3kVA single phase frequency converter troubleshooting

Fault Description
A customer bought a 3kVA single phase 230v 50Hz/60Hz frequency converter in 2017, everything works fine in the Low Voltage mode (0-150v), but when switched to the High Voltage mode (0-300v, with yellow button), following happens:
3kVA frequency converter

Without load:
The voltage and the frequency are still displayed and they do react to the voltage and frequency settings.
But with the Voltage ADJ set to 100% the maximum output voltage at 60Hz is only 26.5V.
Frequency converter shows 60Hz 26.5v

When the frequency is now set to 370 Hz the frequency becomes unstable and varies between 365-373 Hz and the output voltage is now 41.3V although the voltage setting is the same as in the picture above.
Frequency converter shows 41.3v

When the Voltage ADJ setting is then set to below 40% the frequency and voltage decrease:
Frequency converter voltage decrease
At the lowest possible voltage setting it displays 50Hz / 13.8V.

With load:
When a load (bulb 230V/50W) is now connected to the frequency converter, the output collapses to all zeros.
Frequency converter collapses to all zeros

Troubleshooting guide
CBB65 Capacitor Measurement
CBB65 Capacitor

Tools: multi-meter, slot type screwdriver, cross screwdriver.
Preparation: cut off input power supply, turn off input switch, open the left side cover.
Measure steps:

  1. Pry one side plugs on the capacitor by slot type screwdriver, refer to Fig.1, and Fig.2, do it one by one.
  2. Shift the multi-meter to capacitance tab to measure the capacitor, refer to Fig.3, the measured values should be greater than 20uF, otherwise, it's failed.
  3. Plug the wires back on the capacitor, then measure the next one from the first step.
CBB65 capacitor measurement 1 CBB65 capacitor measurement 2
CBB65 capacitor measurement 3 CBB65 capacitor measurement 4

Power on the frequency converter, switchover the Low/High voltage switch, check the contactor is closed or not.
Contactor status

Power on the frequency converter, measure the voltage of CN4 plug on the mainboard, see if it's 151v or not.
3kVA frequency converter CN4 plug measurement

Switch to High Voltage mode, measure the actual voltage on the output terminals of the frequency converter, see it's normal or not.

Customer Feedback
Customer followed the troubleshooting instructions, and feedback with good result.
STEP 1: CBB65 measurement: We tested both 25uF capacitors: both were approx. 30uF so they are OK
Frequency converter CBB65 capacitor measured 30.1uF

STEP 3: Then measured the voltage on the CN4 plug on the mainboard
3kVA frequency converter CN4 plug measured 151.8v

STEP 2: Contactor Test.
When switching over the low/high grade switch we noticed that the low grade contactor opened and closed but the high grade contactor did nothing at all (as its action should be the opposite of the low grade contactor).
A closer examination revealed that the black wire (marked with 1 on the picture) wasn't really secured. It could very easily be removed without using the screwdriver. The red wire (marked with 2 on the picture) had a similar problem. It was secured a little tighter than the black wire but could also be removed easily just by pulling the wire.
Frequency converter contactor test

After correcting these two issues we tested the frequency converter again.
Frequency converter works again

Everything works fine again.

We're very glad with GoHz frequency converter. It's the best way to test stuff over here that's works on a different frequency and to test functionality over a voltage range (especially SMPS).- - - - - - - - by Peter


Related articles: Modify GoHz Single Phase 240v Converter to Split Phase 120v/240v; GoHz 10-20kVA 3-phase Frequency Converter Troubleshooting

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