Another Generator Voltage Question

[jedens]

My generator has two 120v 20amp outlets with standard three prong configurations and one 120v/240v 20amp outlet with a 4 prong twist lock configuration. I need to get 120 volts 30 amps from it. Each 120v circuit is capable of delivering 20 amps independently and I assume that the same two 120v circuits are what are applied across the two legs of the 240v outlet. Is there some type of transformer that I can get to plug into my generator with 240v 20 amp on the input side of the transformer and 120v 40amp (only need 30) on the output side? Or is there some other device that I could plug both of the independent 120v outlets into on an input side that would synchronize the two circuits have 120v on the output but allow the current to be increased as it pulled current from both sides of the input?
My basic problem is that I need 120v 30amps in one circuit and I've got two 120v 20 amp circuits available???

 

[chim]

There's a good chance the only things you need are an outlet and some changes to the internal wiring. Do you have an electrical bud who can see it in person? The standby generator at our house can be connected for different things inside the terminal box on the genset. I opted for 120 only, since we can live without all our 240 volt stuff...............chim

 

[Anonymous Poster]

generator amperage

i doubt that you will be able to make your generator work to give you 30 amps on one leg, of 120 volts. can you split the load into two different loads totaling 30 A. ? since the generator will only give you 20A per side, there is no way it can give you 30A. if you could devide the load, then you could draw part from each leg of the generator, or you need a bigger generator to give you more power.

what you are asking is for a gasoline engine which is probabley about 8hp to deliver the power provided by a 12-14 hp engine. it takes about 2 hp to give 1KW of electricity you are asking for 7200w of power from a generator that will only give you about 4800W. so that is the critical issue.

alex

 

[BB_TX]

You can buy a step-down transformer that will convert the 220 VAC to 120 VAC and get near double the amps (minus losses of the transformer. Power out = power in minus losses). I am not sure how much they would cost. Check with a local electrical supply house and explain what you want, voltage and current.

 

[hayden]

I was able to do this by rewiring the connections in the generator. Only try this if you are comfortable that you know what you are doing, and even then be careful. Don't rely on my feable description alone.

The generator I did this to was an el-cheapo coleman 5kw generator that had 2 110V@20 outlets, or a 220V@20 outlet, and I also needed 110V @ 30A, which is actually well under the rated watage and output capacity of the engine.

My generator was wired with two windings, and each winding had two wires. Let's call them L1 and N1 for the first winding, then L2 and N2 for the second. They came from the factory wired like this (N1 and L2 are tied together)

L1 N1-L2 N2
| | |
|-- 120 ----|--- 120 --|
|--------- 240 ---------|


The windings are rated for 20A each and can be loaded acording to spec.

I changed it to run the two windings in parallel rather than series so they could share a load up to 40A @ 110V (20A in each prallel winding). The trick to making this work is to be sure you have the two winding in phase, not out of phase or you'll create an internal short circuit. The resulting wiring looks like:


L1-L2 N1-N2
| |
|-- ---120 ----|

You give up 220V completely, but the 110V will pack a whollop.

Be sure to fuse or change the breaker to 30A and protect the circuit, and be sure to use a 30A rated plug, wiring, etc.


I suspect the transformer approach will end up costingmore than buying a new generator, so the wiring trick may be worth a try.

Peter
Good luck

 

[jedens]

Hi Peter,
Thanks for your detailed post. You are getting to the heart of exactly what I am trying to do. I know the generator has the capacity for 120v 30amps, its just broken up into to discreet circuits. I am very familiar with the concept of using DC voltage sources such as 12V or 6V batteries wired in parallel or serial circuits in order to provide more amperage or more voltage, but these of course don't have a frequency component as does AC voltage.
You said "The trick to making this work is to be sure you have the two winding in phase, not out of phase or you'll create an internal short circuit." I assume you are talking about the phase of the 60Hz frequency. How do you insure that you are keeping them in phase when you wire them in parallel? I assume that the frequency and phase of each winding is dependent upon some type of rotating element (a rotor?). If the rotor of each winding is turning at the same speed that should take care of the frequency but I'm not sure how to determine the phase of each and then to insure they are synchronized?
Thanks again for all of your help.

 

[hayden]

It's just line having two 12V DC batteries. If you wire them in parallel plus to plus, minus to minus, you get twice the current capacity at 12V. If you wire them in parallel plus to minus, plus to minus, very very bad things happen because you create a short circuit.

The two circuits in the generator are wound around the internals of the generator right along side each other. The frequency is determined by the armerture rotation speed. Most small generators are wound so they produce 60 Hz when the gen/motor are rotating at 3600 RPM. Some higher end generators will run at 1800 RPM.

If you open up the electric box on your gen, you'll see the wires that make up the 120/240 outlet circuit. It should look like the diagram I drew. Mark the wires then rewire as shown.

What I did to be sure was to connect together one side of the windings, but not both. I then started the generator and measured the voltage between the two wires that I had not yet connected together. It should measure zero volts. If it's 220V, you have the windings connected wrong.

By the way, this is exactly why generators like the Onan RV generator are set up to produce their full power via a single 120V circuit. They are only 4KW generators, but they will produce a full 30A through a single 120V circuit. That's the generator I picked for my solar home for exactly that reason -it needs all it's power from a single 120V circuit.