Best practice for freezing temperatures and lifepo4 batteries

alex01

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Hi everyone, I have campervan which I am planning on upgrading to a lifepo4 setup. I live in the PNW and do a fair amount of ski trips in the winter so I will be exposing the batteries to freezing temperatures from time to time. I have tried to find as much information as I can around what to do to manage lithium batteries in cold temps but no where seems to indicate the a recommended or best practice setup. I am hoping someone could shed some light.

In my system I have alternator charging as well as a 200w solar with a Epever MPPT controller. Most batteries BMS have some sort of low temperature cut off for charging. But when the BMS cuts off charging, wouldn't this damage the Solar Charge Controller as it's always recommended to connect the SSC to a battery and the low temp cut off disconnects this? Since many SSC's have external temp sensors, are they smart enough to cut off charging at a temperature?

The battery I'm looking at is the older Renogy lifepo4 as there's some sales right now, but its especially annoying as when it goes into protect mode you cant even turn it on unless you have a Renogy charge controller. So I'm seeing if I can find a way to not let the battery get below this temperature.

Is there a best practice to handle this? Some are saying use a heat pad and a temp sensor which turns it on. But doesn't seem like everyone agrees. Hoping someone can answer this.

Thank you,
Alex
 

kernel

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In a vehicle you could use electric heat pads or the coolant which is heated by the engine. Since you have a battery to battery charger, electric makes sense and is less wet! Insulate your battery compartment and add heat. Most heat pads are thermostat controlled to turn off at 38-40 deg. F and so are automatic. Two wires, a switch, fuse and holder, couple crimp connectors and a half sheet of 1 inch foam or several layers of good double bubble!
 

alex01

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That makes sense. I didn't realize heating pads gave built in thermostats. That would work while I was using it. However, what I'm not sure about is I have it parked for weeks at time sometimes and I don't really want the heat pad to just keep cycling, especially at night where there's no solar, I think this would just eat up the battery unnecessarily. If I turned the system off in this case, how do I also turn off the solar charge? I hear just killing the connection to the battery from the solar controller is bad practice unless the incoming power from the panels is also disconnected.
 

MisterSandals

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Hopefully you have some kind of array disconnect from your SCC. If not, you should consider a disconnect along with fuse/breaker solution.
LiFePO4 should hold a charge on its own for a long time unless you have some battery draw, in which case disconnect the load too if possible.
 

astronom

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Maybe you're already aware but a remark about charging LiFePO4 with an alternator: it can go wrong if the system is not made for it.
See for instance
where they explain what can happen if the alternator is inadequate and how to prevent the issue. I didn't get all the details but I believe the very low internal resistance of LiFePO4 batteries compared to LA is why a common alternator is not fit for the task.

Otherwise I agree with the others to isolate your panel before switching the battery off, this way you don't have any problem when you shut your system down.
 

tictag

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Couple of points to consider:
  1. Some battery manufacturers offer internal battery heating. I believe Battle Born's new product range will have this.
  2. LTO (Lithium Titanate) batteries have relatively low voltage per cell and a lower specific energy than others but are very safe, offer high charge and discharge capability and can be operated at sub-zero temperatures (e.g. 80% capacity at -30oC)
 

kernel

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That makes sense. I didn't realize heating pads gave built in thermostats. That would work while I was using it. However, what I'm not sure about is I have it parked for weeks at time sometimes and I don't really want the heat pad to just keep cycling, especially at night where there's no solar, I think this would just eat up the battery unnecessarily. If I turned the system off in this case, how do I also turn off the solar charge? I hear just killing the connection to the battery from the solar controller is bad practice unless the incoming power from the panels is also disconnected.
Heaters can and should be on a switch (or relay) same as pv source circuits. The ability of turning your system and loads off is for both safety and convenience.

There are relays that can be controlled by chargers and the logic that drives them can be set to do most any operation including being called to come on when you are on the way to use your cabin.
 

alex01

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I do have a DC to DC charger from the alternator (although not a lithium one) I think the voltage only goes to 13.8V

It sounds like there's no best practice/out of the box system to dealing with sub freezing charging, it's all just diy as you need it for lifepo4.

