ac power question

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ac power question

August 30, 2016, 02:50:20 pm

I have a'69 Dodge 270, a '78 Travco and my '92 Grand Villa. They all three have the 50Amp connector on the umbillical. The '69 can connect to either the generator or a pedistal. I think it's generator has 240vac output and the two legs are separated in the breaker panel. I swapped positions with the two coaches one time and the Travco main breaker blew. Took a lot of my measly brain power to figure that out! How does the 270 work when plugged into 30amp female socket at the pedistal with the short adapter from 50 to 30 amp on it's umbilical?

Thanks,

Jim

Re: ac power question

Reply #1 – August 30, 2016, 03:19:01 pm

Jim- mine works fine on 30 amps- just remember you need to use only 1 ac at a time ad watch your other electrical devices.
30 amps works but 50 is much better for our U270's.

Re: ac power question

Reply #2 – August 30, 2016, 03:34:28 pm

Assuming this is an RV 30 amp (one hot, one neutral and one ground), a 30 male to 50 female adapter connects the single hot on the 30 end to both hots on the 50 end.

Re: ac power question

Reply #3 – August 30, 2016, 08:04:51 pm

thanks, folks - and to Brett - I suspected that about the adapter but was not sure. I may catch on to this stuff sometime down the road....

Jim

Re: ac power question

Reply #4 – August 31, 2016, 03:01:57 pm

I do not know of any motorhome generator which is configured to output 240 VAC.
It is not reasonably possible to load balance the output of two armatures while providing both 120 VAC and 240 VAC.
My 96 U320 10Kwatt Powertech has two 120 VAC outputs which are shorted together at the genset, then two hots (red & black) go to the AC power panel. The amps in the red hot and black hot will be different, however the amps (and volts) from each genset output are always identical and are 120 VAC. The output of the genset can easily be converted to 240VAC, however, having 120VAC available at the same time would require a complicated load balancing system.
Note the confusion caused by 30amp and 50 amp designations. A 30 amp shore power plug(three pins) provides 30amps, while a 50 amp shore power plug (four pins) provides 100amps because there are two hot pins at 50amps each.
Confused? Not to worry, this is an often misunderstood concept. Just be aware that 240VAC is seldom available in motorhomes.

Re: ac power question

Reply #5 – August 31, 2016, 04:09:50 pm

Quote from: P. Wyatt Sabourin – August 31, 2016, 03:01:57 pm

I do not know of any motorhome generator which is configured to output 240 VAC.
It is not reasonably possible to load balance the output of two armatures while providing both 120 VAC and 240 VAC.
My 96 U320 10Kwatt Powertech has two 120 VAC outputs which are shorted together at the genset, then two hots (red & black) go to the AC power panel. The amps in the red hot and black hot will be different, however the amps (and volts) from each genset output are always identical and are 120 VAC. The output of the genset can easily be converted to 240VAC, however, having 120VAC available at the same time would require a complicated load balancing system.
Note the confusion caused by 30amp and 50 amp designations. A 30 amp shore power plug(three pins) provides 30amps, while a 50 amp shore power plug (four pins) provides 100amps because there are two hot pins at 50amps each.
Confused? Not to worry, this is an often misunderstood concept. Just be aware that 240VAC is seldom available in motorhomes.

I don't know how Foretravel configured the balancing of loads, but my 1981 motorhome came with a 240 volt electric stove along with 110 volt only electric water heater, residential refrigerator and other 110 volt appliances. Never had any problems with the generator after rebuilding the engine that had blown up do to storage issue in 1994. Still works as it is my house back-up incase of earthquake.

Re: ac power question

Reply #6 – August 31, 2016, 05:35:40 pm

I "think" I remember metering two hot terminals at the 50amp female socket in the old '69. I believe that is what prompted me to modify the socket on the side of my house after the main breaker blew in the '79 Travco. I remember having to make a short jumper wire to use inside the socket on the side of the house I was plugged into. It's been a lot of years ago. When I get the kohler going again, I'll double check I could probably look at the wiring but I will use this as a reason to get off my butt and get the generator going again. Thanks, everyone.

Jim

Re: ac power question

Reply #7 – August 31, 2016, 07:34:22 pm

Wyatt explained it all. And there is one more discussion point about neutral wire load. When the gen is jumper-wireed for 120 volts like Wyatt noted, the white neutral wire carries the sum of the red & black amps.

