a four season fifth wheel. He left the furnace on at a very low setting, somewhere around 45° F. It ran out of propane. Fortunately, the weather was been quite mild so the batteries likely never got below 35° F.

His approach to keeping the batteries warm is going to cost him a lot of propane now that we're getting into colder weather. He'll either have to put in a warming system and more PV or simply remove the batteries. Short term, I suspect he'll keep filling the propane tanks.
 
Just set the BMS low-temperature charge cutout to a temperature where maximum available charge current is acceptable. That way, if it does get cold and there is good sun, charging will be prevented until temperature rises enough.

Given the density of batteries, it could be hours before the temperature of the battery comes up enough for them to be charged.
 
Given the density of batteries, it could be hours before the temperature of the battery comes up enough for them to be charged.

That's fine.
It would be months before a shipment of replacement cells arrived from China.
If you're not there keeping the place warm, probably don't need so much power.
Go ahead and add insulation, electric battery warmer, whatever. But set a "circuit breaker" via BMS to prevent charging when battery is below the temperature where it can handle available charge current without damage.
 
A friend recently installed LiFePO4 batteries in the basement of his fifth wheel along with an inverter/charger. This is a four season fifth wheel. He left the furnace on at a very low setting, somewhere around 45° F. It ran out of propane. Fortunately, the weather was been quite mild so the batteries likely never got below 35° F.

His approach to keeping the batteries warm is going to cost him a lot of propane now that we're getting into colder weather. He'll either have to put in a warming system and more PV or simply remove the batteries. Short term, I suspect he'll keep filling the propane tanks.

we dont run out of propane when we are stationary... 320 gallon tank...
 
Cheers Will! I always wanted to know the answer to that. I believe that one should avoid charging them under 5 to 10 'C to promote longevity.
 
The article quoted is saying that with the correct electrolyte and anode construction, charging at minus 40deg C is possible.

Not sure how much access the author has to the better manufacturers, but anode construction is continually evolving.

I guess the post should be “why your cheap LiFePO4 cells can’t be charged when frozen”
Evolving doesn’t mean it is available on the open market in mass quantities.
 
SO I am glad I found this thread. I live in the great north, and it does get cold. I thought my charge controller was protecting my battery system, and NOT charging them when it was below temperature. I accidentally found out that it is not true, when I saw current going to my batteries when it was VERY cold. It was 20F and charging at about .05C. I normally do not go out and check on my batteries when it is cold, because it is well cold and a very remote location and requires a pretty long walk.

So I was initially panicking and confused at the same time. I have watched Will a long time. My system is about 3 years old and has MANY times seen below -10F. At least 25 days where the high temp is below 5F . The last full capacity check (ie battery full and going nearly depleted) I was still above 100%. How could my batteries not be damaged. Now I know. MY system has LOTS of batteries, and my solar array and charge controller is relatively small.

The average day in the winter I charge at .05C and the best day would be .15C rate of charge per battery. I have lots of batteries. It would always start at a low C rate and ramp up, which will warm the batteries up as the charge. When it is very cold it is when it is likely sunny, but the sun still comes up slowly and the power would ramp up very slowly. The normal condition is NOT sunny and VERY cloudy, which is why I have lots of batteries. I can get as little as 5% of my power requirements in a day on the coldest of day. A normal day is about 25-40% of my peer requirements. I charge them up on "warm days" I can go about 8-10 days or so between charges.

I occasionally charge my batteries with generator but only when it is above freezing, and always do it before a cold spell. And I start slowly and warm up the battery box to 3-4C before I turn on my big charger.


Thoughts?
 
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