Need help. Isolation transformer bad or could it be something else?

[Pmcsurf1]

I think my isolation transformer might be bad.
Last marina we stayed at was showing 100v at the panel in boat. I talked to a electrician (unrelated to this) and he said this marina was notorious for low voltage. Long runs down docks etc. I assumed it was 100v coming out of the pedestal. I asked my neighbor. He said he had 118v on is panel. Next step was to check voltage at pedestal. 118v. Next was voltage on my shore power connection cable. 118v. Next was check aft shore power voltage. (I was bow in) 100v at panel. Both aft and forward hookups showing 100v at panel. I started gen set. 120v at panel. I called my electrician and asked if my gen set goes through the transormer and he said no.
It seems my power comes in forward and aft, goes to isolation transformer and then back to panel.
My questions are this.
Do isolation transformers "routinely" go bad? What would cause the loss of voltage?
Info. 2004 Mainship 400 with original transformer. Charles 12KVA iso transformer.
Any electrician types with an idea?

 

[High Wire]

When transformers go bad there is usually lots of foul smoke involved. Are you sure it hasn’t always been like this indicating a connection problem?
Do you have a connection diagram?

 

[Xsbank]

What was your load? Battery charger, hot water, fridge, lights, a/c? Cell phone chargers, kettle, water maker?

If you are on a 30 amp post, your limit is about 2500 or so watts. If you load up more than 2500 (roughly), which is a kettle and a battery charger (only) you will see a lower voltage. This kind of loading is why there are melted terminals on shore power cables. Overheating but not a short so breakers don't pop.

Plug your multi-meter into a socket and turn on things and watch the voltage plummet. Might not be a transformer (in my experience you may have overheated it by overloading it and it may have failed) but check this other stuff out first. Transformers produce a lot of heat so adding to the heat can kill it.

If this is not the solution, turn off all power (disconnect from the shore etc.) and look at the wiring connections inside the transformer, check for signs of overheating.

 

[CharlieJ]

The label that this xfmr is a nominal 50A/250V 12kW. Are you supplying it with 50A/240VAC shore power? 240VAC split phase input yields 104/208VAC output. The turns ratio is 15:13 so input of 118VAC on a leg, will yield 118VAC x 13/15 = 102VAC. It appears to me to be working to specification.

 

[DavidM]

How are you measuring the voltages- hot to ground or hot to neutral. On my 2006 Mainship 34T the builder failed to hook up the boat side electrical ground to the isolation transformer's chassis. In that case if you measured hot to ground you would not get an accurate reading.

The simplest way to check is to use an outlet tester. If it shows an open ground then check your transformer. Easy to connect it as the wire is right there.

Hold it stop a minute, I just noticed that your isolation transformer has a 240/120V primary and a 208/104V secondary. Hmmm, don't know why they aren't both 240/120. That may be why you have low voltage. I would have a conversation with Charles Industries about this.

David

 

[twistedtree]

I agree that the name plate suggests it is working correctly. Besides, transformers don't "fade" in voltage like this.


What's odd is the use of this transformer, according to the name plate. More typically you would see provisions for 120V, 240V or 208V input, and 120/240V output. That name plate suggests it's essentially working backwards. Now maybe it's actually installed with primary and secondary hooked up in reverse. That could actually be fine, provided ground isolation can be handled correctly.


From your description, it sounds like your shore power is 120V, 30A? Is it only that, or is their also a 50A 120/240V inlet?

 

[twistedtree]

Oh, I might get it.


I think you have a 120/240V 50A shore connection, and 120/240V on the boat. But your shore power is actually 208V, which is not uncommon. On shore, you are measuring Line to Neutral which will be 120V nominal, and 118V in your case. But if you measure Line to Line, it will be 208V (nominal), not 240V. Your transformer only uses the two Line connections as inputs, so it's receiving 208V. It then creates an isolated 120/240V with neutral on board, but it does that by segmenting the 208V input, giving you 104V/208V nominal.


So you have discovered the need for a boosting transformer. I'm 90% certain that the Charles transformer that you have can be wired with a selector switch so it can accept either 240V or 208V input, and boost the 208V to 120/240V output. The Charles ISOBoost transformer does this automatically, but is no longer made. But it's not a big deal to have a switch that you position based on the input voltage for the marina where you are located.

 

[CharlieJ]

As usual; RTFM comes to the rescue!
http://www.charlesindustries.com/marine_manual/93-IXFMR12I-1_PR4.pdf

 

[Pmcsurf1]

What was your load? Battery charger, hot water, fridge, lights, a/c? Cell phone chargers, kettle, water maker?

