Blown Up Projecta Battery Charger Repaired
A new customer was using a Projecta 2500W battery charger to keep his caravan batteries charged. Recently, he heard a loud bang from the unit and it stopped working.
He pulled off the covers to inspect the damage and found a blown resistor. At this point he decided to bring it to me, in its disassembled state.
As I examined the resistor, I searched the internet for a schematic – however, none could be found. This resistor, although not burned beyond recognition, could not be identified by its band colours. I even tried to join the 2 halves in the hope that I would get some sort of readings – no such luck!
Why did this resistor blow? I checked all the usual suspects – the fuse, varistor, bridge rectifier, chopping Mosfet and anything else associated with the protection circuit. All were in good condition. I had to look further.
I looked at the components after the main filter capacitor. At this point I noticed a burn mark on the main heat sink.
I had a closer examination of the parts nearby. A diode was a suspect, with some strange readings on the board. After removal and testing on the bench, however, the diode proved to be perfectly fine. I had a closer look.
I did some testing on an IC, (VIPER22A SMPS primary switcher). This was definitely faulty, with shorts right across the entire chip. But what caused this to fail? I had a closer look.
A nearby capacitor had glue or electrolyte that had leaked. This in turn, had become conductive over time. It had leached over to the IC, which, in turn had failed due to internal shorts across the pins. I now believe the chain of events were as follows.
Over time, the glue had leaked over to the IC. At that point, due to the fact that it was conductive, it had shorted the IC. The resistor that had blown up originally was a protection resistor, which was sacrificed.
After removal of the IC, the damage could be clearly seen.
The capacitor was removed from the board and tested with a Blue ESR meter. Rather than being within the 3Ω range, (400Volt 10uF Capacitor), it read up to 29Ω!
The diode that I originally thought had shorted, was removed and tested.
When removed, I could see that the glue from the capacitor had reached only one side and therefore had not damaged the diode.
Still, I had the problem of the resistor that had blown. I had no indication of its value via reading the bands. It would not connect when joined to get some resistance readings and there was no schematic to examine.
Although I had an idea, I reached out to Jestine Yong for some advice. After providing a rough back-engineered diagram (sorry it’s not built to scale or painted…😉), Jestine agreed that this was a protection resistor and probably 0.1 Ω to 1 Ω or 1 Ohm plus. I checked what was available for a reasonable cost within the 3-Watt range. I decided that a 1.2Ω resistor could be used. This proved to be fine.
After all the damaged components were replaced, it was time to test the unit. I used my isolation transformer as well as a 100-Watt globe in series. As you would expect of a Switch Mode Power Supply, the moment the power was turned on, the globe lit dully for a second and then went out.
After testing the output of the charger, all the features and modes, I connected it to a battery. It completed the charge and the cut off voltage was reached (13.7 Volts).
Further monitoring of the operation of the charger showed that it was now in the ‘float’ stage (0.8 Amps in photo) and would continue to top up the battery as it naturally drained.
I was now able to hand the charger back to the happy customer. He was so pleased with the repair I did, that he has got me to do automotive repairs as well.
If you are interested in this repair, you can see a video on my channel following the link below:
This article was prepared for you by Mark Rabone from Australia.
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Note: You can check out his previous repair article on Roborock H6 Handheld Vacuum Cleaner Burning Hot
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Parasuraman S
January 12, 2025 at 6:14 pm
Excellent fix and a descriptive article covering all the relevant points which are very essential. Glad to see another valuable article coming from you, Mark! Many thanks for sharing!
Waleed Rishmawi
January 12, 2025 at 7:09 pm
Loved the article in its details and part descriptions, thanks for sharing. Good job on the repair and also a job well done in knowing the value of the resister (jestine) have a blessed day