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Home›Repair guides›Cummins/Onan›Float Voltage Adjustment

Cummins/Onan CHG-4 — Float Voltage Adjustment

Adjustments · Battery charger float potentiometer

For the Cummins/Onan CHG-4, from the Cummins/Onan service manual.

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Before you start

  • Battery electrolyte can cause severe eye damage and burns to the skin. Wear goggles, rubber gloves and a protective apron when working with batteries.
  • Ignition of explosive hydrogen gas given off by the battery can cause severe personal injury. Do not smoke or cause any spark, arc, or flame while servicing batteries.

Procedure

  1. Remove all load from the battery. If connected to a standby generator set, disconnect the genset battery leads, the negative (-) lead first.
  2. Connect the voltmeter directly to the battery terminals. The charger must not be in current-limit mode of operation (Foldback Override indicator light on).
  3. Compare the battery voltage reading with the recommended nominal float value: 13.2 for a 12-volt charger, 26.4 for a 24-volt charger, referenced at 77 F (25 C).
  4. Use a small flat-blade screwdriver to turn the float adjustment potentiometer counterclockwise to decrease or clockwise to increase voltage. Adjust in small increments (0.1 VDC max).
  5. If the battery is connected to a generator set, reconnect the battery leads. Connect the positive (+) lead first, and the negative (-) lead last.

Tools required

  • small screwdriver Amazon
  • accurate voltmeter (0.5% accuracy) Amazon
  • hydrometer for checking specific gravity Amazon

Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.

Specs & values

  • Float voltage factory-set at correct value
  • 12-volt Amazon eBay $11.99 FridayParts $65.01 charger nominal float 13.2 VDC
  • 24-volt SinoCMP $247.50 charger nominal float 26.4 VDC
  • Reduce voltage by 0.8% for every 10 F (5.5 C) above 77 F (25 C) ambient; increase by 0.8% for every 10 F (5.5 C) below
  • Adjust in increments of 0.1 VDC max

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.

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