DIY Li Battery Heater...A REAL TEST!

Rbertalotto wrote:
DIY Battery Heaters...A REAL TEST!...got down to 7F degrees last night. At 7am the battery compartment is at 35 degrees. Controller is set to turn on at 35F and off at 38F........The batteries are at 90% on the monitor.....Working GREAT!... http://rvbprecision.com/rv-projects/lithium-battery-heating-project.html

http://rvbprecision.com/rv-projects/lithium-battery-heating-project.html

well done, but like others I question the wattage of the heater. if you went with a hard sided rotomolded cooler you could probably get away with even less wattage, as the usage of the battery would probably generate enough internal heat to keep it good and your pads would only be a back up. but you do sacrafice a bit of portability that way.

Steve

be aware they now sell bms's with heating ports for DIY packs. people say they work well.

Rbertalotto wrote:
I'd have to measure it. But about 5" X 9".....

That's 45 sq in. Assuming 25w of heat output, I'd guess it'll heat to around 115-125f in open air (at room temp). I'd measure it with an infrared temp gun to be sure.

Delete - double post

I'd have to measure it. But about 5" X 9".....

Rbertalotto wrote:
Agree on the pad size. I bought a smaller, 2amp pad to try in the truck with the one battery to see how it works. Stay tuned!

How large is this 2a pad? I do know a single 25w (12v) 80x100mm silicone heating pad (which draws 2a) can get as hot as 160-170f. That's hot enough to burn your finger. Could be too hot for a plastic battery case. That's the primary reason why we used 4 of these same 25w heating pads wired in a parallel/series configuration. It distributes the same amount of heat as one 25w pad over a much larger area. With the 4, 25w pads wired parallel/series, each pad only heats to 110-120f (vs. 160-170f), and only draw 2a of total current (vs. 8a all wired in parallel).

otrfun wrote:
Great job! Very clean, well organized. For those planning on doing something similar, they'll find your pictures and videos very helpful. With all this cold weather we've had lately, it's a perfect time to test everything.

One observation. Got to wonder if such a high wattage heating pad is necessary. 78w (6.5ah) is quite a high draw---especially if you're boondocking and trying to conserve. Realize you're trying to heat your 100ah lifepo4 cells indirectly, by heating the exterior plastic case. No doubt there's some inefficiencies at play here.

We've found 4, 24w 80x100mm silicone heating pads (wired parallel/series) have the capability to heat our 200ah lifepo4 battery pack to 60f with an ambient of 0f. I'd guess they could probably maintain the cells at 35f with an ambient of -15f. Since the 4 pads are wired parallel/series they only consume 24w total (2a at 12vdc). This is a portable, completely self-contained battery with everything located inside an uninsulated Group 24 battery box. In cold weather we typically keep our lifepo4 cells at a constant 50f 24/7 so we can safely do .4c charges and .6c discharges at any time. We've found at 15f ambient, the heating pads (thermostat controlled) only draw approx. .75ah while keeping the cells at 50f. That's approx. the same overall draw as our inverter's parasitic, no-load draw.

Agree on the pad size. I bought a smaller, 2amp pad to try in the truck with the one battery to see how it works. Stay tuned!

Great job! Very clean, well organized. For those planning on doing something similar, they'll find your pictures and videos very helpful. With all this cold weather we've had lately, it's a perfect time to test everything.

One observation. Got to wonder if such a high wattage heating pad is necessary. 78w (6.5ah) is quite a high draw---especially if you're boondocking and trying to conserve. Realize you're trying to heat your 100ah lifepo4 cells indirectly, by heating the exterior plastic case. No doubt there's some inefficiencies at play here.

We've found 4, 24w 80x100mm silicone heating pads (wired parallel/series) have the capability to heat our 200ah lifepo4 battery pack to 60f with an ambient of 0f. I'd guess they could probably maintain the cells at 35f with an ambient of -15f. Since the 4 pads are wired parallel/series they only consume 24w total (2a at 12vdc). This is a portable, completely self-contained battery with everything located inside an uninsulated Group 24 battery box. In cold weather we typically keep our lifepo4 cells at a constant 50f 24/7 so we can safely do .4c charges and .6c discharges at any time. We've found at 15f ambient, the heating pads (thermostat controlled) only draw approx. .75ah while keeping the cells at 50f. That's approx. the same overall draw as our inverter's parasitic, no-load draw.

I hope some hardy soul will do this at more seriously low temperatures. Or that Li titinate will become affordable.

Rbertalotto wrote:
DIY Battery Heaters...A REAL TEST!...got down to 7F degrees last night. At 7am the battery compartment is at 35 degrees. Controller is set to turn on at 35F and off at 38F........The batteries are at 90% on the monitor.....Working GREAT!... http://rvbprecision.com/rv-projects/lithium-battery-heating-project.html

http://rvbprecision.com/rv-projects/lithium-battery-heating-project.html

It doesn’t take much to keep them warm, I set mine at 50f with 25 watt silicon heat pads. We got down to 8 degrees this week and no problem keeping my two 280 ah LifeP04 batteries warm. It’s nice hoping into the truck at 8 degrees and having a heated throw on your seat.