Each wire in the 50-amp cable that runs from generator's junction-box to transfer-switch to the main breaker, is rated at 50 amp. And since the white neutral could be asked to carry 10kw gen's max output of 83-amps, the white wire and the transfer-switch neutral points could be overloaded, overheated and burnt.

When the coach has a 12kw generator, the potential for overloaded components is amplified. And when a transfer switch's points are disadvantaged from wear over time and being transferred under load, they cannot even safely carry their rated loads, and have been known to fail.

These problems are not present with campground 50-amp / 240 volt connections and when a generator is wired for 240 volts.
Campgrounds are known to have some sites with dual 50-amp circuit breakers wired from same single underground leg where the neutral could be loaded with twice its rated capacity triggering problems. In real-life situations, motorhomes with two roof airs seldom have total loads that would overload wires.

Being aware of campground limitations is always a good idea.

Re: ac power question

Reply #8 – August 31, 2016, 08:07:11 pm

Quote from: Barry & Cindy – August 31, 2016, 07:34:22 pm

Wyatt explained it all. And there is one more discussion point about neutral wire load. When the gen is jumper-wireed for 120 volts like Wyatt noted, the white neutral wire carries the sum of the red & black amps.
.

I am not an electrician so I won't try to explain why the neutral never carries more than the hot wires. Something about cycles and the current in the neutral runs back and forth.

Re: ac power question

Reply #9 – August 31, 2016, 10:08:21 pm

IF, repeat IF the two hots are from opposite sides of the box (i.e. 240 between them) then the neutral only carries the DIFFERENCE in load between the two legs.

So, if L1 has a 40 amp load and L2 a 30 amp load, the neutral only carries 10 amps.

If both hots are on the same side of the box (i.e. zero VAC between them) the neutral carries the SUM of the amps. So 40 plus 30= 70.

Re: ac power question

Reply #10 – August 31, 2016, 11:12:59 pm

I found that the neutral contact in the automatic selector switch for the Shore/Genset selection was discoloured, when I purchased my motorhome. This surprised me until I realized that the neutral wire from the genset could easily be overloaded, as explained by Barry. I replaced the automatic selector switches in my coach with 65 amp, hot switchable manual ones.

Re: ac power question

Reply #11 – August 31, 2016, 11:42:14 pm

Craneman's comment about why the neutral never carries more than the hot wires does not apply when generator is commonly wired for 120-volts. It only applies when the generator is wired for 240-volts and when the campground is correctly wired, something that should not be assumed.

Wyatt's finding may be more common than we realize. Where the neutral wire and points of the transfer switch are working, but stressed.

Keep in mind that all would be ok in all situations if we manage our 120-volt loads so we usually have less then 50-amps in total between the two legs. Just because our coaches can run two air conditioners, microwave, electric heating, etc, etc, there are advantages to not running them all at the same time. Managing limited resources is part of the RVing lifestyle.

Re: ac power question

Reply #12 – September 01, 2016, 12:29:14 am

My comment was about the '81 Foretravel that I have that is wired for 240. Reply # 5

Re: ac power question

Reply #13 – December 24, 2016, 03:37:07 pm

Craneman:
When repairing a 240 VAC residential stove in our house, I was surprised to find that the only items which actually used 240 VAC were the broiler and oven elements. Everything else (stove top elements, lights, controller boards) used 120 VAC. This is facilitated for a residential stove by using a stove power cord which has four pins (two hots, one neutral, one ground), which in turn dictates that the wall plug must include a neutral wire. It would be possible to run the broiler and oven elements using two 120 VAC HOTs if the elements have a center tap (to which is connected the neutral wire). I believe that this is how Foretravel wired your coach to accommodate the 240 VAC stove. So, while it appears that your 1981 coach was wired for 240 VAC, it was actually wired for 120 VAC. You could prove or disprove my theory by measuring the VAC between the HOT wires going to the stove with the generator running. I am very interested in knowing how your stove is wired, are you planning on attending the Quartzsite gathering in January?

