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My little ~2 kWh Powerboard
#11
I've retested all cells and rearranged my packs, it is 7S40P now. The lowest capacity cell I used is 1960mAh I think and the average is probably something like 2100mAh. Total energy is now about 2.2kWh. Once assembled I'll test the usable capacity and energy. I didn't use Repackr this time, instead I rely on statistical randomness to even the packs.

Once assembled there will be a theoretical maximum of 577mA of current per cell and that is never going to happen. The usual maximum will probably be more like 100 to 200mA. Most common application is probably charging my phone and that means 23mA per cell Smile
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#12
Two months later, a quick update of what happened in the meantime Smile

A while back I got some new toys, like a Junsi iCharger 4010 Duo, a DPS5020 and a Meanwell 1kW 48V PSU.
This week I found the time to build my busbars:


Not the greatest craftsmanship, but oh well. They are three solid 1.5mm² wires twisted together, so total area is 4.5mm². Seemed appropriate for a 40p pack with cells tested to 1A, they will handle 40A. I will never use 40A though, so they are more than fine.

Today I've used the first two of them to build the first of seven packs:


The cells weren't charged, so I'm doing this now. I started at 30A and everything is fine. The pack will handle more obviously, but the 4mm banana plug connectors, the 12AWG wires and the clamps won't. Maybe I'll use the synchronous mode of the 4010 with double 4mm connections and 10AWG wires to go 2x20A or 2x25A.
I will test the usable capacity of the packs to see whether my random cell distribution worked. Doing that at 20A probably which is a realistic maximum for the packs.

Getting appropriate fuse wire was a bit difficult, but a friend helped me out with some stranded wire and the single strands are 0.26mm / 0.05mm² / 30AWG which will certainly fuse pretty quickly on a 40p pack.

I sill haven't got my battery powered spotwelder which I wanted to show, but it will be on its way very soon (I hope). In the meantime we can say hi to these little badboys:


My RC days are gone and I've missed a bit of technological progress as it seems. These belong to the latest generation of RC LiPos, 6Ah capacity and 65C continuous discharge, 130C peak. That's 390A/780A. The iCharger calculates the resistance of the cells including wires and connectors to 0.8mR. Just crazy. You can't really use 390A continuous on these as the internal connections as well as the main cables and the XT90 connections will just give up. I haven't seen any specs from Turnigy, but SLS sells this kind of LiPo as well and they say 65C for 20s maximum.
Good enough for the spotwelder though and I will use two to power it. Tests have shown that one battery is enough because the pulses are very short but I like a slightly bigger margin.

Just thought I will probably make a new thread for the spotwelder though.

So, yeah, progress is slow, but there is some Smile I will build the other six packs in the following days and then we see what's the worth of statistics when distributing cells Smile I think it will be fine though.

And now I will go and fix my fume extractor, something in there went haywire. The second fan suddenly started turning the other way as if polarity was suddenly reversed or something...
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