Generator question

noway2

noway2

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I frequently see comments to the effect that portable generators, aka noise and fume makers, don't have true sine wave output. If this is true, from an electrical perspective, I am curious as to why? When I Google this subject I get a lot of hits to non sine wave inverter output (more below) but not generator.

It seems to me that an engine driven generator would turn a winding / rotor shaft in a magnetic field. The output would be a sinewave with a voltage and frequency determined by the number of magnetic poles, the field strength, and the rotor RPM. Unless they are rectifying or have some other sort of electronic output, they're not going to get a sqaure-ish wave and even harmonics should be minimal. What causes these to be non sinusoidal?

* - with respect to inverters there are a few ways to generate the output. One would be to switch pass devices (FET's IGBTs, GTOs, etc) in such a manner as to generate a stair step waveform that approximates the sine wave. This is going to have A LOT of harmonic content to it because of the non linear wave shape. This used to be the old school way of making inverters. Thanks to advancements in semiconductors .....

The other way is to PWM a DC voltage on and off and modulate the pulse width with a 60Hz reference and then low pass filter the output. This will generate a sine wave. This is where the semiconductor advancement has come in to play in that the speed at which they turn on and off has improved (they dissipate significant power during the transition) as well as the current handling capacity. The key to this design is in the filtering and this is where things will get expensive as you will need filter elements that can handle the voltage and more importantly the current. You also need steep filter cut off to pass 60 Hz and remove or sufficiently attenuate 180Hz (and up) or you will get a "fuzzy" sine wave that has an envelope approaching 60Hz made up of a lot of little wiggles - kind of like a poorly demodulated AM radio signal. I am certain that the massive adoption of variable frequency motor drives has pushed a lot of improvement in this area.
 
Sorry you lost me before your post...........LOL. interested in seeing answers

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noway2 said:
I frequently see comments to the effect that portable generators, aka noise and fume makers, don't have true sine wave output. If this is true, from an electrical perspective, I am curious as to why? When I Google this subject I get a lot of hits to non sine wave inverter output (more below) but not generator.

It seems to me that an engine driven generator would turn a winding / rotor shaft in a magnetic field. The output would be a sinewave with a voltage and frequency determined by the number of magnetic poles, the field strength, and the rotor RPM. Unless they are rectifying or have some other sort of electronic output, they're not going to get a sqaure-ish wave and even harmonics should be minimal. What causes these to be non sinusoidal?

* - with respect to inverters there are a few ways to generate the output. One would be to switch pass devices (FET's IGBTs, GTOs, etc) in such a manner as to generate a stair step waveform that approximates the sine wave. This is going to have A LOT of harmonic content to it because of the non linear wave shape. This used to be the old school way of making inverters. Thanks to advancements in semiconductors .....

The other way is to PWM a DC voltage on and off and modulate the pulse width with a 60Hz reference and then low pass filter the output. This will generate a sine wave. This is where the semiconductor advancement has come in to play in that the speed at which they turn on and off has improved (they dissipate significant power during the transition) as well as the current handling capacity. The key to this design is in the filtering and this is where things will get expensive as you will need filter elements that can handle the voltage and more importantly the current. You also need steep filter cut off to pass 60 Hz and remove or sufficiently attenuate 180Hz (and up) or you will get a "fuzzy" sine wave that has an envelope approaching 60Hz made up of a lot of little wiggles - kind of like a poorly demodulated AM radio signal. I am certain that the massive adoption of variable frequency motor drives has pushed a lot of improvement in this area.
Click to expand...
The easiest a and most direct response to that is without all the in depth technical stuff is that you will never get an engine to run at a steady RPM

The drop and rise of as little 5 rpm will throw the harmonics of 60 hz out as much as IIRC 7 %
 
I’ll add my question in here since you nerds are talking generator stuff.

My house is wired up (thanks to a lot of help from a CFF member) to accept two 120V generators...one wired to each phase. This lets me run the whole house minus the A/C, range and dryer.

My understanding is the inability to get the two generators to run in sync so that I could power the three 240V items if needed. That there would be the highly probably danger of only getting 160-180V when the two phases are combined since they’re not in sync.

I went with two smaller units (inverter style) so they’d be more portable, I could loan one to my mom and still have one if needed, the much quieter operation, etc. But is it possible to run them though some type of equipment that will sync them up before hitting the house panel?

I have workarounds to go three items I can’t power:
1. Whole house fan plus ceiling fans (heat will run in winter, so no issue there)
2. Microwave, hot plate, air fryer, gas grill with side burner
3. Drying racks, which is where a majority of our clothes go anyway...but I can’t imagine laundry being a high priority during an outage unless it goes for days

But having the A/C would be nice...
 
GoWolfpack said:
If your generator doesn't make 220 volts, there's no way to make it power a 220 volt appliance. There is no way to ensure that the potential difference between two generator outputs remains the same.
Click to expand...

