A better alternator delete

[Daox]

I didn't know how well a large bottom and top plate would actually fit up against the cells, so I printed out a small section. I wanted to see how stiff the plate would be and how well the cells would fit in the recesses as well. Here is what we have.







The cells fit very nicely into the bottom plate. The top plate (which is the same as the bottom plate) was a bit more difficult to get the cells to drop into place. I think I will make some tweaks and make another test with a 3x3 cell holder.

[Piotrsko]

Nice. Are you compensating for how hot these cells sometimes get?

[Ecky]

Perhaps I missed it in the thread, but what are you going to use to connect them? Spot/tap welder and tin strips?

[Daox]

Originally Posted by Piotrsko

Nice. Are you compensating for how hot these cells sometimes get?

Compensating how? They have a small gap between them for airflow. However, I really don't anticipate them getting that warm. I don't plan to charge them to 100% capacity. Most of the heat generated is in the last bit of charging. Also, the discharge rate isn't that high. The cells will never even see 1C discharge. I am planning on monitoring the heat during charging once the pack is assembled to see if I am way off base.

Originally Posted by Ecky

Perhaps I missed it in the thread, but what are you going to use to connect them? Spot/tap welder and tin strips?

I'm not totally sold on this yet, but I am thinking thin aluminum strips. We're talking .025 to .040 thick by 1/2" wide. That is plenty to transmit the current we're talking about. It also allows it to be easily deformed to make good contact with the cells.

[Daox]

I printed another set of test plates out. This time the bottom got a deeper recess to hold the cells more vertical. The top plate got a generous chamfer around the cell recess to help guide the cells into the recess. This set of cell plates was 3x3 as I wanted to see how hard it was to align the top plate to the cells. To my delight, it actually worked very well. I stuck the cells in the bottom plate, aligned the top plate and jiggled it a little and it dropped into place.

[teoman]

For maximum benefit do you have a way of measuring the capacity of each cell?

[Daox]

I do have a capacity testing charger. However, I was not planning on testing them. 40 cells would take quite some time to do one at a time. I'll just assume 90% capacity and not discharge them too far. Thats the plan at least. Perhaps I'll capacity test the whole pack once I am done building it.

[teoman]

Depending on your luck you would lose some capacity. Especially if you risk having dead cells.

[redpoint5]

Yeah, having a balanced pack is very important. If these are used cells, I wouldn't be surprised if some of them only had 50% capacity remaining, and that would limit the total capacity of that series string to 50%.

[Daox]

The batteries that I bought were actually brand new and unused. They have been sitting in storage though. However, all the cell voltages are uniform so that is a good start.