Electronics > Projects, Designs, and Technical Stuff

Petrol Generator Mod - Inverter AC Output

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WanaGo:
The other side of the question is about these Inverters I linked.

I got a reply from one of the sellers, who explained they are designed to convert Modified Sine Wave AC into Pure Sine Wave AC.
But they appear to do so by rectifying the Modified Sine Wave back into DC again to start with.
So this is where my logic of, if they are just inputting essentially HV DC and creating a Pure Sine Wave output, then I could do the same from my generator, rather than doing what its designed for and coming from some sort of Modified Sine Wave device.
They then talk about getting 16VAC by wrapping a few turns around the transformer (I assume which is in the first stage in the Modified Sine Wave device) to get this out, then the 16VAC is fed into the board, rectified and filtered into DC and regulated down to 5VDC for the driver board to run off. You can see this on some of the photos, and one of the boards even mark where the DC input can go instead of feeding in 16VAC. So I could feed in DC from the 12V supply of the generator for this.

There are a lot of smart people on here, so I was hoping that someone could have a peek and see if they think that logic sounds reasonable from what is shown on the links.

Thanks

james_s:
I have a similar Chinese pure sine inverter board that I use to get 240V 50Hz power over here in 60Hz land. It works ok, however I had to make some modifications to get it to perform adequately, the mosfets and the output filter inductor it came with were crap. It also needs a reasonably well regulated DC voltage input in order to get the correct voltage output.

Computers are not particularly sensitive, the modern switchmode power supplies are very robust and they run just fine off cheap generators. The noise and fuel efficiency is crap but I've never had any problems at all running any sort of equipment off old style generators. If I was on a tight budget and wanted an inverter generator and didn't mind using questionable Chinese parts, I'd just buy a Chinese inverter generator, apparently the ones Harbor Freight sells are decent, certainly it's gonna be better than something you could build yourself. Trying to convert a standard generator you wouldn't get the greatly reduced noise and fuel consumption which is the whole reason inverter generators are so much nicer.

WanaGo:
Hi James_S,

With your inverter, what specifically did you have to change on yours?
Was it FET/Transistor related, or something else?

To All,

I ended up getting an inverter and had it running on the bench, and all looked great really, output was really good etc. I initially tested it at 12V, then 30V then upped it to 200V and then powered it off my generator after rectifying the AC. I put on a small 40W load, everything still good. Then I put on an 850W load from a power tool, and it died. Spun for a moment, then all just went silent. The Generator started kicking like it was under incredible load. The Inverter is rated to 2000W, but I wonder if the surge current has killed a weak component. It was an angle grinder, so I can imagine the inrush is pretty high, but I wouldnt have thought it would have done what it did. The symptoms would suggest one of the transistors has died, to me at least.

The inverter has Infineon 47N60C3 transistors, 650V 47A 0.07ohm RDSon (https://www.infineon.com/dgdl/Infineon-SPW47N60C3-DS-v02_06-en.pdf?fileId=db3a304412b407950112b42dff93492f) on it, the large TO 247 package. However I brought the inverter as a kit, so built it myself. Immediate alarm bells when I saw the transistors, as the legs were cut and they had solder on the legs. Looks like its a classic case of recycled materials. Anyway, had no choice so just assembled it anyway and hoped for the best.
Wonder if one of those transistors has failed ON and is now basically a dead short and not letting the thing pulse away like it should.

The DC input takes 380VDC sort of region and has 2 electrolytic caps on the input. Normally they hold their charge for hours and hours, I tested it the other day about 4 hours later, and the input was still over 250VDC. I will be mounting a 1Mohm resistor across it as a slow drain I think. Anyway, after it stopped working, the input is 0V, so there would seem to be a short circuit. I'll investigate more soon.

For another project I had some of these, and still have 3 in my box of parts, same TO 247 package. https://www.infineon.com/dgdl/Infineon-IPW60R041C6-DS-v02_01-en.pdf?fileId=db3a304327b897500127f24dd83c3c09 . These ones dont look recycled, but did not come in tubes either. Legs are full length and no solder on the legs.
Curious if these would be an appropriate replacement part to use for the dead one, and if I should try swapping one out with one of these. Just not sure if its wise to mix or not. Assuming one is dead of course.

I also have 4 of these IGBT's from another project, but unsure if these are any better for this application. https://www.infineon.com/dgdl/irgp4063dpbf.pdf?fileId=5546d462533600a401535655ee0c2450, same TO 247 package again. These sort of look recycled too, tinned legs but they are full length.

Never really played with this kind of HV stuff and learning as I go. So please bear with me.

Thanks

Zero999:
Yes, it was probably the surge which killed it.

Why use it on an angle grinder anyway? No doubt it has a universal motor which will be happy with the crappy distorted sine wave from the generator.

If you powered the inverter from a rectifier and smoothing capacitor, then the power factor would be poor, which would explain why the generator struggled. Have you checked that it wasn't the rectifier which died?

Ideally you need an inverter with a 230VAC input and 230VAC output, with power factor correction.

james_s:
My inverter came with counterfeit mosfets of unknown specs which I replaced before building it. Then I found that the output inductor was undersized and would saturate well below the rated load. It was overall not a very good design.

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