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mrcandy avatar image
mrcandy asked

auto-switching 3600 isolation transformer cycling on/off

I have an auto-switching 3600W isolation transformer which has been working well for a couple of years. Lately it has started to cycle on/off about every 2 seconds when powered up. The green power LED is on, the yellow 120V LED cycles and the red temperature LED is off. Several relays can be heard clicking within the transformer. The transformer is cool (20 degC) and the fans are not running. I’ve checked input shore power and it is stable at 118.4 +/- 0.1 VAC, 60Hz.

When this problem first started, it would happen once/24h, usually around 1AM. At that time our current draw is around 3A. I would simply disconnect shore power and go back to bed. In the morning on power up it would work normally, even with 20+A loads.

Lately, the frequency of the cycling has increased and it could happen at any time of the day with no discernible relation to whatever loads were on or off. It has now reached the point where it begins this cycling behaviour as soon as it is powered up and I have had to bypass it completely.

Any thoughts/suggestions on what the problem might be?


Autotransformer
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3 Answers
Paul B avatar image
Paul B answered ·

check the incoming voltage is stable ie not dropping off to low levels, is all I could suggest

However

I think you should discuss this with your local victron dealer and then take it in to be checked/ repaired if needed.

these units do not do this usually

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Peter Anderson avatar image
Peter Anderson answered ·

@Mrcandy , same thing just started happening to me. Did you ever get to the bottom of the transformer cycling issue?

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mrcandy avatar image
mrcandy answered ·

@Peter Anderson - not really. I had tried just about all I could think of, and was preparing to take the unit out and take it to the nearest Victron service center (about a 4h trip), when it stopped the cycling.

Mine is installed on a boat and I am not always physically present. However, I do have a monitoring system installed and would be alerted if the power was cycling. Since the problem went away in late July ‘21, I have only had it happen once again (while not at the boat), and only for a few hours.

All of the times I have experienced these power cycles has been in July/Aug - when electric demand is highest. We get some fairly large transient boats at our marina that typically want to run A/C.

I believe that the problem is most likely the auto-switching circuitry for 110/220 detection on the incoming power. If you check the specs carefully they indicate that the input relays don’t close until 87-130 volts (for 110 operation), or 185-250 volts (for 220 operation). With large A/C loads in the marina, I can believe we have momentary drops below 90v and I think the transformer reacts too fast.

I did try looking for incoming voltage dropouts, but I don’t think my multimeter is fast enough to catch short duration transients. It is possible to rent a special purpose meter which would be capable of recording such events, but again several hours drive away, and I never got to it before the problem resolved itself.

I was also going to check to see if there was some kind of adjustment to reduce that 87 volt minimum, but again didn’t get to it before the problem went away.

I would start with a good quality power monitor that is capable of capturing single cycle brownouts events and see if that shows any problems that correlate to your transformer cycling.

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Peter Anderson avatar image Peter Anderson commented ·
@mrcandy Thank you for the reply! This happened just yesterday during a busy summer weekend and perhaps is to do with the marina becoming crowded and power demand increasingly dramatically. Will monitor, thanks!
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