sunnuntai 17. kesäkuuta 2012

Picked up and batteries

Yesterday I took the long way home and got the bike. It's sitting outside in the trailer and just waiting to get the ICE out. The weather is getting better again as well after the rain pour yesterday which would make a nice environment for stripping parts out if it lasts. Let's hope so.

As for the battery part of the post I just finished watching the latest episode of EVTV and became highly intrigued of the 18650 battery cells. They are small AA-like lithium cells of the usual lithium voltage and about 3 Ah of power which makes for about 11 Wh per cell. The interesting bit is that you can get them with integrated protection circuitry which protects the cell from over charge, discharge and current. What that means is no BMS which I'm more and more decided upon on not having. Keep it simple, stupid, as they say and simple is also elegant. Elegant is what I like. Less is more. And so on. Anywho. Panasonic has a nice cell in this form factor which can give about 3 C or 10 A which would probably be enough for me. The math is 72 V motor means about 24 18650s at 10 A each totaling 240 A pairing to a 300 A controller and we're quite close in the numbers. This would also give me a way to get started on the cheap by way of buying just those 24 18650s to get a 72 V * 3 Ah or 0.2 kWh pack, see how that goes and just order more if it's all good.

Next up is taking the bike back from Espoo to home to Pori where it will probably spend the rest of it's life or at least lithium air batteries become viable and there's enough juice to drive around the country.

ps. Updated my EV album page at with current plans.

ps2. After thinking about it for a moment 24 tiny cells in series all by themselves might be a bit much. It's probably better to make a "6s4s4p" combination. That would be six packs of 4s4p in series. 4s4p being four cells in series and four cells in parallel. This would take 96 cells and result would be 72 V 12 Ah 0.864 kWh pack (or about 1 kWh if you count with 3.7 V per cell). These NCR18650As with protection look to be about $6.5 per cell so ordering 100 cells would be $650 and leave some for spares. As a bonus the 4s4p modules could be charged with a 12 V charger. Nice.

Ei kommentteja:

Lähetä kommentti