I don’t think this is strictly true. There are quite a few 120v generators available that are designed to link in parallel pairs to double the output. So it should be just as easy to sync them out of phase to produce 240 instead (double voltage instead of double amperage, resulting in the same double wattage). With a quick search I didn’t find any advertising that capability though.


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JimP42 said:
I don’t think this is strictly true. There are quite a few 120v generators available that are designed to link in parallel pairs to double the output. So it should be just as easy to sync them out of phase to produce 240 instead (double voltage instead of double amperage, resulting in the same double wattage). With a quick search I didn’t find any advertising that capability though.


Sent from my iPhone using Tapatalk
Click to expand...


The plumage (phasing) don't enter into it. All residential power is single phase with two legs, 120 volts hot to neutral and 220 hot to hot.

If one generator produces a voltage potential of 120 between the hot and its neutral, and another produces a potential of 120 between its hot and neutral, there is no way to hook those two together and control the potential between the two hot legs.

A transformer could do it, although your appliances might not be happy only being fed one hot leg 220 volts from neutral instead of two hots each 120 volts from neutral and 220 from each other.

A bigger inverter generator with a 220 volt output is the correct answer.
 
GoWolfpack said:
A bigger inverter generator with a 220 volt output is the correct answer.
Click to expand...
Theoretically, two inverters could sync their 120vac to be 180 degrees out of phase and hence provide the 220/240, but it would be more expensive than a single unit that provides 120/240Vac. This would be somewhere between impractical to impossible with engine / electro-mechanical ones.
 
JimP42 said:
I don’t think this is strictly true. There are quite a few 120v generators available that are designed to link in parallel pairs to double the output. So it should be just as easy to sync them out of phase to produce 240 instead (double voltage instead of double amperage, resulting in the same double wattage). With a quick search I didn’t find any advertising that capability though.


Sent from my iPhone using Tapatalk
Click to expand...

My understanding is that you can combine the wattage in this fashion with some inverter generators that run in parallel, but not voltage.
 
rantingredneck said:
My understanding is that you can combine the wattage in this fashion with some inverter generators that run in parallel, but not voltage.
Click to expand...
Yeah, I can run mine in parallel if I chose to...doubles the wattage (thus doubling the amps), but at the same voltage.

I have no reason to do that at home with the way we wired it up. I haven’t had a need to do it anywhere at this point since both are 3500W. I could see the possibility if they were the smaller 2000W units.
 
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noway2 said:
I frequently see comments to the effect that portable generators, aka noise and fume makers, don't have true sine wave output. If this is true, from an electrical perspective, I am curious as to why?
Click to expand...

Its related to rpm fluctuation in smaller cheaper engines to my understanding and Basically comes down to trying to hit a lower price point market. They could be made to do it with addtional electronics but the market does not bare the cost of additional electronics so they have those as a low price option and invertor options for those that need the true sine wave output. Same holds true for UPS’s, pure sine wave UPS are a premium price point device and not as common unless dealing with electronics usually.
 
noway2 said:
I frequently see comments to the effect that portable generators, aka noise and fume makers, don't have true sine wave output. If this is true, from an electrical perspective, I am curious as to why? When I Google this subject I get a lot of hits to non sine wave inverter output (more below) but not generator.

It seems to me that an engine driven generator would turn a winding / rotor shaft in a magnetic field. The output would be a sinewave with a voltage and frequency determined by the number of magnetic poles, the field strength, and the rotor RPM. Unless they are rectifying or have some other sort of electronic output, they're not going to get a sqaure-ish wave and even harmonics should be minimal. What causes these to be non sinusoidal?

* - with respect to inverters there are a few ways to generate the output. One would be to switch pass devices (FET's IGBTs, GTOs, etc) in such a manner as to generate a stair step waveform that approximates the sine wave. This is going to have A LOT of harmonic content to it because of the non linear wave shape. This used to be the old school way of making inverters. Thanks to advancements in semiconductors .....

The other way is to PWM a DC voltage on and off and modulate the pulse width with a 60Hz reference and then low pass filter the output. This will generate a sine wave. This is where the semiconductor advancement has come in to play in that the speed at which they turn on and off has improved (they dissipate significant power during the transition) as well as the current handling capacity. The key to this design is in the filtering and this is where things will get expensive as you will need filter elements that can handle the voltage and more importantly the current. You also need steep filter cut off to pass 60 Hz and remove or sufficiently attenuate 180Hz (and up) or you will get a "fuzzy" sine wave that has an envelope approaching 60Hz made up of a lot of little wiggles - kind of like a poorly demodulated AM radio signal. I am certain that the massive adoption of variable frequency motor drives has pushed a lot of improvement in this area.
Click to expand...
The answer I would think is the power is not clean enough from variances of being derived from a motor set. If it was cleaned up with some expensive components it would have normal characteristics when viewed on an oscilloscope.

Pulse width modulation has come a long way. Much less expensive but it’s not needed in a portable generator to get the job done. The common person is buying the cheapest generator that produces some voltage to live. The consumer knows nothing of power quality or power factor. And harmonics will not affect a guy out of power or running a campsite.
 
