The customer’s inverter had been connected up properly but had been severely overloaded and it would appear that the protection modules within the inverter had not operated correctly. Therefore a burning smell had been reported, just before final failure.
This was going to be a difficult repair as I had no schematic diagram for the main PCB and I was effectively going to be testing components in isolation using rudimentary methods.
A quick look around the inside of the unit revealed no obvious damage, but upon testing the IBGT transistors on the units’ high voltage output and several Zenner diodes in line with them, revealed serious damage to that part of the circuit.
These components are not cheap and collectively, the cost in parts alone would have been over £50, without my time factored in and without the guarantee that the unit would work again. On that basis, sadly, I had to inform the customer that the unit was beyond my help and probably beyond economical repair. It will therefore be disposed of responsibly at our local amenity tip.
For those wondering what an ‘inverter’ is, let me give a quick explanation: It allows one to use a mains operated device on the move, using a power supply from a motor-home, car or boat, as an example. An inverter ‘inverts’ a smaller voltage to a larger one, usually for most applications. Most inverters sold turn either 12 or 24VDC to 240VAC or 110VAC.
The owner of this one had accidentally connected the input wires the wrong way around, effectively reversing the polarity. Not good. Upon hearing a little ‘pop’ the owner quickly disconnected the power!
Having never worked on an inverter before, I turned to the manufacturer for advice. Sterling Power (UK) were not able to supply any product information on the phone nor via email and were generally not very helpful at all. They did offer a very reasonable 25% discount on a replacement, but were not able to offer much else to save the one I had in the workshop. Never mind.
Back to the problem. Checking the basics, the ‘accident’ had appeared to knocked-out three 25A soldered PCB fuses. Temporarily by-passing the fuses revealed a working unit, so replacing the defective fuses was a good idea at a very reasonable £1.50.
The fuses are mini-blade 25A automotive fuses. Once removed and the new ones soldered in place, the unit worked once more.
Cost of parts, £1.50, cost of replacement unit, circa £160.00.