I will add a relay to disconnect the panels when not in use, I assume it's just a relay on the positive input of the panels to disconnect it.
 

kernel

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You would want a normally open relay to close when the battery is connected. Loss of the battery circuit would allow the relay to open. There has to be power electronics available for this. Victron?

If you are going lithium, your battery to battery charger should follow suit. They are indispensible and do away with most need for a portable generator and its needs and noise.

There are people out here who have been there im sure and could help. Im not one of them. I do not use lithium for a house battery nor have i installed them and so am unfamiliar with off the shelf solutions. For now...

Heaters and relays are another story.

The need to at least insulate, if not heat your battery in order to ready it to accept charge or keep it ready and improve its performance is not just for lithium. This tact may improve your current setup in cold weather and be ready for lithium to occupy the new toasty box.

There is alot about the way you need it to work that nobody knows except for you.
 

alex01

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I just read the article on the new Renogy DC-DC Charger w/ MPPT and I think this would solve my problem, it has built in lithium low temp cut off for charging for the alternator and solar. Seems like a good option. Only problem is now I cannot series connect my panels and am forced to parallel to keep within Renogy's 25V solar input rating (which kinda sucks).

Also don't have an ability to have an external display.

 

kernel

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I just read the article on the new Renogy DC-DC Charger w/ MPPT and I think this would solve my problem, it has built in lithium low temp cut off for charging for the alternator and solar. Seems like a good option. Only problem is now I cannot series connect my panels and am forced to parallel to keep within Renogy's 25V solar input rating (which kinda sucks).

Also don't have an ability to have an external display.

Im hoping thet Renogy will update its B2B charger to allow better than 12v modules..... the difference in cost between 12v panels and 20v and up is 100% in many cases and many are running two or more 300w modules, especially on big RVs.

Not sure what they were thinking there. We just mounted some Hanwha Q cells on a promaster van build and it made for an expensive controller requirement but saved money on mounts, wiring, overcurrent protection and panels.

Just because its a 12v vehicle system doesnt mean we want to employ 12v panels. Making full use of MPPT is always nice too.
 

SolarQueen

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The new KiloVault CHLX will use the solar power to run an internal heating pad. The 1800Wh model uses 96W, the 3600Wh model uses 192W. The BMS will not allow it to charge until it reaches a warm enough temp. By using the solar power instead of the battery to heat it, you are not wasting already stored energy for heat, you just lose the ability to add more until it is warm enough. Also insulating the batteries will help you keep the heat in the batteries, rather than in the RV.
 

bhellis1

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But when the BMS cuts off charging, wouldn't this damage the Solar Charge Controller as it's always recommended to connect the SSC to a battery and the low temp cut off disconnects this?


I don't think this is true but I would be very interested to hear from others on the forum. Once a BMS shuts down the battery, there is no place for a van SCC to put amps. It simply shuts off. There are lots of reasons for SCC to shut off - battery full, system short - and my udnerstanding is that they are designed to handle quick changes w/o damage to the system. I have victron in my van and it deals with bms shutoff for temp batteries, as well as full batteries from the alternator w/o any sign of trouble that I can see.

I think the most difficult part is warming LIFEPO4 batteries. My system has low watt heat pads on a relay switch w/ a thermostat that allows setpoints. I don't like it. I used 12w heating pads seperated from the cells with foam. I didn't want high w heat for concern about spot heating the cells and heavy draw on cold batteries. Seemed best to heat slowly, both the van cabin and the batteries. There has to be a better way/cleaner design.
 
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tictag

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I do wonder whether this 'Do not charge LiFePO4 below x oC' is as black'n'white as it sounds. Nature is rarely so black'n'white. I'll be willing to bet that charging will be on a sliding scale as temperature decreases e.g.
>5oC = 1C
0oC = 0.3C
-5oC = 0.2C
<-5oC = 0.1C
And if this is the case, no need for heaters just a cleverererer BMS that modulates the charge current with sensed temperature. Any current flowing into the batteries will have some heating effect so the batteries will always be warmer than their environment.