If you are on a 30 amp post, your limit is about 2500 or so watts. If you load up more than 2500 (roughly), which is a kettle and a battery charger (only) you will see a lower voltage. This kind of loading is why there are melted terminals on shore power cables. Overheating but not a short so breakers don't pop.

Plug your multi-meter into a socket and turn on things and watch the voltage plummet. Might not be a transformer (in my experience you may have overheated it by overloading it and it may have failed) but check this other stuff out first. Transformers produce a lot of heat so adding to the heat can kill it.

If this is not the solution, turn off all power (disconnect from the shore etc.) and look at the wiring connections inside the transformer, check for signs of overheating.

With no load. Nothing turned on. 100v at the back of panel.

 

[Pmcsurf1]

I agree that the name plate suggests it is working correctly. Besides, transformers don't "fade" in voltage like this.


What's odd is the use of this transformer, according to the name plate. More typically you would see provisions for 120V, 240V or 208V input, and 120/240V output. That name plate suggests it's essentially working backwards. Now maybe it's actually installed with primary and secondary hooked up in reverse. That could actually be fine, provided ground isolation can be handled correctly.


From your description, it sounds like your shore power is 120V, 30A? Is it only that, or is their also a 50A 120/240V inlet?

Sorry, 50 amp 120 240

 

[Pmcsurf1]

2000 watt inverter charger. 240 hot water, ac pump, salon ac, and forward ac. That's it for 240.
120 small magic chef ice maker and fridge (ac and dc type). No microwave. No coffee maker. No electric range. Propane.

What was your load? Battery charger, hot water, fridge, lights, a/c? Cell phone chargers, kettle, water maker?

If you are on a 30 amp post, your limit is about 2500 or so watts. If you load up more than 2500 (roughly), which is a kettle and a battery charger (only) you will see a lower voltage. This kind of loading is why there are melted terminals on shore power cables. Overheating but not a short so breakers don't pop.

Plug your multi-meter into a socket and turn on things and watch the voltage plummet. Might not be a transformer (in my experience you may have overheated it by overloading it and it may have failed) but check this other stuff out first. Transformers produce a lot of heat so adding to the heat can kill it.

If this is not the solution, turn off all power (disconnect from the shore etc.) and look at the wiring connections inside the transformer, check for signs of overheating.

 

[Pmcsurf1]

The label that this xfmr is a nominal 50A/250V 12kW. Are you supplying it with 50A/240VAC shore power? 240VAC split phase input yields 104/208VAC output. The turns ratio is 15:13 so input of 118VAC on a leg, will yield 118VAC x 13/15 = 102VAC. It appears to me to be working to specification.

Yes. 50 amp 240 v single plug.
See pic of back of panel.
Pics are running on gen.

 

[Pmcsurf1]

I agree that the name plate suggests it is working correctly. Besides, transformers don't "fade" in voltage like this.


What's odd is the use of this transformer, according to the name plate. More typically you would see provisions for 120V, 240V or 208V input, and 120/240V output. That name plate suggests it's essentially working backwards. Now maybe it's actually installed with primary and secondary hooked up in reverse. That could actually be fine, provided ground isolation can be handled correctly.


From your description, it sounds like your shore power is 120V, 30A? Is it only that, or is their also a 50A 120/240V inlet?

Transformer is behind a closet. Took three pics to get the whole label.

 

[twistedtree]

Oh, I might get it.


I think you have a 120/240V 50A shore connection, and 120/240V on the boat. But your shore power is actually 208V, which is not uncommon. On shore, you are measuring Line to Neutral which will be 120V nominal, and 118V in your case. But if you measure Line to Line, it will be 208V (nominal), not 240V. Your transformer only uses the two Line connections as inputs, so it's receiving 208V. It then creates an isolated 120/240V with neutral on board, but it does that by segmenting the 208V input, giving you 104V/208V nominal.


So you have discovered the need for a boosting transformer. I'm 90% certain that the Charles transformer that you have can be wired with a selector switch so it can accept either 240V or 208V input, and boost the 208V to 120/240V output. The Charles ISOBoost transformer does this automatically, but is no longer made. But it's not a big deal to have a switch that you position based on the input voltage for the marina where you are located.

I'm quite sure this is what you are encountering.

 

[Pmcsurf1]

I'm quite sure this is what you are encountering.

So if I understand you correctly, when I plug into an actual 50a 240v shore power problem solved?

 

[tiltrider1]

So if I understand you correctly, when I plug into an actual 50a 240v shore power problem solved?

