I have two 5500 watt generator power units running off the same motor how do I wire them as one unit ???
As in two of those small inverter generator units? Each 5500W? And you want to power the same motor using both units simultaneously?
Do the generators have the same specs (amperage/voltage)? And have you checked the manuals? If they’re not the same specs, don’t even think about it. And if the manual(s) says not to do it, don’t. Otherwise, it will depend.
I think he’s saying that the motor (presumably burning gasoline) is driving the generators, not vice-versa.
But there are so many unanswered questions here that he really needs an electrician who can look at the devices in question in person. AC or DC? If AC, how many phases? How are the generators physically connected to the motor-- On the same shaft, geared, through a differential? If the connection is rigid, are the generators physically positioned in the same phase? Is there any regulating on the output? What’s the power of the motor? And so on.
This only matters if they are old-school alternators driven by an engine governed to 3600 RPM. Modern gensets use an alternator that feeds an inverter which puts out 60 Hz, 120VAC power, regardless of how fast the motor is spinning. This means that the inverter output phase is independent of engine crankshaft angle. If you drive two of this type of alternator-inverter unit, you would need some other method to synchronize their phases.
If they were free to rotate just a little bit differently such as driven by belts and pulleys that could slip a little when you drag on one of them, and I’m assuming we’re talking alternating current synchronous machines, you could wire one output together and connect a light bulb between the other two outputs. When the whole thing starts the light bulb will flicker, but if you slow one generator down (it doesn’t take much) the light bulb will start going on and off more slowly. Stop dragging the one down when the bulb is out. Wiring them together will then keep them in phase unless there’s some significant mechanical difference between the two.
Another possibility is to set one alternator aside and get an induction motor for approximately the same rpm instead, and overdrive it by, I dunno, a couple percent (look up “slip” for a better number). Induction motors are cheap and often available. You only need one generator to set the frequency. An induction motor driven faster than the motor frequency will feed its power back into the line, just as one running slower will take its power from the line.
They are not whole generators I took the power unit out of the generator assembly they sit side by side and I have a 22 horse Kohler engine running them with a timing chain set up
Just need to wire the power units together for 11000 watts
Well, expensive ones at least. You can certainly buy brand-new generators of the standard type. Looking at Harbor Freight, they have a 9000 W standard generator for $790, and an 8750 W inverter generator for $1300.
Electrical engineer here. This isn’t as simple as you think.
This is a poor man’s synchroscope, and it works very well. It also illustrates the issue that you are going to have, in that if the outputs are not exactly in phase, the voltage differential between the generators will light up the light bulb. If you physically connect the outputs together while the bulb is lit, then you better hope that you have good overcurrent protection, because each generator will attempt to power the other into phase. Without any protection on the circuits, this could cause either or both generators to experience a “rapid unplanned disassembly” (in other words, they’ll come flying apart, rather spectacularly).
With a timing chain driving the two generators, you can’t alter the speeds and phases of the generators independently, so syncing them together is going to basically be impossible.
Also, you are going to need some sort of load sharing device. Some generators are meant to be tied together and have a load sharing connection. If these generators don’t have this and you just tie the outputs together, they won’t load share. If you have an 11,000 watt load and the generator outputs aren’t exactly equal (which in the real world it’s basically impossible to get them exactly equal without some sort of feedback circuitry coordinating their outputs), you can have one generator trying to power the entire 11,000 watts plus trying to spin the second generator, while the second generator acts more like a motor than a generator. Since each generator is only rated for 5500 watts, this isn’t going to end well.
What’s the make and model of the generators?
But I have this setup that won’t cost me a penny
I don’t see why this is a problem. The speeds are guaranteed to be exactly equal. And the relative phase can be changed by rotating one of them by some fixed number of teeth on the sprocket. Or if that’s not good enough, adjust the distance between the two as well.
How is your health insurance? You have a free setup that is capable of causing serious injury if you get it wrong.
Most university undergraduate power labs have stories of the student that got the phase wrong on the lab experiment with motor and generator and the disaster that ensued. The instantaneous power available during a fault is capable of throwing large bits of metal across the room.
Personally would I feel comfortable building this up? Yes. But I have a pretty good idea what I’m up against and have the test gear to be able to check things are ok.
