To complete my startup current "research", I bought a 2200w 3 phase motor with a decent flywheel attached. One day I'll use it with a VFD for a car turntable project I'm contemplating.





It really jumps when turned on. No VFD or anything. I expected the startup current to be very high, but it's not too bad at 45 amps or so (per phase):

Paging Warp:

Here is my large inverter square wave output, measured with transformer connected and a 70w load. Measured through a HV probe:





But zooming in, there is a dip in the falling edge of the square wave:





Is there any problem with it looking like this?
I think it might be the reason my transformer is buzzing.

The dip doesn't occur in the rising edge.

Maybe I should decrease the size of the dead time capacitor? I think the dip occurs when the inverter output is floating. Which is around 2-3 uS.

Maybe a clue:

The dip and the buzzing noise start to occur after the DC input voltage goes over 200v. The DC voltage was about 350v when the photos were taken above.

  Haxby said  

Paging Warp:

You rang ?


That glitch is only a few uS, and its probably due to dead time, and unsymmetrical because of residual flux in the core. Nothing to worry about.
You will probably see a few weird things until you get all four inverters running properly together.

Quote:

"You will probably see a few weird things until you get all four inverters running properly together."



Warp, and all following this thread:

This single phase inverter is finished and working. All inverter stages are connected.  

I have tested it in recent weeks with gradually larger loads, and today with my air compressor and it works just fine!

But above 200v, there has always been a buzz coming from the transformers and while I could just ignore it, i wonder if it's tied in with the long dead time of the biggest inverter.

The transformers don't buzz when connected to mains, so I think it's something to do with the square wave...

It could well be Phil, I really do not know the answer to that.

You used commercial transformers which will operate at a higher flux density than is really ideal for an inverter, and that may have something to do with it as well.

I used commercial toroids in one of my earlier Warpverters, but I am pretty deaf and would probably not have noticed the difference anyway.

If its really a problem, you could package all your toroids into a pyramid shape, and sink it in a bucket of automatic transmission fluid. That should shut it up, and also increase the overall power rating by a LOT.

Its a bit messy though, although once the whole thing is proven, the transformers should last a lifetime without any need for maintenance or repair.

Ok I'll decrease the dead time and see what happens. I should be able to halve it without any adverse effects.

Ok I changed the 10nf dead time cap to a 4.7nf cap.

Dead time decreased and the square wave looks much much better but there is no change to the buzzing.

I fear that the buzzing will wear out the enamel insulation after some time. As Roger noted, these aerosharp transformers haven't been wound with much care at the factory.

To lower the flux density, I can add turns to both primary and secondary till I run out of room on the transformer right?

As it made no difference it may be safer to go back to 10nF.
A very few additional microseconds of dead time in a 10mS waveform is negligible, almost nothing.
But if you set the dead time a whisker too short and start getting shoot through, that would be ultra bad.

Its probably not the windings that are making the noise, but the actual core material itself.
Magnetostriction causes the crystals in the metal to change shape. Its kind of like the piezoelectric effect.

If you have ever run the choke saturation tester, and wind up the wick, the core can really whine or growl at you surprisingly loudly.

So if I add more windings on both primary and secondary, in the same ratio as the existing windings, that will decrease the core flux density right?

Yes indeed it will.
But there probably will not be enough space left through what is remaining of the hole to make a significant dfference.

Did the Prius idea get abandoned at some point? I did a quick survey of the pages, but I couldn't find any more references to the Prius. Did this just evolve into something different?

