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Converter / charger

A guided diagnosis for RV techs. Each step is a check, a reading or a question.

  1. What is the converter doing? Plug in to shore power. Meter the battery posts: the converter should raise them to 13.2 to 14.4 V within a minute. Listen for the converter fan. Expect: Progressive Dynamics Charge Wizard: 14.4 V boost (LED solid), 13.6 V normal (LED fast blink), 13.2 V storage (blink every 6 to 8 s). WFCO auto mode: 13.6 V normal, 14.4 V bulk when the battery is low, 13.2 V float after a long rest.
  2. Does the converter have 120V in and is it alive? Check the converter's breaker at the panel. Meter 120 VAC at the converter's cord or input terminals. Listen for the fan or a hum. Then look at the converter's own DC output fuses (reverse polarity fuses on the DC side, usually two or three 30 or 40 A ATC). Expect: 120 VAC in, 13.2 to 14.4 VDC at the output terminals
  3. How much is the converter actually putting into the battery? Clamp the converter's positive output cable while the battery is low. Compare to the rating. Expect: Most of the rated output into a battery under 12.4 V, tapering as it fills

Causes and repairs

No 120V to the converter

A tripped breaker, a loose neutral at the panel, or the converter is on a GFCI that tripped (some are).

Tools: multimeter

Reset the breaker, check for 120 V at the converter plug. Find the trip cause if it trips again.

Reverse polarity fuses blown

Someone connected the battery backwards or shorted the output. The converter's DC fuses protected it. Replace them and the converter usually lives.

Tools: multimeter

Replace with the same rating. If a new fuse blows with the battery correct, the converter output is shorted internally: replace the converter.

Converter failed

120V in, output fuses good, nothing out. Internal failure. Check for a thermal cutout that may reset once it cools, and confirm the fan runs (a dead fan cooks them).

Tools: multimeter

Replace the converter. Match the amperage to the battery bank (lead-acid: about 20% of Ah; a 55 A unit for a 200 Ah bank). Pick a model with a lithium profile if the owner may upgrade.

Output not reaching the battery

Converter puts out 13.6 V and the battery doesn't rise: an open or high-resistance path. The charge wire fuse at the battery, the disconnect (some disconnect the charger too), a corroded lug, or an undersized charge wire with big drop.

Tools: multimeter

Meter from the converter output to the battery post with the converter running: the drop should be under 0.5 V. Find the connection that eats it. Check the disconnect position.

Converter fine, battery or loads

The converter does its job. Either the battery no longer holds a charge (load test it), or overnight loads exceed what the bank can hold (furnace blower, inverter, fridge on 12V).

Tools: load tester, clamp meter

Load test the battery. Add up overnight amp-hours. Size the bank or cut the loads.

Converter output weak or restricted

Low output into a low battery means the converter is tired, derated for heat (blocked vents), or the charge path has resistance so the converter sees a full battery that isn't.

Tools: clamp meter, multimeter

Measure drop converter-to-battery under load. Clear vents and check the fan. Replace a converter that can't make rated amps into a low battery with a clean path.

Stuck in float/storage

Some converters go to 13.2 V after a timer and need a trigger to bulk again. Progressive Dynamics: press the Charge Wizard button to force boost. WFCO: the auto mode may never leave 13.6 unless it sees a low battery under load.

Tools: multimeter

Force boost and watch the voltage climb to 14.4 V. If it won't leave 13.2 with a low battery, the controller has failed or the unit has no multi-stage control; upgrade it.

Converter overheating

Blocked vents, a dead fan, or a converter mounted in a hot cabinet with no airflow. Heat derates the output and kills them.

Tools: infrared thermometer

Clear the vents, confirm the fan runs under load, add clearance. Replace a converter with a dead fan.

Ripple or no battery in the circuit

A converter with no battery connected (or a dead one) puts out a pulsing DC that makes lights flicker. A failing output filter does the same with a good battery.

Tools: multimeter

Confirm the battery is connected and good. With a good battery and lights still pulsing on shore power, replace the converter.

Lithium needs a lithium profile

LiFePO4 wants about 14.4 to 14.6 V absorption and no long float at 13.2. A lead-acid converter stuck at 13.6 V leaves a lithium bank at about 80 to 90%. Also, most BMS units refuse charge below about 32°F.

Tools: multimeter

Set the converter to its lithium profile or replace it with one that has it. Check battery temperature before you condemn anything in winter.

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