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Old 07-11-2016, 06:44 PM   #1
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50A vs 30A and converting one to other.

I have a 1988 Fleetwood Southwind, about 34 feet, currently with a 30A land line.

I believe this is because that is what campgrounds were equipped with, back in 1988.

It has a built in 50A generator (6K I think, Onan) that I can control from the cockpit or at the rear generator bay.

On the 30A land line, I can only use one of the roof air conditioners. When on the 50A generator, I can use both air conditioners.

I am doing the research now, to land a cord, a new land line, that will go into the power structure of this Motor Home, so that I can take advantage of modern campgrounds that have 50A hook ups. I plan to hook up this 50A cord into the point where the generator applies power into the power center. I know it automatically switches between the 50A and 30A source, depending on what it sees. If I am still plugged in and start the genny, it will still change automatically. I am presuming it uses a relay or some such switching device.

I see no need to re-invent the power distribution. The power distrubution does not need to know, or care, if the 50A is coming from the genny or the street, it will act the same, when the 2nd 120 volt hot is applied.


Now, here are my questions...

1. If I add this 50A line, should I keep the 30A line?

I am thinking that I want to still be able to plug into the 30A receptacles at older or smaller campgrounds, especially since I only need the 50A part time so I can run the two air conditioners, which is not all the time.

A consideration is question # 2

2. If I use my new 50A land line, can I make an adapter so I can plug it into a 30A receptacal if I need to. If I can, it makes question 1 moot.

3. (not really related, but I am curious) I know I can run my generator at the same time as my engine. Can I, and does anyone else, run the generator while driving, so that I can run both roof air conditioners while driving down the road? Other than fuel consumption, what are the up or down sides?
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Old 07-11-2016, 06:56 PM   #2
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You really have an odd set up , first time I've heard of this 50 amp gen set with a 30 amp shore cord. Inside of the transfer switch must be a real mess; but I digress.

There are 50 to 30 amp adapters available , also 30>50 , 30 >15 etc. so unless you need to make an extension cord , you don't need the 30 amp cord.
Gas mileage is the only consideration when running gen set when driving , do what you have to do stay comfortable.

Safe travels.
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Old 07-11-2016, 07:33 PM   #3
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You don't have a special transfer switch or relay.

What you have is a generator with 2 ,120 volt outputs. At 6k, it probably has a 30 amp and a 20 amp breaker.

Like my 5500, 1 output is 30 amp and the other is 20 amp. The 30 amp side runs the MH circuits and 1 AC.

The separate 20 amp circuit is designed to run the second AC only.

Many of the 2 AC, 30 amp MHs also had a switch to select which AC you want to run, when plugged into 30 amp power.

You really can't just run 50 amps into your MH, mostly because it's a 240 volt circuit, supplying a total of 100 amps, and you have no way to accommodate that kind of power.

What you may be able to do is install a 50 amp shore cord, 50 amp transfer switch and split the 2, 120 legs at the panel after upgrading the breaker panel.

Then run the 2 lines from the generator to the transfer switch.

You do need to reinvent the wheel.

Option 2 would be to pick up a 30 amp transfer switch and wire it in the output of the generator line that runs the AC only. From that, you can run a second 20 or 30 amp cord to the pedestal.

My generator can be re-wired to 240 volts, like 50 amp service, but in doing that I only get 22 amps per leg. A 6000 watt generator would produce about 25 amps per leg.

Running 2 ACs like that, will not leave much for water heaters or microwaves.
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Old 07-11-2016, 07:38 PM   #4
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Here is the layout of the 30 and 50 amp plugs.
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Old 07-11-2016, 07:56 PM   #5
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Twinboat,

Thank you for your explanation.

I believe I understand the wiring, but am happy to learn more.

I agree that my generator is most likely supplying a 30 amp 120volt service, and at the same time, a 20 amp, 120 volt service.

However, the only difference between a 240 volt service and two 120 volt services, is how you apply the load at the other end.

I am sure that if I were to measure between the two 120 hot legs coming out of the genny, I would have 240 volts on my multimeter.

I do not have any loads in my motor home that are wired between the two hots.

On my 30 amp service currently, if I measure between the two hots (the 30 amp service I currently have has two hots and a neutral) I will also get 240 volts. But none of my utilities in my motor home do that. They take one or the other hot, and the other side is the neutral. So the different items in my motorhome (microwave, airconditoner, refer when on 120 volts, battery chargers, etc) all run on 120 volts, but not on all the same hot to neutral. Some on one, some on the other.

On the 50 Amp service coming from the genny (and soon my new land line) I will have only a 50 amp breaker, not a 100 amp breaker. That will give me a 30 and 20, or two 25 amp hots, a neutral and a ground. The only thing that is different, is, as was stated, that the 2nd airconditoner will now also be in the soup.

I have not actually mapped it out, but for arguments sake, I believe it is reasonable to consider that my current 30 amp service, since it has two hots, is simply two 15 amp services, much the same that my future 50Amp service will be two 25 amp services. It is not so much how the power is made available to the power distribution but how it is then consumed.
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Old 07-11-2016, 08:11 PM   #6
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Quote:
Originally Posted by KSagal View Post
Twinboat,

Thank you for your explanation.

