Does anyone know if these things just run at 12V? The reason I ask is that to turn an engine over for 10 seconds would require 256 Farads of capacitance, whereas if they pumped the voltage up to 120V they would only require 6.4F.
AJH
but they might burn out the windings of the starter motor - the insulation might not like 120v.
Not to mention anything electronic. It would be nice to think that everything would have effective protection these days, but do you think it does?
Mind you, I think this is a troll.
Supercapacitors are very low voltage, generally around 2 or 3 volts. So you need a few in series just to get 12V.
And then the capacitance goes down.
If the OP is talking about what I think they are they (not the OP) are LiPo batteries and SMPS to get 12V
Nomad
Well, the energy stored goes down for a given capacitance. The capacitance itself is not related to voltage.
Seems like a bad idea anyway - the voltage on a capacitor drops quickly as energy is removed. It's only going to work with a booster circuit - and that's a chunky booster that can supply several hundred amps.
They're also high resistance.
No, I have seen those but this is what I was referring to:
So I had thought they might store charge at a higher voltage and then control the current in some way.
Perhaps they just have much more capacitance than I thought was possible.
AJH
Yup. They don't hold charge long, though, you normally charge them before use. They *claim* they can steal enough energy from a depleted battery to work, not sure I would want to rely on that. I have a couple of LiPo ones which are great (and hold their charge for several months). Also conveniently have USB sockets for charging phones, and a torch and sometimes flashing red lights.
Capacitors have virtually zero resistance,
Ah, OK, as you were then ...
How much $ ! (& how much - mass)
!!
Nomad
Except when its infinite.
Down to about 5V I think as they can also charge from a USB socket.
A mate has two (different 'powers') and says they do exactly what they say on the tin. ;-)
Cheers, T i m
heh
NT
I have a Li(Po?) one too and that is good. Started a VW 2l diesel with a battery so dead it would not crank once.
But of course, Li batteries tend to hold their voltage over a range of charge, whereas a capacitor loses voltage in proportion to charge (in coulombs) so starts to fall off immediately upon discharge.
Some older ones have a moderate internal resistance (often used for things like memory backup in computers), but the ones used for this are in the few milliohms range, lower than a typical car battery.
yes, obviously.
whoosh!
In excess of 320F internal resistance
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