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Old 22nd June 2009, 09:51 PM   #1
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Default About repairing a 1750 watt power inverter

Hello

I've received, for free, a defective Motomaster Eliminator 1750 watt power inverter. The circuit use a SG3525. It seem to be made by Xantrex and I can not find any schematic of this inverter.

Four of the IRF640 output mosfets are burned.

I presume that those four mosfets was connected in parallel, and one mosfet did goes unbalanced and have to much load and burned, after that the 3 others get all the load and burned ?

I can replaced the 4 burned mosfet, but I was thinking to put a .1 ohm resistor on each source terminal of all the 16 output mosfet for a better current sharing between all those mosfet, is it a good ideas ?

Thank

Bye

Gaetan


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Old 23rd June 2009, 12:45 AM   #2
star882 is offline star882  United States
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Do not try to reengineer it without understanding it first.

Power the inverter with a current limited supply for initial testing. If nothing else, connect a car light bulb in series. Make sure none of the components are heating up.

It is possible that another component is bad which caused the MOSFETs to burn out, but it can also be caused by an overload, incorrect input voltage, or overheating.
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Old 23rd June 2009, 02:16 AM   #3
Eva is offline Eva  Spain
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This looks like a quasi-sine inverter and these blow quite easily because they always have trouble with big inrush currents and very reactive loads like motors. In most cases the MOSFET drive circuit is too simple to suffer damage and replacing the MOSFET is enough.

You should check that the drive circuit works and that the rest of the MOSFET are not damaged, though.
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Old 23rd June 2009, 11:08 AM   #4
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Default About repairing a 1750 watt power inverter

My dear friend you've not told us the details about the input transistors since from my view it seems to be employing smps and also informatio about those other ic's beeing shown in your photo.
Thus try to give adetailled information of other components.
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Old 23rd June 2009, 04:04 PM   #5
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Hello

It's a modified sinewave inverter, here is an image with all Ic numbers.

Thank

Bye

Gaetan

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Old 24th June 2009, 09:17 PM   #6
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Hello

I have talk to the guy who did have this inverter before me. He told me that, by error, he plug a live 120 volt ac wire into the output plug of the inverter.

Thank

Bye

Gaetan
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Old 24th June 2009, 09:31 PM   #7
wg_ski is offline wg_ski  United States
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Default That's pretty hard to do "by error"....

Because that would require an extension cord with male plugs on both ends. What was he trying to do, hook up a solar or wind generator to the house electrical system? If that's what he's thinking, it needs to be a true sinewave inverter and synchronized to the power line. Otherwise, BANG!!!! Ought to thank his lucky stars that he just blew a couple hexfets.
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Old 25th June 2009, 04:17 AM   #8
star882 is offline star882  United States
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I think he was trying to make a large UPS with the inverter. With his dangerously limited engineering skills, he probably thought that by connecting two sources in parallel, he can lose one and still have the load powered. Of course, although that will work to an extent with certain DC sources, it generally won't work with AC.
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Old 25th June 2009, 09:50 PM   #9
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Hello

The first time I ask the guy it was quite short answer, so today I did phone again Robert, the guy who burn this inverter, he told me that he was using it in a big fifth-weel RV for camping, normally he do unplug the inverter from the 120volt system of the RV , before connecting the RV to the 120volt system of the camping.

He just forgot to unplug the inverter wen he did plug the RV to the 120volt system of the camping.

So it was just a plain forgetfulness from the guy.

I presume and hope that only the mosfet are burned, so soon I can have some IRF640, I will replace them.

Thank

Bye

Gaetan
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Old 25th June 2009, 10:24 PM   #10
star882 is offline star882  United States
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Remove the bad MOSFETs and try to run it. You should be able to measure about 170v on some of the large capacitors inside it.
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