| Author |
Message |
Tony Bare
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 01, 2005 - 3:30 pm: | |
I know that I have seen it somewhere but I can't find it in the search section. Does anyone have a schematic of the box with a 30 amp plug and a 20 amp plug going into a receptical to plug a 50 amp plug into to get 50 amps from an rv shore power post. How do you test this setup to avoid damage or injury? |
niles steckbauer (Niles500)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 01, 2005 - 3:42 pm: | |
http://pplmotorhomes.com/parts/rv-power-cords/rv-electrical-plugs.htm |
Gary Carter
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 01, 2005 - 4:50 pm: | |
I have one. Keep in mind you do not really get a 50 amp service, but you do get 240vac. What you do get is 20 amps on one leg and 30 amps on the second, where a true 50 amp service gives you 50 amps on each leg. |
Geoff (Geoff)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 01, 2005 - 5:16 pm: | |
So what happens if the campground is running the same phase on both outlets and you try to run a true 240v appliance? Another problem I have encountered was when the campground not only used the same phase on the 30 and 20 amp outlets, but they reversed the neutral and hot so when you plugged in the second plug the circuit blew. After the second one happened, I simply put a 50 to 30 amp adapter on my 50 amp shore line and let it go at that (and I don't have any 240 volt appliances).
If you really need to use both campground outlets the safest way to do it is to seperate the circuits so the 30 amp and the 20 amp circuits supply their own circuits, some people have it set up so the second 20 amp cord supplies only a second air conditioning unit while the 30 amp circuits supplies the first air and the rest of the house circuits. |
David Hartley (Drdave)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 01, 2005 - 8:07 pm: | |
Phase... You mean LEG not phase.
50 amp power is all single phase, Two legs to two separate pins. With a Neutral pin.
Or A 30 amp RV plug on one leg and a 20 amp outlet on the other leg.
Across the 50 amp plug Leg-Leg you get 240 volts.
Each Leg to Neutral is 120 volts.
Always Test the plug before plugging into any campground outlet or even one a "Lectrician" made up for you.
Why risk your life on someone else's sloppy work. |
John that newguy
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 01, 2005 - 8:16 pm: | |
(oh-ohhh.... hang on Dave.. youse about to get whooped.)
(hee hee) |
Jim Ashworth (Jimnh)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 01, 2005 - 9:20 pm: | |
Except for the word "phase" instead of "leg", Geoff is right on the money. Dave is absolutely correct in saying "test" before plugging in. I have seen many instances where the hot and neutral were reversed. Some campground maintenance people (and I really have met ones dumb enough) just don't understand "black to black and white to white". How much simpler can it get???
Jim |
akrom
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 01, 2005 - 9:55 pm: | |
yup jonnie, yore rite! cuz' a phase is a phase is a phase, as in 480 three phase, and if you take one away itz 240 single phase (as in 120/240) which ain't like chiken legs or Rosies legs, but most lektrishuns knows what yore talkin 'bout Whilst most other guys think its sumpin' you chase tuh git a little of. (as in: "its saturday nite, how 'bout we go to town an have a drink, an git a little leg?") |
Geoff (Geoff)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 01, 2005 - 10:51 pm: | |
Actually, 240 is two legs of 120 on two phases, but you have to think about it to understand, and people aren't used to thinking about it that way. If you take a 240 circuit and check the wave form on each 120 leg you have two phases. Why so you think the neutral is smaller than the hot leads on 240 cable-- it shares the return. |
Sean Welsh (Sean)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 01, 2005 - 11:13 pm: | |
Umm, in the interests of answering the original question, rather than pursuing this debate...
Tony -- I don't have a ready-made schematic drawn up. But the wiring is pretty simple.
Wire the neutrals for both plugs and the receptacle together. This should be isolated from the case of whatever enclosure you use.
Similarly, wire all the grounds together. If you use a metal enclosure, you should also jumper the enclosure itself to this common ground.
For the hots, to be safe, you will need to add a pair of relays. Get ones with 120vac coils, and load terminals rated for at least 30 amps at 120vac.
