Battery Box Design Question - water!!!

750 Views 9 Replies 8 Participants Last post by Raiju1337, 12 d ago

JK-1969

Discussion Starter · 14 d ago

I'm working on the design for my battery boxes that will eventually attach to the bottom of my '75 Honda wagon. One will fit nicely where the gas tank was, and the other above the rear axle. The boxes will be exposed to the elements under there. I am wondering how important it is for them to be sealed tightly, or if they are not completely air tight, then would it be better that they have some strategic drain holes. Mind, I am in Northern California. I will not encounter snow or sever weather driving, and salt is not used on our roads. The boxes will need to be removeable and openable, for maintenance, so there is always a good chance that there will be gaps where water could get in. If it could get in, shouldn't it be able to exit as well? Should I put a couple drain holes at the low points/corners, just in case? How dangerous is a potential spray of water, vs a puddle building up in the box?

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remy_martian

· #2 · 14 d ago

Norcal has gotten, and is predicted over the next while because of El Nino, to get massive rains.

Drain holes on the bottom of the car are fill holes when it inevitably wades through water due to a blocked storm drain.

Humidity can cause water to pool at the bottom of a metal box...not that you have much of it there.

There are drain plugs that close when immersed. I didn't bookmark them, so you'll need to search or someone might chime in on those. Post it here for others when you do find them.

Battboxes can't be airtight - need to be vented for barometric changes, at least.

Having a burst mechanism is also a good idea so it doesn't turn into a bomb in the off chance the cells light off.

Sounds like the tops may be coming off in the passenger compartment. Make sure you make it out of materials that give the occupants time to bail out if there's a fire....think that through.

You do know you need two contactors in each box if over 60V to cut off voltage on each battery lead coming out of it?

This isn't comprehensive and is off the top of my head.

Have fun.

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JK-1969

Discussion Starter · #3 · 14 d ago

remy_martian said:
Norcal has gotten, and is predicted over the next while because of El Nino, to get massive rains.

Drain holes on the bottom of the car are fill holes when it inevitably wades through water due to a blocked storm drain.

Humidity can cause water to pool at the bottom of a metal box...not that you have much of it there.

There are drain plugs that close when immersed. I didn't bookmark them, so you'll need to search or someone might chime in on those. Post it here for others when you do find them.

Battboxes can't be airtight - need to be vented for barometric changes, at least.

Having a burst mechanism is also a good idea so it doesn't turn into a bomb in the off chance the cells light off.

Sounds like the tops may be coming off in the passenger compartment. Make sure you make it out of materials that give the occupants time to bail out if there's a fire....think that through.

You do know you need two contactors in each box if over 60V to cut off voltage on each battery lead coming out of it?

This isn't comprehensive and is off the top of my head.

Have fun.

Planning on the contactors, thanks. And yes, I see your point about being air tight. The boxes will not be accessible from the passenger compartment. I was thinking a removable lid, but have it bolted shut and lifted up into position. Once they are installed, further tinkering or maintenance would require the boxes be unbolted and lowered from the underside. I like the idea of the drain plugs, I'll look at those.

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Zieg

· #4 · 14 d ago (Edited)

Both production batteries I've bought (2nd gen Volt and Pacifica) were sealed against water ingress. Not airtight (the access covers for the accessory fuses weren't sealed on either). Gasketed around the split between the upper and lower shells. The Volt had a removable drain plug kind of like an ICE oil pan, presumably to check for coolant leaks? Neither had an open drain hole, though.

Side note: I saw a pro built drift car that had QD fittings on the outside where a fire truck could hook up and blast water through the battery, and thought that was a pretty awesome idea. Maybe they have a rupture disc on the other end of the battery so the water can flow through? I wouldn't be surprised if something like that made its way onto production EVs eventually. I have half a mind to do something similar to mine.

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remy_martian

· #5 · 14 d ago

This shows how air pressure over a large area will distort a metal box if not properly vented:

https://static.nhtsa.gov/odi/tsbs/2019/MC-10163736-9999.pdf

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cajamatt

· #6 · 14 d ago

Hey, look up Gore vents (same thing as Gore-Tex in your raincoats). They're little plugs you pop in to the side of your enclosure that have a small sheet of gore tex in them that lets air breath in and out slowly but keep ingress out. You still dont want to submerge them though. Looks like the they might be hard to find for consumers, but Amphenol seems to sell a copy-cat through Digikey.

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D&VsEVJeep

· #7 · 14 d ago

Zieg said:
Side note: I saw a pro built drift car that had QD fittings on the outside where a fire truck could hook up and blast water through the battery, and thought that was a pretty awesome idea. Maybe they have a rupture disc on the other end of the battery so the water can flow through? I wouldn't be surprised if something like that made its way onto production EVs eventually. I have half a mind to do something similar to mine.

One could argue that filling the battery with water, while on the surface seems like a good idea, is in actuality the worst thing you can do. It doesn't actually extinguish the fire. Just slows it down. And actually makes a more unsafe condition (like a firework that doesn't go off) and you just waste a lot of water (and that water is now considered contaminated, which you should probably contain and clean up).

If you have the time to connect a hose to QD fittings, it means you should have time to evacuate any people from it, and I would argue that the best thing would be to let it completely burn, use the water to prevent other things around it from catching on fire, and then when the battery is completely burned up (which will happen pretty quick if you don't slow it down with water) you will have a safer condition to clean-up.

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lordmundi

· #8 · 13 d ago

cajamatt said:
Hey, look up Gore vents (same thing as Gore-Tex in your raincoats). They're little plugs you pop in to the side of your enclosure that have a small sheet of gore tex in them that lets air breath in and out slowly but keep ingress out. You still dont want to submerge them though. Looks like the they might be hard to find for consumers, but Amphenol seems to sell a copy-cat through Digikey.

oh that sounds cool. if anyone finds a supplier of these please share a link!

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Bintang 5

· #9 · 12 d ago

lordmundi said:
oh that sounds cool. if anyone finds a supplier of these please share a link!

Vent valve for battery box - EVcreate

The vent valve is waterproof (IP67) and at the same time allows the battery box to breathe or even release pressure quickly.

www.evcreate.com

Battery Pack PRV Vent Blow Off Valve

When building any type of sealed battery box a PRV should be installed to allow pressure equalization and gas release. It must always be placed on the outside of the battery box and bolted on from the inside, such that the edge with the red rubber gasket is against the outside surface of the...

amprevolt.com

Battery Pack PRV Vent Blow Off Valve

shop.fellten.com

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Raiju1337

· #10 · 12 d ago

Bintang 5 said:
Battery Pack PRV Vent Blow Off Valve

shop.fellten.com

Got that one too, but will also install a drain valve I guess.
Sounds like a nice feature.

Also I saw somewhere that someone installed a sensor to have a simple check light if there is water at the ground of the box.
I think it was that awesome guy in france who build a T3 to electric some years ago. Legendary build.

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