Yes, plug into a 50a 120/240v and you will get 120(actually more like 110v). Right now your plug says it’s 120/240v but the marina used a Y transformer so what you are getting is 208v which your transformer splits to 104(actually more like 100v)

 

[twistedtree]

So if I understand you correctly, when I plug into an actual 50a 240v shore power problem solved?

Perhaps, but let me be sure I understand your current situation correctly.


Your boat has a 50A 120/240V shore power cord, and that's what you are plugged into in this particular marina. Correct?


And on the shore side of your iso transformer (pedestal, boat inlet, up to the iso) you measure 118V line to neutral.


Then on the boat side of the iso you measure 100V line to neutral.


My theory can be confirmed by measuring the line to line voltage at the pedestal. I think it will be 208V, give or take, not 240V.


If it measures out that way, then you are on two phases of a 3-phase power system where line to neutral is 120V, and line to line is 208V. They are not at all uncommon in marinas. Other marinas will be delivering a single phase, and the more commonly expected 120V line to neutral and 240V line to line. In that case your onboard power will be the same.


Many isolation transformers, yours included, can be wired to selectively accept 208V input or 240V input, and create 120/240 output in both cases.

 

[High Wire]

I’m not seeing where this xfmr can be connected 208v input/240v output. If you did and moved to a different marina with actual 120/240v shore power then the transformer will output 277v. Am I missing something?

 

[twistedtree]

I’m not seeing where this xfmr can be connected 208v input/240v output. If you did and moved to a different marina with actual 120/240v shore power then the transformer will output 277v. Am I missing something?

You need a selector switch that alters the wiring based on which input voltage you want to use. On this particular xfmr, you do this by first swapping the use of the primary and secondary to gain access to both 208 and 240V input, while the output remains 120/240V. Charles says to do this in the manual. The switch then selects which input taps are used. You need to then have some sort of procedure to determine the shore voltage, set the selector switch accordingly, then apply loads. On my boat my meter shows the incoming voltage even when the main onboard breaker is off. So I can see the voltage, adjust the boost/no-boost switch, then turn on the main breaker. If your meter only reads with the main breaker on, then I think the best procedure would be to always connect in the 240V input mode, and if your meter reads 100ish volts, then switch to the boost mode. But I think I'd do the switching with the main breaker off, not when it's on.


You could also spend $7k-$10k on an automatic boosting transformer, but I think the manual switch is very effective and much less expensive. Besides, who wants to remove and replace a 200lb transformer? Not me. I think you are actually quite lucky to already have a transformer that with a little rewiring can do boosting.

 

[Pmcsurf1]

Update. Yes I have one 50 amp plug. Spent one night at two different marinas. They both showed 118v at the pannel to neutral. 236v hot to hot. It was as you said. Two different marinas and my gen set agree with your assessment. Right now I'm giddy with happiness. I was sure my transformer was toast.

 

[Pmcsurf1]

Twisted,
I was not able to test hot to hot at the first marina. We already left buy im sure you nailed it.
Thanks.

 

[garmstro55]

I don't think you have a bad transformer, you have 208 split phase power at the dock. Much more detail on problem and solution can be found here: https://www.trawlerforum.com/forums/s11/ms400-low-dock-voltage-~100volts-solution-51268.html

 

[Pmcsurf1]

I don't think you have a bad transformer, you have 208 split phase power at the dock. Much more detail on problem and solution can be found here: https://www.trawlerforum.com/forums/s11/ms400-low-dock-voltage-~100volts-solution-51268.html

I'm not able to open that link. What is forum s11?
I've tried searching key words.

 

[garmstro55]

I'm not able to open that link. What is forum s11?
I've tried searching key words.

Surprised the link doesn't work for you. Try searching "MS400 low dock voltage"

 

[Pmcsurf1]

Surprised the link doesn't work for you. Try searching "MS400 low dock voltage"

Thanks. I was able to find it in a search like you said.

 

[hughespat57]

The 208 volt input solution (plus a switch for 240 Input operation) is described on the name plate at the bottom. Per that you use the transformer in reverse setup. H1 H2 H3 become the boat Output side. The X side becomes the input side, you use X2, X4 per the name plate for 208v.

For 240 volt input you use the X1 - X5.
A 240v 50 amp DPDT switch would move the SHORE wire (common terminal on DPDT) between X4 or X5 AND x2 OR X1 as needed.

This is an "International" model transformer its original purpose was to allow American 60hz or Eurpean 50Hz usage. If you use transformer with the optional wiring and switch you lose the 50hz capability. But if you never go europe, no concern.

Double check had to correct some items for clarity...