For each incoming plug, connect the hot leg to one of the relays, both to one of the load terminals as well as one side of the coil. The other side of the coil goes to the common neutral, and the other load terminal then goes to one of the hot legs of the receptacle.
The purpose of the relay is to ensure that there is no "live hot" dangling around on the end of the plug you have not yet connected.
Bear in mind that this is the poor-man's solution, and it is not foolproof (or code-compliant). If you plug both plugs into hot outlets, and then turn a 240-volt load (if you have any) on inside the coach, and then unplug one of the plugs, voltage back-feeding through the 240-volt appliance will hold the protection relay closed, and you will have 120 volts live on the plug end.
One way to resolve this is to use multiple sets of diode bridges and 120vdc relays tapped in the appropriate places. The other way, and this is how commercial units work, is to build an electronic circuit to monitor both inputs and the output, and only pass current through when everything is connected.
Hope this is enough to get you started.
A quick follow-up here on Geoff's comment -- if you encountered a swapped hot/neutral, that is an extremely hazardous condition, and it was just as well that the breaker tripped. I strongly recommend to everyone that they obtain one of those 3-light testers (about $10 at hardware stores) and check every outlet before plugging in. These testers clearly indicate this condition with a red light.
-Sean |
Sean Welsh (Sean)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 01, 2005 - 11:19 pm: | |
Geoff,
Regarding the "one phase, two phase" debate, yes, it is possible to think of 120/240 split phase (the correct term) as two phases that are 180 degrees "out of phase" -- but the standard in the electric power industry is NOT to use this terminology.
120/240 is considered single phase, with a center-tapped neutral. Specifically, it is universally derived from one and only one of the three true phases available on a three-phase delta source.
There is such a thing as "two phase" power (it's very rare), and in true two-phase systems, the phases are 90 degrees apart (not 180).
So the people jumping all over you about this are correct, insofar as the electric power industry is concerned.
-Sean |
niles steckbauer (Niles500)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 01, 2005 - 11:24 pm: | |
Why build it ? When you can buy it properly assembled for $77.00 ? |
John that newguy
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 12:16 am: | |
akrom-
Well..... Geoff is right about phases, but I've been in Dave's shoes
with this topic, and I'm surprised he hasn't been pile driven into
the archives yet..
You 'lecticions out there have it right, but it's the lingo of
the rv world that defeats your arguments and just confuses
things for the average rv guy (like me) that just wants to go
rving and use all his stuff..
In the RV world, when there were only 30 amp rvs, you could
only run both airs and all your stuff, if you used the genset for
power. When plugged into the power pole, one air conditioner
and some of the system was powered from the shoreline. You
could run the genset to power the other air and the rest, if desired.
So, some of us realizing this, would run a separate power cord
through a switch, to the half of the genset circuit that supplied
the half that wasn't getting connected through the shoreline.
And when we'd plug that cord into a power pole's extra 15 or
20 amp outlet, and along with that RVs 30 amp shoreline, we'd
be able to run everything just as if we were running it all from
our genset. Nice trick.
Now comes the RV manufacturers.... Ahh-HA, they says...
So, what they did, was provide a power cord that could provide
both "halves" of that split 110v RV electrical system, if it were
plugged into an outlet that also could provide this "double power".
Sure, it's 220v, if one were to check across the two hot sides.
Just as the genset put out two 110v "legs", a meter across the
two "hot legs" would indicate 220v.
I own a nice, small Honda 6k genset. It's a 50amp, 110v genset.
It's not a 220v genset. It only provides two legs. One is 20 amp
and the other, 30 amp. And the manual is quite clear, when it
tells the user that it is not a 220v generator.
Moving along........ Many RV parks supply 50 amp service.
Some supply it just as an electrician would claim "codes" call for.
Others supply it as two "legs" of 110v, with the total of amps
supplied as 50amps. That's a 20 and a 30 amp leg. And no, no
180 phase. It's simply two legs of 110v power to the 50 amp
outlet. Some parks use whatever power they have, to those
two supplied legs. It can be two 15 amp legs. And yeah, seen it.
