Electronics > Projects, Designs, and Technical Stuff
Petrol Generator Mod - Inverter AC Output
WanaGo:
Hello,
I am after some assistance in a project I am working on.
I got an older 'Silent' Petrol generator, which has a Honda GX120 engine in it, and a 1400W Alternator of sorts, which is 2 pole, and has 220VAC 50Hz and 12VDC 8A outputs.
Looking at the outputs on a scope, they are not very pretty at all. The DC doesn't at all look like DC, but when put on a large cap it smooths out nicely.
The AC is, well, just yuck. I guess this is just how generators of this era were before the inverter ones came on the market.
It works fine when you connect a Drill or Light etc, but I don't suspect it would be very good for more sensitive equipment.
The generator does not 'talk' to the motor, its all governer based, and the motor purely runs at a set 'ish' RPM, and the 3000RPM basically translates into 50Hz based on 2 pole - I believe.
So what I am planning to do is bypass the current AC outputs, rectify the winding phases directly into DC, and then invert the high voltage DC into a more pure sine wave AC. I guess this is just typical stuff really.
The problem I have is most Inverters in the lower price bracket are designed for 12VDC or 24VDC to 220VAC, and not so much for 300+VDC input.
I have been scouring Aliexpress and I found these:
https://www.aliexpress.com/item/Aiyima-2000W-Modified-Sine-Wave-to-Pure-Sine-Wave-Inveter-Board-Driver-EGS002-AC16VDC380V-to-AC220V/32845887806.html
https://www.aliexpress.com/item/2000W-Pure-Sine-Wave-Inverter-Power-Board-Post-Sine-Wave-Amplifier-Board-DIY-kit/32334756548.html
https://www.aliexpress.com/store/product/Aiyima-2000W-Modified-Sine-Wave-to-Pure-Sine-Wave-Inverter-Inverter-Finished-Board-with-Heat-Sinks/1756394_32847801786.html
There are a few others too.
These take a 380VDC intput, along with a low voltage AC (which looks to be rectified and regulated into DC) to power the electronics on the board, which I think are 5VDC based, and you get a Modified or Pure Sine Wave AC output.
I am basically after some input as to what people think. Do these boards look OK? The descriptions are not the best, but you can kind of get a feel that they are using the same sort of Driver boards on them, but the base boards vary a little.
There was also this one, which uses the same Driver board again, but it has some images of them hooking it up in a test situation and a scope:
https://www.aliexpress.com/item/2000W-Pure-Sine-Wave-Inverter-Power-Board-Post-Sine-Wave-Amplifier-Board-DIY-kit/32728282834.html
Am I going about this the right way or is there an easier path?
For the 12VDC output of the generator, I plan on just passing this through a switching regulator, to get a stable 13.8V or so out, to charge batteries etc. I might even make the adjustment more accessible so I can turn the output voltage as required for what I end up powering.
So the main bit I am stuck on is the AC side and how to clean it up, and if this rectified into DC and inverted with something like the above boards, is the way to go.
Any suggestions welcome.
Thanks
james_s:
If you just want to have a big complicated DIY project to show off your abilities then it could be interesting to try, otherwise you will spend far more effort than it is worth and end up with something that likely doesn't work as well as the cheapest Chinese inverter generators on the market. Those older style generators work fine when noise isn't a problem, the output looks a bit ugly on a scope but I have used one before to power lights, refrigerator, tv, computers, etc without issues. They are still popular unfortunately, on the rare occasions when the power goes out here there are at least a dozen of them roaring away within 20 minutes of the outage. The incessant din is unbearable, I can't hear myself think. This is probably worse here in 60Hz land where conventional generators scream at 3600 RPM.
ConKbot:
What do you want to run that's a "sensitive" load? Most computers, and switching power supplies are just going to rectify it to a 340ish volt rail internally, so the benefit of another rectify/invert stage for general use seems dubious.
If you must, though, get a 2kw inverter of whatever price point you prefer and get to hacking. I've done a overhaul on a broken 3kw square wave one i picked up for cheap, it's was just a 2 channel push-pull converter to get the +/- DCV rails, and an IGBT H-bridge for the output. If you could externally supply the DC rails and maybe bypass some undervoltage detection circuits if needed, you could probably trick one into working with either external HVDC or 12/24V in.
Id suggest not going for an absolute cheapest unit, as I worked on a 2kw unit also, that its MSRP was much cheaper than the 3kw one and it was a ratsnest of wires and PCBs and quite miserable to even disassemble. Vs a single PCB and a couple wires to connectors on the 3KW unit.
DrDeke:
If you're open to a different approach, it might be cheaper (and easier) to buy an old double-conversion UPS and connect it between your existing generator and the load.
Here in the US, an old 2 kW double-conversion UPS like a Liebert UPStation GXT or GXT2 can be had for about $100 on eBay. They tolerate being powered from my extremely cheap petrol generator and run on inverter full time to provide a nice output. These particular models don't even seem to need a battery installed to perform this function (although they would obviously lose power immediately in that condition if your generator stops).
These exact models won't work for you, they only work on 100-120 V input (unless you get a 10 kW+ unit, which sounds like overkill in your situation), but perhaps you could find something similar that is designed to work with 220 V.
DrDeke:
--- Quote from: WanaGo on January 08, 2019, 03:38:17 am ---These take a 380VDC intput, along with a low voltage AC (which looks to be rectified and regulated into DC) to power the electronics on the board, which I think are 5VDC based, and you get a Modified or Pure Sine Wave AC output.
--- End quote ---
For what it's worth, I think the output of a "modified sine wave" inverter will probably be worse for your loads than the original output of the generator would be. (That is, to the extent they would have a problem with the generator's output in the first place.)
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