Topic: battery type questions

I'm about to stuff my novena into an old Thinkpad570 case (it's an ultraslim NB with an additional dockingbase). Into the base dock goes the Novena, the battery board and the frontpanel board and maybe a secret compartment (mouse, keybad or something).
The case of the Notebook itself is unused, so I was planning to put "as many battery capacity" into it as possible. BUT the space has a large foodprint, but very little hight. So question is are those "soupbag" LiPolys also usable and if, which is the highest capacity I could use?

Re: battery type questions

OK, to be more precise:
Are these kind of batteries suitable:  (sorry for the german)
and since the case it quite roomy, I was thinking of using 6 pieces of 10.000mAh cells (2 paralllel an 3 of the packs in serial, so that would be a 11.1V/ 20AH battery pack.
Question is: how to wire that and is the senoko able to handle that?

Re: battery type questions

First off, the usual warning about playing with Li-Ion cells (fire, mostly). Be careful and you'll probably be fine, so long as you know they can be dangerous.

That said, the Senoko should have no problem with those cells. They don't appear to have a protection circuit in them, but that's part of what the Senoko is supposed to handle anyway (prevent over-charge/-discharge). The down side is that they'll take a long time to charge. I think you'll get something like 3.5A out of the Senoko max, so you're probably looking at 6-7 hours to charge. Again, not a problem, but an FYI.

For wiring... exactly what you think. Solder two in parallel, 3 in series however fits in your case. You'll obviously need to add leads to each of the cells for balancing taps as well (so you'll end up with ~6 wires going to the Senoko- 11.1V nominal, GND, another 11.1V, another GND, 3.7V, 7.4V, where the latter 4 are for balancing purposes).

Or if you mean the technicalities of wiring, here's what I'd recommend. If you have or can use a spot welder, I'd say weld some longer tabs on there, just to keep a soldering iron further from the cells. Or spot-weld leads on there directly, if you can swing that somehow. You should be fine without doing so, but extra safety is generally a good thing.

Either way, if you're planning on soldering wires onto the tabs, you probably want to sand the tabs lightly with some high-grit sandpaper first, and use flux. That cleans the gunk off and will make the solder wick onto the tabs much better, instead of just balling up and falling off (ie, cold joints). Tin the wires first and put a pool of solder on the tabs, then join the two together. A hot iron in short bursts would probably be best to keep the cells cool, since you're essentially soldering to a relatively poor heatsink.

Now BEFORE you go wiring cells together, you want to at LEAST make sure the ones you're putting in parallel with each other are the same voltage. They'll probably be pretty close when you get them, but doing so avoids the stress you'd put on them by pulling a huge current to balance them when you short them together. The easy way to do that is to short the negative tabs together, then put a smallish resistor between the positive tabs. That way current will flow until they're balanced, but not at an insanely high rate.

I think I used a 100-ohm resistor and just left them for a few days, but you can work out values as you see fit- so long as it's less than 10A going through the resistor, the battery is fine. And so long as the resistor is dissipating less than it's rated wattage, the resistor should be fine.

Hope that answers your question satisfactorily!

Re: battery type questions

Senoko can charge much faster than 3.5A.  It should be able to deliver something like 6-8A, but we never tested that.  The 3.5A limit was due to the compact power supplies we used.

Newer Senoko firmwares are much more conservative in their cutoffs, so you may want to update firmware-senoko before you install the new batteries.