Would I be comfortable getting or giving instructions over the internet to do this? Absolutely No. This is well into the arena where a trivial misunderstanding can lead to arbitrarily bad outcomes.
And it won’t work. So what’s your point?
Again, what’s the make and model of the generators? I can look them up and see if they are designed for load sharing.
How are you going to adjust the chain on the teeth while the generators are running? How are you going to measure how far you need to adjust the chain?
You can start up the generators, see if they are in sync, then keep shutting them down, adjusting the chain, and starting them up again, but that is going to be an extremely slow and miserable process.
Maybe there is a faster way that I’m not seeing.
Been there. Done that. There were three of us in our group and we didn’t notice that we had accidentally put the phases out of order. Fortunately the generator we were trying to sync up tripped offline before anything came apart and went flying across the room.
Nah, that’s about what I had in mind. Of course, an oscilloscope makes it trivial. With a multimeter and some trigonometry, you could probably get a pretty decent first estimate, and then dial it in further with a few more tries. An Arduino and a few extra components would do the trick also.
Mildly annoying, but the whole setup is going to require a fair amount of work in the first place, so the calibration doesn’t seem like too painful an extra step.
When I told my dad about haw some other group had sent their generator flying off the bench when they got the phase wrong, he told me that he had made the same mistake in his rotating machine lab. Except back in those days these weren’t little piss-ant benchtop units, but beefy units that were bolted to the floor - that is, his was bolted to the floor at the beginning of the lab, not so much after…
Ours were also beefy units bolted to the floor. They were motor-generator sets about 10 feet long or so and easily weighing several hundred pounds to give you a rough idea of the size. They were so beefy that I didn’t think anything could damage them.
If you had told me ahead of time that they could come up off of the floor, I wouldn’t have believed you. After that lab, your story about your dad’s becoming unbolted doesn’t surprise me at all. When we threw the switch, they made a horrible noise and moved a lot more than I thought physically possible. Ours didn’t detach themselves from the floor, but I was kinda surprised that they hadn’t.
I can see why universities switched to little piss-ant benchtop units. If the breakers hadn’t tripped as quickly as they did, we would have destroyed one very expensive motor-generator set.
I do have to say though that the lesson stayed with me. That’s not something you easily forget.
Just to float the idea, do you really need to wire them together? If you’re powering a number of things, could you connect roughly equal loads to the generators separately?
If you’re powering a house with typical American circuitry there are two “hot phases” that are 240 V apart and a neutral halfway between. For the 120 V appliances, it doesn’t matter how those hot phases relate to one another, and you could connect your generators to the two sides of the circuit breaker panel. If you have 240 V appliances like clothes dryer, hot water heater, etc, then that’s no good.
Actually, I’m being a bit dumb about this. Francis_Vaughan is wise. I shouldn’t be posting ideas like this. If you go out on the internet and find multiple references that appear reputable and agree with each other, and you have a fairly good idea what you’re doing, then maybe it’s OK (and maybe it isn’t). But if you’re asking us here, that’s probably a pretty good sign that nature says “don’t touch” in this particular case.
Well, you can buy bottles of mercury on Amazon, and hydrofluoric acid gels, and if you want to make a big noise firecrackers are illegal because they’re dangerous so you have to buy guns instead. We don’t live in a foolproof world. If you want to study rotating machinery, that’s great, but if you want to try something lethal based on asking strangers on the internet, you’re not as safe as you should be.
I imagine it’s one of those moments that puts a lot of awe into you about the level of energy you’re dealing with.
Kind of like (but on a larger and less mundane scale) than pedaling a bike up a hill and having it wear you out, and then driving the same hill in a car that doesn’t struggle at all to drive up it at 40 mph.
Would it be any easier to wire the generators in series, rather than parallel, and then put the output through a 2:1 stepdown transformer? You’d still want to match the phase doing that, of course, but I think that the consequence of a phase mismatch would just be that you wouldn’t get as much power out of the setup.
Of course, given the OP’s attitude of “just toss something together from parts I have lying around already”, he probably doesn’t have a 2:1 stepdown transformer.
No, as pointed out above, it’s not going to work. Connecting a light bulb across the outputs really illustrates the problem. Splitting the load is a the only workable solution.
Putting them in series would generate a complex waveform with double the output sometimes and zero at others. Very risky operation!