Insulation material between aluminum case cells.

[Electro Dan-O]

Building my first battery bank and wanted to get some ideas on what materials would be good to use between/around aluminum case(or other) cells. I'm going to be using these in my boat, but would love to see what the DIY crowd has come up with and why for different environments. I've seen thin closed cell foam used and that really seems like a great idea. Well, let's hear it!

 

[Critter350]

Interested in this myself. To insulate between cells or not and how to strap them together, tight or loose etc.
Assume application has a lot to do with it.
Mine will be in a 4x4 (hence vibrations and bouncing) that doesn’t see ambient temps below 0 or above 45°C. I’m also not expecting huge load or charge currents, probably 20A max so self generated heat won’t be great.
I’ve heard that delamination can be more of an issue for prismatics than cylindricals, so strapping them tightly together mitt help this? But at the expense of room to expand / contract. So, yes please, very interested in perspective of others.

 

[Fpoet]

This is also a question that I was about to ask, to insulate the cells from the enclosure, which could be metal (aluminum or stainless steel).

 

[Steve_S]

A) Never install batteries into a metal case without providing electrical isolation between the box & the cells. (short potential)
B) Never use anything that can retain moisture. Moisture & humidity is not good.
C) Insulation between cells is not needed, aside from electrical separation which the blue vinyl (blue aluminium cells). You can add a separator if you wish, keep it thin & rigid.
-- NOTE, LFP cells expand and contract slightly during charge/discharge cycles. BInding cells is very important as that reduces "bloat potentials" and will increase lifecycles. Binding pressure should be no more than 12PSI and done at 25C temp with 50% charge in the cells. The PSI will change with expansion & contraction, so this is an important detail.
D) Spray Foam... ever try to clean that stuff off ? remmenber you may have to service your battery pack. High Density XPS Foam sheet external to battery box works well...

When it comes to Boating & LFP there are two articles which are more or less a "Must Read". Many quirks, foibles & gotcha's lurking there for the unaware.
Electrical Design For a Marine Lithium Battery Bank | | Nordkyn Design
LiFePO4 Batteries On Boats - Marine How To

You may also want to refer to this:
General LiFePO4 (LFP) Voltage to SOC charts/tables 12/24/48V (diysolarforum.com)

Hope it helps, Good Luck.
Steve

 

[Sharky722]

I'm using G10 sheet comes in various thickness.

 

[Critter350]

I’ve come across this thread since my post: Post in thread 'EVE-280 cells should these be clamped tight or spaced for expansion?'

 

[Solarfun4jim]

I used an insulation material that is only 3mm thick. I then compressed the cells with threaded rod and end restraints, such that the nuts were tightened so that i could only just turn the threaded rods by hand. This leaves the pack as one unit, but allows for a very small amount of expansion right in the middle of the pack cells. On the outer edges of the cells, the formed aluminium is stronger and doesn't expand as much as the cell faces. I used 6 threaded rods so that i could measure the exact length between each one, thus ensuring an even distribution of compression over the cells faces...ie not more pressure applied to top of cells than bottom etc. Extra thick insulation between the cells sidewalls and the threaded rod. This setup allows for a larger delta T between the cells, rather than compressed directly together, which should keep the cells cooler on the inside, but more stable as a pack overall.
If i lift one end of the pack, the whole pack lifts in unison, but i would not risk carrying said pack without further support underneath.




Supplied busbars and screws only being used in testing/commissioning phase.

 

[Fpoet]

A) Never install batteries into a metal case without providing electrical isolation between the box & the cells. (short potential)
B) Never use anything that can retain moisture. Moisture & humidity is not good.
C) Insulation between cells is not needed, aside from electrical separation which the blue vinyl (blue aluminium cells). You can add a separator if you wish, keep it thin & rigid.
-- NOTE, LFP cells expand and contract slightly during charge/discharge cycles. BInding cells is very important as that reduces "bloat potentials" and will increase lifecycles. Binding pressure should be no more than 12PSI and done at 25C temp with 50% charge in the cells. The PSI will change with expansion & contraction, so this is an important detail.
D) Spray Foam... ever try to clean that stuff off ? remmenber you may have to service your battery pack. High Density XPS Foam sheet external to battery box works well...

When it comes to Boating & LFP there are two articles which are more or less a "Must Read". Many quirks, foibles & gotcha's lurking there for the unaware.
Electrical Design For a Marine Lithium Battery Bank | | Nordkyn Design
LiFePO4 Batteries On Boats - Marine How To

You may also want to refer to this:
General LiFePO4 (LFP) Voltage to SOC charts/tables 12/24/48V (diysolarforum.com)

Hope it helps, Good Luck.
Steve

Thanks for the info. I have done quite a bit of reading so far, but I had not read the Nordkyn articles. Still learning.

I will be building two 12V 280Ah batteries, and I am still looking for boxes or enclosures to safely contain everything (fixture, bms, cables) in a reasonably compact format. This is why I am considering metal and electrical insulation within the enclosure.

 

[newbostonconst]

Due to your use, and possible chafing, I would put rubber sheet.

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[HRTKD]

If there is a chance that a battery warming system will need to be used, then I recommend against adding anything between the cells. The material between the cells may prevent the spread of the heat from the warming pads.

