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Old 06-19-2008, 11:17 PM   #1
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Get More 110 V amps from generators

Thisis a little nuts, but for a long time I've been agitated about not being able to run the A/C from a 3500 W generator. Why doesn't that work? Well, because all generators that have a 220 capability split the power betwen the two 110 V outlets/circuits. I've seen a few recent generators that have a switch with two positions -- (1) keep the 220, or (2) all power to 110.

You can do this, too, if you're really adventurous. Here's the before (top) and after (bottom) wiring diragram for my generator:

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In order to completely understand what's going on here, the generator has two windings, each providing 110 volts. If they are wired in series and 180 degrees out of phase, you get 220 volts across them and still can have 110 across each winding, with a common neutral. That's the top schematic.

But if you can wire the windings in parallel (and in phase), you lose the 220 capability, but you can now get full power at 110.

Forutnately, my generator neutral wire was easily accessible on top of the wire bundle on the windings. Cutting a bit of the linen and lacquer freed up the wire (be extremely cautious not to nick the insulation on the windings (it's just lacquer) or cut a wire by accident!!!). Cutting one winding away from the neutral and providing a fourth wire from this winding out to the sockets was all that was needed to provide full power at 110V. Here's the business end of the generator with the rotor support frame removed:

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Here'sthe two windings soldered to the neutral wire. Just cut one of the windings away and attach a fourth lead to the lose winding.

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I retained the separate 110 circuits and wired the existing 220 connector so that you need a pigtail to short the two 110 circuits together.

I'm not sure that retaining the two independent 110 V circuits is of any value, but if the pigtail is not plugged in, the electrical characteristics of the generator are unchanged, except you don't have 220 volts available any longer. The existing circuit breakers still function to independently limit the current in each winding. If you happen to screw up the phasing of the windings, the circuit breakers will tell you right away!

Yay! Now I can run my A/C no problem. I never did use the 220 capability anyway. (took about 3 hours, including missteps...)

Zep
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Old 06-20-2008, 12:00 AM   #2
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Nice job Zep!

Makes perfect sense to me .......really!!!
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Old 06-20-2008, 07:15 AM   #3
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If I remember correctly I did something similar. I do not however remember if my generator had 220 capacity or if it just had it's power split between 2 110 circuits. As per someone's instructions, I wired the two together to get a full 3500w of power on one 110v circuit. Yes, it worked, but it is my unscientific belief that it GREATLY reduced the life of the generator. ie. It conked out... practically blew itself to bits.
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Old 06-20-2008, 07:44 AM   #4
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p.s.
Kudos....
I do believe this is different than what I did?

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Old 06-20-2008, 08:08 AM   #5
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Quote:
Originally Posted by AirstreamGypsy View Post
... I wired the two together to get a full 3500w of power on one 110v circuit. Yes, it worked, but it is my unscientific belief that it GREATLY reduced the life of the generator. ie. It conked out... practically blew itself to bits.
No, you can't just wire the two 110 outlets together--that would be like a dead short across both of them. Unless, of course, your generator had split windings already and you could wire the outlets in phase instead of out of phase.

Changing the wiring like I did does not increase the load on the generator, necessarily. The 220 socket was always able to deliver the full 3500 W, and you could always have plugged in two 110V loads that each used 1500 W. Taking all the power to one 110V load is no different as far as the horsepower required from the engine is concerned. It is possible, however, that the advertised capability is 3500 W, but in reality the design is intended to deliver something less on a continuous basis.

BTW, the lower photo in post #1 is a little misleading--each winding has two wires, so you have to cut both of those wires at the arrow.

Zep
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Old 06-20-2008, 09:23 AM   #6
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I thought I'd better insert a a remark about paralleling generators. Honda can do it because their generators are really DC with a high power inverter. The inverters can be kept in perfect phase by tieing the inverter clocks together, even though the generator RPM and DC power output aren't necessarily matched.

In most generators, however, the frequency of the AC depends directly on generator RPM, which in small generators is not very stable, nor is it locked to 60 hertz. So you can't tie two non-inverter generators together because they would not be in phase and you'd pop circuit breakers, like right now.

In my example above, not only are the windings always in perfect phase, but they are really just one winding with four wires (which can be split into two windings 180 degrees out of phase to get 220V), so the voltage output is also essentially identical. Consequently, paralleling the windings is no big deal, electrically speaking.

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Old 06-20-2008, 10:37 AM   #7
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How about taking two two different size AC gensets plug them into two transformer rectifiers and run the output of them through a single inverter
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Old 06-20-2008, 10:55 AM   #8
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Quote:
Originally Posted by Aerowood View Post
How about taking two two different size AC gensets plug them into two transformer rectifiers and run the output of them through a single inverter
I think you will need one of these to do that.



I will post the details yesterday...
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Old 06-20-2008, 03:09 PM   #9
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Smile Why does everything have to be a science project?

Quote:
Originally Posted by Zeppelinium View Post
I thought I'd better insert a a remark about paralleling generators. Honda can do it because their generators are really DC with a high power inverter. The inverters can be kept in perfect phase by tieing the inverter clocks together, even though the generator RPM and DC power output aren't necessarily matched.

In most generators, however, the frequency of the AC depends directly on generator RPM, which in small generators is not very stable, nor is it locked to 60 hertz. So you can't tie two non-inverter generators together because they would not be in phase and you'd pop circuit breakers, like right now.

In my example above, not only are the windings always in perfect phase, but they are really just one winding with four wires (which can be split into two windings 180 degrees out of phase to get 220V), so the voltage output is also essentially identical. Consequently, paralleling the windings is no big deal, electrically speaking.

Zep
It was you that said this, yes? My head just spun around as much as the windings.....
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Old 06-20-2008, 04:21 PM   #10
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good one zep, now you know how we stack coils in transformers to make 120/208 three phase service at the power company!

looking for work? i know a couple of engineers here that you could outsmart!

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Old 06-20-2008, 05:21 PM   #11
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good one zep, now you know how we stack coils in transformers to make 120/208 three phase service ...
Is that Wye or Delta?
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Old 06-21-2008, 05:02 AM   #12
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wye would you ask?

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Old 06-21-2008, 10:19 AM   #13
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Excellent info, but not for the timid.
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Old 06-20-2010, 01:08 PM   #14
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The final design is a bit modified from the above description. I decided it wasn't safe to have a standard connector that really was going to perform the shorting plug function. So a standard 110V, 30A connector is installed on the genset. Now, when you plug in you get power from just one winding or, when you close the switch, you get it from both windings. This allows the two 15A connectors to function on separate circuits with separate circuit breakers.

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I have a 10-gauge umbilicial with a standard 30A male on one end and a 30A trailer female on the other, in order to connect the trailer to the genset.

I tested this by running the old Armstrong AC and found less than 1 volt voltage drop. Happy, Happy. Burning man dust storms, take that. Pow. Wham. Zap.

Zep
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