Isolation transformer, jumper overheating

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skipmac asked Apr 26, '19

Isolation transformer, jumper overheating

I have a 3600 isolation transformer. Recently one of the jumpers on the AC input started overheating to the point of smoking. This is the jumper between J17 and J20 used for 115 V input. The transformer feeds through a Victron inverter/charger to my AC panel. I have had this setup for several years with no problems but with usually small AC loads, Just installed an air conditioner that draws 10-12 amps running. Ran this setup for a few days at the yard before moving to a marina. Ran fine plugged into 30 amp 115V shore power at the yard and I didn't notice any problems. Moved to the marina also connected to a 30 amp 115V outlet. Noticed two things. One, the air con has trouble starting and the inverter kicks in to boost the shore power when the compressor first tries to start. Then after the air con had run a while I started smelling smoke. Shut down all power and checked all the wiring AC and DC and could find nothing even warm. Restarted everything and smelled smoke again and finally traced it to the isolation transformer. Open the case and found the jumper smoking and very hot. My guess is there's a problem with the shore power at this marina but would welcome any comments or suggestions.

Isolation Tranformer

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Answer 1 · 2019-04-26T07:32:39Z

Paul B answered · Apr 26, 2019 at 07:32 AM

Hi I would suspect that you have a bad connection on the jumper ends

Please replace the Jumper and clean the terminals and make sure the new plugs are very tight,

if need be solder them into place if you are ok with using a soldering iron, or get someone who is.

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skipmac commented · Apr 26, 2019 at 05:14 PM

Unfortunately not that simple. The installation is dry and well protected but I did check the jumper carefully. It was tight and corrosion free. However it had overheated to the point of blackening the end connectors so I replaced it with a new jumper, heavy gauge wire and properly crimped (with an Ancor ratcheting crimper) and that jumper also immediately started getting hot. By that time the batteries were mostly charged so was drawing a lot less amperage through the unit so the jumper did not get quite as hot but still hotter than it should.

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Answer 2 · 2019-04-26T11:46:51Z

kai answered · Apr 26, 2019 at 11:46 AM

As a follow on to last response, the issue could have been high resistance in the jumper itself as well. The jumpers are heavy gauge and I could remember having to force them into the right positions. If the installer kinked the jumper its possible for jumper to fatigue over time which causes high resistance.

Its easy to check with a DMM.

High voltage (but not rediculously high) at the shore power inlet shouldnt cause heating issues for the jumper in and of itself.

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skipmac commented · Apr 26, 2019 at 05:19 PM

Thanks for the comments but again I don't think it's going to be an easy, obvious answer. I didn't check the jumper with a meter but it worked just fine a few days prior and had not been touched in between. Visually the jumper was straight, not bent or kinked at all.

Instead of high voltage I'm suspecting low voltage based on the difficulty getting the air con compressor to start. I guess it's time to take my Fluke to the pier and start checking the outlets.

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