Lithium auxiliary battery and cold weather charging

shade

Well-known member
I look forward to seeing how this works out. I'm going to have to develop a mounting solution, and incorporating heating at the same time makes sense. I'll have to rely on keeping the heat source as diffused as possible, possibly a using low output pads on five sides. In a nod to John, my goal will be to maximize longevity.

This is one of the times when having a store bought battery isn't beneficial. I suppose I could shuck Victron's blue box, but that isn't going to happen until a cell dies out of warranty.
 

john61ct

Adventurer
That's pretty legit. A perfectly sized box up to the shoulders of the cells made of aluminum, with an additional 0.75" interior space. Then slide a 0.25" aluminum plate between each cell. It'd be a pain in the pecker to make though as you'd want everything absolutely flush and perfect so dividing plates make acceptable contact with the bottom and the walls., i'd imagine. Then put that box in another box.
Sure, ideally.

But just the end-between-plates, bottom edges extended below to creat an air gap, sitting on the silicon pad(s)

would be good enough IMO. High-temp control in that gap or touching a middle plate.

Top/bottom/sides exposed to the box-ambient air.
 

john61ct

Adventurer
I suppose I could shuck Victron's blue box, but that isn't going to happen until a cell dies out of warranty.
Just treat as a unit, inside the warmed box, just take a bit longer to get the cell interior warm.

Y'all have seen those self-warming drop-ins too right?

Not recommending, just FYI
 

luthj

Engineer In Residence
Unless you are worried about a cold soak recovery (which would not be often), a simple insulated box with a few heating pads, no more than 2W per square inch, sub 1W is ideal. Just have it stay warm 24/7. With decent insulation its pretty minor power requirements in most cases.
 

shade

Well-known member
Just treat as a unit, inside the warmed box, just take a bit longer to get the cell interior warm.

Y'all have seen those self-warming drop-ins too right?

Not recommending, just FYI
Yeah, but the Dutch haven't released that tech yet. ?

With alternator charging available, I won't have to worry too much about consumption, so I plan to leave whatever I use active as long as the temperature goes low enough to justify it. My only concern would be extended time away from the truck, with the potential for snow to prevent solar charging. If that went on long enough, that's when the LVC would earn its keep.

I'll also be removing the battery when it's not needed. No need to beat it up doing daily driver duty.
 

shade

Well-known member
Unless you are worried about a cold soak recovery (which would not be often), a simple insulated box with a few heating pads, no more than 2W per square inch, sub 1W is ideal. Just have it stay warm 24/7. With decent insulation its pretty minor power requirements in most cases.
Yep. I may even find a decent battery heating blanket that does it all. I have a few silicone engine heaters on hand, but they're far too hot.
 

luthj

Engineer In Residence
I was looking at thin film heating material for floors. Its available in pretty low outputs and DC voltages. This could easily be placed between cells, or wrapped around them. If you need more output it could be stacked in multiple layers.

 

luthj

Engineer In Residence
Yep. I may even find a decent battery heating blanket that does it all. I have a few silicone engine heaters on hand, but they're far too hot.

Wiring the heaters in series will drop the output.
 

shade

Well-known member
I was looking at thin film heating material for floors. Its available in pretty low outputs and DC voltages. This could easily be placed between cells, or wrapped around them. IF you need more output it could be stacked in multiple layers.

Now that's an interesting solution, and it shouldn't be difficult to work it into an enclosure. I can't tell from the page; is that film on a roll cut-to-fit?
 

luthj

Engineer In Residence
Now that's an interesting solution, and it shouldn't be difficult to work it into an enclosure. I can't tell from the page; is that film on a roll cut-to-fit?

Yes, the conductors run down the left/right sides. It can be cut at any point perpendicular to the long sides.
 

shade

Well-known member
This may work, too. Need to figure out the output at 12VDC, though.

 

hour

Observer
Damn dude if I had an off the shelf $1600 battery I'd probably look at something a little less... shittierchinese. Gotta be some purpose built battery wrap @ 12v that you can then control independently via DIY or another $20.
 

luthj

Engineer In Residence
The floor heating films are pretty reliable. Its just carbon and copper printed between two sheets of plastic. The major advantage is you can cut to length pretty easily, and they have lower output per unit area, so its suitable for wrapping a whole pack for even heat.

With a good BMS if the heating pads fail, you won't break anything.
 

shade

Well-known member
Damn dude if I had an off the shelf $1600 battery I'd probably look at something a little less... shittierchinese. Gotta be some purpose built battery wrap @ 12v that you can then control independently via DIY or another $20.
Well, it was only $1500, so I have a little headroom to work with. :)

I'll keep looking, but I like the idea of some thin film surrounding the case, outputting low, even heat. I'm surprised there aren't 12V options designed for LFP batteries.
 
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luthj

Engineer In Residence
Does the Victron BMS support heater control?

I saw this enclosure calculator. Enter the enclosure size and insulation. It will tell you the passive cooling load, which is the heat transfer to the exterior. For a a 1 cubic foot box with 1" insulation, in 0F ambient and 50F internal temps, the heating load is only 20W.

 

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