capacitor array for starting engine

[star882]

How big of a capacitor array would be needed to start a typical 6 cylinder automobile engine? (Assume only the starter motor is powered by the capacitors and the ignition and controls are powered by a battery as usual.) The idea is a simple hybrid that stops the engine when the car is stopped and restart it when it begins to move again, without having to use a large battery like current hybrids do.

[Fenris]

1 Farad = 1 amp for one second. Figure on 3 seconds (minimum) for a reliable start and probably something like 30 amps for the starter motor (depending on engine size, compression, etc). Add in the losses for the ESR of the capacitor. Probably something like 100 Farads or so. Unless you need to try again, in which case you'll need to recharge the capacitors first. And don't forget that capacitors do self-discharge, so you'll have to factor that in.

[analog_sa]

Dunno if such caps exist. 200A over a couple of seconds?

[Conrad Hoffman]

Electrostatic field is a lousy way to store energy compared to chemical conversion methods, i.e., batteries. No doubt super capacitors will continue to advance, but IMO there's a limit to how much surface area you can pack in a given volume and support a given voltage. I think 100F is far too conservative for a practical application- think about what happens as it discharges.

There are certainly new and better ways to do things but a good read on energy fundamentals at Don Lancaster's site is highly recommended to anybody contemplating designing such things. He also has some interesting things to say about hydrogen and other alternates-

http://www.tinaja.com/

[star882]

The starter will not be a regular one. A special one will have to be used in order to withstand being used dozens of times every day, so you can make it just about any voltage you like (within reason).

[DigitalJunkie]

My friends old Honda Insight only had a small (30AH?) battery for the engine..about the size of a small lawn/garden battery. I'd assume any cap bank able to supply that kind of juice would be larger than the battery.

I remember reading a while ago about truckers who would put some 'ultracaps' in parallel with the starter batteries to help kick the starter motor over. http://www.maxwell.com/ultracapacitors/

[star882]

Originally posted by DigitalJunkie
My friends old Honda Insight only had a small (30AH?) battery for the engine..about the size of a small lawn/garden battery. I'd assume any cap bank able to supply that kind of juice would be larger than the battery.

I remember reading a while ago about truckers who would put some 'ultracaps' in parallel with the starter batteries to help kick the starter motor over. http://www.maxwell.com/ultracapacitors/

The original Insight actually uses a 144v array of NiMH D cells.

[infinia]

Originally posted by star882

The original Insight actually uses a 144v array of NiMH D cells.

Have you ever opened a NiCd D cell... I think it's the same Ah/weight as an AA. I'll have to look for the NiMH D cells.

I once measured the peak starting current on a normal compression and ambient temp V8 and it was interestingly an Amp for every Cubic inch. Not sure if there is any correlation but it was a good mnemonic for the time.

[DigitalJunkie]

Ahh,you're right.. There's a DC-DC that feeds the 12V battery,for the 'usual' automotive stuff.

[theAnonymous1]

Maybe a product from BatCap would be suitable. Not cheap though.