Cummins/Onan — Check and Adjust Battery Charger Float Voltage
Adjustments · Float battery charger
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Ignition of explosive battery gases can cause severe personal injury.
Procedure
- Turn genset operation selector switch to OFF and disconnect starting battery (negative lead first).
- Connect a fully charged battery (negative lead last) and verify charge with a hydrometer.
- Connect voltmeter directly to battery terminals and measure voltage.
- Compare reading with Table 3-3; adjust if above or below recommended float voltage.
- Turn adjustment potentiometer counterclockwise to decrease, clockwise to increase float voltage.
- Adjust in small steps and wait five minutes for voltage to stabilize.
Tools required
- Fully charged test battery Amazon
- Hydrometer Amazon
- Small screwdriver Amazon
- Accurate voltmeter (0.5% accuracy) Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Lead-acid 12 V float voltage 13.3 V
- Ni-Cad 1.38 to 1.45 volts per cell
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.