If you call 100 parks and ask if they provide 220v service
at the power pole, I doubt you'll find 10 that say yes. If you
ask if the same ones that say no, if they have 50 amp service
available, most all will say yes. If there has been a 50 amp
outlet installed, they'll claim to be able to provide you with a
stick your 50 amp plug into.
So, that device that Tony would like to build, isn't anything
unusual or dangerous. It's essentially what's already in the
average older RV that has a 50 amp cord sticking out of it.
Two 110v legs in one cable, only with one plug to connect..
(there, Dave. That oughta' take the heat off ya') |
FAST FRED
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 5:29 am: | |
"If there has been a 50 amp
outlet installed, they'll claim to be able to provide you with a
stick your 50 amp plug into. "
Unless the campground is quite new , most simply ADD a 50A socket and wire the old 20A or 30A legs into the new socket.
That way the can list in Woodals et all that they have 50A 240V.
This makes good sense as a REAL 50A 240v setup will deliver more electric than the site costs per night.
The places that DO have "Big Electric" will usually have a METER , so you can pay for the service.
FAST FRED |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 11:15 am: | |
snip "Specifically, it is universally derived from one and only one of the three true phases available on a three-phase delta source."
I was always under the impression that single phase came from any two of the three phases of a delta transformer. These phases are typically identified as Phase A, Phase B or Phase C. In electrical diagrams and on transformers they are many times identified as H1, H2 and H3.
To derive single phase (for example) H1 and H2 of the (generally) high voltage of the three phase distribution system is connected to the two inputs of a step-down transformer (H1 and H4).
The secondary of this transformer would typically have four connections, (X1), (X2), (X3) and (X4). X2 and X3 are connected together and is the Neutral (N) connection of the output.
X-1 and X-4 are the two hot legs providing 120 volts between X1 and N and also 120 volts between X4 and N. These two outputs are 180 degrees out of phase with each other.
The voltage between X1 and X4 is 240 volts, single phase, and these two legs are 180 degrees out of phase with each other. This is really not two phases in electrical terminology. It is typically referred to as two legs.
Phase is typically referred to as any one of the three phases of a three phase distribution or power system. i.e. Phase A, Phase B or Phase C and these phases are 120 degrees out of phase with each other.
The above information was derived from my handy-dandy Electrical Engineering Pocket Handbook (10 pages on transformer connections alone).
BTW, if anyone is interested in obtaining a copy of this handbook, you can contact my daughter Shawna at: shawnap@atlasmarinesystems.com for a copy. 70+ pages of useful information I compiled over a period of time several years ago. Most came from a NEMA booklet but it is several years old and some of the data may not be current with the latest NEC, NFPA and other regulatory bodies. It is provided at no cost
Richard |
Sean Welsh (Sean)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 11:59 am: | |
Richard,
IIRC, on delta sources, each pair of hot wires delivers what is considered one phase (as opposed to wye sources, where each hot wire delivers one phase, WRT neutral, and there is also a phase-to-phase voltage).
120/240 split-phase is derived from a center-tapped neutral mid-point between two of the "phase wires" on one of the three phases.
Voltage from this center-tapped neutral to either hot side of the phase in question will be 120. Phase voltage between any two of the three phase wires will be 240. And voltage from the neutral to the remaining phase wire will be 208. (If I remember my transformer connections correctly.)
So the 120 volt part of the system is one half of one phase, not a separate phase in and of itself.
I think we are essentially saying the same thing, based on your comment: "Phase is typically referred to as any one of the three phases of a three phase distribution or power system. i.e. Phase A, Phase B or Phase C and these phases are 120 degrees out of phase with each other."
-Sean |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 1:32 pm: | |
Sean, see my responses below. I have put your comments in quote marks after your name to distinguish them. I need to learn a little HTML so I could post my response in red. LOL .
Please understand that my responses are in general. There are many exceptions including open delta, Scott connected three phase to two phase, Scott connected two to three phase, grounded leg, auto transformer, buck boost and probably many others. Richard
” Sean: IIRC, on delta sources, each pair of hot wires delivers what is considered one phase (as opposed to wye sources, where each hot wire delivers one phase, WRT neutral, and there is also a phase-to-phase voltage).”
