gen sets et al and using a big alternator

[Heckler]

the working theory is that the more you put into the excitation circuit on an alternator the more voltage you get out, has any one tried getting a second hand 24 volt wagon (big and beefy) alternator, scrapping the excitation controller and then feeding 12v thru a potentiometer to the excitation circuit to see what comes out?
i know in angola, where i was head of maintenance, my mechanics took a liking to caterpillar 24 volt alternators and were playing with them to deliver lighting.

 

[pampas]

Have bench tested 100s of alternators without regs ,Max field current is usually around 2 Amps for 12 volt models pushing the full load volts to around 15v wth a simular proportional raise for 24v. what the open circuit voltage is I do not know.
Why mess around when you can buy 240 Alternators at a reasonable prices. Diodes and windings would not last very long at the higher voltages as the insulation varnish used on these low voltage machines is not suitable for higher voltages.

 

[William_H]

High Stu you havn't said why you want more voltage out of an alternator and how much.
Yes an alternator will give more voltage with large field current. ( and higher speed)However using a 24V alternator with 12 volt supply to field will give less current hence 1/4 power to the field so you would get more magnetic field using a 12v alternaor.
The 3 phase windings of the 24 v alternaor will give more voltage However much of the voltage limitation of an alternator at high current is a result of the resistance of the 3 phase windings and losses in the recifiers. So a similar sized alternator(in watts) for 24 volts will have higher resistance of windings and bear in mind that a voltage drop for a 24v system is less significant in % terms than in a 12 v system.
So if you a seeking a higher voltage at high current from your alternator for charging batteries fast then a high current rating 12v alternator may produce more current at the higher voltage you need than a 24v alternator assuming full field current. Plus the unknowns of overheating the 24v alternator.
Sure experiment if you have the spare alternaors but I think a high current 12v is the way to go. Unless you have a very high current 24 v that can be under rated. olewill

 

[nedmin]

once you saturate the metal (with magnetism) you can put as much current as you like in but you wont increase anything,just burn it out.

 

[Heckler]

point i was making was can one get 240 volts out of one?

 

[William_H]

Probably not Stu. Perhaps if you could spin it fast enough (without it flying apart) but the frequency would be very high so only suitable for lights and of course only available as 3 phase which would I think need to be equally loaded. So buy a proper one phase 240 volt AC alternator and run it at 3000RPM to get 50 hertz (or 1500 if it is so designed)
olewill