I believe I understand the wiring, but am happy to learn more.

I agree that my generator is most likely supplying a 30 amp 120volt service, and at the same time, a 20 amp, 120 volt service.

However, the only difference between a 240 volt service and two 120 volt services, is how you apply the load at the other end.

I am sure that if I were to measure between the two 120 hot legs coming out of the genny, I would have 240 volts on my multimeter.

I do not have any loads in my motor home that are wired between the two hots.

On my 30 amp service currently, if I measure between the two hots (the 30 amp service I currently have has two hots and a neutral) I will also get 240 volts. But none of my utilities in my motor home do that. They take one or the other hot, and the other side is the neutral. So the different items in my motorhome (microwave, airconditoner, refer when on 120 volts, battery chargers, etc) all run on 120 volts, but not on all the same hot to neutral. Some on one, some on the other.

On the 50 Amp service coming from the genny (and soon my new land line) I will have only a 50 amp breaker, not a 100 amp breaker. That will give me a 30 and 20, or two 25 amp hots, a neutral and a ground. The only thing that is different, is, as was stated, that the 2nd airconditoner will now also be in the soup.

I have not actually mapped it out, but for arguments sake, I believe it is reasonable to consider that my current 30 amp service, since it has two hots, is simply two 15 amp services, much the same that my future 50Amp service will be two 25 amp services. It is not so much how the power is made available to the power distribution but how it is then consumed.
A 30 Amp RV service has two hots and a neutral? It should be one 120v hot, one neutral and one ground.
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Old 07-11-2016, 08:26 PM   #7
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Quote:
Originally Posted by Skip426 View Post
You really have an odd set up , first time I've heard of this 50 amp gen set with a 30 amp shore cord. Inside of the transfer switch must be a real mess; but I digress.

There are 50 to 30 amp adapters available , also 30>50 , 30 >15 etc. so unless you need to make an extension cord , you don't need the 30 amp cord.
Gas mileage is the only consideration when running gen set when driving , do what you have to do stay comfortable.

Safe travels.
Nothing odd about it at all. My 1994 Bounder had a 7000 watt that ran both AC on the Gen but only one at time on shore power. My current 2004 Southwind has a 5000 watt generator that will run both AC at a time no problem.
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Old 07-11-2016, 08:45 PM   #8
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Quote:
Originally Posted by KSagal View Post
Twinboat,

Thank you for your explanation.

I am sure that if I were to measure between the two 120 hot legs coming out of the genny, I would have 240 volts on my multimeter.

(I don't believe you will. The two winding circuits tie together before the breakers.)


On my 30 amp service currently, if I measure between the two hots (the 30 amp service I currently have has two hots and a neutral) I will also get 240 volts.

(Again not true. As explains by others it is a single hot 120 volt line. The other points are neutral and ground.)

On the 50 Amp service coming from the genny.

(That you may be able to do by tieing the 2 120volt lines together.)


and soon my new land line

(Be carefull wiring to half a 50 amp pedestal.)



I have not actually mapped it out, but for arguments sake, I believe it is reasonable to consider that my current 30 amp service, since it has two hots, is simply two 15 amp services, much the same that my future 50Amp service will be two 25 amp services.

(Again, not true. 30 amp is 30 amp@120 volts, single breaker.
50 amp is 50 amp X 2 at 120/240 volts. A 50 amp service has double breakers. )


.
Good luck and keep us posted.
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Old 07-11-2016, 08:53 PM   #9
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You don't have anything switching power between 30 amp and 50 amp, you have the front A/C connected to the 30 amp shore cord or the generator, switched by the transfer switch or physically plugging the shore cord into an outlet powered by one circuit of the generator. The rear A/C is only wired into the other circuit on the generator.

You could install a plug and outlet on that second generator circuit and add a second, 50 amp cord, or better yet, a 30 amp cord with a 30/50 adaptor to plug into the 50 amp outlet on the campground pedestal.

You would have to extensively re-wire the RV to change it to 50 amp service. 30 amps is just 30 amps @ 120v, 3,600 watts. 50 amp service is two legs of 50 amps @ 120v, or 120,000 watts, almost 3 times as much. A new, 100 amp service panel, divided roughly into half the load on one leg, half on the other, a 50 amp transfer switch, cord, and plug.
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Old 07-12-2016, 04:21 AM   #10
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Thanks for all this information. I will take a bit of time to digest it. I believe I may have over simplified the situation. This is the reason I do the research.
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Old 07-12-2016, 04:56 AM   #11
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Here is an article explaining RV power. Hope it helps.

http://www.rvtechmag.com/electrical/chapter3.php
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Old 07-12-2016, 05:54 AM   #12
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Wow...

First...if it wasn't answered. No...do not keep the 30 amp service cord. They make a readily available dogbone adapter to connect the 50 amp plug into a 30 amp service pole receptacle.

