How to Test a RV Converter Charger

by John Cagney Nash
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A converter charger in a recreational vehicle (RV) is powered by 120-volt alternating current when the RV is hooked-up to shore power, or when a properly connected generator is running. The primary purpose of the converter charger is to recharge a discharged or partially discharged coach battery or bank of batteries, so that a full supply of 12-volt electricity is again available. It does this by converting 120-volt alternating current (AC) electricity to 12-volt direct current (DC) electricity. To test the function of an RV charger converter is a relatively complex procedure, and the test must be performed in sequence.

Step 1

Use your voltage meter to test across the 120 volt AC terminals to determine whether or not power is being sent to the converter charger. Plug the RV into shore power or a running generator. Shore power hot will typically be a blue or black wire; shore power neutral will typically be a white wire. The reading should be approximately 120 volts AC. If no power is present, check the fuse or circuit breaker dedicated to the converter charger.

Step 2

Use your volt meter to test across the coach battery terminals. Coach battery hot will typically be a red or black wire; coach battery negative will typically be a white wire. The reading should be approximately 14 volts DC. If no power is present, the fault lies within the converter charger.

Step 3

Determine whether your converter charger has separate outputs to the vehicle’s 12-volt systems and to the charger. Do this with shore power or a generator plugged in. Use your voltage meter to test the vehicle’s 12-volt systems at a socket or light fitting. If the 12-volt accessories are reading approximately 14 volts and the battery charge terminals are not, the converter charger is faulty. If the battery charge terminals read approximately 14 volts but the coach battery fails to charge, then the battery is probably faulty.

Step 4

Test the transfer relay switch, also called the solenoid, which allows charging voltage to be sent to the coach battery. It should be energized whenever the RV is connected to shore power or a generator (you will hear it click when it senses the power come on). If it is not, ensure all power has been disconnected from the converter charger. Remove the case of the converter charger and spray the transfer relay switch with electrical contact cleaner. Test it by plugging the RV in again.

Step 5

Test the transformer using your voltage meter. It should have approximately 120 volts AC at its input terminal, and approaching 14 volts DC at its output terminal. If it has the 120-volt reading but not the 14-volt reading, the transformer is faulty. If it does not have approximately 120 volts AC at the input terminal, there is a dead-fault in the system before the transformer.

Step 6

Consider whether the diode or diodes may be faulty. There may be up to four diodes. Consider whether the resistor and/or the resistor gates may be faulty. Testing diodes and/or resistors and/or resistor gates is not practicable for even a competent amateur electrician.

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