Electrical (gen-set) question

If a person had two small 110VAC generators. Ganged the commons and fed one generator into each leg of a 220VAC single phase circuit, would it work? I'm thinking 220v well pump, small transformer type welder, clothes dryer etc.

If it would work, would the two gen-sets need to be the same size?

There is probably some simple reason why this is a really bad idea, but I don't have enough electrical background to see it.

Thanks,

Bill

Reply to
Bill Marrs
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First, it's good to think outside of the box. But not always.

I'd think you'd run into significant trouble in trying to get both generators to be in phase with each other. I'd hazard if they aren't, the one leading in phase will be feeding the other.

Reply to
Louis Ohland

no

Consider carefully what will happen if one spins at 61 Hz, and another at 59 Hz

i
Reply to
Ignoramus26157

Definitely won't work connected as you indicate, for the reasons other posters noted.

It is possible to parallel two small gensets, and in this case you'd need to feed a suitably sized step up transformer if you needed 240V. There was an extensive thread on paralleling generators a week or two ago on alt.energy.homepower presumably you can find archives of it.

Reply to
Pete C.

No way to synch the phases between the two...

Reply to
gil

gil fired this volley in news: snipped-for-privacy@4ax.com:

Well... there is a way. Couple the two shafts, so the gensets run in tandem. There's nothing written that says two gasoline engines cannot power the same shaft.

This would require that you establish the phase positions of each set before locking the shaft coupling, and it would also assume that the machines are not of the "writable stator" variety. Only very expensive units with frequency control would have that feature anyway.

It would probably also mean running both in the same direction, so something akin to cogged belt drive between the shafts would be more appropriate than just linking them up head to head.

All in all, this would be a major project -- no time in my life for that sort of cobbling.

LLoyd

Reply to
Lloyd E. Sponenburgh

Bill. What the others have written is true. However, if you are buying new generators, look at the ones for RV type use that are actually generators that run solid state inverters that allow two to be connected together. One as master, the other as slave. The electronics are connected by cable to allow both to sync together and provide combined power. And yes, they are the same size.

Paul

Reply to
co_farmer

Isn't that more or less how those tractor pull loons stack engines?

Reply to
Pete C.

The Honda EU series and also Yamaha equivalents. Actually the only connection between them is paralleling the outputs. There is a perception that because you are supposed to use a special paralleling cable set, there are some control signals on it, but that is not the case.

If you look at the schematics, the parallel cable connections directly connect to the inverter output. The reason for the special cable set is simply safety - the shrouded banana plugs prevent you from potentially contacting the live output connections if you plug / unplug them.

A "suicide" cable with two regular 5-15 plugs will work properly, but presents the safety hazard potential to have a live male plug. Many people operate them this way to save a buck over buying the parallel cable kit. Many smarter people order shrouded banana plugs and make their own safety parallel cable set to save a buck.

Of course you still have the issue of 240V, since these are 120V generators. You'd need a step-up transformer if you really needed 240V.

Pete C.

Reply to
Pete C.

In spite of what the others have said about synchronizing things, in theory it can be done. In practice, with small generators, NOT A CHANCE!

consider: first unit is running at full speed and half power into a load. Disconnect the field windings on the second unit, bring it up to speed, match the speeds as precisely as you can. Slowly bring the field current. If (when) the 2nd unit is going a bit too slow, generator #2 will act like a motor and try to speed up engine #2. And the additional load on generator #1 will tend to slow that engine down. Similarly, if #2 is too fast, it will act like a generator and slow down engine #2, etc etc. Bringing the field current up slowly will allow the units to find a compromise condition where both are putting full power into the load. The power company does this all the time for their generators.

Reply to
RoyJ

OK---I've got the part about phase syncronization, and understand that as a practical source of 240VAC there are some real problems, but I'm still not getting the part about needing a step-up transformer.

240VAC Single Phase is 2 120v legs and a common. Either leg to ground is 120v, and leg to leg is 240v. We aren't talking 3 phase here.

SO why wouldn't two synchronized generators be a source of 240v single phase?

Bill

Reply to
Bill Marrs

A: Because they still won't be synchronized, unless you parallel the outputs. and B: If they were synchronized, you would get 120 from either hot to neutral, and 0 V from Hot to Hot. You need to have them synchronized AND 180 deg out to get 240 Hot to Hot, and that aint going to happen (easily)

jk

Reply to
jk

Well heck----If it was easy everybody would be doing it! I think I'll shut up and go do something I understand. Time to make some chips.

Bill

Reply to
Bill Marrs

It can indeed be done, and the low rotating mass of the small generators actually makes it easier to do and more tolerant of phase mismatch on sync-up. Go read the thread on alt.energy.homepower I referenced, particularly the posts from Neon John, a credible poster who parallels two $100 Chinese generators to run an A/C unit for his semi.

Reply to
Pete C.

The best way is drive a 120V to 220 V CT transformer. Martin

Mart> gil fired this volley in

Reply to
Martin H. Eastburn

Look for the thread "parallel generators"

Reply to
Louis Ohland

Honda inverter generatorss can be synchronized via a special cable. It is a very special application, not applicable to the general case.

i
Reply to
Ignoramus26157

On Mon, 17 Sep 2007 14:33:20 -0500, with neither quill nor qualm, Ignoramus26157 quickly quoth:

It won't sound nearly as bad as those out-of-sync engines in the old Flying Fortresses or Liberators going over the house back when they were used for fighting fires. (I missed WWII.)

Reply to
Larry Jaques

When I was in school, we synchronized a generator with the utility power by connecting a light bulb between them. When the bulb went out, they were in phase, and we threw the switch. After that, they were self-synchronizing, because if our generator slowed down, it would start to draw power from the line, and come back to speed.

But synchronizing two generators in SERIES (instead of parallel) is a whole nother thing.

Someone asked why you need a X-former. Kuz, if you're running two 120 v generators in parallel, you getg 120 volts. The transformer gets you up to

240. The OP asked about a way to get 240v out of two generators. He didn't say he needed two generators to get the required wattage. ONE generator and a X-former would do it if the power is high enough to run the load.

Take a look at the geneerator panel--Many or most of them have a 240 volt output, in which case you won't even need the X-former.

Reply to
Leo Lichtman

SNIP

Hey Leo,

Old "Preston Chronicle" newspaper report:

--------The cause of death was trauma caused by exploding machinery when the new plant operator threw the switch to connect the building generator to the incoming supply. In his previous place of employment, they had used a "lamp out" system, while this plant used a "bright light" system to detect phase synchronization.------

And the same is possible if the "lamp" burns out at just the wrong time, as it is prone to do with the voltage fluctuations during run-up. Bright-light is not as sensitive, but somewhat safer.

Take care.

Brian Lawson, Bothwell, Ontario.

Reply to
Brian Lawson

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