Richard: I think we are saying the same thing. Any two hot leads of a three phase wye or delta system will deliver single phase. One hot lead and the neutral from a three phase wye system will deliver single phase also. Probably better to not even discuss wye systems in this discussion since the phase to phase voltage is 208 volts instead of 240 volts.
”Sean: 120/240 split-phase is derived from a center-tapped neutral mid-point between two of the "phase wires" on one of the three phases. “
Richard: I agree, except leave out the “on one of the three phases”. You can not, in my opinion, derive anything from one phase of a delta system.
” Sean: Voltage from this center-tapped neutral to either hot side of the phase in question will be 120. Phase voltage between any two of the three phase wires will be 240. And voltage from the neutral to the remaining phase wire will be 208. (If I remember my transformer connections correctly.)”
Richard: You are now mixing wye and delta connections and that causes terminology problems. There is no 208 volts in a three phase delta system. There is no neutral in a three phase delta connection.
” Sean: So the 120 volt part of the system is one half of one phase, not a separate phase in and of itself.”
Richard: Almost. One half of the voltage between phase A and phase B. This is not typically available unless a step-down or isolation transformer is installed. There is no center tap available on the distribution system lines.
”Sean: I think we are essentially saying the same thing, based on your comment: "Phase is typically referred to as any one of the three phases of a three phase distribution or power system. i.e. Phase A, Phase B or Phase C and these phases are 120 degrees out of phase with each other."”
Richard: Yes. I believe we are both saying about the same thing. Proper terminology in discussing anything electrical is so important and yet we both get chided sometimes for suggesting corrections to something someone has posted.
Richard |
Geoff (Geoff)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 2:12 pm: | |
Sean answered my question:
120/240 split-phase is derived from a center-tapped neutral mid-point between two of the "phase wires" on one of the three phases.
Thanks, Sean! |
Sean Welsh (Sean)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 2:31 pm: | |
First off, let me apologize to everyone that we have gotten so far off the original question on this thread.
Richard -- I think you and I are in complete agreement, except for this:
You are now mixing wye and delta connections and that causes terminology problems. There is no 208 volts in a three phase delta system. There is no neutral in a three phase delta connection.
Yes, in straight 3-phase delta. However, in 3-phase, 240v delta with 120v (which is derived from a center-tapped tranformer on one phase-phase pair), there is a ground-bonded neutral for the derived 120v system. And, if you happen to measure voltage from this neutral to the third phase, you'll get 208v.
It's difficult since we can't do drawings here on the board, but I found one hunting around on the net, here:
http://www.kilowattclassroom.com/Archive/DELTAWYEPhasors.pdf
The "third leg" is also called the "wild" leg.
As you will see in the drawing, the voltage from the center-tap ground to the wild leg is 1.732*120 or about 208, as I mentioned. Note that this is the voltage measured at that point, I'm not suggesting that it can actually be used for anything :-)
Geoff -- 240 is what you get between two of the hot wires on a three-phase, 240v delta system. If you go to the diagram above, you will see that the 120 volts is derived by center-tapping on the distribution side on one (and only one) of the hot pairs.
The waveforms, if you look at them with a scope, on both the 120 volt sides will appear to be 180 degrees "out of phase" with each other, so, yes, you can think of it as two 180-degree phases. However, they are really just mirror images, because they are two sides of the same winding on the transformer. The power industry considers them two halves of the same phase.
When you say "two of the three phases 180 degrees apart" you are confusing looking at them with respect to the center-tapped neutral versus looking at them with respect to each other, where you will find that they are, indeed, 120 degrees apart.
-Sean |
Sean Welsh (Sean)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 2:55 pm: | |
Geoff,
Am I losing my marbles, or did you edit your last post in the time it took me to quote it, above?
-Sean |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 3:15 pm: | |
Sean, we are now in complete agreement with your statement above "one (and only one) of the hot “pairs”." Pairs is the qualifier that identifies that single phase is derived from any two legs of the three phase distribution system.
