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Old 01-21-2020, 01:20 PM   #1
Mini-Skoolie
 
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Need a little electrical understanding

I am going to set up with a 50A service. I have done a lot of residential wiring, and even more 12V wiring, so I understand both systems. Crossing the two together, I am having some difficulty with, but I get the mechanics of it. One thing I can't seem to grasp is the relationship between volts and watts. If someone can dumb that down to my level I would appreciate it.

I understand the 50A 220V service is actually just 2 110V circuits. Applied to a standard house type breaker box, this gives me 2 different services to split the different loads throughout the bus. Common and ground bars need to be separated in the box on the bus, that connection happens in the pedestal. I get that. When a 50A service isn't available, ie. RV park with 30A service, an adapter is used to work off the 30A with diminished capabilities in the bus. I get that. A splitter type adapter can be used to access the 20A and the 30A services if available on the pedestal.

Here is where my confusion starts. I assume the common leg of both the 20A and 30A are connected inside the pedestal so there isn't some sort of out of phase cosmic clash in the electrical grid, allowing both legs plugged into the pedestal to connect in the adapter before it goes into the bus service plug allowing both legs inside the bus to work as expected with a little less diminished capability than just one 30 amp due to 20 and 30 amps rather than 50 amps. (I hope this is as clear as mud...)

First question. My 5500 watt generator was able to power both A/C units when they all lived together in the motorhome, so I assume it produces enough amps to run the whole system. I want to assume that it will also be able to power the 50A service in the bus without any diminished capabilities. How do I figure out if that is the case?

Second question, when using an adapter to plug my 50A service into a 30A pedestal, does the adapter simply tie the two 110 legs of the 50A service together to run off the 30A service? Or are there resistors/diodes/black magic going on inside that adapter?

Third question. If I plug my 50A bus into one of those 20-30 amp splitter adapters, can I then plug the 20 and 30 amp plugs into 2 smaller separate generators? I don't think so, because the common leg isn't connected between the two generators. But would it become possible if the two generators were parallel connected with each other.

I haven't removed the generator system from the motor home yet, so I don't know exactly how it was incorporated into it. I do know it was tied right into the system, it had a starter button on the dash, and you didn't have to go out and plug the shore power into the generator. If I can, I plan to incorporate that fully into the bus, but only if it will run the whole electrical system of the bus.

One other thing to note. When the motor home was plugged into shore power, there was a selector switch to allow either the front or rear A/C to run, but not both together. With the generator running, both units worked at the same time no matter which position the selector was in. This makes me think the generator must have the capability to run 2 separate 110 circuits like a 50A service. But then, I'm just guessing and hoping that is the case.

Ideally I want a 50A shore power service so I can run everything electrical I have on the bus at the same time, not that I would, but that is what 50 amps is for. Also, I would like to push a button on the dash and start the generator that will run, at the very least, both A/C units, fridge, and microwave, at the same time. I know at the end of the day with enough money, anything is possible, but in reality, is this feasible?
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Old 01-21-2020, 03:37 PM   #2
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You asked a lot, I'll try to get it all.

Watts is the power delivered, So watts = amps x volts

So your 30 amp rv plug has 3 prongs.

a 120v 30 amp power
a neutral
a ground

This plug has the capability of 3600 watts of power.

Your 50 amp rv plug has 4 prongs

a 120v 50 amp power
another 120v 50 amp power that is out of phase of the 1st one
a neutral
a ground

This one has the capability of 12,000 watts of power.

The phase offset of the hot legs is what allows you to have 240 volt power available. It also eliminates your ability to tie both hot legs together on one wire.

So, to answer your questions now.

1.If your generator is 5500 watts it won't power your 50 amp service. Like said earlier, You'll need something with 12000 watt minimum to fully power a 50 amp rv plug. Your 5500 watt generator will power a 30 amp plug no problem though.

2. A 30 male to 50 female plug simply ties both hots on the 50 plug to the single hot on the 30. Making the max amps available 30 amps, and you would no longer have 240 volts available.

3. I've never seen a splitter adapter that you talk about, or used a multimeter to see how they're connected. But I would assume that one hot leg of the 50 amp would be provided by the 20 service, the other hot leg would be provided by the 30 service, and the commons and grounds would all be connected together. But I don't know, and I'm not sure if I'd really want to run something like that.