I have absolutely no evidence to back this up, it's just a hunch.
 

ghostwriter66

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I don't think this is true but I would be very interested to hear from others on the forum. Once a BMS shuts down the battery, there is no place for a van SCC to put amps. It simply shuts off. There are lots of reasons for SCC to shut off - battery full, system short - and my udnerstanding is that they are designed to handle quick changes w/o damage to the system. I have victron in my van and it deals with bms shutoff for temp batteries, as well as full batteries from the alternator w/o any sign of trouble that I can see.

I think the most difficult part is warming LIFEPO4 batteries. My system has low watt heat pads on a relay switch w/ a thermostat that allows setpoints. I don't like it. I used 12w heating pads seperated from the cells with foam. I didn't want high w heat for concern about spot heating the cells and heavy draw on cold batteries. Seemed best to heat slowly, both the van cabin and the batteries. There has to be a better way/cleaner design.

Totally agree -- the BMS shuts off CHARGING not the Battery being used .. we STOP charging our LiFePO4 batteries at 35 degrees BUT will run the batteries down to -20 ... therefore the battery is still hooked up to the SCC and giving it power .... BUT YES running a SCC with panels active and NOT hooked to a battery will let out the factory smoke ...
 

Solarfun4jim

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I do wonder whether this 'Do not charge LiFePO4 below x oC' is as black'n'white as it sounds. Nature is rarely so black'n'white. I'll be willing to bet that charging will be on a sliding scale as temperature decreases e.g.
>5oC = 1C
0oC = 0.3C
-5oC = 0.2C
<-5oC = 0.1C
And if this is the case, no need for heaters just a cleverererer BMS that modulates the charge current with sensed temperature. Any current flowing into the batteries will have some heating effect so the batteries will always be warmer than their environment.

I have absolutely no evidence to back this up, it's just a hunch.

I think you might be correct, but i'd guess at a logrithmic relationship....tails off very quickly, perhaps like this below...COLD CHARGING SCALE.png
 
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astronom

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I didn't want high w heat for concern about spot heating the cells and heavy draw on cold batteries. Seemed best to heat slowly, both the van cabin and the batteries. There has to be a better way/cleaner design.

Heavy draw of the battery in the cold doesn't seem to be a concern for their health, actually I think it's better, the natural aging of the battery is slowed down in the cold. Discharging it will even have the benefit of warming them up a bit via Joule effect. However, you loose (temporarily) capacity in the cold, but if you're using the energy to warm up the cells to be able to replenish them with a charge I guess that's worth it.

About a better design, there are in theory heat pumps that can be a better source of heat than the 100% yield of resistors (often displace around 4 times more heat energy than the electrical energy used to run them). Compressor based heat pumps are too big and expensive for the task here but Peltier elements based heat pumps might do the trick. I will try soon to build something like that and keep you updated. Then here the added benefit compared to heat pads is that you heat the air surrounding the battery, so the thermal distribution should be pretty homogeneous. Also an extra bonus: you can use the system in reverse to cool the battery in summer with all the excess power you have, and keep it around 20°C to limit it's aging.
 

Freddmc

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I presume this will be in a motorhome so, given that lifep04 batteries give off no gas why couldn't you put them in the living space, like a closet? Presumably the living space will be heated.
 

alex01

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You could do that (it's what I do), but there's always the time when you're away for a few days and the temperature drops below freezing.
 

Freddmc

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"You could do that (it's what I do), but there's always the time when you're away for a few days and the temperature drops below freezing. "

True enough. But from his original post he indcated that he likes to go on ski trips so I took that to mean short periods of time during which the motrohome would be heated.
And if you were away and the temp did go below freezing (for whatever reason)you can still draw from the battery, you just can't charge it. So you would be faced with raising the temp of the battery before charging.(pehaps from a heater that gets its power from the battery.)
So from a practical standpoint you go skiing for the day and the temp. outside is 20 below 0. Heat is on in the motor home and the solar panels (if you have them) charge during the day. No problem. Next day you will be away for a few days so you turn off the solar panels so they wont charge in anticiation of batteries being below freezing.
Also, another consideration is that if its below freezing you not only have to worry about batteries but also have to ensure that your water system doesn't freeze up as well.
 
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