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Old 08-21-2014, 07:06 PM   #1
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Best way to get 120V 30 AMP from a 5 KW generator

For years I have seen the Honda adaptors wherein an adaptor with two 15 amp plugs is plugged into standard spacing wall recepticals to get 120V 30 Amps to a shore line for RV.

Now I am seeing adaptors that convert a four prong 240V plug to a 120V 30 Amp shore line.

I have a Powerback 5000/6250V generator with a double set of standard 120V recepticals with 20 amp breakers and it also has a four prong round plug for 240V with 20 amps each leg. It has a 7 gal tank and is supposed to run about ten hours at half load.


I have two RV 25 ft extensions so I can get the unit about 75 feet away and face the muffler outbound.


What is the consensus of opinion of how to go on getting 30 amps to the AS?

I assume if one does this a ground rod needs to be driven in and hooked to generator?
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Old 08-21-2014, 07:30 PM   #2
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The problem exists in that. You have a 3 wire system in your coach. Not a 4 wire system.
It is possible, but you would need a split buss (240 volt type) panel in your coach. Which may be there, with a jumper between the 2 busses.
You would not have a true 30 amp system. It would be a split 20 amp system. Which would give you a total capacity of 40 amps at 120 volts.
There would be a need for a 4 wire power cord from the generator. 2 of the wires would be for the L1 and L2 legs; one wire would be the neutral and one would be the ground.
There are some inherent risks in a system of this type. If you ever have an "open neutral" situation. You would have 240 volts on the 120 volt system. Which would destroy a number of items in the coach.
As for the ground. Unless you drive a ground rod deep into the soil. There would not be much protection. The typical ground rod installed near your home is 8' long. Once it is in the ground it is virtually impossible to remove it.
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Old 08-21-2014, 08:04 PM   #3
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Quote:
Originally Posted by Hummer View Post
I have a Powerback 5000/6250V generator with a double set of standard 120V recepticals with 20 amp breakers and it also has a four prong round plug for 240V with 20 amps each leg. It has a 7 gal tank and is supposed to run about ten hours at half load.

What is the consensus of opinion of how to go on getting 30 amps to the AS?
Some generators actually have two separate windings, each powering a 120 volt circuit, and connected so that they also can provide 240 volts. However, the 120 volt windings cannot be paralleled to increase the capacity on the 120 volt side. I suspect your generator is of that type. That way they can call it a 5000 watt generator, but in fact the load has to be half on one winding, half on the other to provide that capacity.

20 amps x 120 volts = 2400 watts on each side. Two such windings gives 4800 watts, probably upped a little to make a nice round 5000 watt advertised rating.

If you have that type of generator, unless the manufacturer shows you how to change it internally, you cannot get 30 amps at 120 volts, only a maximum of 20 amps.

I had an Onan 6000 watt RV generator which was wired so it would produce all 120 volt power, or 50 amps. I wanted to re wire it to produce 120/240 volt power. Onan had instructions on how to do that, but from what I understand it is only possible with some generator winding systems, not all.

So, you may not be able to get more than 20 amps 120 volts from your system, unless your generator manufacturer tells you how to re wire it.

BTW the inverter generators work differently, and many can be paralleled to increase their output at 120 volts, so what you see of Honda and others may not apply to your generator.
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Old 08-21-2014, 08:06 PM   #4
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Maybe not the best answer but it might be easier to get a generator with a 30 amp plug. I got one of these for $300 at tractor supply and it seems to be a good unit... Champion Power Equipmentâ„¢ 3500W/4000W Portable Generator - Tractor Supply Co.

Sounds like your generator has two 20 amp legs on each of your 120 double receptacles? I don't think it is going to be an easy, cost effective way to get 30 amps at 120 out of your unit. And it would be easier to get a different unit than to set up your trailer for 240.

I'm not sure about the honda adapter that you are talking about. I've heard about adapters like that for a 50 amp RV plug so that both legs can get 120v for that type of outlet. But trying to take 2 different 120v sources that may or may not be in phase and trying to get them into phase and have the amps become additive is a far more complex problem. You could potentially have two circuits that are in-phase, opposite phase, or just plain out of phase. I'm not an electrical engineer, but I think that they need to be transformed to be in-phase in order to have additive amps on one circuit.

I'm actually in the process of installing a piece of equipment that kind of does that and it is very expensive (shore/generator power augmented by inverter power).
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Old 08-21-2014, 11:02 PM   #5
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The two 110v sides of your generator are out of phase. That would require some type of converter not just an adapter for what you want to do..

