How many ATX power supplies do I need to jump start a car

@cinebox my car expects a 900 cold-cranking amp battery. that's >10kW of power.

it'd be fun to find the real answer to this!

@jauntywunderkind420 You can buy a USB-C power brick with lugs on it for jump starting a car. must be using a bunch of capacitors or something because I cant imagine getting kilowatts out of a LiPo that small

@cinebox i would not be surprised if this $55 3S lipo could start my car. it's 5.5Ah and 140C, which is 770 amps of output; less than what my car is specced to need, but i suspect it would work great.

i don't know exactly how "cold cranking amps" are specced, whether it means my battery can drop 900A, under load , while not fully charged. and that under-load voltage drop is going to be colossal. i should measure. lead-acid is _not happy_ about high loads usually, where-as lipos are usually a bit worse performing in the opposite case, very slow discharge.

this lipo would probably have way less voltage drop. but it has way less reserve capacity, so it's going to start going down the discharge curve. the drop from 12.6V down to 11.7V will be very fast. from there it'll be a "slow" drop to 10.2 which might/might not be enough for a car. probably ok.

what's really fun though is 5.5Ah / 700A is 0.00714h, or ~25.7s. my diesel better start fast! mercy i kind of want to try this.

@cinebox also i rather suspect my starter does not actually drain 900A (which equals 10kW, or 13.5HP!). again one of those things that would just be so so fun to actually see.

pardon i just enjoy running this figures, seeing these absurd numbers stack up. i am curious how these jump starter things work. i suspect half of the design is just battery charging, that when you connect it up it dumps charge into your faded car battery to allow it to better provide some amps too. i dunno, just a theory. most cars are not big diesel engines like mine though & starting them happens in split seconds; definitely a good application for some capacitors & the car battery feels pretty optional at that point.

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