Quote:
Originally Posted by Enki
As a side note, the 650s have a bank leakage of about 9 mA (as opposed to the 3k farad caps total leakage of 31.2 mA), so adding the cap bank would probably make my drawdown issue worse.
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The leakage current isn't constant though (I think). I assume the datasheet lists the leakage at full rated voltage. Even with the balance LEDs on my 350F bank, the voltage only drops 0.07v per day when charged to 13v (2.17v each). I'd bet leakage is logarithmic, and hope to test this at some point.
Quote:
Originally Posted by Enki
At 14.4v peak, a balancing circuit isn't needed, and here's why I say this:
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my argument is that a cap bank of identical condition/make/model capacitors will always self balance to a degree; what that degree is, I'm not sure, but the variance on my bank was only 5.186% from most charged to least charged. I'd wager that over time, that number would likely reduce slightly, and that the most charged capacitor(s) could likely hold more voltage before having an issue anyway.
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For the caps to not need a balance circuit would mean they self balance, but I haven't seen any evidence of this yet. If they don't self balance at all, then a small difference in voltage could become a significant difference in voltage over time. However, I agree with your assumption that a balance circuit isn't necessary if there is even slight self-balancing at play. This needs to be tested, and the way to test it is to monitor voltage leak on a single cap at various states of charge. If it leaks more at higher charge (likely), then it's self balancing.
Quote:
Originally Posted by serialk11r
Wow, at 70A draw for the starter yes a plain lithium sounds like it's probably good enough, certainly. What I was talking about was smaller capacitors however, for an additional layer of surge protection to the battery....
I haven't measured my car, no. I'm guessing it's low because I don't have remote control key fob and no anti-theft alarm that I know of.
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From a cost perspective, I don't think you will save money overall on batteries by having a capacitor bank. Perhaps the batteries would only live 5% longer.
Since your car doesn't have power doors or an alarm, I think it's even more important to discover what the parasitic draw is. If it's low enough, you could get away with just capacitors and no battery. If you park outside, a very cheap solar maintainer should keep it topped up.
I see the battery as a last resort, when parasitic draw is too great and the vehicle is parked in a garage. Then, if a battery is necessary, and it's capable of supplying the starting amps with plenty to spare, then I don't see the advantage of running the caps.
My TSX takes 290A to start, so it would cost a lot in LiFePO4 batteries to forgo the capacitor bank. This is a situation where the hybrid pack might be the best option. However, I'm now thinking that I might wire up an alternator kill switch and size a LiFePO4 pack large enough to both start the car, and run for 90min, charging in the garage at night. Spending $210 and wiring 3 banks of the LiFePO4 batteries in parallel would give me 30Ah and 300 cranking amps. Now I just need to figure out how to disable my alternator and measure typical power consumption.