I cannot find spot weld professionals!

[Arbol]

I have tried to find professionals who can spot weld batteries in Barcelona. Usually I find everything I want to find in my city ... but so far, I have failed miserably with this one.

Even, there is a shop arguing they spot weld batteries, but when I talked with the manager, he told me (very scared) they only spot weld up to 6 cells! And he would not do it, for "security reasons".

There are at least two well-known professionals doing something like this, one is em3ev, the other is Schwibsi in Germany. But I would like somebody local.

I am quite convinced the main issue about e-bikes is batteries, both quality and geometry.

There are at least two projects I would like to entertain if I could build my own batteries:

1. The easy one: build triangular boxes out of 18650 batteries. em3ev has some, but they are of specific sizes, and also the geometry (angles of the triangle) cannot be chosen. Centering the weight of the batteries inside the frame, as well as making the whole structure safer, seems a no brainer to me
2. The complex one: foldables. There are some e-foldables, even with hidden batteries, like the Woosh Zephyr, but there is none, AFAIK, which folds as well as an Ori or Brompton, and which has cells inside the frame. Foldables seem the solution to urban electric vehicles: due to wheel size, they can be the most powerful bikes given the 25km/h limit, and the problem of where charging which cripples electric motorcycles and even big MTB, with foldables is a non-issue

In the end, everything is a problem of batteries and frames, which batteries to build, and how frames can be adapted to that. Motors and controllers are trivial in comparison.

How could I find a good spot welder? Even, could I learn, or could I make somebody learn?

 

[amigafan2003]

Have a read:-

http://endless-sphere.com/forums/viewtopic.php?f=2&t=2633

 

[cwah]

I have a spot welder at home (in paris). I can help on that.

Check what I've done before:

i'm looking for someone to buy cells together and share shipping cost. Do you already have the cells or have a supplier in mind?

 

[cwah]

 

[Arbol]

Hello cwah, great battery build!

I don't have the cells, but I have done some search about Chinese suppliers. When I have asked people with experience on these suppliers, they tell me the key issue is to purchase packages of 200 pieces, since 18650 battery boxes are usually shipped wholesale in 200 piece packages.

If one does that, it is very likely the Chinese supplier will just buy, or use recent inventory, a box of 200 pieces and will ship it to you.

Instead, if one buys say 65 pieces (for a 13s5p configuration) it is likely some fake or faulty cells are added into the order.

I can share with you the names of the suppliers I contacted with. Probably it would make sense to make a new round of bids once we know how many cells we want to purchase.

For example, the cells I saw had a good quality price relationship were the Samsung 22P, which were in the range of $2 to $2.5 each, for 200 piece orders. Suppliers with best prices, and with extensive cell lists, were not willing to sell less than 100 or 200 pieces.

I still do not know how many I want for me, but possibly it would be in the range of 50 to 100. I do not know how many you want, but it would be ideal to reach 200.

For BMS, we could try either em3ev (which uses Samsung 22P for his value triangular package) or bestechpower. Bestech only sells 2 pieces or more, so if you do not have a BMS, we could also share costs, if we reach an agreement.

The other issue is if you would want to help me build my package, and how we could put that into practice. I would want a triangular shape for the battery.

 

[cwah]

Yes I know the Samsung 22P but they are definitely not as good as other (such as the konion ones) for the same price.

I've found a supplier for some experimental cells for very decent price 2USD/cell with 5C discharge capacity and 2.2AH (with 2AH true capacity). It's quite good for the price.

I go back to paris in May for a couple of days... so I'd have to order that quickly if we want it to happen.


Best way is to get these 18650 cells holder for now. They provide safety against cells chaffing and vibration. You need to use a cardboard first and see how it can fit your bikes depending on capacity required. I did that on my dahon Jetstream knowing that I wanted a 72V20AH capacity. So massive amount of battery. In term of space, you can consider that each cell takes 20.2mmx20.2mmX68mm volume. Compare that to your battery box volume to see how many you can fit inside (minus controller and DC-DC converter)

 

[Arbol]

It depends what kind of performance you want. For example, em3ev suggests a 14s6p should use a controller of max 25A. Since 6p is slightly more than 12Ah, this means these cells should be 2C max.

I have been thinking about a 13s7p, which allows a triangle geometry with 13-12-11-...-2-1 cells (91 in total). I have drawn a triangle in a sheet of paper with 26cm-26cm (2cm*13) and it fits in my triangle. Not by much, but it fits. Even, I could put a controller on top of the battery, which would be close to the top tube.

I would use either a S12S or a S12P, with 22A and 30A max amperage, approximately fitting the requirements above.

Of course, a Sony VTC4 would be much better, but they are double the price.

The Panasonic PD have 2.9Ah and are 10A cells, so with a 7p max amperage would be 70A.

What does "experimental" mean?

Which holders are you talking about?

 

[cwah]

I mean unknown brand. I purchased 10 of them for extensive testing:
- discharge test at 3C over 50 cycles allowed me to project over 80% capacity after 500 cycles.
- they have higher true capacity than others cells.
- I don't know if they have good calendar life however. So bet would be in this area.

Cost is 2USD/cell as I told you.

But of course, you have to consider shipping cost, paypal fees, customs fees and construction material.

Ps: the holders are the black plastic bloc around the cells

 

[cwah]

For the dimension of the battery, you have need at least 28.28*28.28cm right angle triangle (2.02cm*14 cells). That's for inner dimension of the battery box. The outside dimension would probably be closer to 29cm*29cm (depending on the material used).
And that's for a perfect right angle triangle of 14*14/2= 98 cells inside the battery box.

 

[Arbol]

cwah, I would like to contact you regarding this issue. I have sent you an MP. Thanks.