BlackGun said:
The answer I would think is the power is not clean enough from variances of being derived from a motor set. If it was cleaned up with some expensive components it would have normal characteristics when viewed on an oscilloscope.
Click to expand...
That makes sense, things like frequency fluctuations and flicker. Of course when you read “non sinusoidal” the first thing that pops into your head is some funky square wave-ish thing with lots of ringing, which didn’t make sense from a rotating coil and magnet.

Years ago, I was doing a test on a 480vac static transfer switch with the big heat sink fans cooled by the incoming (and outgoing) line power. I had a waveform injector that would introduce various harmonics, including odd ball ones besides 3rd, 5th, 7th, etc, basically letting you induce negative and zero sequence components. You could hear the interesting effects on the fan motor, which would speed up or slow down and get some interesting beat frequency oscillations.
 
noway2 said:
That makes sense, things like frequency fluctuations and flicker. Of course when you read “non sinusoidal” the first thing that pops into your head is some funky square wave-ish thing with lots of ringing, which didn’t make sense from a rotating coil and magnet.

Years ago, I was doing a test on a 480vac static transfer switch with the big heat sink fans cooled by the incoming (and outgoing) line power. I had a waveform injector that would introduce various harmonics, including odd ball ones besides 3rd, 5th, 7th, etc, basically letting you induce negative and zero sequence components. You could hear the interesting effects on the fan motor, which would speed up or slow down and get some interesting beat frequency oscillations.
Click to expand...
You know what’s fun (non thread related). Pumping up a big main breaker and slamming the f...er on. Makes you a bit tense standing in front of it. My only experience with industrial size motor generator sets and static UPSs was at a fiber optic plant I worked in for 15 years.
 
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BlackGun said:
You know what’s fun (non thread related). Pumping up a big main breaker and slamming the f...er on. Makes you a bit tense standing in front of it. My only experience with industrial size mother generator sets and static UPSs was at a fiber optic plant I worked in for 15 years.
Click to expand...
Funny story. I worked for that company twice in two different locations. Once was up in OH where they had a sister division that I think is long gone called Joslyn High Voltage that made utility level switch gear. I went to the facility and was getting a tour from a former coworker at a place we both left. He said, here press that button. ;) I did. :eek: BOOM as I jumped sky high. They guy had me activate a vacuum bottle recloser.

Yeah, those spring activated breakers are, fun. You learn not to stand in front of them. We were doing a test on a large, as in 4000A transfer switch, one source utility the other a 1MW diesel. Something went wrong and it started going back and forth between the two sources, which weren’t always in phase(* see below). It went back and forth a couple of times then went boom. Opened the upstream 400A breaker, the 600A breaker on the generator, and stalled the diesel out. Yeah, we used a broom stick to press the buttons on that one.

We had a technique called Dynamic Inrush Constraint that would take a flying leap guess (calculation) of the flux vector in the transformer core and time the activation of the oncoming alternate source in a manner to try to match it close enough to make the disturbance effect manageable. Theoretically you could transfer 180 degrees out of phase into an inductive load. Yeah, it would thump the transformer pretty good, and you could watch the damped oscillations on a scope, but it worked.
 
They had to replace a bad GFCI panel at my Home Depot, the spring loaded lever broke the collar bone on the electrician.
 
Button Pusher said:
2,000 Amp.
Click to expand...
That’ll hurt.

Button Pusher said:
Joslyn was acquired by T&B in 2007 and ABB acquired T&B in 2012.
Click to expand...
I worked for the sister division before T&B acquired them, back when Danaher owned them. They rode the tech telecom bubble and bust. They acquired a small company in Richmond VA, and planned to shut down the OH facility and relocate it to VA. The guy in charge was bragging to the guy in VA about his plans. What he didn’t know was that this guy bragged to a sales rep of the same and the daughter of that rep was married to a guy who was a former engineer with us. Hence we knew the plan. After the bust and a 3/4 of the entire staff lay-off, they had weekly meetings with the guy. You could put questions in a bin and I waited till after ours and deposited one about his VA plans. Meeting time, he gave his spiel then read the question. You could see his neck and face turn crimson, his hands shook, and he bellowed about not paying attention to rumors. Intents proven and he was mad that he didn’t know how we knew.

I went back to work for them in VA about a decade ago after T&B acquired them. One of the worst, most paranoid, totalitarian companies I’ve ever had the displeasure of working for. It was ok at first, as I was hired by my former boss to help out with technical problems they were having. The guy in charge got replaced and they ousted him and did a shake up below and anyone associated with my boss became persona non grata. I was pleased to leave when I got the chance.

After it was acquired by ABB, I spoke to our ABB rep who commented that the place was the most effed up company he ever saw. Last I saw, a coworker I liked stuck it out and became the head of their engineering division. It’s no longer part of ABB, which just wanted the SPD / TVSS business.
 
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