Not many of us use a warming system, but I figured it wouldn't hurt to throw that out. I do not have anything between the cells that are used in my RV trailer. My compression frame has kept the cells from moving/shifting and my RV has been down some rough roads.

 

[Cdkipp]

If there is a chance that a battery warming system will need to be used, then I recommend against adding anything between the cells. The material between the cells may prevent the spread of the heat from the warming pads.

Not many of us use a warming system, but I figured it wouldn't hurt to throw that out. I do not have anything between the cells that are used in my RV trailer. My compression frame has kept the cells from moving/shifting and my RV has been down some rough roads.

What size cells are you using in your RV? I am wondering whether I should stay below 200 amp hours.

 

[Hedges]

-- NOTE, LFP cells expand and contract slightly during charge/discharge cycles. BInding cells is very important as that reduces "bloat potentials" and will increase lifecycles. Binding pressure should be no more than 12PSI and done at 25C temp with 50% charge in the cells. The PSI will change with expansion & contraction, so this is an important detail.

Is "PSI will change" a warning, or a description of desired condition?

If solidly held at a particular thickness, pressure would vary as the cells try to swell.
If compressed by spring clamping force, pressure would remain fairly constant as cells swell (in which case compliant busbars would be desireable.)

Do you know which would be better?

 

[HRTKD]

What size cells are you using in your RV? I am wondering whether I should stay below 200 amp hours.

280Ah cells. 4s2p configuration. Each 4s battery is independently compressed and mounted to the compartment floor.

 

[EasyStreet]

I used an insulation material that is only 3mm thick. I then compressed the cells with threaded rod and end restraints, such that the nuts were tightened so that i could only just turn the threaded rods by hand. This leaves the pack as one unit, but allows for a very small amount of expansion right in the middle of the pack cells. On the outer edges of the cells, the formed aluminium is stronger and doesn't expand as much as the cell faces. I used 6 threaded rods so that i could measure the exact length between each one, thus ensuring an even distribution of compression over the cells faces...ie not more pressure applied to top of cells than bottom etc. Extra thick insulation between the cells sidewalls and the threaded rod. This setup allows for a larger delta T between the cells, rather than compressed directly together, which should keep the cells cooler on the inside, but more stable as a pack overall.
If i lift one end of the pack, the whole pack lifts in unison, but i would not risk carrying said pack without further support underneath.


View attachment 29115View attachment 29116View attachment 29117

Supplied busbars and screws only being used in testing/commissioning phase.

I am so glad I watched the Big Battery Tour and heard them talk about the positive terminal being connected to the outside of aluminum case batteries. Clamping these batteries together without the insulation between them is a recipe for disaster. In my opinion, as in your post, this extra step should always be part of the conversation every time clamping aluminum cased batteries together is discussed. I'm taking my batteries apart to add the insulation material right away.

 

[Gazoo]

I am so glad I watched the Big Battery Tour and heard them talk about the positive terminal being connected to the outside of aluminum case batteries. Clamping these batteries together without the insulation between them, as shown in your post, is a recipe for disaster. In my opinion this extra step should always be part of the conversation every time clamping aluminum cased batteries together is discussed I'm taking my batteries apart to add the insulation material right away.

Could it be leakage?

Heltec BMS' (up to 350A) with Active Balancing & Independent Active Balancers | Page 5 | DIY Solar Power Forum (diysolarforum.com)

 

[EasyStreet]

They are made that way. In the video they said the positive was tied to the case of the cells. The (thin) blue wrap keeps them from shorting out when connected in a battery pack. I confirmed it on my Eve cells with a meter.

Look at the 6 minute mark on this youtube link We took a Tour of BigBattery.com's Warehouse! - YouTube

 

[Electro Dan-O]

I decided to use thin(.030") plexiglass that I got from an old picture frame that was heading to the trash. I polished them and the cells with automotive wax to hopefully keep friction down. I feel good about it.

 

[EasyStreet]

Nice. Looks like a perfect. I have 1/8 neoprene that should do the trick.

 

[Gazoo]

They are made that way. In the video they said the positive was tied to the case of the cells. The (thin) blue wrap keeps them from shorting out when connected in a battery pack. I confirmed it on my Eve cells with a meter.

Look at the 6 minute mark on this youtube link We took a Tour of BigBattery.com's Warehouse! - YouTube

I know that's what they say. And I know you will see voltage between the negative cell terminal and the cell case. But regarding the EVE cells, the amount of current is so small it is not a cause for concern as posted in the thread I linked to. I don't see case positive mentioned in any of the spec sheets I have reviewed. I used to think it was a big deal too and was posting concerns about it until it was discovered it's leakage voltage.

I wonder if Big Battery is aware of this. Did they check to see how much current is flowing between the negative terminal and the case?

I am not implying it's a bad idea to put some insulation between the cells. But I don't think there is a big cause for concern leaving it off. I left it off.

 

[EasyStreet]

Leakage voltage? That would be a short. I've heard of current leakage but that's different. The voltage I read was full cell voltage at the case. I can't find a good picture of the construction online. I'm thinking that when the cell is built the cathode is on the outside and touches the case. Either that or it is an intentional physical connection. I can do a low amperage test. It would be interesting to do a high amperage test on a battery nobody cares about. Might be a cool video too.