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Cummins/Onan OT UCD 280 — Battery Float Charge Adjustment

Adjustments · Battery charger module 6

For the Cummins/Onan OT UCD 280, from the Cummins/Onan service manual.

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Before you start

  • A high specific gravity, bubbling of electrolyte and loss of water indicate excessive float voltage.

Procedure

  1. Connect the fully-charged battery (verify charge condition with the hydrometer for lead-acid batteries).
  2. Connect the voltmeter directly to the battery terminals.
  3. Measure the battery voltage; if above recommended float voltage proceed to high-voltage step, if below proceed to low-voltage step.
  4. If voltage is high: insert a small screwdriver through the hole in the front panel of battery charger module 6 and turn counterclockwise in small increments to decrease float voltage.
  5. After five minutes, measure battery terminal voltage again; repeat until voltage stabilizes at the recommended float voltage.
  6. If voltage is low: note charge current rate on charge ammeter on meter-lamp panel.
  7. Insert a small screwdriver through hole in front panel of battery charger module 6 and turn clockwise in small increments to increase float voltage.
  8. In approximately one hour, or when charge current has decreased to initial value, recheck battery terminal voltage; repeat until voltage stabilizes.
  9. Check the battery terminal voltage periodically during the first few weeks of operation.

Tools required

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

Specs & values

  • Float voltage 13.3 volts for nominal 12-volt Amazon eBay $11.99 FridayParts $65.01 lead-acid batteries
  • Float voltage 26.6 volts for nominal 24-volt SinoCMP $247.50 lead-acid batteries
  • Float voltage 14.0 to 14.5 volts for 10-cell nickel-cadmium batteries
  • Float voltage 28.0 to 29.0 volts for 20-cell nickel-cadmium batteries

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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