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Old 10-30-2019, 01:08 PM   #1
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Isolation Transformer shorted out?

Help!
Yesterday the circuit breaker on the dock popped. Through a process of elimination, it appears the Charles Industries isolation transformer is the cause.
This has been in the system, working fine for over ten years. There are no moving parts. Has anyone heard of these shorting out?
Still waiting for Charles Ind. to respond...
Thx.
Duncan
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Old 10-30-2019, 01:14 PM   #2
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Ground fault or actual overcurrent?
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Old 10-30-2019, 01:20 PM   #3
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Ground fault, not inrush. I disconnected the output leads and it still pops immediately. When I initially disconnected the input leads, everything was fine, so it’s not the cord, plug or faulty circuit breaker.
(Old school shorepower, no GFI)
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Old 10-30-2019, 01:44 PM   #4
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I had a Westinghouse or a GE isolation transformer (forgotten) and it gave up the ghost after about 15 years. I think its partly because we tend to spec the smallest we can get away with (cheaper) instead of a larger unit and then heat becomes the issue.
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Old 10-30-2019, 01:56 PM   #5
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Yes, likely an insulation failure. The best diagnostic instrument is the Fluke 1503, which I have 6 feet away. But, with no output connected, and it trips out a 30 or 50 Amp breaker, I think that is all the real test you need. It's bad....
Most of the intrinsic value is copper, not iron, so rewinding is likely not a consideration.
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Old 10-30-2019, 01:56 PM   #6
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Thanks Xsbank,
I don’t think it was overloaded. It’s a robust (235 lb.) unit rated for 50Amps. I remember it getting lukewarm at most. I’m curious how yours failed....did it short out or ?
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Old 10-30-2019, 02:03 PM   #7
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I'd check the incoming ground wire and connections. It should be connected to the internal shield of the isolation transformer (not the output ground of the transformer). Measure resistance of the incoming ground to the incoming power wires (with shore power disconnected of course). If the short is truly internal to the transformer, it would need to be replaced.
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Old 10-30-2019, 02:12 PM   #8
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Quote:
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Yes, likely an insulation failure. The best diagnostic instrument is the Fluke 1503, which I have 6 feet away. But, with no output connected, and it trips out a 30 or 50 Amp breaker, I think that is all the real test you need. It's bad....
Most of the intrinsic value is copper, not iron, so rewinding is likely not a consideration.
Thanks Diver Dave,
Iím still in the grieving process here. I just started shopping for a replacement 😳
Iíve had drug habits cheaper than this!
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Old 10-30-2019, 03:30 PM   #9
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Thanks Diver Dave,
Iím still in the grieving process here. I just started shopping for a replacement 😳
Iíve had drug habits cheaper than this!
Try calling Charles, if you havenít already, to see if they can suggest a cause. I was told by an ABYC electrician who installed many of these units that they donít often fail but a replaceable circuit board is often the cause when they do. Please post what you learn.
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Old 10-30-2019, 05:26 PM   #10
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Angus99,
I just got off the phone with a great guy in customer support. After my description, it sounds dead to him. He said a bench test with a “variac “ (sp)
could confirm it but doesn’t look good.
BTW: this is an older unit with no circuit board, basically just a big copper coil.
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Old 10-30-2019, 08:50 PM   #11
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I sold Charles isolation transformers for over 10 years. I stopped selling it a few years ago because of too many warranty issues and news that Charles is discontinuing production soon.

The transformer is held in the case with a rubber like potting material, no fasteners. The potting material does not go all the way down to the bottom. There is a 2 or 3 inch space at the bottom. Heat causes the potting material to come loose from the case and the transformer drops sometimes breaking wires.

Also had issues with the transformer quitting shortly after installation and received a few with low output voltage.

