Home » Public Forums » GMCnet » Installing a current transformer in a 30/50 amp system
| Installing a current transformer in a 30/50 amp system [message #237865] |
Tue, 28 January 2014 20:20  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Ok Ken, Ken or other.
I am not a EE, but I have been involved in all sorts of things that exist on ships and elsewhere. I was following Rob's thread and thinking that might be handy at the price of the unit that KenH picked.
Problem:
Our stock coaches are wired as 3-wire 240 for 50 (40) Amp. I started out thinking of a trick I did a long time a go where to measure both sides of a 3-wire supply and get the sum of the two, I put the feed lines through the current transformer in opposite directions. This did give us the sum of current going into two 120 heaters.
I was thinking (dangerous, I know) that the same trick could work for us.....
But - - On the APU or most campgrounds we are just 2-wire 120 for 30 Amp.
Then I turned the thinking to the 30 Amp case. OOPS......
If I am not mistaken, it would always read Zero.....
Now, I have never had an AC supply overload issue, so this may be a complete waste of personal processor time. But does anybody have an idea how to get one CT and display to do anything worthwhile in our case.
The only answer I see is buy two (2) and mentally add the numbers for 30 or watch for 50 maximum whichever is appropriate at that time.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Installing a current transformer in a 30/50 amp system [message #237881 is a reply to message #237865] |
Tue, 28 January 2014 21:39  |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Guys,
Click on the link below and let me know if I'm correct.
http://www.gmcmhphotos.com/photos/showfull.php?photo=52716
Regards,
Rob M.
Sydney, Australia
-----Original Message-----
From: Matt Colie
Ok Ken, Ken or other.
I am not a EE, but I have been involved in all sorts of things that exist on ships and elsewhere. I was following Rob's thread and
thinking that might be handy at the price of the unit that KenH picked.
Problem:
Our stock coaches are wired as 3-wire 240 for 50 (40) Amp. I started out thinking of a trick I did a long time a go where to
measure both sides of a 3-wire supply and get the sum of the two, I put the feed lines through the current transformer in opposite
directions. This did give us the sum of current going into two 120 heaters.
I was thinking (dangerous, I know) that the same trick could work for us.....
But - - On the APU or most campgrounds we are just 2-wire 120 for 30 Amp.
Then I turned the thinking to the 30 Amp case. OOPS......
If I am not mistaken, it would always read Zero.....
Now, I have never had an AC supply overload issue, so this may be a complete waste of personal processor time. But does anybody
have an idea how to get one CT and display to do anything worthwhile in our case.
The only answer I see is buy two (2) and mentally add the numbers for 30 or watch for 50 maximum whichever is appropriate at that
time.
Matt
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Installing a current transformer in a 30/50 amp system [message #237887 is a reply to message #237881] |
Tue, 28 January 2014 22:35 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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OK Rob,
I clicked on your wiring diagram.
I even looked at it up side down.
It was the same thing just a little harder to read.
I then asked Smokey 2 to look at it and his response was "o9iiiiiiiiiiiiii9"
"Correct" about what?
It is a bad night here because I also do not understand what Matt is up to in his posting.
I think I'll take up drinking. Maybe that will help.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Installing a current transformer in a 30/50 amp system [message #237894 is a reply to message #237865] |
Tue, 28 January 2014 23:09 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Matt,
I'm afraid, at this late hour, that you're right: I spoke before engaging
brain. Having a 30A coach, I didn't even consider the more common 50A
arrangement.
To make things worse, I momentarily thought, "just run both hots through
the donut." While that should work in the case you mention, where the
campground is wired as 2 x 120 vac, you're right that the wires need to run
through in opposite directions for a "properly wired" circuit -- at least
that's what I THINK right now. :-)
Off hand, the only solution I think of is a DPDT relay wired between the
two hots. A properly wired circuit would activate the relay and route one
wire through the transformer "backward". A 2 x 120 vac circuit would not
close the relay, leaving the two wires routed the same.
Needs more coherent thought -- and probably a bench test.
Yes, Rob, your red circle is where we're talking about inserting the
transformer.
Ken H.
On Tue, Jan 28, 2014 at 9:20 PM, Matt Colie wrote:
>
>
> Ok Ken, Ken or other.
>
> I am not a EE, but I have been involved in all sorts of things that exist
> on ships and elsewhere. I was following Rob's thread and thinking that
> might be handy at the price of the unit that KenH picked.
>
> Problem:
>
> Our stock coaches are wired as 3-wire 240 for 50 (40) Amp. I started out
> thinking of a trick I did a long time a go where to measure both sides of a
> 3-wire supply and get the sum of the two, I put the feed lines through the
> current transformer in opposite directions. This did give us the sum of
> current going into two 120 heaters.
> I was thinking (dangerous, I know) that the same trick could work for
> us.....
