Protection from freeze charging LiFePO4 battery

[rharries]

My (self installed) DC system includes a 175 watt panel, Victron MPPT controller and 100 Ah Renogy LiFePO4 battery with heating function.
For alternator charging, I have a Victron Orion non-isolated DC charger.
I also have a Victron BMV 712 with temperature probe that I use to monitor state of charge and other interesting data points.

The past weekend I noticed that the BMV was recording a significant charge (200 w) when driving away from my frozen campsite. The battery temperature was recording 0*C. I am aware the damage that can occur if a Lithium battery is charged below ~5*C, so I disabled the DC charger.

The low temperature relay on my BMV was disabled for a test the prior week and I forgot to turn it back on.

My question is: Would the power from the DC charger have be directed to initially heating the smart self heating Renogy battery, or did I potentially damage my new battery?

I am hoping that the battery is smart enough to not accept a charge to its cells in freezing temperatures based on the attached screenshot from Renogy website, but verification would be much appreciated.

Thanks,
RH

 

[sunshine_eggo]

My question is: Would the power from the DC charger have be directed to initially heating the smart self heating Renogy battery, or did I potentially damage my new battery?

I don't know the product definitively, but that is how it should have worked. Was 0°C on the battery or the BMV? The BMV temp sensor on the battery post is going to almost certainly be colder than the cells inside where the Renogy temp sensor is.

The BMV can't distinguish between charge current and "heater" current.

I am hoping that the battery is smart enough to not accept a charge to its cells in freezing temperatures based on the attached screenshot from Renogy website, but verification would be much appreciated.

That's a very reasonable expectation, and I would be shocked if a heated battery didn't also have low temp charge protection built into the BMS as well.

It's also not a line in the sand where on one side damage occurs, and it doesn't on the other side. It's graduated, but since manufacturers rarely publish safe charge currents at lower temperatures, everybody just says, "no charging below freezing."

200W / 13.6V = 14.7A = 0.15C, which is a pretty low rate for LFP - well under the typical 0.5-1.0C charge rates. I would not presume that any damage was done even if the full current from the charger went to charge the battery.

 

[rharries]

Thanks for the response. It seems better to not utilize the low temperature relay function on the BMV, as it would limit the ability to supply power to the cell heating elements in freezing conditions.

 

[RV8R]

Thanks for the response. It seems better to not utilize the low temperature relay function on the BMV, as it would limit the ability to supply power to the cell heating elements in freezing conditions.

I have a DIY Van, & being Canadian & wanting a 4 season Van I have AGMs. I have “coined” LFP with a phrase “The 3 Cs”;

Cash
Cold
Charge “Complexity“



You are suffering the last 2 in combination.


The “Cash” side of LFP, IMO now has significant dropped off ,,, that is they have become more cost effective from Days of Yore.



”Better” ???. I would analyze what is “safer”. Safer for You & Your Batteries.

 

[sunshine_eggo]

Thanks for the response. It seems better to not utilize the low temperature relay function on the BMV, as it would limit the ability to supply power to the cell heating elements in freezing conditions.

I'm concerned you think the BMV relay is something it isn't. The relay on the BMV is a control relay, i.e., it opens or closes based on SoC, temp or voltage criteria, but it in no way limits current through the shunt. If your particular MPPT has a control relay, you could have the BMV relay open at low temp while connected to the control relay on the MPPT. This would prevent the MPPT from charging until the BMV relay closes.

Otherwise, I think your thinking is correct. You don't want to externally terminate charging since the battery should be diverting any incoming current to the heater when cold.

 

[RV8R]

I don't know the product definitively, but that is how it should have worked. Was 0°C on the battery or the BMV? The BMV temp sensor on the battery post is going to almost certainly be colder than the cells inside where the Renogy temp sensor is.

.

I am thinking of a situation where thermal inertia is @ play ?


The difference between “possibility“ & “probability” here I do no know, but I think it would be “possible” to have the cells colder than the BMV temp sensor.

I have thought of “upgrading” my Van to FLP from my AGMs, but in a bit of a quandary of “If it Ain’t Broke, Don’t Fix It”

 

[Partimewages]

I am thinking of a situation where thermal inertia is @ play ?


The difference between “possibility“ & “probability” here I do no know, but I think it would be “possible” to have the cells colder than the BMV temp sensor.

I have thought of “upgrading” my Van to FLP from my AGMs, but in a bit of a quandary of “If it Ain’t Broke, Don’t Fix It”

Nearly no way for this to happen if the temperature sensor is placed correctly. It should get cold before the cells.

 

[Ep1phany]

The difference between “possibility“ & “probability” here I do no know, but I think it would be “possible” to have the cells colder than the BMV temp sensor.

I have thought of “upgrading” my Van to FLP from my AGMs, but in a bit of a quandary of “If it Ain’t Broke, Don’t Fix It”

I also live in Canada and I have mounted a temperature sensor inside my SOK battery (no built in heater) to turn on a DIY heating pad, it's in direct contact to a cell. My experience has been it takes a much longer time to cool and heat the cells than I first initially thought. Earlier this month when temperatures went from +15C to -10C, my cells stayed above 0 for a couple of days with no heat in a semi-insulated battery enclosure inside my trailer (not used, heat off). The Victron smart shunt temperature sensor on my battery terminal was always colder than inside with the cells.

Heating the battery took longer as well, but I'm only using about 12 watts so that needs to change if I want to camp in very cold weather, but for moderate cold it's kept the battery above 0.

I am SO glad I'm not dragging around two Trojan T-125's anymore.

 

[RV8R]

Nearly no way for this to happen if the temperature sensor is placed correctly. It should get cold before the cells.

I’m just not that lucky with nearlys, ifs, & shoulds ?

 

[rharries]

I'm concerned you think the BMV relay is something it isn't. The relay on the BMV is a control relay, i.e., it opens or closes based on SoC, temp or voltage criteria, but it in no way limits current through the shunt. If your particular MPPT has a control relay, you could have the BMV relay open at low temp while connected to the control relay on the MPPT. This would prevent the MPPT from charging until the BMV relay closes.

sunshine: As you suspected, I had assumed that the programmable relay settings in the Victron connect app were to govern current through the shunt. After further reading (and inspection of the back of the display unit) I now know that the relay is used for connecting devices such as the situation you describe. thank you for explaining this.