You have to run heavier gauge wire on the runs protected by 50amp breakers. You will have to see the schematic of your transfer switch to see if it can accept the two service legs...if not...a new transfer switch.

I think, honestly, you will need to consider changing the sevice panel if you want to take advantage of the 50 amps...as most 50amp panels split out two buses for the different legs. Chances are...your panel is only rated for 30 amps...buss conductor isn't suitable for 50 amps without overheating.

You could wire one leg to your 30 amp panel...keeping the 30 amp breaker on it to protect it...and add a heavy amp rated double pole switch for the second air conditioner...by added a small breaker/disconnect to protect the wire on the second 50 amp leg...with a separate ground and neutral from your shore power side. Basically it would allow you to select shore power or generator for the second A/C unit.

If you really want to take advantage of 50 amps...

Shore power cord
Transfer switch
Distribution Panel
Load mgmt system
Converter

are the components that would be needed. If you have
room for more batteries...you could also put some circuits on an Inverter or Dual purpose Inverter/Converter... solar charge controller etc...

It's important to plan...know what your goal is.

If it's just to be able to run the second A/C on shore power there are easier ways...

If you want to run your water heater and microwave at the same time as your primary air conditioner...then you will need a different service panel, converter, etc...to do all of that...

All of these things are doable...just require a bit more planning and aquisition of the proper componenets.
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Old 07-12-2016, 09:25 AM   #13
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Wow...

First...if it wasn't answered. No...do not keep the 30 amp service cord. They make a readily available dogbone adapter to connect the 50 amp plug into a 30 amp service pole receptacle.

You have to run heavier gauge wire on the runs protected by 50amp breakers. You will have to see the schematic of your transfer switch to see if it can accept the two service legs...if not...a new transfer switch.

I think, honestly, you will need to consider changing the sevice panel if you want to take advantage of the 50 amps...as most 50amp panels split out two buses for the different legs. Chances are...your panel is only rated for 30 amps...buss conductor isn't suitable for 50 amps without overheating.

You could wire one leg to your 30 amp panel...keeping the 30 amp breaker on it to protect it...and add a heavy amp rated double pole switch for the second air conditioner...by added a small breaker/disconnect to protect the wire on the second 50 amp leg...with a separate ground and neutral from your shore power side. Basically it would allow you to select shore power or generator for the second A/C unit.

If you really want to take advantage of 50 amps...

Shore power cord
Transfer switch
Distribution Panel
Load mgmt system
Converter

are the components that would be needed. If you have
room for more batteries...you could also put some circuits on an Inverter or Dual purpose Inverter/Converter... solar charge controller etc...

It's important to plan...know what your goal is.

If it's just to be able to run the second A/C on shore power there are easier ways...

If you want to run your water heater and microwave at the same time as your primary air conditioner...then you will need a different service panel, converter, etc...to do all of that...

All of these things are doable...just require a bit more planning and aquisition of the proper componenets.
First, the OP's question was answered by a number of responders by trying to let him know where he was wrong in some of his original assumptions. Second, some of your suggestions don't make electrical sense. Why replace the 30 amp cord with a 50 amp one? Always having to use a dog leg to plug it into a 30 amp outlet makes little sense. A 30 amp RV has one hot, one neutral, one ground. His transfer switch would also be wired to handle that service, along with the breaker panel. A 50 amp cord and plug has two hots, a neutral, and a ground. The two hot leads are 180 out of phase so the neutral doesn't have to be sized to handle both hot leads at once.

How would you wire a 30 amp transfer switch (or breaker panel) to handle the extra hot leg? Why would an RV manufacturer, in 1988, install a 50 amp transfer switch in a 30 amp RV?

You also suggest installing a new converter and energy management system. What would be the advantage of a new converter? An energy management system is only needed when a 50 amp RV is plugged into 30 amp service. He has a 30 amp RV, the expense of re-wiring the whole RV would cost probably at least $1000, is it worth it to do so?

The OP stated he has a 50 amp generator. That's correct, usually split by the generator into two circuits of 30 amps and 20 amps. His generator is hooked up by transfer switch or plug/outlet to the RV's 30 amp service. The 20 amp is connected directly to the rear A/C.

A 50 amp (5500 watt) generator is not the same energy as 50 amp RV service. A 50 amp RV has 100 amps available in two legs of 50 amp service. A 50 amp generator has just 50 amps, half as much as a 50 amp shore cord.

You are correct, anything is doable, but at what cost?
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Old 07-12-2016, 09:45 AM   #14
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FWIW assuming you are not interested in throwing a lot of money at what you have or rewiring the system.. Start by checking your generator specifications. If you have 30 A 120 on one leg and 20 A 120 on the other are they separate windings or one winding with two breakers off the buss? If separate windings do they have a common neutral? Depending on the answers to that one side of a standard 50 Amp shore cord would probably give you what you want. Alternatively, assuming they can be the same neutral you could use a 50 A cord to feed each side with the common neutral. Just add a disconnect that can be breakered or fused for the correct current to the loads involved. You won't get the full power a properly set up modern system provides but you probably won't care either. You will have all the power you are used to now with the generator but have it all the time.
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