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Home›Repair guides›Float Voltage Adjustment

Cummins/Onan CHG-4 — Float Voltage Adjustment

For the Cummins/Onan CHG-4.

Applies to: Cummins Onan Chg 4

Before you start

  • Battery electrolyte can cause severe eye damage and burns to the skin. Wear goggles, rubber gloves and a protective apron.
  • Ignition of explosive hydrogen gas given off by the battery can cause severe personal injury.
  • Do not disconnect the negative lead to prevent arcing.

Procedure

  1. Remove all load from the battery.
  2. If connected to a standby generator set, disconnect the genset battery leads, the negative (-) lead first.
  3. Connect the voltmeter directly to the battery terminals.
  4. Ensure the charger is not in current-limit mode of operation (Foldback Override indicator light on) while adjusting the output voltage.
  5. Compare the battery voltage reading with the recommended nominal float value (13.2V for 12-volt charger, 26.4V for 24-volt charger).
  6. These float voltages are referenced at 77° F (25° C).
  7. Use a small flat-blade screwdriver to turn the float adjustment potentiometer counterclockwise to decrease the float voltage, or clockwise to increase the float voltage.
  8. Adjust in small increments (0.1 VDC max) and allow battery charge level to stabilize before making further adjustment.
  9. Reduce the voltage by 0.8% for every 10° F (5.5° C) above 77° F (25° C) ambient.
  10. Increase the voltage by 0.8% for every 10° F (5.5° C) below 77° F (25° C) ambient.
  11. If the battery is connected to a generator set, reconnect the battery leads, connecting the positive (+) lead first, and the negative (-) lead last.

Tools required

  • Small flat-blade screwdriver
  • Accurate voltmeter (0.5% accuracy)
  • Hydrometer

Specs & torque values

  • Recommended nominal float value: 13.2V for 12-volt charger, 26.4V for 24-volt charger
  • Reference temperature: 77° F (25° C)
  • Temperature compensation: Reduce 0.8% for every 10° F above 77° F, Increase 0.8% for every 10° F below 77° F

Source: manual:901-0604 Onan 305-0856 Charger Install Manual.pdf. Figures and steps are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.