Seed germination mat as a lithium battery heater

RMo

I haven't seen much discussion on keeping Lithium batteries warm (enough) in the winter and I'd be interested in knowing what others are doing.  I bought an 40W AC-powered VivoSun seed germination heat pad a few weeks ago but wasn't sure how well it would work.  I finally got the chance to see last night as it got down to 6 F. -- the under-bed battery compartment was at a toasty 46 F in the morning.   I'm assuming now that I'll be OK at 10 or 20+ below - the goal being to keep the battery above -4 F.  An interesting thought is that if the mat works that well, you could keep the battery warm enough using the inverter to power it, and we could use it when winter camping.  Anybody using their LiFePos in the winter, and how do you warm them?

VictoriaP

Interesting idea. I’ve read they can’t be charged below 32°F. So why would the goal be to keep them above -4°F?

RMo

VictoriaP said:

Interesting idea. I’ve read they can’t be charged below 32°F. So why would the goal be to keep them above -4°F?

My understanding is that they can be used, but not charged, under 32, but should never be exposed to temps under -4.  That is what my battery manufacturer recommends as a minimum temperature for storage.

RFraer

I just got back from a three week trip to the TX, AZ area. I have three SOK LiFePos  Batteries located under the bed. I spent a night at a Walmart in Fort Stockton TX. During the night there was high winds (20-25 MPH) and the temperature when I got up was 20F. When I tried to use the sink there was no water. Apparently the outlet line from the fresh water tank had frozen. I then checked the battery temperature through my Victron VE.Bus Smart Dongle that is attached to one of the batteries, it indicated 80F at the battery.  The Alde heater that is in the compartment next to the batteries kept them toasty, I am not going to be adding a battery heater. I will be looking into a tank heater but it will be 12v. Luckily there was no damage to the water tank line.  I concluded that my tank froze because of the high winds that got under the floor through the large frame holes. Later in the trip I encountered low temps again but no wind and did not have a water freezing issue. I will also be looking into a temporary way to plug the frame hole during cold temperatures.

RMo

I haven’t been brave enough to go out in the serious cold, maybe someday.  For now I’m just trying to keep the battery above -4 with the camper in the driveway.  Not sure it’s absolutely necessary but the specs say to store above -4, other things I’ve read say it doesn’t matter.  I’ll err on the safe side.

RMo

VictoriaP said:

Interesting idea. I’ve read they can’t be charged below 32°F. So why would the goal be to keep them above -4°F?

@VictoriaP I’ve done some more research on why I thought Lithium batteries shouldn’t be stored at below -4F.  I used to own a class b Sprinter and in the ClassB Forum the common understanding is that you should avoid -4.  I also see many manufacturers specs listing the minimum storage temp as -4.  Elite Power Solutions goes as far as to say:

"Temperatures below -4°F (-20°C) will cause the electrolyte to freeze which will cause permanent damage to the batteries if it does not kill them entirely. If storage temperatures will go below -4°F then you will need to heat the batteries to above -4°F to prevent damage to the battery. There is no exception to this." 

Hope that Helps

VictoriaP

RMo said:

VictoriaP said:

Interesting idea. I’ve read they can’t be charged below 32°F. So why would the goal be to keep them above -4°F?

@VictoriaP I’ve done some more research on why I thought Lithium batteries shouldn’t be stored at below -4F.  I used to own a class b Sprinter and in the ClassB Forum the common understanding is that you should avoid -4.  I also see many manufacturers specs listing the minimum storage temp as -4.  Elite Power Solutions goes as far as to say:

"Temperatures below -4°F (-20°C) will cause the electrolyte to freeze which will cause permanent damage to the batteries if it does not kill them entirely. If storage temperatures will go below -4°F then you will need to heat the batteries to above -4°F to prevent damage to the battery. There is no exception to this." 

Hope that Helps

That’s good to know, thanks!

I’m still on the side of “If you’re going to go to the effort of heating, may as well make sure you can charge too,” which is why I’m leaning towards self-heating LiFePo4 instead. But your solution should at least protect the batteries from damage.

tphaggerty

-4 F is the discharge limit, at least for Renogy LiFePo batteries (per the spec sheet). -13 F is the low storage limit. The Renogy (and Battleborn) have low temp cutoffs programmed into the BMS (battery management system) controller for the batteries. Charging cutoff is about 35 F (I have tested this), discharge cutoff is -4 F (I have not tested this). 

I think the biggest difference between “premium” Li batteries (Renogy, Battleborn, SOK?) is that they have the BMS programming *and* the necessary temp sensors to do these cutoffs. Some of the more budget level batteries just don’t (Will Prose is a great resource for this info and testing on YouTube). It pays to be careful anyway, but I think having batteries capable of handling low temp situations is, IMO, worthwhile.

With that said, if I were buying batteries now, I would spring for the self heating ones, both Renogy and Battleborn have them at about $100 upcharge per battery. I’m trying to determine if it is worth adding some sort of heating to my battery compartment since we do winter camp and my batteries are not self heating… ☹️

RMo

I’m a big fan of Will and of David Poz.  From their reviews it’s becoming clear that it’s increasingly possible to get inexpensive batteries with effective BMSs with low temp cut offs.  Me being a value shopper (aka cheap with standards), I went with the highly rated EG4LL 400ah lithium for $1499.  It fits nicely under the bed of the 2019 400 and let’s me run the A/C for hours.  For us the heat mat works fine as we have AC power in the driveway.  We haven’t winter camped yet so the temp cut offs haven’t mattered.

AnOldUR

Slightly off topic, but what inverter are you, @RMo, using to power the AC with that EG4LL battery?

RMo

AnOldUR said:

Slightly off topic, but what inverter are you, @RMo, using to power the AC with that EG4LL battery?

We use a Giandel 3000w.  Works well.

Denny16

@RMo! Interesting, how many hours can you run the Cool Cat AC of that setup?

I have looked into doing something similar, using a 3K inverter.
 Cheers 

RMo

Theoretically it would run 4 plus hours, depending on conditions, but I’ve only run it for about 2.5, which used about 60% of the battery.  We usually just use the A/C on battery for lunch stops in the heat of the day.  The battery also works well for the microwave.