The inverter is running off rectified mains through a Variac for final testing before I try it in the Prius. It's basically ready for that step. The ultimate aim is to use the Prius inverter combo for camping and building an off grid cabin (weekender). So it has to easily power up an air compressor and miter saw without any issues whatsoever. Hence the startup current tests above. A slight non-technical complication is that in the months after starting this project, my wife has taken to our Prius as her daily driver  

Once done, I'll be very interested in the fuel consumption of the Prius per KWH generated. I suspect it will be very good. If it ends up around $0.60 of fuel per kWh then the cabin could end up being powered by the Prius for all cooking, heating, cooling, and water heating. So just a small battery bank would be needed for night time LED lighting and laptop consumption.
Though with the cost of solar panels decreasing, the other purpose for it could be to run the cabin directly from solar, similar to what Warp did for his home. The Prius battery pack could be diode coupled at a naturally lower voltage (200v) than the panels (say 300v string) and the inverter could happily work off whatever is available.

Wow, this sounds really cool. Great job on getting all that sorted out so far. I hope to see you get around to see whether or not the Prius is economical or not. Got my fingers crossed for you.

I thought this would be a great link to how the Prius (though this is the Prius/Prime 2017 models) transaxles work. This guy's shop/university is amazing. The dual electric motors and how they work together is so cool, along with the internal combustion engine. The Spragg clutch is particularly interesting.

Weber Automotive University
Edited 2021-05-10 06:18 by Kamak

You should be thinking about how to create your inverter driven from the Prius along with how to "back" drive the Prius electric motor(s) from wind power (lol A very large rotor indeed). All mounted on a tower 30ft up. lol I can see it now, a wind turbine rotor connected to a nacelle with a Prius I.C.E(internal combustion engine) and transaxle all inside.

Can you imagine the wind turbine required torque that would need to be applied to the CV(wheels) axile to back drive the EV motors, via the transaxle?

  Haxby said  

Once done, I'll be very interested in the fuel consumption of the Prius per KWH generated. I suspect it will be very good. If it ends up around $0.60 of fuel per kWh then the cabin could end up being powered by the Prius for all cooking, heating, cooling, and water heating. So just a small battery bank would be needed for night time LED lighting and laptop consumption.

Out of curiosity I once compared the cost of grid powered kilowatts, to running a small internal combustion engine (intermittently) on natural gas to charge up a battery.
It did work out a lot cheaper for just the gas, but when the expense of regularly rebuilding the engine is included, that makes it uneconomic.

One big advantage of natural gas as a fuel is that it comes in unlimited quantity down a pipe without needing to refill a tank.
And the reduced fire risk of not having to store bulk liquid fuel.

The Prius makes much more sense though, and I will be very interested to see how this all goes.

  Warpspeed said  

Out of curiosity I once compared the cost of grid powered kilowatts, to running a small internal combustion engine (intermittently) on natural gas to charge up a battery.
It did work out a lot cheaper for just the gas, but when the expense of regularly rebuilding the engine is included, that makes it uneconomic.

One big advantage of natural gas as a fuel is that it comes in unlimited quantity down a pipe without needing to refill a tank.
And the reduced fire risk of not having to store bulk liquid fuel.

The Prius makes much more sense though, and I will be very interested to see how this all goes.

And on that note, where are all the NG I.C.E. (Internal Combustion Engine) hybrid E.V. vehicles? With engines specifically made to run on NG. They must exist, right? I mean real factory-build NA vehicles don't have that bad of a maintenance record, do they?

And on that double note, where are all the Hybride Wind Turbine/NG I.C.E. back-driven transaxle Generator systems?
Edited 2021-05-11 03:34 by Kamak

The problem with compressed natural gas as a road fuel is the cost of compressing the gas.
The gas itself is so cheap its almost free, but to compress it overnight to the several thousand psi required to refill your vehicle is just uneconomic in both Kwh or compressor horsepower.

Its not like propane which is a liquid. Natural gas stays a gas under extremely high pressure.

If you use solar power to drive say a scuba tank compressor, its still not economic. Much more energy efficient to use the same solar power Kw to recharge a vehicle battery direct, and its no slower to do either.

Only people using compressed natural gas in Australia are very large organisations that can get very good rates for bulk off peak electricity. Even then its only marginally cheaper than using diesel fuel.

I have some first hand knowledge of all of this when I worked at the research laboratory of the Gas And Fuel Corporation in Melbourne.