Can I use portable power bank to charge prius?

Ok, but the square-wave and "modified" wave were common features of cheap electronic inverters, because it's the real sine wave that is difficult for power electronics to faithfully produce.

The whole reason for more expensive inverters to do all that work to duplicate a sine wave output is because a sine wave output is what you always naturally got by putting magnets on a round rotor and spinning it ... mechanically.

Are you saying inexpensive portable generators are all taking the naturally sinusoidal output of the spinning generator, rectifying it, then passing it through a cheap MSW inverter?

Maybe they are, I haven't checked. To use the generator output directly, they would have to regulate the engine speed very closely to produce the right frequency.

-Chap

 

I don't know for sure, but I suspect poor frequency regulation is the reason for the small generator warnings in the PiP manual. You are quite correct that the most straightforward way to generate electricity is by spinning an alternator, which would naturally produce a nice sine wave unless there was some kind of interference or loose connections. Frequency control is the big challenge with a small generator.

 

One problem is a small generator has to respond to the charging load fast enough to not trip out. There is a YouTube about failed attempts using a Honda generator to charge a Tesla. The eventual solution was to start with the slowest rate on the Tesla and then increasing it slowly so the generator could go into higher power modes without tripping out.

Now if the generator engine was geared down to make 60 Hz, and spin at a constant speed, the throttle plate might respond fast enough. But I don't think that is what is sold.

The only way that makes sense is to have a significant battery bank with a solid-state inverter feeding the car and the battery bank charger fed from the generator. This allows the battery drain to increase the electrical load on the generator slow enough the engine can respond.

Bob Wilson

 

well - it's not me saying ...

Choosing between a conventional, silenced or an inverter generator - Greengear
.

 

That's exactly what they're doing. Except maybe not the cheap msw part... some are actually doing very clean waveforms and the models that do it best aren't cheap.

In practical effect it decouples the throttle from output frequency regulation, so under low-load conditions you burn a lot less fuel, and that also lends itself to lower operating noise and reduced risk to sensitive loads.

 

Ok, but the very article you have cited is a comparison between generators that are built that way, and conventional ones that aren't, and just produce the waveform you get from spinning magnets on a stick.

Which turns out to be sinusoidal....

-Chap

 

Well, you would hope for that anyway, but unfortunately a single cylinder 4-stroke engine has a hard time doing that even with a decent flywheel to smooth it out. The crankshaft and its magnet stick is accelerating through 180° and then decelerating through the next 540°. You just can't get a balanced sinewave out of that across the whole range of load.

Honestly though the real reason to get an inverter generator is the fuel savings.

 

That's true enough to make for a truthy-sounding explanation, but on reflection it sounds a lot more like a sine wave with some minor periodic frequency variation. Not anything like the earlier-posted picture of the output of a square or MSW inverter. And not necessarily something you'd expect to be troublesome for most electronics.

Actual oscilloscope shots would be interesting here. If a really ugly waveform is found coming out of a conventional generator, I might be hunting for other ways to explain it, like how the regulation was being done, stuff like that.

-Chap

 

I don't disagree. I know my genny isn't putting out a steppy square wave, but I'm also not the guy who posted that plot.

I wish I had a scope; I'd take a measurement next time I do a check run. Plus it would be neat to compare it to the inverter output.

 

I have looked at generated electricity on an oscilloscope (admittedly from a fairly big three-phase generator,) and the sine wav was smooth as buttah. On the other hand, the power coming from the public utility was full of hash because of a corroded high voltage fuse holder that they would not replace.

 

A few years ago I installed a few different open-source linux apps: xoscope, osqoop, and sndpeek.

They all do similar things, but each has something cool compared to the others. They can all graph the input from the sound card.

Put together a ÷200 or so resistor network and the plug from an old vacuum cleaner and you're good to go.

The sndpeek app is cool for a mode it has for doing a Fourier transform and showing you a 'waterfall' display of the various components in your spectrum.

-Chap