Battery Crash Protection

General Discussion about electric bicycles.
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hias9   100 W

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Battery Crash Protection

Post by hias9 » Nov 21 2020 1:58pm

On one bike I have a large triangle battery inside a frame bag. Crash protection should be light and not too wide, so knees won't touch the frame bag while pedaling.
At the moment I am using a 6mm yoga mat on both sides. Knees don't rub on the frame bag while pedaling, but it is really close.
And the material is quite soft, I can push a screwdriver through it, so I am not sure if it can protect the battery in case it hits a sharp stone.

Would a thin carbon fibre plate on the outside and closed cell foam on the inside be a good idea? Would a carbon fibre sandwich plate (carbon fibre plate - closed cell foam - carbon fibre plate) be a better idea?
Last edited by hias9 on Nov 21 2020 4:05pm, edited 1 time in total.

john61ct   100 GW

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Re: Battery Crash Protection

Post by john61ct » Nov 21 2020 2:18pm

CFK ?

Aluminum plate, foam on the inside

hias9   100 W

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Re: Battery Crash Protection

Post by hias9 » Nov 21 2020 4:05pm

Carbon Fibre plate. sorry

john61ct   100 GW

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Re: Battery Crash Protection

Post by john61ct » Nov 21 2020 5:57pm

I think the dimension of strength most critical is Puncture resistance.

Carbon Fibre would vary a lot between implementation

while 6061 at 1/8" or even 3/16" would likely be greater, certainly standardized.

Tensile and Compressive strenth are a different story, relies on the angle/tubing at the corners as well as the skin

and increase the box dimensions of course.

Not much point protecting the pack so well it emerges unscathed from a crash fatal to the owner. . .

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LeftieBiker   100 kW

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Re: Battery Crash Protection

Post by LeftieBiker » Nov 21 2020 6:02pm

The dense but flexible plastic foam used to protect things like laptops in shipping would be my choice. It's also fairly puncture resistant. A thin carbon fiber plate between the foam and the battery would make it even more puncture resistant.
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John in CR   100 GW

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Re: Battery Crash Protection

Post by John in CR » Nov 21 2020 7:14pm

As long as the battery is well secured inside the triangle it's pretty darn safe. For some added peace of mind get some 3 or 4mm plywood and a roll of duct tape. I've had battery packs protected only by duct tape or duct tape plus a layer of cardboard mounted inside triangles function for years and I've never seen crash damage on one. The handle bars, front wheel, and pedals keep the space from what's inside the triangle. I've never used a bag, just rigid mounting. How secure is the bag?

What kind of riding and crashing are we talking about, since you mention a stone puncturing thru? How wide is the battery pack itself?

john61ct   100 GW

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Re: Battery Crash Protection

Post by john61ct » Nov 21 2020 10:45pm

LeftieBiker wrote:The dense but flexible plastic foam used to protect things like laptops in shipping would be my choice. It's also fairly puncture resistant. A thin carbon fiber plate between the foam and the battery would make it even more puncture resistant.
The foam on the inside works better, the puncture "point PSI" gets spread out to take advantage of foam's excellent compression resistance.

Also daily wear & tear, even more so, the secondary goal "protect the foam" is actually a good stand-in for "protect the cells" as a byproduct.

hias9   100 W

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Re: Battery Crash Protection

Post by hias9 » Nov 22 2020 4:32am

The pack is about 68mm wide. At the moment plus 2x 6mm yoga mat on each side.
I don‘t want more than 4mm on each side. With the yoga mats knees are almost rubbing on the frame bag.
I don’t do hard offroad riding with this bike.
The bag is secure while riding (secured by about 10 velcros). When crashing it would move 1-2cm to the other side.

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dogman dan   100 GW

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Re: Battery Crash Protection

Post by dogman dan » Nov 22 2020 7:27am

I made protective boxes out of coroplast, the plastic cardboard used on political signs and such for years. Worked real good, many crashes riding dirt with vulnerable pouch batteries in a bag somewhere on the bike.

Other materials would be stronger, thin aluminum plate, or even steel sheet like roof flashing steel. But the signs are on the roadside, free, all the time. Often posted illegally, or just blown into the ditch. And they work fine, very light.

Before I discovered coroplast, I used to box up batteries in boxes I made from aluminum baking pans.

John in CR   100 GW

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Re: Battery Crash Protection

Post by John in CR » Nov 22 2020 7:51am

Regarding aluminum or carbon fiber, I don't like putting anything conductive other than my battery leads near the terminals of a battery, or the cells making up a battery. That just makes more protective layers required to prevent shorts.

At under 70mm wide, it's unlikely to get hit. If you're concerned then I still say duct tape and very thin plywood, or as someone else mentioned a thin but rigid plastic (polycarb, acrylic, or even colorplast if you can find it thin enough) and duct tape it into place. I'd go with plywood myself, because it's cheap and easy to cut.

hias9   100 W

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Re: Battery Crash Protection

Post by hias9 » Nov 23 2020 12:34am

Do you think a sandwich (plate of hard material - foam - plate of hard material) has any advantages over just hard material outside and foam inside?

john61ct   100 GW

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Re: Battery Crash Protection

Post by john61ct » Nov 23 2020 2:29am

no so long as you mean the total thickness & weight is the same

in fact the foam cushioning the pack's movement, shock / vibration is a good thing.

Hard on both the inside and out, no point in the foam

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LeftieBiker   100 kW

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Re: Battery Crash Protection

Post by LeftieBiker » Nov 23 2020 6:31am

Hard on both the inside and out, no point in the foam

I disagree. Hard impacts can break connections inside and outside of the battery. Lessening impact force is as important as preventing physical deformation of the pack.
2018 Nissan Leaf SL with Pro Pilot
2009 Vectrix VX-1 Maxi Scooter W/ 18 Leaf modules
2018 Magnum Metro with noisy motor
2019 GreenBike folder
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dogman dan   100 GW

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Re: Battery Crash Protection

Post by dogman dan » Nov 23 2020 7:23am

Yeah, coroplast inside the aluminum would be ideal. Not metal touching cells. I used to do a lot of searching around for just the right aluminum or steel box, depending on the type of cells, shape of the battery. So the end result would be metal box, with coroplast liner box, plus often some foam as needed to take up the slack. The goal was no rattling around inside an ammo box or tool box. I used yoga mats a lot to cushion the bottom of metal boxes a bit.

When I was using a frame bag, I just put the battery inside it, but the battery was already in its coroplast box.

I wasn't racing that bike, or riding it off road, so that was plenty of protection for it in that case. You could easily make some protective sides for your frame bag, by sandwiching an aluminum cookie sheet with coroplast sheet.

Other creative ideas we have seen here include peel and stick floor tiles, carbon fiber sheet, lexan sheet, and thin plywood.

But my opinion, few things beat the coroplast. Tougher than cardboard, has some crushability to cushion an impact, and really, by the time coroplast punctures you are already screwed. Cells dented at least.

I have had a metal battery box fly over my head, and land on the ground without damage. Its not like bike falls over, the thing catches fire if you just have it in a padded frame bag.

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