Re: ac power question

Reply #14 – December 24, 2016, 06:09:12 pm

Quote from: P. Wyatt Sabourin – December 24, 2016, 03:37:07 pm

Craneman:
When repairing a 240 VAC residential stove in our house, I was surprised to find that the only items which actually used 240 VAC were the broiler and oven elements. Everything else (stove top elements, lights, controller boards) used 120 VAC. This is facilitated for a residential stove by using a stove power cord which has four pins (two hots, one neutral, one ground), which in turn dictates that the wall plug must include a neutral wire. It would be possible to run the broiler and oven elements using two 120 VAC HOTs if the elements have a center tap (to which is connected the neutral wire). I believe that this is how Foretravel wired your coach to accommodate the 240 VAC stove. So, while it appears that your 1981 coach was wired for 240 VAC, it was actually wired for 120 VAC. You could prove or disprove my theory by measuring the VAC between the HOT wires going to the stove with the generator running. I am very interested in knowing how your stove is wired, are you planning on attending the Quartzsite gathering in January?

I am planning to make it but in my '99 I will check the voltage in the '81 later. I am fighting a issue with no inverter ac power getting to the refrigerator. cord power passes through. Will be trouble shooting the inverter ATS Foretravel installed. The problem is not the inverter. would the cord power show the same voltage as the generator? seems it should and it is hooked up to shore power at this time.

Re: ac power question

Reply #15 – December 24, 2016, 07:00:00 pm

cman,

You should find that your fridge is wired in through breaker # 3 in your main breaker panel, which OEM was not on the inverter. The icemaker was wired through breaker #1 in your inverter breaker panel (the little one or sub panel). You should find out for sure if you look at your A-2700-03 print. (I don't have an A- 2700 /03 that I can attach)

Your power on the fridge cord/plug should be the same whether on generator or shore.

You should have 2 plugs behind your fridge 1 white and 1 brown or black. One is for inverter and one is for shore/generator.

Pamela & Mike

Re: ac power question

Reply #16 – December 24, 2016, 07:25:25 pm

Quote from: Pamela & Mike – December 24, 2016, 07:00:00 pm

cman,

You should find that your fridge is wired in through breaker # 3 in your main breaker panel, which OEM was not on the inverter. The icemaker was wired through breaker #1 in your inverter breaker panel (the little one or sub panel). You should find out for sure if you look at your A-2700-03 print. (I don't have an A- 2700 /03 that I can attach)

Your power on the fridge cord/plug should be the same whether on generator or shore.

You should have 2 plugs behind your fridge 1 white and 1 brown or black. One is for inverter and one is for shore/generator.

Pamela & Mike

The '81 is unique it came from the factory with a 21 cu. ft. residential refrigerator, a 12.5 kw Yanmar generator, all electric water heater, garbage disposal, Mr Steam sauna 2 Red Hunter diesel fired forced air heaters, 4 ft. skylight and many other one of a kind items. It was intended to go from pedestal to pedestal as it had no inverter in it. When I bought it I added the Trace 4024 inverter and 6 golf cart batteries and only boon docked with it for 18 years. No ATS switch, the generator was hard wired into a junction box receptacle and a cord that you either plugged into the receptacle or shore power. One leg went to half of the motorhome and the other leg to the other half of the coach. It has one large red wire one large black wire and a white common.

Re: ac power question

Reply #17 – December 24, 2016, 07:52:10 pm

Cman,

I thought you were having trouble with your '99 that you were referring to in post #14. The info in post #15 was for your '99 not your '81.

Pamela & Mike

Re: ac power question

Reply #18 – December 24, 2016, 09:16:45 pm

I was replying to reply 13 kinda mixed it up.
The problem on the '99 is in the 2nd ATS I have inverter power going in and not coming out. I haven't posted any thing separately on it until I've exhausted everything I can think of. I have a residential fridge that was in the coach when I bought it and just discovered the issue when I unplugged to check something out.
Thanks for the info

Re: ac power question

Reply #19 – December 24, 2016, 09:48:29 pm

Quote from: craneman – December 24, 2016, 09:16:45 pm

The problem on the '99 is in the 2nd ATS I have inverter power going in and not coming out.

That could be a bad closing coil not pulling down the contacts or bad/burnt contacts(some ATS have replaceable contacts).

Pamela & Mike

Re: ac power question

Reply #20 – December 25, 2016, 11:11:25 am

I can manually push the contactor down and make the connection. I am trying to trouble shoot the activation of the coil at this time.

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