I now sell the Victron Energy isolation transformers. They don't have a 50 amp unit yet but the 30 amp manual transformer is less than $700
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Old 10-30-2019, 09:06 PM   #12
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I sold Charles isolation transformers for over 10 years. I stopped selling it a few years ago because of too many warranty issues and news that Charles is discontinuing production soon.

The transformer is held in the case with a rubber like potting material, no fasteners. The potting material does not go all the way down to the bottom. There is a 2 or 3 inch space at the bottom. Heat causes the potting material to come loose from the case and the transformer drops sometimes breaking wires.

Also had issues with the transformer quitting shortly after installation and received a few with low output voltage.

I now sell the Victron Energy isolation transformers. They don't have a 50 amp unit yet but the 30 amp manual transformer is less than $700
Thanks syjos,
Iím not sure what is going on. Charles support told me there is usually scorched electrical smell. I have none of that and this afternoon I bypassed the unit and shorepower is driving my inverter crazy. My shorepower is 240v but the wiring is suspect. Tomorrow I research that 🤞 That would be the cheapest cure.
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Old 10-30-2019, 10:15 PM   #13
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50 amps isn’t really very much - a heater or two, a/c, hot water tank, lighting, battery charger? It adds up pretty fast. If you add too much load the voltage drops and it starts to heat up, then the resistance rises...

When you are on your boat, all snug in the warmth, tied up at the dock, stick your volt meter in any 120 volt outlet and read the voltage. Anything below the voltage at the dock pedestal and you are overloaded. Unplug something.
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Old 10-30-2019, 10:50 PM   #14
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Acme Transformer General Purpose Encapsulated 15KVa, multi voltage in, 120/240 out, price about $1000 US. As good as any you'll get. Sorry the model# isn't handy, find it easy enough...
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Old 10-31-2019, 08:31 AM   #15
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Acme Transformer General Purpose Encapsulated 15KVa, multi voltage in, 120/240 out, price about $1000 US. As good as any you'll get. Sorry the model# isn't handy, find it easy enough...

And they now have models with the proper dual/isolated grounding for marine use. And don't be scared by the "Acme" name. It's quality stuff, not roadrunner junk, and now part of Hubbell.
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Old 10-31-2019, 11:17 AM   #16
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And they now have models with the proper dual/isolated grounding for marine use. And don't be scared by the "Acme" name. It's quality stuff, not roadrunner junk, and now part of Hubbell.
I had an Acme isolation transformer on the previous boat and it worked without issue for 14 years.

They need to be mounted on top of a rubber pad to isolate hum.
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Old 10-31-2019, 12:05 PM   #17
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Thanks syjos,
Iím not sure what is going on. Charles support told me there is usually scorched electrical smell. I have none of that and this afternoon I bypassed the unit and shorepower is driving my inverter crazy. My shorepower is 240v but the wiring is suspect. Tomorrow I research that �� That would be the cheapest cure.
I'd recommend you sort out why you're having dock power and inverter issues with IT bypassed. On most vessels, an onboard IT should ideally be in place to deal with dock wiring issues not boat wiring. Are the docks you're plugged into the new marina code GFIC setups?
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Old 10-31-2019, 01:02 PM   #18
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A failed transformer may not have smell or visual indications. In bypassing your transformer you have likely left the Neutral floating - the incoming N is not used with the transformer and would have to be wired.

These encapsulated models from Acme have been shielded (a ground wire comes out from the windings, isolated from the case) for as long as I've put them in- some 25 years.

Here is a connection diagram, from Canada's Ships' Electrical Standards for Inspected Vessels:
Attached Files
File Type: pdf Transformer wiring.pdf (61.4 KB, 41 views)
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Old 10-31-2019, 01:57 PM   #19
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...

Here is a connection diagram, from Canada's Ships' Electrical Standards for Inspected Vessels:
Hopefully, those transformers never have a primary to shell short!
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Old 10-31-2019, 03:58 PM   #20
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The Canadian Standard referenced in #18 is not in accordance with ABYC E-11.
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