Do LFP produce heat with discharge?

[Wycowboy]

So here is the deal. I’m building my new battery, (see other posts) it will be house in a well insulated but not heated shed that mostly does not get below 20-25 deg f. Usual the coldes it hits is 34 or so. But we do get some cold snaps out here I. Wyoming.

And how if LFP batteries do produce some heat during discharge, and I build a well insulated battery box like maybe r15-24
Will the low draw we have at night( which is only 20-40 watts) keep the cells warm enough? To charge?


Love the thoughts’
Thanks a ton!
Jeff

 

[Wycowboy]

So here is the deal. I’m building my new battery, (see other posts) it will be house in a well insulated but not heated shed that mostly does not get below 20-25 deg f. Usual the coldes it hits is 34 or so. But we do get some cold snaps out here I. Wyoming.

And how if LFP batteries do produce some heat during discharge, and I build a well insulated battery box like maybe r15-24
Will the low draw we have at night( which is only 20-40 watts) keep the cells warm enough? To charge?


Love the thoughts’
Thanks a ton!
Jeff

Actually I’m not sure it has ever gotten down to 25. But I suppose it possible

 

[Diesel Pro]

From an output perspective I say yes. On the marine side guys with fishing boats running lithium starting batteries have reported that if they get too slow cranking when cold they run their power trim motor up and down a couple of times and then resume cranking. What that relates to as far as charging temps remains to be seen. A BMS with bluetooth and low temp protect would be handy in this regard to test.

 

[Sojourner1]

I have over 5.5 years of everyday use and they show no heat gain from the cells at such a low draw of a 100w through the night. I can see all individual cells live time.

Here's an example of my cell temps and compartment temps but if you look at the cell temps from first reading till I started the generator to throw a small charge into the bank. Some of the cell heat gain is from the inverter working in the compartment warming it. The bank always has a 100w load on it.

If cold is a concern a heat pad can easily be figured into your build for that just incase.



Here is from a couple consecutive day readings.

 

[HRTKD]

As the temperature of the battery approaches 32° F, the charging amps should decrease such that when you get to 32° F no charging takes place. If you keep the batteries warmed well above 32° F then the concerns about charging decrease.

My RV trailer LiFePO4 battery bank is designed to provide power for days at low current draws. Because of the low draw, I see almost no temperature change. In the summer I do remove the rigid foam insulation to ensure the batteries can dissipate heat should the need arise.

If you plan to draw at high current rates, then your battery bank may see a temperature rise. Enough to keep the batteries from freezing? I wouldn't count on that and a warming system should be considered.

 

[Wycowboy]

Really good info!
I will work some sort of heat into the build!
Much appreciated !!

 

[upnorthandpersonal]

Will the low draw we have at night( which is only 20-40 watts) keep the cells warm enough?

No, even with the BMS in the same box. The efficiency of the battery is so high (well into the 90%) that there is no waste heat to speak of even at high draws.

To keep them warm, you can use:

- A polyimide heating pad like this:
https://www.amazon.com/12V-Flexible-Polyimide-Heater-Plate/dp/B07P2RJDPL
(couple it to an aluminium block or something)

- Thermostat like this:

Amazon.com

 

[100 Proof]

No, even with the BMS in the same box. The efficiency of the battery is so high (well into the 90%) that there is no waste heat to speak of even at high draws.

To keep them warm, you can use:

- A polyimide heating pad like this:
https://www.amazon.com/12V-Flexible-Polyimide-Heater-Plate/dp/B07P2RJDPL
(couple it to an aluminium block or something)

- Thermostat like this:

Amazon.com

That's exactly what I'm using.

 

[newbostonconst]

That 10% round trip efficiency lose all goes to heat.....the quicker and more you cycle the battery the more heat produced. There are cabinet heat lose calculators for commercial electrical panels that likely will show your storage panel is letting the heat out, so add some insulation.....

 

[Sojourner1]

That 10% round trip efficiency lose all goes to heat.....the quicker and more you cycle the battery the more heat produced. There are cabinet heat lose calculators for commercial electrical panels that likely will show your storage panel is letting the heat out, so add some insulation.....

"IF" this was the case and the cells actually warmed up with any significance wouldn't they over heat in the summer with all the insulation added?

 

[newbostonconst]

"IF" this was the case and the cells actually warmed up with any significance wouldn't they over heat in the summer with all the insulation added?

If you are worried about that then make if removable in the spring and replace it in the fall. Or have an automatic heater that wastes energy.

 

[Sojourner1]

I'm not worried about it because I've shown the batteries don't produce significant heat under the the low C appliance the OP asked about.

 

[Sojourner1]

If you are worried about that then make if removable in the spring and replace it in the fall. Or have an automatic heater that wastes energy.

So much for letting it work in the background peaceful now you want to make it an on going project.

 

[newbostonconst]

So much for letting it work in the background peaceful now you want to make it an on going project.

Sliding in and out a couple pieces of foam isn't really a project if designed right....or foam around the outside. Much of the time just holding the warm air in will make the biggest difference. Also each side you do reduces heat loss by 1/6th so you don't have to do the whole thing either, but if it is open to the air insulation isn't going to make much of a difference.

 

[Wycowboy]

That's exactly what I'm using.

Good to know, how many pads are you using? How big is your battery bank if you don’t have a 12 V system how do you tie them in? I was kind of thinking about using something like this below it seems only be around 20 White’Good to know, how many pads are you using? How big is your battery bank if you don’t have a 12 V system how do you tie them in? I was kind of thinking about using something like this below and gives me really good temperature control
The 2 mats will allow the calls to sit enteral on them or on the side

Amazon.com

https://www.amazon.com/gp/aw/d/B01ANCB24W/ref=ox_sc_saved_image_1?smid=A1RUFFFCQ74BCW&psc=1

 

[upnorthandpersonal]

I'm using one 7W pad for each of my 16 cell batteries (14kWh each). It doesn't take much to keep them at temperature if your box is properly insulated.
You can use a 12V DCDC converter.

 

[Wycowboy]

How had it been working for you? Have you had it tested with a some cold days ? So if you have 16 of them that’s like 112 watts

Did you look at the links I included? Any thoughts?

Truly appreciated the help!!!! ?

 

[upnorthandpersonal]

How had it been working for you? Have you had it tested with a some cold days ? So if you have 16 of them that’s like 112 watts

No, I mean just one pad for the entire 16 cell battery. It gets pretty cold here, -16C last week - and the building they're in isn't always heated. The pad doesn't even have to be on all the time to keep the batteries warm.

My guess is that those things in your links will work, it's just that you're driving it through the inverter so it has to be on all the time, and 20W is perhaps overkill.

 

[wiseacre]

I have an insulated box made of 2" foam board (4' long x 2' high x 2' wide)
one end and back is permanent. the other end, front and top are loose
the loose end and front boards sit on the floor, the top is just placed on the side's edges. (with a weight on top to keep it "secured/sealed"
There's quite a bit of empty space

(2) 8s (long) DYI batteries with plate and compression rods sit side by side lengthwise
A seed starting heating pad sits on edge between the batteries. (with temp controller off to the side)
https://www.amazon.com/VIVOSUN-Seed...6MKY7C8/ref=pd_lpo_1?pd_rd_i=B016MKY7C8&psc=1

 

[Wycowboy]

No, I mean just one pad for the entire 16 cell battery. It gets pretty cold here, -16C last week

Wow that is great! Can you send me a pic of the configuration or described it.
Solar shed is not heated at all but well insulated it stays pretty stable
Really only 5 cm pad!