I just purchased 6x
350F capacitors ($77 shipped
) to test out in various applications, both with a LiFePo battery and without. I don't have the battery yet, but I do have an ATV with a dead lead acid battery. My first test will be with the ATV, to see how long it can sit and still start with just the capacitors.
The nice thing about having it in the ATV is that if it fails to start, there is a pull cord as a backup.
Next, my truck has 2 very weak batteries that will barely start the Cummins motor after 3 days of sitting. I'm wondering if throwing the capacitors in parallel with the batteries will give it the extra cranking oomph it needs.
Unfortunately, I don't think I can cheaply replace the lead acid batteries with a boost pack because the grid heaters suck down serious amps. Since the speedo on my truck doesn't work, the grid heaters continue cycling even though I exceed the cutoff speed.
Another vehicle I'd like to replace the battery with a boost pack is the TSX. I've already measured the parasitic load at 0.041 Ah, so sizing a LiFePo battery for my needs should be simple.
Last, I have a CBR600 motorcycle that I'm curious if it could loose the lead altogether and just run capacitors. The problem is that it charges using a generator instead of an alternator, and that means it doesn't charge below about 1,500 RPM. In other words, I'm draining the capacitors anytime I'm stuck idling. Even worse, if I idle too much the engine temps rise enough that the E-fans kick on. Fortunately, bump starting a motorcycle is easy enough.
I'll start a new thread when I begin experimenting and report back my findings, but it will be a few weeks to a month before I have anything to share.
Any update?
I just measured my TSX draw at 41mAh today. With 12.4v on the battery, that is just barely more than half a watt drain.
As I've just learned, capacitors don't behave the same way as batteries when placed in series. 6x 3000F capacitors in series has only 500F capacity at ~14V.
The formula
(Vmin + Vmax)/2 * F / 3600 = Ah is used to convert F to usable Ah.
I'll assume my car is happy with voltages down to about 10V (correct me if you think it might be different).
(10 + 14) / 2 * 500 / 3600 = 0.83 Ah
If my calculations are right, 6x 3000F capacitors in series and charged to 14v would give me 0.83 Ah and with a drain of 0.041Ah, my car would go for 20hrs before the voltage dropped below 10v and the computer dies.
Someone please analyze my assumptions, formulas, and arithmetic.
Here is a series/parallel capacitor calculator ->
Electronics 2000 | Series / Parallel Capacitor Calculator
I wonder why supercapacitors only exist in the 2.5-2.7v range? If someone could just come out with a 15v rated supercapacitor, there would be no need for a series configuration and the resulting loss in capacity. Wiring in parallel to boost capacity would come at zero penalty.