Cummins/Onan — Battery Charger Float Voltage Adjustment
Adjustments
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. Do not smoke or cause any spark, arc, or flame while servicing batteries.
- Always disconnect the battery charger from its AC source (remove the charger's AC input fuses) before disconnecting the battery cables.
Procedure
- Turn the generator set operation selector to Stop and disconnect the starting battery (negative [-] lead first).
- Connect a fully charged battery (negative [-] lead last) and verify charge condition with a hydrometer.
- Connect the voltmeter directly to the battery terminals and measure the voltage.
- Compare the voltage reading with the recommended float voltage in Table 2-3.
- Turn the adjustment potentiometer counterclockwise to decrease float voltage and clockwise to increase it.
- Adjust in small steps and wait five minutes for the voltage to stabilize before further adjustments.
- Close and lock the transfer switch cabinet door.
- Disconnect the voltmeter and the test battery (negative [-] lead first); reconnect the starting battery (negative [-] lead last).
Tools required
- fully charged 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; 24 V float voltage 26.6
- Nickel-cadmium float charge 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.