4. It has to have had some sort of automatic transfer switch, so that when the generator is powered, the shore service was disconnected, and vice versa. Transfer switches come in multiple sizes so finding one to work isn't hard. Not installing one isn't an option IMO, unless your generator has an outlet, and you plug the rv cord into that.

Quote:
Ideally I want a 50A shore power service so I can run everything electrical I have on the bus at the same time, not that I would, but that is what 50 amps is for. Also, I would like to push a button on the dash and start the generator that will run, at the very least, both A/C units, fridge, and microwave, at the same time. I know at the end of the day with enough money, anything is possible, but in reality, is this feasible?
It's all feasible, and is done regularly in most rv's. 50 amp shore power is a good idea. 2 of your larger roof top ac units will be surging nearly 6000 watts, which will be out of reach of a 30 amp service. You'll want to have a generator that provides more then your surge rating, otherwise you'll run into overloading issues when trying to run anything with the ac units kicking on and off. Onan makes a variety of units that have the ability to be remotely operated, and provide the power you're planning on needing. And they can be fueled by gasoline, propane, and diesel, so you would only have to carry one fuel source onboard as well.

Are you sure your current generator is 5500 watt? Can you run both ac units, fridge, and microwave on it now?
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Old 01-21-2020, 04:40 PM   #3
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I know that was a lot of questions, sorry, when I get on a roll.... You should see how much more I deleted to save for next time!
You packed a lot if info in that answer, thank you!

The donor motor home has been in my back yard for about 12 years. When I originally got it, I was going to repair the fire damage until I realized how bad the roof leakage was, then decided to scrap it out...eventually.
I did have it hooked up to shore power to test things, that's how I know shore power would only power one A/C at a time. While running the generator, it would run both A/C units, and the fridge. It didn't have a microwave in it to test them all at the same time. I'm going from memory on it being a 5500 watt generator, haven't looked at it for several years. Now that I have a use for all the pieces, I will spend the next few weekends taking it all apart and testing/running everything to make sure it all still works. This may all be just an info gathering mission if none of it works and I have to buy all new stuff. In a way that would be nice so I can customize every part to what I want, just a lot more pricy.

Here is the 20A-30A to 50A adapter. I realize it would still only allow 30 and 20 amps, but that is better than tying the two legs together and getting only 30 amps.

https://www.etrailer.com/RV-Wiring/Camco/CAM55025.html

Any thoughts on running this adapter with two smaller generators that are paralleled together? I know it would still be limiting the amps on each leg, but still better than running one single 30A adapter to into the 50A cord.
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Old 01-21-2020, 04:49 PM   #4
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Not 240

Remember that a RV hookup is not 240, you cannot use a home oven or dryer receptical, get a RV plug.

Edited
You can use a house service panel but you must jumper the two 110 bars if you install a 30 amp service, a 50 amp service already has two 120v wires
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Old 01-21-2020, 05:13 PM   #5
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Quote:
Originally Posted by bubb, the real one View Post
You can use a house service panel but you must jumper the two 110 bars
Please explain this. I'm not sure what you mean by jumper the two 110 bars. I know how to wire the 4 prong outlet used in the 50A service, but I'm confused by this statement.
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Old 01-21-2020, 05:30 PM   #6
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I was wrong, I edited that post, if you install a 50 amp service no need to add a jumper wire between the 2 bus bars in the service panel, but in a 30 amp install only one service panel bar will have power unless you jumper them
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Old 01-21-2020, 06:17 PM   #7
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Thanks for clarifying. I have been banging my head against the electrical wall long enough I thought I completely missed something.
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Old 01-22-2020, 09:02 AM   #8
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https://youtu.be/GoOR2AJGjOI

Here is a video that might better explain.

