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Putting DIY battery in Ammo box

cwilken

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May 21, 2021
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My son just finished a 14S10P DIY battery made from 14S 10P cells from skateboards (battery hookup)
It is 58 volts and about 30amp hours. We tested it out for a few days in this old tool box but I would like to make a nice home for it in this Ammo Can. I believe these cells are not quite as safe as lithium iron phosphate.
If anyone could share a picture of their build on one of these or their ideas. It has an air tight seal and very HD.
Any way to :
1. Put terminals comming out the side that are isolated from metal box (finding isolated product is hard)
2. Isolate and insulate the BMS from battery (temperature)
3. evacuate air from inside and put heat sinks to metal walls???
4. Cooling system? I would like to keep it outside my house along a north facing wall.



PXL_20210827_223839485.MP.jpgbattery fin1.jpgammo can.jpg
 
This looks like a great product for isolating my terminals...Thanks!!!
 
I'm just skimming... But if that BMS is fan-cooled you need to make sure you get the heat out of the box.

People go wrong with batteries around testing. It can take a really long time to thermally soak a large Mass.

Remember to test your latent failure modes!

If your cells are causing the BMS to do a lot of balancing... Heat can build up. I would mount my BMS heat sink directly to the case of the ammo box.

Screenshot_20211225-085107.png

... I built many ammo can batteries over the years. My preference now is to use a knockout and a watertight, strain relieved, bulkhead attachment.

A knockout is a tool that cuts perfectly round holes in metal. Found in the electrician industry. It's like a hole saw, but it's actually a punch.

This will get you to a standard diameter... That will allow you to use industry available bulkhead fittings.

-methods
 
I'm just skimming... But if that BMS is fan-cooled you need to make sure you get the heat out of the box.

People go wrong with batteries around testing. It can take a really long time to thermally soak a large Mass.

Remember to test your latent failure modes!

If your cells are causing the BMS to do a lot of balancing... Heat can build up. I would mount my BMS heat sink directly to the case of the ammo box.

View attachment 77108

... I built many ammo can batteries over the years. My preference now is to use a knockout and a watertight, strain relieved, bulkhead attachment.

A knockout is a tool that cuts perfectly round holes in metal. Found in the electrician industry. It's like a hole saw, but it's actually a punch.

This will get you to a standard diameter... That will allow you to use industry available bulkhead fittings.

-methods
good point about heat issues that only become apparent after hours+ of demand.

when building a pack that may sustain long periods of high demand, ensuring the BMS MOSFET heat is transmitted to the outside world, rather than the battery cell material, may improve endurance performance

heat dissipation ?
 
Totally agreed!
Get the heat out of the box.

Those are a nice bulkhead fitting. Thanks for posting the link. I have used them before and they definitely work.

After having a few battery mishaps over the decades (LOL) I have a pull-away rule for my batteries that are larger than a couple kilowatt hours.

I still use the old 350 amp Anderson connectors that you can yank open. I developed this habit when I started working with 400V to 1000V systems in the 100KW range.

It can be terrifying if a battery starts going thermal.

...
But
I'm talking about building with sketchy pull-down cells. If you're building with new cells and a quality BMS then you can't beat screw terminals for the price.

I use the hydraulic crimpers. They are heavy and slow... But they make a hell of a crimp! You can get them for 40 bucks on Amazon.

The best crimpers I've seen are tool pack based. Light and fast but expensive.

I've used plenty of the leveraged crimpers that are about 2 ft long. I've had three pair explode... And throw shrapnel.

... Good luck on your adventure!

-methods
 
I'm just skimming... But if that BMS is fan-cooled you need to make sure you get the heat out of the box.
upon closer inspection, the fans are mere decals, so this case the BMS has no fan, and heat dissipation occurs primarily via direct conduction and convection of air with bms case.

dear @cwilken, what sort of Discharge Load Amperes is expected?

if its not close to the BMS max, then mounting the BMS inside the case with the cells might be workable.

good to test stuff and put a thermometer inside, close up, put load on battery, observe

good luck and nice work so far
 
Good to know!
I saw those BMS on Amazon and wondered about the fan.

With the lower end Chinese BMS, the high RDS-ON (internal resistance) of the charge and discharge mosfets can create quite a bit of heat.

On the higher quality BMS, with name brand mosfet... Charge and discharge heat can almost be eliminated.

...
Balance Heat
These days mostly... The BMS's only do top balancing with a couple hundred milliamps. If you get all 12 or 16 cells balancing... That too can create a ton of heat.

Convection...
Is a place that many people get tripped up when they go from open air to a sealed enclosure.

Convection works magnificently well in open air. In an enclosed environment, it fails miserably. The only thing you can do is thermally soak your mass

So
For a sealed enclosure I always Mount the BMS to the outside wall. In this way you're soaking the metal case instead of the battery... And convection can happen out on that surface.

... All moot if you're not producing a ton of heat. I usually work with 1 KW hour batteries dumping at 20 or 40 C. With a huge battery dumping at less than 1C...

Plenty of thermal Mass, not that much heat generation

-methods
 
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