> But - - On the APU or most campgrounds we are just 2-wire 120 for 30 Amp.
>
> Then I turned the thinking to the 30 Amp case. OOPS......
> If I am not mistaken, it would always read Zero.....
>
> Now, I have never had an AC supply overload issue, so this may be a
> complete waste of personal processor time. But does anybody have an idea
> how to get one CT and display to do anything worthwhile in our case.
>
> The only answer I see is buy two (2) and mentally add the numbers for 30
> or watch for 50 maximum whichever is appropriate at that time.
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: Installing a current transformer in a 30/50 amp system [message #237896 is a reply to message #237865] |
Tue, 28 January 2014 23:48 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I'm reading what you want to do and trying to match it to our three power situations your trying to read.
1. 240 VAC shore power.
2. 120 VAC Onan
3. 120 VAC shore power
In the case if item #1 If you run both leads through the pickup transformer with one reversed it should read double the actual current (I think). I'm not sure how this thing will determine the voltage. It might also be doubled. Also the frequency may be cancelled? But I think not.
My head is swimming over this one.
I'm thinking why not just get two an then try it with one.
If it does not work as planned, put two separate pickups in and switch between the two depending on 120 or 240 volt feed. The 120 volts pickup could be placed on the neutral feed rather than the hot leads. A small 240 volt AC relay could be used to automate the switching. You only have two states of power feeding across the two mains. 240 volts (power out of phase) or 0 volts (power in phase or no power applied). Switch pickups (current transformers) based on those two states.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Installing a current transformer in a 30/50 amp system [message #237900 is a reply to message #237894] |
Wed, 29 January 2014 00:29 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Ken,
Let's let Ken have a couple of drinks that way he'll be able to "see" the red circle on my photo and understand what Matt's saying!
If not maybe his new kitty (Smokey 2) can explain it to him! ;-)
Reference: http://www.gmcmhphotos.com/photos/showfull.php?photo=52716
What if I buy two (2) current transformers and run the black wire from the power cable through one of them and the red lead from the
power cable to the other one.
I could wire the meter to the center poles of a double pole double throw switch and the current transformers to the outside
connections. I could switch back and forth to read the amps on both wires. I would have to add them up in my head for a total but
that would be fairly easy and if I can't my Samsung Galaxy phone has a built in calculator.
Regards,
Rob M.
-----Original Message-----
From: Ken Henderson
Matt,
I'm afraid, at this late hour, that you're right: I spoke before engaging brain. Having a 30A coach, I didn't even consider the
more common 50A arrangement.
To make things worse, I momentarily thought, "just run both hots through the donut." While that should work in the case you
mention, where the campground is wired as 2 x 120 vac, you're right that the wires need to run through in opposite directions for a
"properly wired" circuit -- at least that's what I THINK right now. :-)
Off hand, the only solution I think of is a DPDT relay wired between the two hots. A properly wired circuit would activate the
relay and route one wire through the transformer "backward". A 2 x 120 vac circuit would not close the relay, leaving the two wires
routed the same.
Needs more coherent thought -- and probably a bench test.
Yes, Rob, your red circle is where we're talking about inserting the transformer.
Ken H.
-----Original Message-----
From: Ken Burton
OK Rob,
I clicked on your wiring diagram.
I even looked at it up side down.
It was the same thing just a little harder to read.
I then asked Smokey 2 to look at it and his response was "o9iiiiiiiiiiiiii9"
"Correct" about what?
It is a bad night here because I also do not understand what Matt is up to in his posting.
I think I'll take up drinking. Maybe that will help.
--
Ken
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Installing a current transformer in a 30/50 amp system [message #237901 is a reply to message #237900] |
Wed, 29 January 2014 00:34 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Am I blind or what. I see a wiring diagram and NO RED CIRCLE. Smokey 2 went to sleep so I did not have him look.
Ken
| USAussie wrote on Wed, 29 January 2014 00:29 |
Ken,
Let's let Ken have a couple of drinks that way he'll be able to "see" the red circle on my photo and understand what Matt's saying!
If not maybe his new kitty (Smokey 2) can explain it to him! 
Reference: http://www.gmcmhphotos.com/photos/showfull.php?photo=52716
What if I buy two (2) current transformers and run the black wire from the power cable through one of them and the red lead from the
power cable to the other one.
I could wire the meter to the center poles of a double pole double throw switch and the current transformers to the outside
connections. I could switch back and forth to read the amps on both wires. I would have to add them up in my head for a total but
that would be fairly easy and if I can't my Samsung Galaxy phone has a built in calculator.
Regards,
Rob M.
-----Original Message-----
From: Ken Henderson
Matt,
I'm afraid, at this late hour, that you're right: I spoke before engaging brain. Having a 30A coach, I didn't even consider the
more common 50A arrangement.