Do you need 30amps at the Airstream? If you are not running the A/C unit, 20 amps from just one of the generator's 's 110v outlets is enough. Buy a simple plug adapter like this one:


Even if you do need the A/C while on generator power, just be careful not to run too much else while the A/C is on. Worst that could happen is the breaker would trip on the generator.
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Old 08-22-2014, 12:38 AM   #6
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You have 2 20 amp 120 volts outlets on the generator. Along with one 240 volt outlet.
There are 4 connections to the generator itself which are related to these outlets.
L1, L2, N, G
On the 20 amp 120 volt outlets.
L1 is connected to Outlet 1
L2 is connected to Outlet 2
N is connected to both Outlet 1 and 2
G is connected to both Outlet 1 and 2

L1 and L2 are out of phase by 180 degrees. Which is how you get 240 volts between L1 and L2.
N is center tapped equally between L1 and L2. Which is how you get 120 volts.
The 4 wire 240 volt outlet gives you 240 volts between L1 and L2. Plus it gives you 120 volts between L1 and N as well as between L2 and N.
The capacity of you generator is 5,000 watts.
120 x 20= 2,400 watts on one 20 amp 120 volt outlet
The second 120 volt outlet is also 2,400 watts.
You can draw 4,800 watts total from the 2 120 volt 20 amp outlets.
OR
You can draw 20 amps on each of the L1 and L2 legs of the 240 volt outlet. 20 x 240= 4,800
But you can't do both.
The L1 connection to the 120 20 amp outlet is the same as the L1 connection on the 240 volt outlet.
The same goes for L2 except the 120 20 amp is connect to the other 120 20 amp outlet.
No special converter is required. Just the correct wiring.
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Old 08-22-2014, 03:10 PM   #7
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You guys just confirmed what I was afraid of and thanks for the heads up.

I have a Champion as identified but haven't got around to opening it up as yet. Was just going to sit on it for awhile and see how I got on after the wreck and whether it was going to be possible to get the Sovereign back on the road.

I have a military MEP017 2A042and it is wired up and I have had 4000 watts on it no problem but entirely too big to take camping haha.


I also have a small Onan that I can count on to put out 2265 watts and still have at least 58/59 cycles.

Also have a Honda EZ3500 but with the adaptor it won't power up AC long before it trips a breaker.

I have been running some tests and just today I was starting a new series on a Powerback Devilblss and got a real wake up as I finally got a multimeter that would read hertz as well as volts.

I cranked it off this morning with about a 3500 watt load on it and to my surprise the hertz was way high, upwards of 80. Voltage was around 113.


I had to run it 19 minutes under load before the hertz dropped back into the 57-63 range. All I had on it was heaters, lights and electric motor with no load on it.

The data sticker on unit says run it five minutes before applying load.
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Old 10-31-2014, 01:09 PM   #8
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Just a small comment as a point of interest... A minor technicality to TG Twinkie above. The 2 phases that make up line 1 and line 2 are actually 120 degrees apart, not 180 as suggested. American Grid AC power is balanced 3 phase, which is where/why we get the 120 degree separation for each phase/leg.

I know this as I am in Bulk Electric Grid Operations for the local power company.
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Old 10-31-2014, 09:47 PM   #9
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Best way to get 120V 30 AMP from a 5 KW generator

My comments were in regards to the output of a single phase generator.
Most single phase generators run at 3,600 rpm to generate 60 cycle power. Which means they are 2 pole devices.
Two poles spaced 180 degrees apart. The number of poles has nothing to do with the output voltage , only the frequency. The number of turns on the windings determines the voltage output at speed.
A 4 pole generator would run at 1,800 rpm to develop 60 cycle power.
4 poles spaced 90 degrees apart.
As for grid power. Most if not all homes are supplied with single phase power. Transformed down to 240/120. The primary of this type of transformer is connected to a 4 wire 3 phase system. But only between one hot leg and the neutral. Not between 2 different phases such as L1 and L2.
So the 120 degree angle thing doesn't fly.
The term phase was technically not correct. Since it is SINGLE. Phase. It can't be 180 degrees out.
The potential difference is derived from how the transformer is wound.
Most are wound for 240 volts between L1 and L2 with a center tapped neutral for the 120 volt equipment. On the secondary side.
Hope this helps clear up the 180 degree thing.

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