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Crank Engine with power supply instead of battery

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rvalente:
Hello Mates,

me and my dad have a few cars that are "out of service" but we'd like to turn their engines on more often.

Its common to have to crank old engines a LOT for the fuel system to blead, specially diesels so the battery often dies, even with a charger in parallel.

Automotive lead acid batteries are a pain, they are expensive and gets destroyed if they go flat (deep cycle discharge).

I'd like to have a 14V high current power supply to crank the engines, I've thought of a few options and I'd like your suggestions:

#1 - Get a 250A DC stick weld, modify the output transformer to lower the voltage (or maybe just the feedback) and increase (or maybe not) the rectification, and use it in parallel with not so good battery, as capacitor

#2 - Use a few server power supplies in parallel. They often 12.5 V @ 50...60...70A output current, maybe 4 in parallel could work.

Any way, I'm looking for options

Greetings, renan

SeanB:
Server supplies would work, as you need around 300A to crank most vehicles.. the simpler thing is to get an old oil cooled iron core welder, and look among the taps for one with around 10VAC output, and use a bridge rectifier (going to be a big one at 300A) to provide brute boost power, using a lead acid battery in parallel as a smoothing capacitor and some voltage regulation. Common to get in car dealerships used as a boost pack to start those vehicles that have flat batteries, and very reliable, though will kill a battery if left on it for long without cranking.

Carel:
I once started my car with a rectified welder, it was an emergency, the only option. Could have been destructive. For regular practice you should measure what happens voltage wise, and a battery to buffer.

Started someone else's scooter with a power supply (0-30V, 0-10A). Wait for the Amps to go down, before starting. Fried one off the six regulating transistors. Problem with the scooter was that it needed 10-11 volt for sparks. Too little margin.

langwadt:
a battery on a cart, kept on a maintenance charger when not used

james_s:
A potential problem with a welder is that most are deliberately leaky (as in the inductive coupling) in order to limit the current. IIRC MIG welders are constant voltage so one of those would probably work. A potential problem with server PSUs is the overcurrent protection is very sensitive, I had trouble one time trying to use one to power a 12V winch that was well within the capability of the PSU but the inrush at startup would make it shut down.

You could make a start cart similar to what is used for older aircraft with large piston engines, either mount a few large automotive alternators on a suitable small engine or use one or more large lead acid batteries on a cart. The sort used in big trucks and large boats and such that are several times the size of a typical car battery.

Keep in mind the duty cycle of the starter motor, in general they are not intended to crank the engine for much longer than the battery can hold out.

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