If you are able to procure a large truck alternator, they will already output 24 volt. 28 to be exact.

Then you'll avoid the need for an external step-up PSU.

All the other advice provided by other posters still applies.

 

Common auto alternators will output voltages up to 120 volts for short periods and 24 volts no problem at all. The limit is how hot the field coil gets with the increased voltage on it. 24 volts output will not take much more field voltage than 14 volts normally found in the car so you will not have any problem at all. The alternator will have to be run at a speed that will generate the desired output voltage of course. For 24 volts this will be around 3000 rpm. This is the alternator RPM. The engine can use belt ratio to run it at lower RPM to reduce noise. The alternator will generate its full output current at the higher voltage. Note that the engine driving the alternator will have to generate the required horsepower. Figure a minimum of 1hp for each 700 watts of output. For example, 24 volts at 10 amps is only 240 watts so a small lawn mower engine will be loafing. See youtube videos for more ideas on hookup for higher voltage out of alternators.

 

Unless you already have an alternator you could just buy a 24 VDC alternator. They are really quite common in heavy duty vehicles like trucks, ambulances and marine applications. The first unit in the link is about $80 USD which I see as reasonable. That is a 40 amp alternator leaving you plenty of reserve and also a one wire unit.

Ron

 

Unfortunately I did blow up an alternator not long ago by balancing a battery that was too big half in the battery space & putting the leads on loosely to start the car. Ok yes, that was stupid. The battery moved, one of the leads came off, the engine stopped & the alternator was no more. Most car manuals warn against disconnecting the battery with the engine running. Newer alternators might be more resistant but they're often v expensive to replace, is it worth the risk?

 

Alot of the expense is because alternators are often hidden in some dark corner of the engine where even angels fear to tread

 

Common auto alternators will output voltages up to 120 volts for short periods.

Even a bicycle dynamo can give you a shock if you spin it with no load.

That's a bit beside the point because bicycle dynamos are permanent magnet and car alternators are a completely different animal.

AFAIK: if you put enough voltage into the field coil - the alternator can over volt its rectifier without any difficulty at all.

Most of the regulator would be out of circuit in that situation - but the voltage sensing bit wouldn't be.