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Originally Posted by redpoint5
Excellent post!
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Thanks! I try. I actually messed up and originally posted this in the already linked battery thread. Lol.
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Originally Posted by redpoint5
I've been charting the leakage of my 350F series of capacitors over the course of the past few days and will put it into an Excel sheet soon. Mine are balanced by the LED/diode method, so most of the initial "leakage" is just driving those lights. Do you find balancing to be unnecessary? I've wondered if higher charged cells would also have a higher leak rate, effectively balancing themselves. This would be a worthwhile experiment since eliminating the balance circuit simplifies things and lowers the parasitic drain.
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My final product (in the project car) will be balanced. For 6 cells (ideally 7), balancing *may* not be required if all the cells are relatively close; the cells that charge faster probably have a higher failure voltage threshold as well, so I feel that for generic use like my jump pack, a non-balanced setup should be fine. I forget if the "fatter" charging cells have a higher leak rate (my earlier posted results may bear this out...?) but I'd wager that if balancing is not required after the initial charge (all cells at a safe voltage, starting from 0v) then it shouldn't be required at all (potentially, of course; this would require repeated, analytical testing which I'm too lazy to do).
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Originally Posted by redpoint5
Your parked parasitic draw of 250mA is extreme. I'd only expect that draw on a cheap aftermarket alarm system install, or a failing electrical component. Have you measured the drain after letting the car sit for a longtime without opening the door or messing with the door locks? I ask because my TSX has a higher draw just after parking, and whenever the door has recently been opened. It eventually settles to 40mA.
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The numbers were pretty sobering, for sure. What I did was close everything up, key off, then I put my multimeter in line with the positive and the battery to find the draw. Then, I set up the cap bank, withe the multimeter set up to measure voltage only (lest the meter catch fire), started the car up until voltage stabilized, then shut it down and watched the draw. That data looks like this:
Time (minutes) - Volts
0 - 13.77
5 - 13.62
15 - 13.23
30 - 13.05
As a side note, calculating usage via farad method, my Mazda draws about 550-570 amps when starting (cold or hot).
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Originally Posted by redpoint5
The 14v-10v 560mA figure in your spreadsheet is very helpful because I found conflicting methods of how to calculate it (please PM me your spreadsheet or the formula). It looks like my truck, with a 20mA parasitic drain, can only sit for 28hrs before your 3000F caps would fail to start it. I believe I can get the drain down much further after disabling a thermometer with constant LED back-light. I'll try that tomorrow.
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Not a problem. None of this is secret; it just took me a while to figure out how to do it, but I'm still fairly new to this as it is.
Bank_Amp_Hours = (Max_Volts - Min_Volts)*Farad_Rating/3600
Hours_of_Runtime = Amp_Hours/(Multiplier*Draw)
Quote:
Originally Posted by redpoint5
Can you explain the V+W -> A and the V+A -> W table a little further? I know how they are calculated, but I'm just wondering what the figures have to do with replacing a car battery with capacitors. I'm also curious what you are planning with those resistor calculations.
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It's just wattage/amperage/voltage translation. With any two of the three, the third can be calculated:
Watts / Volts = Amps
Amps * Volts = Watts
Watts / Amps = Volts
Edit: This math also helps figure out charging rates when using lightbulbs as charging ballast.
As for the resistor calculations, those are for charging ballast for the capacitor bank. More on this in the next sectioned quote/reply.
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Originally Posted by redpoint5
I bought 2 amp loggers to measure the amps going into, and out of a capacitor or battery so that I can determine the charge/discharge efficiency between capacitors, LiFePO4, and lead-acid. When I start getting more than 1 day off per week, I'll start experimenting and share my methodology and results.
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I can tell you right now that the efficiency/speed of charging for those three energy storage methods will be in this order:
1. Capacitors
2. LiFePO4 (a very distant second)
3. Lead Acid (a fairly distant third)
Originally, I hooked up my bank to a "smart" battery charger. It was initially supplying 6 volts to the bank, unknown amps. Thing sounded like it was going to burst into flames at any moment, so I hooked a car headlight up to it as a charging ballast to limit current flow (dead capacitors act like a short, after all; that should tell you what you need to know about charging rates). This is where the resistor equation comes in, though I've since decided on using small, switched halogen lights in the 12 volt range (20-50 watt) for charging the bank, as they are a great visual aide for charging/discharging the bank as well as potentially providing a working light.
As for discharging:
Here's a video going over the discharge rate of an older, 2600 farad 2.5 volt capacitor and bank:
Some warnings:
Do *NOT* charge a dead capacitor bank off your alternator unless the farad rating is *LOW* or your vehicle is set up for SPL competition (car audio loudness) otherwise you could hurt your electrical system/melt wires.