To make things worse, I momentarily thought, "just run both hots through the donut." While that should work in the case you
mention, where the campground is wired as 2 x 120 vac, you're right that the wires need to run through in opposite directions for a
"properly wired" circuit -- at least that's what I THINK right now. 
Off hand, the only solution I think of is a DPDT relay wired between the two hots. A properly wired circuit would activate the
relay and route one wire through the transformer "backward". A 2 x 120 vac circuit would not close the relay, leaving the two wires
routed the same.
Needs more coherent thought -- and probably a bench test.
Yes, Rob, your red circle is where we're talking about inserting the transformer.
Ken H.
-----Original Message-----
From: Ken Burton
OK Rob,
I clicked on your wiring diagram.
I even looked at it up side down.
It was the same thing just a little harder to read.
I then asked Smokey 2 to look at it and his response was "o9iiiiiiiiiiiiii9"
"Correct" about what?
It is a bad night here because I also do not understand what Matt is up to in his posting.
I think I'll take up drinking. Maybe that will help.
--
Ken
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GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Installing a current transformer in a 30/50 amp system [message #237911 is a reply to message #237865] |
Wed, 29 January 2014 06:29 |
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SeanKidd
Messages: 747
Registered: June 2012
Location: Northern Neck Virginia
Karma: 4
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Senior Member |
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The issue to overcome is, with 240V shore power, the two hot legs will have opposing current flow, during onan an 120V x2 operation, the current flow in the two hot legs are cumulative.
The red circle on your diagram is the handle tied breaker...2 single poles acting as a 2 pole.
If you add a ct to the onan circuit, just before the breaker on the drawer, and one on the red/black with the red entering ct in opposite direction.
The leads from the ct to the meter would then need to be switched, using a DPDT toggle as someone mentioned. Actual both ct could be adjacent to each other...
One with both leads entering same direction (120x2) and one with one hot leg from either direction (240)
Sean and Stephanie
73 Ex-CanyonLands 26' #317 "Oliver"
Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD Honda 6500 inverter gen.
Colonial Travelers
[Updated on: Wed, 29 January 2014 06:40] Report message to a moderator |
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| Re: Installing a current transformer in a 30/50 amp system [message #237945 is a reply to message #237911] |
Wed, 29 January 2014 10:15 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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| SeanKidd wrote on Wed, 29 January 2014 07:29 |
The issue to overcome is, with 240V shore power, the two hot legs will have opposing current flow, during onan an 120V x2 operation, the current flow in the two hot legs are cumulative.
The red circle on your diagram is the handle tied breaker...2 single poles acting as a 2 pole.
If you add a ct to the onan circuit, just before the breaker on the drawer, and one on the red/black with the red entering ct in opposite direction.
The leads from the ct to the meter would then need to be switched, using a DPDT toggle as someone mentioned. Actual both ct could be adjacent to each other...
One with both leads entering same direction (120x2) and one with one hot leg from either direction (240)
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Now there you go Sean....
One instrument, two CTs and a DPDT switch.
Would it even need to be DPDT?
Wouldn't just selecting one lead of the either CT do it and leave the other two common?
Put that one away in the note book. I've already spent this years new project money. But it can wait.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Installing a current transformer in a 30/50 amp system [message #237948 is a reply to message #237945] |
Wed, 29 January 2014 10:37 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Matt Colie wrote on Wed, 29 January 2014 10:15 |
| SeanKidd wrote on Wed, 29 January 2014 07:29 |
The issue to overcome is, with 240V shore power, the two hot legs will have opposing current flow, during onan an 120V x2 operation, the current flow in the two hot legs are cumulative.
The red circle on your diagram is the handle tied breaker...2 single poles acting as a 2 pole.
If you add a ct to the onan circuit, just before the breaker on the drawer, and one on the red/black with the red entering ct in opposite direction.
The leads from the ct to the meter would then need to be switched, using a DPDT toggle as someone mentioned. Actual both ct could be adjacent to each other...
One with both leads entering same direction (120x2) and one with one hot leg from either direction (240)
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Now there you go Sean....
One instrument, two CTs and a DPDT switch.
Would it even need to be DPDT?
Wouldn't just selecting one lead of the either CT do it and leave the other two common?
Put that one away in the note book. I've already spent this years new project money. But it can wait.
