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Old 19-06-2012, 10:10   #31
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Re: Isolation transformer problem

Unless this is a relay with built-in delay mechanism, I don't believe the delay is enough for building up the magnetic field on the Charles transformer. I used to have an old one and the sound of the inrush surge was very clear and lasted about a second at least I think.

I agree to test for a leak to ground by disconnecting the shore ground conductor. Just make sure everything is disconnected from power when making the change (use multimeter to make sure) and keep hands clear from any metal parts when activating the shore breaker.

I would be surprised when a leak to ground appears while it doesn't show up on DC resistance test but I've learned anything is possible

cheers,
Nick.
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Old 19-06-2012, 12:49   #32
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Re: Isolation transformer problem

My meter is a Fluke i410 that pairs with my Fluke Model 88V DMM. I don't see anything in the literature that says it has inrush current capability. I think I soon have to seek out an electrician.
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Old 19-06-2012, 12:52   #33
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Re: Isolation transformer problem

s/v Jedi. I have been wondering the same about the delay time for the relay. Charles folks say the delay time needed is 20ms or so, equivalent to cycle time (not sure I know what that means exactly). But they indicated to me that this softstart is suitable for use with their transformer. Of course my experience so far says it is not so suitable.
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Old 19-06-2012, 14:52   #34
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Re: Isolation transformer problem

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Originally Posted by donpjr View Post
s/v Jedi. I have been wondering the same about the delay time for the relay. Charles folks say the delay time needed is 20ms or so, equivalent to cycle time (not sure I know what that means exactly). But they indicated to me that this softstart is suitable for use with their transformer. Of course my experience so far says it is not so suitable.
Disconnect the secondary connection (output) from the transformer and try again. A load on the secondary might make a difference.

That said, my Victron uses 3 relays: first one energizes transformer with series resistor, then a couple of seconds later I hear the 2nd relay shorting the resistor and seconds after that the 3rd relay switching power to the output terminals after measurements show it has stabilized.

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Old 19-06-2012, 16:35   #35
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Re: Isolation transformer problem

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Originally Posted by s/v Jedi View Post
Unless this is a relay with built-in delay mechanism, I don't believe the delay is enough for building up the magnetic field on the Charles transformer. I used to have an old one and the sound of the inrush surge was very clear and lasted about a second at least I think.
Nick,

No argument that a transformer specific delay is ideal, as the unique transformer characteristics dictate how long in-rush current will last.

So the generic soft start theory is to clamp the first couple cycles of current (which are exponentially the highest) to an acceptable rate. From that point on, the hope is the in-rush is an acceptable value.

As you know, a 25W resistor isn't going to handle very many seconds of 3kW of in-rush.

FWIW, my 6250va torroid pulls <30a in-rush @240v. Not a problem since I have it on a 50a 240v shore power. (Yes, I have the primary winding protected to less than 50a)
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Old 19-06-2012, 20:36   #36
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Originally Posted by DotDun

Nick,

No argument that a transformer specific delay is ideal, as the unique transformer characteristics dictate how long in-rush current will last.

So the generic soft start theory is to clamp the first couple cycles of current (which are exponentially the highest) to an acceptable rate. From that point on, the hope is the in-rush is an acceptable value.

As you know, a 25W resistor isn't going to handle very many seconds of 3kW of in-rush.

FWIW, my 6250va torroid pulls <30a in-rush @240v. Not a problem since I have it on a 50a 240v shore power. (Yes, I have the primary winding protected to less than 50a)
This is why you need multiple relays. The transformer output mst be disconnected until the magnetic field is build up and stable. Only then the transformer output should be connected to the load.

If done like that, you do not have any other load through the resistor than needed for the build-up of the field plus internal loss.

cheers,
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Old 24-06-2012, 11:07   #37
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Re: Isolation transformer problem

Hello again and thanks to everyone for the help and advice. After several consultations with Charles Industries, today I did some tests that confirmed the transformer was wired incorrectly at the factory. By reversing two wires on one of the input coils I was able to correct the problem and now the unit is working. Thanks again. DON
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Old 24-06-2012, 12:45   #38
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Re: Isolation Transformer Problem

Great!

I hope you expressed frustration with Charles and the installer for never testing the unit prior to or after installation.

I'm glad it's working!
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Old 24-06-2012, 14:14   #39
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Quote:
Originally Posted by donpjr
Hello again and thanks to everyone for the help and advice. After several consultations with Charles Industries, today I did some tests that confirmed the transformer was wired incorrectly at the factory. By reversing two wires on one of the input coils I was able to correct the problem and now the unit is working. Thanks again. DON
Oh.... the windings were in parallel instead of series?

cheers,
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Old 24-06-2012, 14:52   #40
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Re: Isolation Transformer Problem

You can bet I will be letting my frustration be known to them. Poor quality control in my opinion. Thanks for the help along the way. Don
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