DIY Inverter Generator (Scratch Build)

Ok the rotor and stator came in today. So yeah I can now confirm it is a tapered socket on the rotor. I ordered the adapter and appearently the wind blew it away after Amazon dropped it off. So ordered another one.

So I pulled the trigger on a new engine and cart for this project today. I decided to go with the DuroMax 500cc engine with electric start and ordered a hand cart for its chassis to make mobile. Oh and almost forgot I ordered a set of 10 inch duct flanges to create the stator/rotor housing.


Those duct flanges are a lifesaver. Thanks for reminding me to buy a few!

I’m following this build with great interest.


Can you post a pic of duct flanges? I just wonder what the Swedish equivalent would be.


This is what they look like. They are just angle stock rolled into a flange with holes pre drilled. Im sure you have an industrial supply or other ways to get them. I cant imagine them not being available this is a comon product in weld fabrication. If not you will have to make it by hand. I am going to cut my parts on the CNC. Those that DIY this will need to cut these parts out by hand. For the housing shell just find something that is already rolled like a tank or something that is already close the diameter. You can man handle from there.


Thanks Matt, that looks real nice, i’ve never seen something like that for sale here in Sweden though.
I’ve bought for some years ago, a very heavy-duty roller-bender, old one, originally used on a company that made wagon wheels, with the roller they made the steel ring for the wooden wheels.
This machine had already been modernized with an electric motor, and my intention was to make a set of rollers with a “slot”, to be able to roll angle iron, for making flanges just like this.
Seems i have to look around here some more.


I can hardly imagine that angle iron in the “slot” could bend and stretch unless it is a very large circle.


To me, they seem pretty pricey (they probably aren’t in reality), but it might be extra motivation to make the slotted rollers.


Hi Don and Sean, well, you know i need to try, i’ve seen angle iron cold rolled that way, and maybe i need to heat them in the forge, it would be nice to be able to make them by my self.
I found a pic of the roller, i’ve bought it but not dragged it home yet, very heavy.
As i look at the pic i remember there is a slot already.

Edit: sorry for messing up your thread, Matt.


LOL yup. Honestly until about 3 months ago, I thought they were just cut from fleet sheet. But apparently for flat stock it is called ‘bending the hard way’ which I assume has to do with the super long leverage handle needed to bend it on a manual bender. It might take more then one pass to get it to bend to the right shape with your machine depending on thickness.


MattR. are you going to be parting out your one 8750 for it’s Inverter?
Buying also a new wild frequency and voltage, for three phase inputs Inverter as listed on Amazon?
Or have another plan-idea?
Steve Unruh


Nope Im going to rob the inverter from the 9500 but build this as if I bought it from Amazon. The stator and rotor from that unit will go on the 8750 and Ill update the inverter later on.


Ah, I see, I think.
Repurpose the 9500 with all of the thousands of engine running hours on it.
See if you can make up a more friendly just plug-in-a-new off-the-shelf engine as needed system.

Fun with IC engines indeed.
Steve Unruh


Exactly the end goal.

Not to mention I estimate Ill have less than half the cost of buying new one.


Ok the taper adapter showed today and unfortunatly it dont fit. I drew it up in CAD so I could figure out the angle and it has a 2.8* angle.

So what I did was; is I drew up another one based on the dememsions directly from the socket and I come up with a 5.25* angle from center line. So 10.5* total. So unless we can find a 1 inch bore with this angle, you will need to machine it or get a shop to make you one.

I have a lathe so Im going to order some aluminum to custom make it.


I don’t know if this helps but it might be an SAE standard taper given you mentioned a 1" shaft. But if the taper has an actual name it is easier to google. :slight_smile:


So yeah I got this shiny new 500cc DuroMax engine today! Today while I cut parts on the CNC I wasted no time getting to work on this. Chucked up the aluminum stock in the lathe and whipped up the addapter. It was pretty easy to make, I just set up the tool holder axis to five degrees and started widdling away.

I assumed this engine is all metric so I ordered like 80 bucks worth of metric hardware today. Then I come in to work on designing the housing and needed the manual for those demensions. Then I found the call out of the hardware and its SAE just fine thread. The shaft end takes a 3/8-24 bolt and the mounting holes that I will use are 5/16-24. There are two sets of holes on the back but the outer larger holes would require stand offs or the plate would need a huge hole cut into to clear the inside hole set as the outer holes surface is sunk.

So anyways I have to cut the mounting plate first. Once I bolt the rotor on the shaft I dont want to mess with pulling it. So going to create the adapter plate tomorrow and get that bolted on and then assemble the rotor. Then on to the next part figuiring out how long the housing will need to be and building that up.


Hey MattR
What do you think of the possibility of reversing the mountings.
The output coils assembly could stationary on the engine side plate mounting holes.
Now with your own shaft adapter that reversed inserted from the outside in the rotor hub butting up against the crankshaft step or an added shaft collar ring lock.

Sure. Have to stand off the coils from the get hot engine side plate for space for an air gap/circulation.
Add an extractor fan to the flat backside of the magnetic rotor to draw thru the cooling air.
Get this off of the 8750 maybe.


I had thought about doing that but how would you get it apart? You would have to pull the adapter out some how as the rotor would be locked in place.

It will be easier to align the stator from the outside I think as well. It will be bolted to the mount plate and then Ill wrap this with cardboard to fill the air gap when installing. Ill then lock this plate down and then drill and dowel it in place. Then take it apart and remove the cardboard.

Yeah I have been thinking about heat disapation. Not sure how Im going to tackle that yet. Yeah it would be nice if they sold that with the rotor / stator assembly. Might have to put an electric fan on it somewhere. But the goal is to DIY this with off the shelf parts only. Even though Ill will use the inverter box off the 9500. But that we know we can also buy. Im doing a Youtube series on this build and the goal is to DIY it with off the shelf components only. Those that have a doner than that just makes it all that much easier.


If you look at the rotor in the pics. You see the four spokes with the vacant holes in each of them. That is where the fan is supposed to bolt on.


I think I may have figured that out. If we were to use a split shaft collar at the shaft before the assembly you could lock it all down. Then to take it apart you would split that collar and pry it out. Then get a big socket and place that over the output shaft and against the rotor and give it a good smack and it should pop apart.

I think Im going to get a small 6 inch automotive cooling fan and run it off the DC system.