12V battery build, some doubts

[kiaora_]

Hello,

First of all, it is my first post here and I would like to thank you for this mine of information on the forum, it's great to have so much technical information in one place, bravo!

I'm going to assemble my first battery with LFP cells and I would like to have your opinion and advice to be sure to do things properly.

I have ordered from Jenny (Docan) 160Ah EVE cells and a 200A JBD BMS (with the heater port) which should arrive soon.
The battery will be used as an auxiliary battery in a small Campervan to replace an aging AGM battery. The van is used, all year long, in Europe, that's why I tried to thermally insulate the cells and added a heating pad.

I share with you some illustrations of the assembly I plan to make:





I have some doubts about :
- compressing the cells : I have the impression that this is a subject of debate here, is it worth it for 160Ah cells ? in the idea I left a gap to eventually compress the foam a bit when tightening the case, but I have no idea of the effort that will be applied.
- heating pad : it's a 15W pad, with a possible outside temperature of -10°C, I have no idea if it will be enough to bring the cells above 0°C or 5°C for the recharge.
- heating pad : it's a 5$ pad on Aliexpress, do you have any feedback on the durability of this kind of pad ? risks in case of failure ?
- insulation and heat dissipation : I decided to insulate the cells for the cold but as a consequence it also limits the heat dissipation. The battery will be charged either by a solar panel with 20A maximum, or by a DCDC booster with 30A. I don't realize how much energy is dissipated per cell and if there is a risk of overheating the cells during the charge or discharge.

If you have any comments or feedback, I'm interested! Thanks

 

[Zil]

Don't use foam against the cells or as restraining plates. The foam has not enough "firmness". Something like 1/4 aluminum plate is needed. I have not investigated using plywood for the restraining plates, but I believe I have seen some engineers use it. I think the wood of the box would provide enough insulation using a heating device. The aluminum under the bank would help spread the heat. It could be less than 5mm. We have Home Depot that sell thinner, 2mm, aluminum sheet that could be bent up the battery a bit and be a splendid heat sink/radiator.

 

[HRTKD]

I have plywood on each end of the compression fixture. That serves as my "insulation" there also. I would not use foam at the ends of the battery. This is in a mobile environment so you want the cells well secured against movement. The foam could allow movement depending on what type of foam you're using.

I used 12 watt pads on the long sides of the battery. I specifically chose to not put the heating pads on the bottom. I didn't want the weight of the battery to cause any damage to the heating pad. That may be a paranoid theory on my part, but I'm OK with that. Here is my writeup on my heating pads:

LiFePO4 Battery Warmer Install

This is my install of a custom set of battery warmers from Ultra Heat. I had contacted them through email asking about a warming profile for LiFePO4 batteries. They responded with a design to my specifications, including warming pads that fit my batteries exactly. While I initiated the...

diysolarforum.com

 

[kiaora_]

Don't use foam against the cells or as restraining plates. The foam has not enough "firmness". Something like 1/4 aluminum plate is needed. I have not investigated using plywood for the restraining plates, but I believe I have seen some engineers use it. I think the wood of the box would provide enough insulation using a heating device. The aluminum under the bank would help spread the heat. It could be less than 5mm. We have Home Depot that sell thinner, 2mm, aluminum sheet that could be bent up the battery a bit and be a splendid heat sink/radiator.

Closed cell foams can be quite stiff when compressed over a large area but I don't know the behavior over time.
Yes, I'm considering a 1.5mm thick aluminum plate to dissipate heat from the pad.

 

[kiaora_]

I have plywood on each end of the compression fixture. That serves as my "insulation" there also. I would not use foam at the ends of the battery. This is in a mobile environment so you want the cells well secured against movement. The foam could allow movement depending on what type of foam you're using.

I used 12 watt pads on the long sides of the battery. I specifically chose to not put the heating pads on the bottom. I didn't want the weight of the battery to cause any damage to the heating pad. That may be a paranoid theory on my part, but I'm OK with that. Here is my writeup on my heating pads:

LiFePO4 Battery Warmer Install

This is my install of a custom set of battery warmers from Ultra Heat. I had contacted them through email asking about a warming profile for LiFePO4 batteries. They responded with a design to my specifications, including warming pads that fit my batteries exactly. While I initiated the...

diysolarforum.com

Thanks for the link to your writeup about heating pads, I will read your post.
Regarding your paranoid theory, have you ever heard of a heating pad failure that goes wrong? That is also one of my concerns.

 

[HRTKD]

Regarding your paranoid theory, have you ever heard of a heating pad failure that goes wrong? That is also one of my concerns.

No, but I don't want to be THAT GUY that posts about my experience in the Up In Smoke subforum.