Cummins/Onan — Flashing the Field (UR Regulator)
Repair & overhaul · Rectifier bridge assembly CR21
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
- Assemble a 6-volt battery and 12 amp 300 V diode.
- If using 12V or 24V set battery, add a 20-ohm or 40-ohm, 2 watt resistor in series.
- Start set and operate at normal rpm.
- Touch positive lead to + terminal and negative lead to - terminal of rectifier bridge until voltage builds up.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
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.