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Old 05-26-2020, 05:24 AM   #1
dicky96
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Default Laminator blows fuses and trips the mains - but not when on my ispolation transformer

Hi guys
So here is a 'weird device' it is an IKON IP-450 A2 Paper laminator

The customer says it was warming up then suddenly tripped out the 220V mains

He replaced the 5A fuse which had blown but it did the same thing straight away as soon as powered on, it trips out the power in his apartment. He tried another power lead and tried it at a friends address but the same occurs

So he brought it to me, having fitted a new fuse again.

I plugged it in and it worked fine - it was drawing about 3Amps and warmed up to maximum working temperature no problem in about 5 mins.

Having scratched my head as to why, it occurred to me the only thing I was doing different was that I had it connected to my 220V isolation transformer.

So I connected it to a normal power outlet, it blew the fuse instantly and tripped the mains out. The fuse is vapourised.

I then replaced the fuse, put it back on the 220V isolation transformer and it works fine

Thing is I can't see any shorts to explain this, either across the power or to ground. The heating element does read short circuit on my multimeter, but it obviously works OK.

The only thing I can see is one of the plastic terminal blocks that connects the power to the heating element has melted and looks a mess, but there is no short form this terminal to ground or to the screw next to the terminal block

So what's going on and why does it work on the isolation transformer?
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Old 05-26-2020, 07:40 AM   #2
petehall347
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

earth leakage ..isolation transformer won't have an earth .
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Old 05-26-2020, 08:27 AM   #3
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

that or the isolation transformer is current-limiting
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Old 05-26-2020, 10:43 AM   #4
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

Quote:
Originally Posted by stj View Post
that or the isolation transformer is current-limiting
+1

3A @ 220V is 660VA -- probably a sizable load for an isolation transformer. If it was fused at 5A then it is likely that it draws close to that (at least at some point in its operation).

If there was a partial short (to earth or elsewhere), it would have to be significant (enough to make a difference between a ~3A operating current and a >>5A fuse trip current) for the fuse to "blow instantly" -- not likely something "moving" from thermal expansion, over time.

Put a light bulb in series with the load and measure current draw off the mains (w/o transformer).
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Old 05-26-2020, 10:50 AM   #5
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

a lot of these things use a halogen lamp inside a metal roller, the cold inrush is huge!
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Old 05-26-2020, 10:55 AM   #6
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

I would disconnect the heat element and see if the short is still there, it could be that the heat element is shorting to ground, maybe only when it heats up.
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Old 05-26-2020, 11:58 AM   #7
dicky96
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

OK I can try with the heater disconnected

Just to clarify a few points raised...

My Isolation transformer is 220V:220V and rated at 2000VA continuous. It's good up to about 8 Amps (I know that from previous usage) It has a built in thermal trip and it did not trip out.

That connects to my Variac which is also rated 2000VA. On the Variac I had it set to 100% output voltage and the Laminator was connected to that. I do have a light bulb I can switch in series with the load but when i first turned on the bulb did not light so I bypassed it.

The Variac has linear voltage and current meters - that is how I know it was drawing 3A at 220V.

I had it on for a good 5-10mins until the led went green to signify the laminator is up to the set temperature. The owner who was there says this is normal behaviour. So I honestly don't think the isolation transformer is an anyway acting to decrease the load

To vapourise the fuse a lot of current must have flowed instantaneously when I connected it directly to the mains. My thoughts were the same as some here - a short to ground. But I can't see it on my DMM.

Last edited by dicky96; 05-26-2020 at 12:03 PM..
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Old 05-26-2020, 12:12 PM   #8
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

Look in the pic, the terminal block has melted and is shorting to the mounting screw.
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Old 05-26-2020, 02:20 PM   #9
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

With the laminator on the isolation transformer, when the short occurs you will be able to measure a/c voltage between a/c line and what would normaly be chassis ground. Without the short there should be next to 0 volts between a/c line and ground. And as mentioned above, it could be the shorting right at the white terminal strip

Last edited by R_J; 05-26-2020 at 02:23 PM..
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Old 05-26-2020, 03:33 PM   #10
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

Quote:
Originally Posted by redwire View Post
Look in the pic, the terminal block has melted and is shorting to the mounting screw.
Yes I thought exactly that as well. And as I posted on the OP I checked the terminal to the screw (or chassis) reads open circuit
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Old 05-26-2020, 03:35 PM   #11
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

Quote:
Originally Posted by R_J View Post
With the laminator on the isolation transformer, when the short occurs you will be able to measure a/c voltage between a/c line and what would normaly be chassis ground. Without the short there should be next to 0 volts between a/c line and ground. And as mentioned above, it could be the shorting right at the white terminal strip
Yes, This. Very good suggestion, I will try that tomorrow. Thanks mate. I did check that white terminal already though, and it reads fine. Tomorrow I will remove it and fit something new just to eliminate it anyway.

Last edited by dicky96; 05-26-2020 at 03:37 PM..
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Old 05-26-2020, 04:36 PM   #12
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

Quote:
Originally Posted by dicky96 View Post
Yes I thought exactly that as well. And as I posted on the OP I checked the terminal to the screw (or chassis) reads open circuit
Uh, give it a wiggle
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Old 05-26-2020, 05:29 PM   #13
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

lol
and a good place for a ceramic terminal block and bootlace-ferules!
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Old 05-27-2020, 10:29 AM   #14
dicky96
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

OK it's fixed. It was that screw where it went through by the melted terminal block. It read open circuit from the terminal to the screw on my multimeter, even if I tried waggling the connector which actually would not move. But once I removed the screw and cut the melted part of the connector away I could see there was some bare metal inside and it had been arcing in there.

I didn't have any ceramic connector blocks so I soldered the wires and used heatshrink and then that white heatproof sleeving.

It works fine now

Rich
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Old 05-27-2020, 06:32 PM   #15
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Default Re: Laminator blows fuses and trips the mains - but not when on my ispolation transfo

BTW, Did you tighten all the screws on that terminal block, the one that melted was due to bad contact resistance so it got hot and melted the terminal black.
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