Quote:
Originally Posted by Isaac Zackary
For starters, (is that a pun?), where I life it gets super cold. Like -40° F (-40° C) cold. There are several problems with running batteries. The lead acid ones of course have a hard time putting out amperage at those temperatures. I'd bet LiFePo4s probably do to. Not only that, but if the lead acid batteries drain completely out then they turn to water on the inside, freeze, and can even bust open the battery! Lithium batteries normally aren't rated for that cold of weather either. So the idea of ultra capacitors that can put out full amperage even at those kinds of temperatures is really appealing to me.
But what about the self discharge rate. Solar panels with a foot of snow on top probably won't work.
|
I would certainly build a bank of 6-series connected 350f or 600f supercaps to help with cold starts in those extreme temperatures. I've started my TSX with just a bank of 350f supercaps that were charged to 10v. The rate of self-discharge below 13v is very low. The parasitic drain of the electronics of the vehicle will exceed the self-discharge rate of the caps.
LiFePO4 cannot be charged below freezing temperatures, so it makes them a bad candidate for your cold climate.
You might be able to use a solar panel to maintain the charge of supercaps as long as they have a balance circuit or if connected to a lead acid battery that will drain the excess charge. Without a means of bleeding off excess charge, supercaps can very quickly be over-volted.
Quote:
Originally Posted by Isaac Zackary
This is the self discharge rate I came up with for a 6 pack of caps to fall from 14V to 12V. Obviously a fall from 14V to 10V would take twice as long.
FCell mA 2V change
310 .45 63.8h or 2.7 days
350 .3 108h or 4.5 days
650 1.5 40.1h or 1.7 days
1200 2.7 41.2h or 1.7 days
1500 3 46.3h or 1.9 days
2000 4.2 44h or 1.8 days
3000 5.2 53h or 2.2 days
3400 18 17.5h or 0.7 days
|
It would take many times longer for self-discharge to go from 14v to 10v compared to 14v to 12v. I would say months. The self-discharge is fairly high near the voltage limits and drop exponentially as the voltage drops. I've got a bank that I charged up about 4 months ago and the LED balance circuit is still giving off a lot of light.
I don't think self-discharge is much of a consideration.
I'm a fan of the kit on Ebay for the 350f caps that comes with the printed circuit board and balance hardware. It was fun to assemble and reasonably priced at the time I bought.