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Davidson Sales Company

Flash A Generator

How to "flash" a generator when output is lost due to loss of excitation.

Residual magnetism in the generator exciter field allows the generator to build up voltage during start-up.  This magnetism is sometimes lost due to shelf time or improper operation, among other reasons.   Restoring this residual magnetism is possible and is sometimes referred to as "flashing the exciter field".

To restore the small amount of residual magnetism necessary to begin voltage buildup, connect a 12 volt battery to the exciter field while the generator is at rest, as follows:

  1. Remove exciter field leads F+ and F- from the voltage regulator.  CAUTION: Failure to remove the field leads from the regulator during flashing procedures may destroy the regulator.

  2. Measure the exciter field resistance from the F+ to the F- lead.  You should be able to read some resistance as you are measuring a continuous winding.  An infinite resistance reading would indicate an open in the exciter field.  Also check to be sure there is no path to ground.

  3. Connect F+ to the positive pole of the battery.

  4. Hold the F- lead by the insulated portion of the lead wire, touch F- to the negative pole of the battery for about 5 to 10 seconds, then remove.

  5. Reconnect F+ and F- to the regulator.   Repeat the procedure if the generator fails to build voltage.

Specific generator service manuals for Marathon Electric products are available from Marathon Electric (715) 675-3311 or by contacting Davidson Sales Company.


generator parts and instrumentation

Davidson Sales Co Power Generation Distributors: Sales / Parts / Supplies, Manufacturer Of Panelsource Generator Metering Panels.