How to / DIY > Generators
SDA /SDT Generator Manual copy available and question on de-magnetised generator
Alexdick:
I have a manual for an SDA + SDT Generator (see below) if anyone wants a copy I will scan a PDF over to you.
also I have de-magnetised it by shutting down whilst it was still powering my house! Help, how do I re-magnetise it? I am a TOTAL novice so two questions:-
1. Is there an idiot's guide to doing this job myself (photo of generator plate below) or;
2. Can anyone recommend someone in the Berkshire (UK) area to do it for me?
Many thanks
Alex l
mike90045:
http://www.dieselduck.info/machine/03%20electricity/flashing_generator.htm
you need to re-flash the generator
https://www.stationaryengineparts.com/st-alternators-instructions-for-operation-and-maintenance-1926-0.html
instructions:
To stop
1, Remove the load(s) from the output by opening the output switch(es).
2, Stop the prime mover.
Cautions:
Be very careful not to allow short circuits at the output of the generator. This can damage the rectifier diodes in the voltage regulating circuit.
Before stopping the generator, remove all output electrical loading first before turning off the prime mover. If you turn off the prime mover while the generator is under load, the resulting spin-down and gradually reducing electric fields may erase the residual magnetism in the rotor that allows the generator to start self excitation.
If the residual magnetism in the rotor is too weak to start self-excitation, the rotor will need to be re-magnetized.
Problems and Troubleshooting
First, verify that all internal and external connections are correct. Once this has been verified, if there is no voltage output then possible causes are:
Loss of residual magnetism
The rotor’s residual magnetism, which enables self-excitation, may be lost over time if the generator is unused for a long time or suddenly if the alternator’s prime mover is turned off while the electrical load is still connected to the generator.
To re-magnetize the rotor, flash connect a 12V storage battery to the field winding terminations F1 and F2 observing the polarity while the generator is rotating. Do not connect the battery in the reverse polarity and only connect the battery momentarily.
ajaffa1:
Hi Alex, Mike is absolutely right sbout how to flash an ST head. Sadly you have a Brush head which is very different. In an ST head the AC windings are stationary and the field is rotated by the diesel motor, the field is energized by feeding it DC voltage via the slip rings.
In a Brush head the field windings are stationary and the AC windings rotate, 240 volt AC is collected from the slip rings.
To complicate things further the generator also acts as a starter motor requiring further dc motor windings and a commutator ring, it also works as a dynamo to provide 12/24 volts to charge the batteries.
I believe that what you need to do is flash the auxiliary field windings. Please see the photo attached and the rather poor quality circuit diagram.
You will need to remove the cover on the back of the generator to access the rectifier and rheostat shown in the photo. Flash the field by connecting a pair of jump leads to a 12 volt battery, very briefly (half a second) touch one jump lead to either end of the rheostat shown on the left of the photograph. Doing it this way you do not need to worry about the polarity as the bridge rectifier will only allow current to flow in the correct direction. Please see drawing.
Good luck, let us know how it goes,
Bob
ajaffa1:
Hi Alex, further to my previous post, it is probably safer to disconnect the wire from one end of the rheostat, wouldn`t want to fry the rheostat.
Bob
mike90045:
When I had to flash mine, I used a automotive tail light bulb in series with the battery, to limit amps, just to not burn anything out. And just one zap is all it takes to refresh the mistake.
I added the ST head instructions, the reiterate the "remove loads" before stopping the engine, it's a universal requirement.
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