You are absolutely correct when you mention wild leg and I purposely avoided that to try and keep the discussion as simple as possible. The grounding of one phase leg is typically done at the customer facility on the secondary of the distribution transformer. I do not believe it could be done on the distribution side. I have never worked on anything like this so my knowledge is limited by what I have read or heard. I would assume that you could place a center tap neutral/ground connection between, for instance, phase A and phase B and obtain 240/120 single phase power. However you could not then also place a neutral/ground connection between phase A and C or between B and C. To do so would create a short circuit between either of these and the tap between A and B.
Richard |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 3:31 pm: | |
snip "120/240 split-phase is derived from a center-tapped neutral mid-point between two of the "phase wires" on one of the three phases."
Geoff, Sean and I have agreed that a little more properly put would be "mid point between two of the "phase wires" or between any two of the three phases".
Specifically that the neutral must be taken from between phase A and B, A and C or B and C.
Richard |
T. (Bluegrass)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 4:33 pm: | |
"Three Phase Transformer Info"
I did a search at Google on 3 phase Delta system and Its all here.
http://www.elec-toolbox.com/usefulinfo/xfmr-3ph.htm |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 7:40 pm: | |
That is an excellent site with some very good drawings. Unfortunately it does not discuss the problems or provide a drawing to illustrate how 240/120 volts single phase power is derived from a 240 volt three phase system.
Richard |
Jtng
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 7:57 pm: | |
How's yer head doin', Tony? |
Chuck Newman (Chuck_newman)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 02, 2005 - 8:11 pm: | |
Hi Tony,
I reversed engineered the "Y connector" and made a simple schematic, but it won't change anything mentioned here. As many here have stated, it is a device with good intention, but may or may not work for the reasons described above regarding some parks with poor wiring.
But even if the park wiring IS correct, it won't work with a ground fault receptacle in the 15/20 amp circuit. If you're really interested, email me and I'll send both diagrams. The second drawing shows why the GFR will trip.
Camping World and other retailers sell this as a
"50 Amp RV Adapter" for 79.99. The ad also states "will not work if campground has GFI circuit breakers". An obvious red flag.
As John or someone said, the most reliable setup is a totally separate input to the bus that plugs into the 15/20 receptacle. I've designed my system so one A/C and all other loads will run from the 30 amp receptacle, minus the rear A/C and washer/dryer. Either the rear A/C or the W/D will run on the 15/20 receptacle -- but not both at the same time.
If I want to run two A/C's, and W/D, and microwave and coffee pot at the same time, I have two choices:
1) A true 240 vac 50 amp outlet (12,000 watts).
2. Run the generator.
Chuck Newman
Oroville, CA |
FAST FRED
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, June 03, 2005 - 5:23 am: | |
"2. Run the generator. "
Any diecent park does NOT allow noisemakers at any time.
So if you need a noisemaker to exist ,
you will be 'Camping" at the highly scenic Flying J.
Not MY WAY!!!, but enjoy ,
FAST FRED |
Chuck Newman (Chuck_newman)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, June 03, 2005 - 11:12 am: | |
Fred,
You're right. And I LOVE the smell of diesel in the morning.
Chuck Newman |
T. (Bluegrass)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, June 03, 2005 - 9:27 pm: | |
Mine Is doing OK but I can tell that your haveing a problem with yours.
Tony |
John that newguy
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, June 03, 2005 - 10:29 pm: | |
Tony-
Nuttin' wrong with my noggin', Tony, not yours, either..
I just wondered if you got a headache reading through
this deluge of information, after asking a simple question.
Sean's explanation of the wiring inside that box will get you
through the night. I'd personally leave out the relays, since
the commercial version of this adapter does not use them.
Just don't run any 220 appliances if you don't have the true
version of a 50 amp supply at the power pole.
Let's face it.... If you're like me, and stay at parks where such
a contraption is needed, you'd better be prepared to test voltages
and grounding at the power pole before you use attempt
to plug in. Buy one of those voltage sensors that detect AC with
a simple touch of the probe:
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=03482174000 &tab=spe
And use it to check the power box shell for voltage before
you touch it. Then use a meter, or plug-in tester, to test for
proper voltage and ground on the proper pins.
I'm still hunting for schematics... |
|