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Don't buy this GTI

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I bought this GTI on eBay. Well it worked fine for a couple of months until today. Now i have opened this before when I bought it so i know that things have changed somewhat.

I pluged in my lawnmower next to the GTI and pulled the trigger. At which point i heard a pop and nothing happened. The circuit breaker for the house sockets cut out. After swapping cables and checking fuses it became apparent that the GTI itslef was damaged. The photos show the results. Now I've never seen a ceramic capacitor "leak", the stuff is quite solid despite me opening it about 10 minutes after to bang. The output fuse which was a soldered in one blew the cap off (which is what the pop sound was).

Any ideas if this will work if I change the blown parts. the confusing bit is the "leaked" ceramic capacitor (rated for 400V). It looks like the control circuitry has gone wrong and let a large current in. (I only had 90W of panels connected and these normally output about 50W)

The seller of this "thing" on ebay is sungoldpower

It looks like a mixture of melted polyester dielectric and aluminium. Nice! I guess a voltage spike from the lawnmower caused a dielectric breakdown which led to a short. Usually semiconductors nobly sacrifice themselves to save cheap components, so I would check all the diodes and transistors before risking running it again.

Well the blown capacitor is right up the other end of the board near the 12V in side although it is near  a bridge rectifier so might be something to do with the first boost stage that makes the 12v into something around 240V. I'm not really looking to repair this, one failure is one too many, it is indicative of a design issue. This is not the first time I've used the lawn mower right on top of it

A GTI is comprised of four parts: DC-DC converter which boosts the battery voltage to above the mains peak voltage (around 370V in this case as it's rated to 260V), the inverter part which converts the high voltage DC to AC, a filter and the control circuitry.

The output from the GTI is constant current in phase with the mains with the current being dependant on the power in more than the mains voltage, although there will be more current at lower voltages.

I have a horrible feeling that cheap and nasty inverters inject a non-sinusoidal current into the mains which is not good for appliances, especially those containing induction motors, although your lawnmower will contain a universal motor so this isn't the case here.

Well I was putting 50W into the inverter so it's output would hardly affect a 900W motor. The worrying bit is that it also blew a 30A circuit breaker so it took one hell of a pasting from the mains which I suppose explains the exploded 5A fuse.

The output is supposed to be a pure sine wave, it must be close as it is connected to the mains and if it does not follow that mains waveform closely it will be either trying to put out too much current or it will start to absorb current. I'm assuming (and based on the poor english in the manual) that it outputs a voltage just slightly higher than the mains voltage, just enough to get it's current to feed into the mains.

I suppose i could use the case to make a variable load device for testing stuff  :'(


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