Quote:
Originally Posted by bubb, the real one View Post
Remember that a RV hookup is not 240, you cannot use a home oven or dryer receptical, get a RV plug.
Um, it is 240v though. Those 120v legs are out of phase giving you the 240 volts. You can definitely use 240v home appliances with the 50 amp rv plug. The only difference there is the 50A rv plug has a neutral. Your 240v house oven plug won't have that neutral. So you can't plug your rv into your house oven/drier outlet, because the load in your rv won't be balanced.
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Old 01-25-2020, 08:26 PM   #9
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I finally got out to take a look at a few things on the donor motor home. Talk about a wiring nightmare! So the generator is 6500 watts. The box mounted right next to the generator has a pile of wiring in it. I don't know enough about generators to know what I'm looking at, but it appears to be two separate 110V lines coming out of it.

This connects to some romex and disappears under the floor to somewhere I didn't find yet. I ran out of daylight, so that mission is put off for a few weeks.

Can anyone tell me anything about this generator?
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Old 01-26-2020, 10:06 AM   #10
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Quote:
Originally Posted by bubb, the real one View Post
Remember that a RV hookup is not 240, you cannot use a home oven or dryer receptical, get a RV plug.

Edited
You can use a house service panel but you must jumper the two 110 bars if you install a 30 amp service, a 50 amp service already has two 120v wires
50 amp RV service is 240 volts. 30 amp is 120 volts.
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Old 01-26-2020, 11:34 AM   #11
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I like the onan generators. I have a 4000 watt one and am pleased with it. It looks like the data tag does not show dc volts. So it is likely it runs off the house batteries, and does not charge them. Somewhere in the motorhome should be a built in battery charger/power supply. This is how the batteries get charged when the genny is running.
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Old 01-26-2020, 12:53 PM   #12
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JackE, greetings.


I have that same model in my sticks and staples ol girl.
Yours looks pretty beat but might run with a good cleanup. New plugs, change the oil etc. I would get it running before even thinking of pulling it out for your bus plans to use it.
You'll need battery to get it started and run, having an electric fuel pump and choke. You can find parts but I found them pretty expensive as in a set of points, roughly 100CA $. They got you over a barrel if you need new parts.
So, clean off the dust bunnies and give it a go.
The circuits you mentioned coming out of it feed your main panel busbars.
I do like them as does Ronnie but you have to be pretty good at small engines to keep them running well.

I have a 4kw Onan also but mistakenly shut it down under load. A no-no, lots of smoke escaped, so turn all breakers off in the house panel before shutdown of the genny.

See if it will start at the genny and from the remote start/stop inside the rv, as you will want and need both.
If it runs just let it run without turning the 2 breakers on and see if it holds the rpms at 1800. Then when you add a load it should maintain that same rpm if the governor is operating properly.
Definetely check the electric choke operation for winter/cold weather starts.
Spark plug wires on yours seem well weathered so you might get it going or not with them, but that allows dampness into the wires so misfires, which carbon the engine up pretty bad.
Best to try all this while it is mounted securely in that rv.


Good luck,


John
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Old 01-27-2020, 09:22 AM   #13
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Quote:
Originally Posted by BlackJohn View Post
JackE, greetings........


.....Good luck,


John
Thanks for the info. If you saw the state of the rest of the motor home, you would see how impossible it is to test the unit out before removal. When I got the thing 13 years ago, it did run pretty good, but that was 13 years ago. I am very capable when it comes to fixing things, I spent over 10 turning wrenches in a shop before I changed careers. Getting the gen running isn't something I'm as worried about as I am understanding the electrical side of the unit. I did find 2 breakers mounted on the side of the unit. This also leads me to believe it is producing 2 separate 110V circuits. If I am understanding the amps/volts/watts math right, there must be 2 separate circuits that are making about 27 amps each to make a 6500 watt generator. When the generator was running, I was able to run both A/C units at the same time, but when it was on shore power, there was a selector switch to choose either front or rear only. There is an on-board charging unit with a combination of breakers and 12V fuses, but it looks like it's in pretty bad shape. I don't even want to attempt to use it. I found where the shore power line comes in, it is tied to a single 110V romex wire. I didn't trace it any farther yet. The box in the pic is where the generator connects to two separate 110V romex lines, which is why I think it is producing two separate circuits. I also haven't traced those any farther yet. I ran out of daylight and weekend. Next weekend is a supply run to the big city, so it will be a few weeks before I can revisit this project.
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