Cummins/Onan — Flashing the Field (Standard YD)
Repair & overhaul · Exciter field
From a Cummins/Onan service manual covering: 15.0YD-3G, 20.0YD-3G, 20.0YD-5DG, 25.0YD-3G, 25.0YD-5DG, 30.0YD-3G, 30.0YD-5DG, 6.0-3CS1, 7.5-3CS1. Check it applies to your exact model before use.
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Before you start
- Do not keep excitation circuitry connected longer than 5 seconds or damage may occur.
Procedure
- Locate terminals 7(-) and 8(+) on voltage regulator PC board VR21.
- Use a six volt dry cell battery with two clip leads and a 12 amp, 300 volt diode.
- Start engine.
- Touch positive lead to +8 and negative lead to -7 until voltage starts to build up.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Generator residual voltage should be at least 20 VAC at rated speed
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.