Some discussion ensued !!
Looking at my old notes which are a bit faded and my writing has always been bad
Using an old Bosch 12V 60A alternator with 12V excitation these voltages were achieved;
engine RPM/voltage; 1200/56v, 1500/65v, 2000/90v, 2300/100v, 3000/140v, 3600/170v
The alternator was driven at about 2x the engine RPM. No load. NOTE dangerous voltages produced !!!
Using normal 12v Bosch alternators the excitation can be supplied by 3 internal diodes provided for that purpose, there is a brass finger which makes contact with the regulator for this supply. I generally used an older style brush holder off the even older external regulator alternators which was a simple brush holder and connections. Then the regulator did not get in the way. Just manual control of the exciter current.
To control the exicitation I made up a simple board with quite a few 5 W resistors and plug in sockets. Not much cost at DS at the time but probably more than a length of nicrome wire
. As I was designing for someone else to use I tried to make it easy. However I found that he just left it at full voltage and after quite a long time the rotor winding failed in 24V truck alternator. So continuous running full voltage exicitation at full output power is not recommended
However by that time it was superceeded by another bigger generator.
For the big battery bank we got a 24V Bosch 50 A truck alternator, powered by a 8 HP B&S motor which ran OK at governed speed of around 3600RPM and the alternator put out up to about 60 A continuous for many hours into the 2500AHr batteries. The excitation resistance was fixed minimum ~8 ohm + ~8+ variable. Pulley size was 8" to 5" pulleys at ~1.6/1 over driven. Manual control is OK as the big battery bank voltage moves up slowly at 50/60A some a check every hour is OK.
Next generator was a DC welder of 250A. Hear how he burnt that out
PS jaahn wrote: People have used them in the past to produce 110V AC and they do OK.
What did they do with the unregulated variable voltage and frequency (varies with load) 3phase AC output???
This was out in the islands 20 years ago and I believe they used it for lights and heating which is ok on that raw power !