Supercapacitor Jump Starters

The Project Farm youtube channel has several jump pack comparos. Good Medicine. (Plus Todd is a fun guy. )

Cheers

Phil Hobbs

A lead acid battery at 9-10V is without any meaningful charge and won't be able to supply any energy to a supercap.

A lead acid battery will have some residual charge after the point it cannot supply the power to turn over a starter. However the terminal voltage after a short recovery will be more than 12V.

Supercaps have an incredibly low internal resistance. I don't know enough about their internals but I am aware a bank of them, or two, can supply megajoules to a magnetic coil-gun:

On a sunny day (Sat, 30 Dec 2023 13:20:16 +0000) it happened Cursitor Doom snipped-for-privacy@notformail.com wrote in snipped-for-privacy@4ax.com:

It's simple, the battery open circuit voltage is much higher so say 14V The sup[p]er capacitor will charge to that in a while.. When the battery is directly on the start motor the high internal resistance of an almost empty battery will cause the voltage to drop to a useless low value, nothing happens.

The internal resistance of a sup[p]er capacitor is extremely low, So connecting it will put the full 14V or so on the starter motor. So it is long charge time at a low current versus starting at a high current in a much shorter time. The amount of charge in - and out (energy) is the same, All that said I once had a Peugeot station where I could stick the crack in and start it with real muscle power.

I have one containing about a 15Ah lead-acid, so still easily liftable with one hand without being an explosion risk. Lithium is smaller and lighter with less self-discharge but as you say, a bit risky.

I have had one for a few years now. I got it early in the pandemic when my Golf R would lose charge whilst not being used. It could only tolerate ~3 weeks of non use. It has served me quite well.