RCAF D311 genset

Loss of residual magnetic field from sitting unused.

If it had residual, it would build some voltage even without an operative regulator and exciter field.

Do you know how to flash it?
Sliprings and commutator clean?
Brushes free in the holders?
Good spring tension?

[quote="ccjersey"]Loss of residual magnetic field from sitting unused.

If it had residual, it would build some voltage even without an operative regulator and exciter field.

Do you know how to flash it?
Sliprings and commutator clean?
Brushes free in the holders?
Good spring tension?[/quote]

Hey CCJ,
Thanks for the reply.
Being in college in the 70s, I know how to flash but I don't know how to flash a exciter.
Sliprings and commutator appear clean. The genset has about 100 hours on it since overhaul.
Brushes are free in the holders.
Spring tension is the same on all 4 holders. I'm not sure if its good or not but it's the same.
The genset was working then after about 6 months of non use, it stopped working.
I suspected a rectifier or the regulator going bad. The regulator looks good and I can't find the rectifier so my next test was the looking for voltage on the brush leads.

Tom

To flash, you need to touch a battery to the brushes on the commutator. I like to use something like a automotive test light that has a bulb so you can tell that you made a circuit (bulb lights) and the bulb also limits current so you don't make an arc and burn up something. With a bulb in the circuit you can use a 12 volt or other starting (high amperage) battery more safely. Get the negative connection made up ahead of time and clip the test light to the battery positive terminal......then touch the positive brush with the test light probe

You need to determine positive and negative brushes before you flash it. Look to see if any brushes are connected to the frame (negative) while the other (pair?) are insulated from the frame (positive).

You can try this with the engine stopped and it may build up when the engine comes up to speed. Or you can do it with engine running at full speed and watch the volt meters to see it build up or if you get a voltage blip or not.

Some generators used the exciter to crank the engine over for starting. This process of making the exciter generator motor over restores the residual every time. If it doesn't do that, and uses a separate starter or pony motor for cranking, there may be an auto flash relay that is supposed to take care of it. Some later model military sets up you must hold the start button in until voltage builds up before releasing it.

[quote="ccjersey"]To flash, you need to touch a battery to the brushes on the commutator. I like to use something like a automotive test light that has a bulb so you can tell that you made a circuit (bulb lights) and the bulb also limits current so you don't make an arc and burn up something. With a bulb in the circuit you can use a 12 volt or other starting (high amperage) battery more safely. Get the negative connection made up ahead of time and clip the test light to the battery positive terminal......then touch the positive brush with the test light probe

You need to determine positive and negative brushes before you flash it. Look to see if any brushes are connected to the frame (negative) while the other (pair?) are insulated from the frame (positive).

You can try this with the engine stopped and it may build up when the engine comes up to speed. Or you can do it with engine running at full speed and watch the volt meters to see it build up or if you get a voltage blip or not.

Some generators used the exciter to crank the engine over for starting. This process of making the exciter generator motor over restores the residual every time. If it doesn't do that, and uses a separate starter or pony motor for cranking, there may be an auto flash relay that is supposed to take care of it. Some later model military sets up you must hold the start button in until voltage builds up before releasing it.[/quote]

I traced out the circuit today using the (REGOHM) regulator makers online manual. It was a retro fit so of course it didn't follow REGOHMs hookup exactly. I couldn't find anything that looked bad and everything appears to have continuity.

This genset uses a pony motor. I think you are spot on the diagnosis of having lost my field residual magnetism. I appreciate your static flashing procedure and will give it a try tomorrow. I have several very stout 24vdc supplies and will float one across a bulb as a current limiter. My son-in-law has a load bank headed my way so if I can get it in the charging business again, I'll put the load bank on it and keep my fingers crossed it will clean up the wet stacking problem. I would really rather not have to pull the engine down for a broken ring or something. I know it would be a character building exercise but I really don't need any additional character at this time. Maybe later but not right now.

Thanks for the help!
Tom

Don't believe you need a Stout 24 volt? - have done this with a 9 volt battery from my door opener. Bob

If it is only loss of residual, a pair of D cells in series will do the job if connected directly. But its usually more convenient to use the starting battery that's sitting right there. It really doesn't take more than a quick touch to restore the residual if you want to do without the light bulb.

If you flash it and it doesn't build at least some voltage while your flasing connection is in place, then suspect a shorted stator. Have an old Onan pto generator that quit genning during a power outage. Checking voltage on it with a meter, I found something like 7 volts on one wire and zero on the other two (3 phase generator). It didn't look or smell burned but I took it to local rewind shop and they were able to cut the stator laceings and lift the splices to the output leads enough to discover and reinsulate a short between the two windings that had no voltage before.

[quote="ccjersey"]If it is only loss of residual, a pair of D cells in series will do the job if connected directly. But its usually more convenient to use the starting battery that's sitting right there. It really doesn't take more than a quick touch to restore the residual if you want to do without the light bulb.

If you flash it and it doesn't build at least some voltage while your flasing connection is in place, then suspect a shorted stator. Have an old Onan pto generator that quit genning during a power outage. Checking voltage on it with a meter, I found something like 7 volts on one wire and zero on the other two (3 phase generator). It didn't look or smell burned but I took it to local rewind shop and they were able to cut the stator laceings and lift the splices to the output leads enough to discover and reinsulate a short between the two windings that had no voltage before.[/quote]

I'll give it a try. Kind of a nasty day here today and prefect for playing on a indoor project.
Thanks!