Matt
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Do it with a relay and make it automatic as I suggested in my posting.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Installing a current transformer in a 30/50 amp system [message #237974 is a reply to message #237948] |
Wed, 29 January 2014 15:48 |
cadelec
Messages: 303
Registered: September 2011
Location: Brisbane Australia
Karma: 1
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Can some one please bring me up to speed on how your 220 volt system works
i assume that there is
110 volts between black and white
110 volts between Red and White
are these two voltages 180 degrees out of phase
or are they in phase
Trevor
Brisbane Australia
Siesta Koala 76 Edgemont (old Bobby Moores)
71 Cadillac Eldo Convert
58 Cadillac Eldorado Brougham Project
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| Re: [GMCnet] Installing a current transformer in a 30/50 amp system [message #237983 is a reply to message #237974] |
Wed, 29 January 2014 16:24 |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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Our (USA and North America) system uses a center-tapped distribution winding of a nominal 240 - 250 Volts. Each side is provided in the "house" at 120 - 125 Volts. The 240 V primary is one single phase. However, at any peak instant, one side will be 120V positive with respect to neutral and the other side will be negative with respect to neutral. In other words, both lines are in phase with each other, but opposite in polarity to neutral. MOST GMCs that came with the 120-0-120 wiring can be run equally well from the 120V output of the Onan OR the split system that is 240V across both lines. That is how I power my coach here at the house. You can also (with an adapter) power from a 120V/30A cord as long as you don't exceed the 30A power draw.
I suggest you seriously consider using 220 V / 50 Hz for your coach where practical/affordable. Existing wiring will work fine as long as you follow color code standards for Line/Neutral/Safety ground.
Some items will run okay using a "conversion" transformer such as those Rob Mueller is using. Motor devices designed for 60 Hz operation will likely run hot on a 50 Hz supply. As Rob has said, you need to run such motors on 100 - 105 V maximum for safety and continued life.
Change out your "converter" (power supply/charger) to Aussie standards. Replace clocks. Replace air conditioners with 50 Hz units when the 60 Hz units die. Clocks will run slow, etc.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~~ k2gkk @ hotmail dot com ~~
~ ~ USAF and FAA, Retired ~ ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
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~~ k2gkk + hotmail dot com ~~
~ www.gmcmhphotos.com/okclb ~
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*--OO--[]---O-*
> To: gmclist@temp.gmcnet.org
> From: trevor@cadelec.com.au
> Date: Wed, 29 Jan 2014 15:48:38 -0600
> Subject: Re: [GMCnet] Installing a current transformer in a 30/50 amp system
>
>
>
> Can some one please bring me up to speed on how your 220 volt system works
> i assume that there is
> 110 volts between black and white
> 110 volts between Red and White
> are these two voltages 180 degrees out of phase
> or are they in phase
>
> --
> Trevor
> Brisbane Australia
> Siesta Koala 76 Edgemont (old Bobby Moores)
> 71 Cadillac Eldo Convert
> 58 Cadillac Eldorado Brougham Project
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| Re: [GMCnet] Installing a current transformer in a 30/50 amp system [message #238008 is a reply to message #237983] |
Wed, 29 January 2014 19:12 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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| k2gkk wrote on Wed, 29 January 2014 16:24 |
...As Rob has said, you need to run such motors on 100 - 105 V maximum for safety and continued life. ...
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I have to disagree with that, especially as it applies to motors. A motor in an appliance, such as a refrigerator (other than the swint motors in the old Norcold dual voltage refrigerators), has to apply a fixed amount of power to do its job. Elecrically, power = voltage X current. Reduce the voltage, and the current goes up to achieve the same amount of power output. More current means more internal heat in the windings.
If you have a 120V/60Hz appliance, apply 120V/50Hz to it and hope for the best. The biggest problem with them is that the same slower rotation that runs the device also turns the fan it uses to cool itself, so it runs hotter. Also, the lower the frequency, the less efficient the transformer. So 50Hz stuff is inherently less efficient, and pulls more current. Those two factors are what make 60Hz stuff vulnerable running at 50Hz.
Any practicing EEs want to disputer any of that, please do so. It has been more than 30 years since college, and I made a living doing communications stuff instead of power stuff.
Also, I lived 9 years in places with 220V/50Hz power, and ran a lot of 120V/60Hz stuff on tansformers. I was never anyplace with 220V/50Hz power for more than 3 years at a stretch, but I never had any 120V/60Hz stuff die on 50Hz power. Vacuum cleaners always sucked worse than on 60Hz (literally), but I never ran one enough to burn it up.
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| Re: Installing a current transformer in a 30/50 amp system [message #238024 is a reply to message #238015] |
Wed, 29 January 2014 20:04 |
cadelec
Messages: 303
Registered: September 2011
Location: Brisbane Australia
Karma: 1
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Senior Member |
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My brain is turning but i don't trust it some times . so here is a quick think of measuring current in both situations shore and generator using 1 current transformer
please pick it to pieces
this should measure the combined current in each phase when running on shore power
and the current thru the Neutral leg when running on generator
Link to CT placement
Trevor
Brisbane Australia
Siesta Koala 76 Edgemont (old Bobby Moores)
71 Cadillac Eldo Convert
58 Cadillac Eldorado Brougham Project
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