Tiny Battery?

[rocwandrer]

My daughter did a 2 hour off road ride with me Saturday and used 75w-hr on a borrowed ebike that weighs 60% of her body weight. Based on that, I'm looking for about a 3-4 Ah 36v battery with at least an 8a and preferably 10a continuous rating. Last time I did this sort of build was a decade ago, and I went with 2x 20v RC car batteries in a Walmart plastic clamshell. Better options now, short of building my own pack?

 

[Chalo]

That sounds like a job for a cordless drill battery. It's easy to find generic power sockets for those.

 

[rocwandrer]

That sounds like a job for a cordless drill battery. It's easy to find generic power sockets for those.

I had this thought too, I was thinking I can even just use the ones I already own. But they take up a ton of space in an inconvenient form factor for off road use on a tiny full suspension bike with no space inside the triangle.

 

[jetpackjbd]

I had this thought too, I was thinking I can even just use the ones I already own. But they take up a ton of space in an inconvenient form factor for off road use on a tiny full suspension bike with no space inside the triangle.

With a drill battery, or really any battery, you’ll have to get creative in placement.
Under the seat or on the seat pole are both decent options. Especially if you can incorporate the seat stay

 

[rocwandrer]

With a drill battery, or really any battery, you’ll have to get creative in placement.
Under the seat or on the seat pole are both decent options. Especially if you can incorporate the seat stayView attachment 369032

It's a suspension bike with a dropper post. I was thinking strapped to the bottom of the DT low enough to clear the front tire during fork compression. or a stay only mount rear rack. If a small enough battery with a big enough seat bag of the type that clamps to the seat rails could be made to work, that would probably be better.

 

[docw009]

You can look at the 20 cell 10S-2P hoverboard packs.They should be rated for 7AH these days. I used to run two 36V4AH packs in parallel which were good for about 120 watt-hours each.

I have built my own. With the 21700 form factor, a 1P battery becomes practical. I tried 13S-1P with Molicell P45B's in a rectangular form and then tried two bottle formats, Samsung 50S in a 10S, and Samsung 35E in 13S. The Molicells are about 3,7AH, but haven't ridden the Samsungs yet on a bike, Expect to be around 4.2AH, as both are 5AH cells.

Here are all three.

 

[dgc]

Like this, this is my Boardman 29er with a 48V TSDZ2B mid-drive powered by a 7ah battery slung under the down tube with a 3D printed cover over it, I put in a set of m5 thread inserts to attach the battery to the frame, if the battery were 36V then it would be 10ah.

 

[rocwandrer]

You can look at the 20 cell 10S-2P hoverboard packs.They should be rated for 7AH these days. I used to run two 36V4AH packs in parallel which were good for about 120 watt-hours each.

I have built my own. With the 21700 form factor, a 1P battery becomes practical. I tried 13S-1P with Molicell P45B's in a rectangular form and then tried two bottle formats, Samsung 50S in a 10S, and Samsung 35E in 13S. The Molicells are about 3,7AH, but haven't ridden the Samsungs yet on a bike, Expect to be around 4.2AH, as both are 5AH cells.

Here are all three.
View attachment 369064

I know some hoverboard batteries are better than others. Any recommendations?

 

[dgc]

Are the skate board battery packs these ones that are made up of the cells and bms wrapped in the blue shrink wrap, the option there could be if you know someone to 3D print a box for the pack, one in the photo houses a 48v 13s3p pack. The batteries I have came from China mostly but that's is all up in the air at the moment, lucky I have some spares batteries from Germany.

 

[docw009]

I know some hoverboard batteries are better than others. Any recommendations?

I bought mine in 2017. Dubious, but they were better constructed than my ebike batteries. Today, I don't know what's out there. Maybe UL certification has made them better. I bought them from a surplus recycler.

Here's another surplus seller I have used. He has these surplus segway packs that you might find useful. They're worth a gamble in my opinion. I have bought other used segway packs in the past. I consider them high quality, tough and reliable, given they spent all their time in rental scooters out in the streets, Mine came long extruded aluminum cases, and too unwieldy to fit an ebike, so I cut them in half and folded them. Been a few years. Never seen a cell fail with the LG and panasonic cells that were inside.

The JAG35 guy says they're either Eve or LG cells, which are both considered good, It's the unknown chinese brands that start deteriorating inside that become potential fire risks, Sure, brand name cells can do that too. Nonetheless. if you want to be safe, go with a tool battery,

 

[classicalgas]

My daughter did a 2 hour off road ride with me Saturday and used 75w-hr on a borrowed ebike that weighs 60% of her body weight. Based on that, I'm looking for about a 3-4 Ah 36v battery with at least an 8a and preferably 10a continuous rating. Last time I did this sort of build was a decade ago, and I went with 2x 20v RC car batteries in a Walmart plastic clamshell. Better options now, short of building my own pack?

Ryobi "40v" yard tool packs come as small as 3"x4"x7" for 6Ah at 2.8 lbs. Terra Firma makes a pretty solid, easy to use 3d printed mount, prewired. I might reinforce it for offroad use, though.