The 'centre tapped resistor is (from memory) 150ohm overall but the outer ends are connected giving 75 ohm. This resistor is permanantly connected between D & F to quench the considerable back emf when the voltage or the current regulator contacts open.
If you're measuring 500 ohms between D&F on the reg I think something is awry.
The field resistance is ~6 ohms increasing to 7 when the dynamo is hot. With 12-15 volts it won't be much above 2 Amps.
With a SIF engine you won't want to do that.
The dynamo will stuff 25 amps into a discharged good battery (12 ish volts) and will be held back because it won't be reaching it's maximum torque (rpm) at this load.
Sorry, I don't quite follow the above.
Yes, a diode will prevent the dynamo motoring, however a a decent relay across the diode will (as with the one I made) allow the dynamo to auto start the SIF
No! Been there. These dynamos will only produce useful output turning clockwise looking at the drive end. Rotating then anticlock they will only produce about 2-3volts with D&F connected at 6000rpm.
The one I cobbled together about 20 years ago and is still going strong has a three coil regulator which can be overidden by a switch. The engine is overloaded when this was done so I've added a 4R7 resistor to the field which allows the poor little engine to get on its cam!
By the way the generators fierld current max's out at 2 amps (pushing 27 amps into a flat, good, 220 ah battey) but beware, always keep at least 100ohms between the field-F and the armature -D as the open circuit back emf if opened without will surprise!
There's some (big) pic's of my bodge at
for more, if you're brave
change the last bit to 2.JPG to 6.JPG
Sorry to go on so much,