Crank Engine with power supply instead of battery

[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.

[coromonadalix]

you need a battery who act as a huge capacitor to help the starter kick the motor, a server supply would need tons of amps ... no server psu will help

2 ways exist to start a motor,  by compressed air in maritime boat or electric starter

you can substitue a battery with  supercaps, it must start at least once or two in a week,   youtube videos show its possible
But supercaps may take a very long time to charge ... some may need at least 15-20 minutes of charge depending of the charger used, it will need many amps  too

have you measured how many amps is needed to start your car (motor) 

In my father boat  he use a Diesel Volvo Penta 6 cylinder motor, you need at least 1000 amps to crank it,  and he use an compressed air starter in case of the electric starter failure

For gaz motor,  you can measure it with a clamp meter in the 100 600 amps ??

[TheMG]

Power supplies alone won't work, unless you get some power supply setup with some really serious current capability. The starter motor is almost a dead short when at a standstill, so the initial current required to get the motor spinning is several hundreds of amps, could be approaching 1000A depending on the size of the engine and starter. That will undoubtedly trip the overcurrent protection on server supplies even with 10 of them in parallel.

A current limited power supply (not the foldback type) paired with a supercapacitor could work.

But the simplest and easiest solution I would just get a decent size "smart" charger and a large lead acid battery, such as an 8D battery, and set it up on a mobile cart.

[JDubU]

Do a search for "Dual Purpose Battery". 
A compromise between deep cycle endurance and engine starting capability.

For example:
https://anchor.travel/dual-purpose-vs-deep-cycle-for-trolling-motor/#2_Dual_Purpose_Batteries

[Benta]

300 A is optimistic depending on the engine. A 1.6l petrol engine will probably draw that, a 3l diesel will easily pull 600 A.

[glentek]

I built a 200A battery charger years ago from an inverter transformer, it was a 24V Sunsine 1.5kVA sinewave inverter from about 1992 from memory. Transformer had 2 14.4V primaries, 230V secondary that I used in reverse. Large diodes and a massive heatsink, it weighs about 30kg. It easily turned over my V6 commodore at the time.

[bdunham7]

To do this with a PSU requires that it not trip off even at severe overloads.  It's OK if it sags, even a lot, but it needs to be short tolerant for a few seconds. 

Also, you can't crank an engine forever even if you have the power because the starter motor will overheat.  Typically by the time your battery is low, the starter is roasting hot anyway and you need to stop cranking.  I'd suggest you either run the engines more often,  find a better way of bleeding your fuel systems or fix whatever is allowing them to bleed down.  You shouldn't have this issue unless either there is an issue or you are letting them sit for a very long time.

[james_s]

You could try starting fluid or even propane to get the engine started quickly so the fuel system can prime itself. As an experiment I poked a hose into the carburetor of a small engine and connected it to a propane torch head, opened the valve and when I pulled the cord the engine started right up. Even just manually metering the fuel flow by turning the knob I could control the engine fairly easily, propane unlike gasoline burns over a very wide range of AFR and under little or no load you don't even need a throttle, you can control the engine speed by adjusting the fuel flow like a diesel.

[viperidae]

I go with either maintenance chargers on all the cars, or a jump starting cart with a large battery.
Unless you have multiphase power available. Even a conservative 500A at 14V, you're looking at 7kW. I had an old Subaru with just a 2L engine, it's starter was rated at 900A.

In saying that, you wouldn't draw the full current rating of the starter while it is cranking, only for a brief period of time as it starts spinning. Still going to be a few hundred amps continuous though.

[BrokenYugo]

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

This is what I've seen done in repair shops, big 12V truck/tractor battery (probably 1000 CCA or so, ideally) strapped to a hand truck with a set of heavy gauge jumper cables hanging on it.

Also agree with bdunham7, you have problems if fuel systems are bleeding down on any reasonable timescale (perhaps half a year tops), unless we're talking about carbureted cars, those do lose prime quickly (as the fuel evaporates from the vented bowl), but in that case it's generally easy to open the air cleaner and top it off with a squirt bottle full of gas.

It should also be pointed out that just firing up an engine and letting it idle every so often isn't terribly good for it, unless you're using these cars (loading the engine and properly warming everything up) when you start them you're probably really just putting more moisture and junk in the oil. The correct way to store an engine/car long term is to oil the cylinders and set/maintain some rodent traps.

[NiHaoMike]

Thinking laterally, if the cars have manual transmissions, might it be possible to jack up one of the drive wheels and spin it with an AC motor with the transmission in highest gear?

[DTJ]

Buy a commercial battery charger with a start option. You can get them from around $100 up to $1000

My $700 unit was stolen and I replaced it with a $100 ebay unit. It works fine.


This sort of thing

https://www.edisons.com.au/catalogsearch/result/?q=truck+charger

[james_s]

That seems like it would be challenging and dangerous. You'd need a chassis dyno essentially, something rigidly mounted that the car's wheel could sit on, and then you'd have to be able to activate it remotely while sitting in the car. It just seems a LOT safer to start the engine with the starter motor already attached to it.

[geggi1]

You will need a lot of amps for the starter motor to turn over the motor.
For 4 cylinder petrol engines you will need something in line of 400-600A and for diesels you will need even more maybe up to 1200A.
If you are speaking about V8 you will probably need even more current.
At 12V this is 4,8kVA to 14,4kVA output of your transformer so it will be heavy and you must also consider avalable power at your workshop.

If the cars are out of service you should consider removind the battery and keep it stored with some kind of maintenance chargeing. This charging can be just a tikkel charger with a few 100mA.

Depending on the age of your cars it might be possible to manual prime the diesel system if the diesel pume is fitted with a primer pumpe. This will reduce the time you have to crank over the motor to get the fuel system primed.
Another trick that wirks on some old diesels (CAT) is to slightly open the fittings on the injector nossle and bleed until the diesel starts dripping.

[tszaboo]

you can start a car without a battery. Get 3 guys together and start pushing it, second gear, feet on the clutch.

[NiHaoMike]

you can start a car without a battery. Get 3 guys together and start pushing it, second gear, feet on the clutch.

Might be true of really ancient cars but anything remotely modern needs the control electronics powered up.

[james_s]

Even with an old enough car, you don't want to start the engine without a battery present, the charging system expects a load. You can push start a car that has a battery that is almost dead though, I have done that on mine before.

[Renate]

Not directly related, but many small generators for RV's use an electric fuel pump that only starts when you hit the crank button. The first seconds of cranking are wasted because the system is dry. You can add a prime pushbutton to run the fuel pump without cranking.

[james_s]

Not directly related, but many small generators for RV's use an electric fuel pump that only starts when you hit the crank button. The first seconds of cranking are wasted because the system is dry. You can add a prime pushbutton to run the fuel pump without cranking.

It may not actually be wasted. If these engines have pressurized lubrication systems then they might assume that when the fuel pressure has bled the oil pressure will also have bled, so the dry cranking may serve to build up some oil pressure before the engine starts. Some large engines have a pre-oiler pump to handle that task.

[amyk]

Peak current even on a small starter motor will be >1000A. Total DC resistance of the whole circuit is sub-ohm. PSUs are likely to trip the overload protection on that peak.