Isolation Transformer Problem

[sy_gilana]

I see you have the ground wire connected to the transformer.
Please check with your mm between the "G" terminal and the "SHR" terminal on the transformer. If there is continuity there it is NOT working as an isolation transformer. IE if you can put your MM between your hull and the earth or ground terminal on shore and get a reading, you are not protected.
I am also a mech-eng.

My isolation tx is only fed with 2 wires from shore. My earth or ground is set up inside the boat. The isolation tx IS the ground inside.

The inrush current is the current required to set up the flux field from zero. This transient peak can pull 9 x the rated load. Once the flux is "up there" the thing bounces at a frequency that is directly proportional to the mass of the Fe in the tx. provided it is a Fe cored and not a toroid.

You could wire up your shore lead to have two male plugs provided they plugged into the same phase, and you would be able to start it on both then disconnect.

Please do take some precautions. This is not mumbo jumbo...
DO measure between your hull and the ground of the dock, on both AC and DC scales. You should see nothing, or at the very least, your boat should be the cathode.
DO get a silver coin, drill it, solder a wire to it, place it in the water at half of your draft, at the quarters, midships and bow, both sides at the same distance from your hull. The measurements will be relative, record them, do it again a month or so apart. Changes are a warning. Use the Millivolt DC scale.
DO get extra anodes, hang them on tinned insulated heavy (6mmdia) cables between your hull and the dock. Check them in a week and if they are eroding, be thankful you have them....
I hang 2x 15 Kg anodes if I am on a dock, some older docks are very bad at leaking current into the water. Other boats bad installations are also a risk.

(of course you could just tie up next to an aluminum boat and then you will be fine :O )

[sy_gilana]

Originally Posted by DotDun

That's interesting as the higher frequency is easier on the transformer. They stress test a 50/60hz transformer at 50hz.

From our friends at wikipedia.....



Transformer - Wikipedia, the free encyclopedia

Yes indeed BUT the higher freq tx's are lighter, you have confirmed what I said.

A 50 design one will be inefficient at 60 exactly 20% hotter. and vice versa...

I do not have the formula at hand but its out there on the net...

[DotDun]

Originally Posted by sy_gilana

Yes indeed BUT the higher freq tx's are lighter, you have confirmed what I said.

A 50 design one will be inefficient at 60 exactly 20% hotter. and vice versa...

I do not have the formula at hand but its out there on the net...

Sorry, but I think you have it backwards.

Using a transformer built for 60Hz in 50Hz land is a disaster. Using a 50Hz in 60Hz land is no problem.

[sy_gilana]

I will check the facts I have at hand...

[sy_gilana]

Transformers are designed to run at or near saturation. A 60 running on 50 would overheat by oversaturation. On the saturation theory alone, you would be correct BUT...
In order to produce the same current, a 50 running "in 60 land" is and would be 20% less efficient, therefore, the loads are now drawing the same current as they would, but as the tx is now less efficient, more heat is produced. Its the same both ways in the final analysis although the cause of the stress is different. One is oversaturation of the flux density and the other is under...at least thats what I think at the moment based on some sums, and by putting my hand on my transformer while plugged into Florida Light and Power. ( and why do the mfg of tx's bother with making two lines? and why dont all 50 Hz customers buy 60 Hz tx's theyre 20% smaller?, but they dont.)

[DotDun]

Originally Posted by sy_gilana

Transformers are designed to run at or near saturation. A 60 running on 50 would overheat by oversaturation. On the saturation theory alone, you would be correct BUT...
In order to produce the same current, a 50 running "in 60 land" is and would be 20% less efficient, therefore, the loads are now drawing the same current as they would, but as the tx is now less efficient, more heat is produced. Its the same both ways in the final analysis although the cause of the stress is different. One is oversaturation of the flux density and the other is under...at least thats what I think at the moment based on some sums, and by putting my hand on my transformer while plugged into Florida Light and Power. ( and why do the mfg of tx's bother with making two lines? and why dont all 50 Hz customers buy 60 Hz tx's theyre 20% smaller?, but they dont.)

V/Hz dictates the amount of magnetic flux required. A transformer's core size directly equates to how much magnetic flux it can hold while still giving a linear response. If you exceed that amount the inductance plummets, current skyrockets just before the transformer melts/dies. 60Hz transformers are physically 20% smaller than the equivalent 50Hz transformer.

230v/50hz = 4.6
240v/60hz = 4.0

A transformer built for 60hz with have a "core size" of 4.0 and will melt down running @ 4.6. The other way around is no problem, the drop in efficiency is more of a physical nature, you have a bigger/heavier device than required. The key is to never exceed the V/Hz design limit.

I would guess your experience is due to other issues, i.e. you are running more current through the transformer, or maybe the temperature sensor that engages the cooling fan is spoofed to engage at a different set point when run at the higher frequency.

The bottom line for this thread is that isolation transformers built for the marine environment are (or should be) designed/tested for 50hz. They will then run at 60hz with no problem.

[donpjr]

Hello all, thanks for all the advice. Latest update.

I removed all wires from the transformer and confirmed that resistance measurements are as they should be. Between the two input coils the resistance is infinity, same for the two output coils, and the ground wires, and any measurements between input and output they all show infinite resistance. All measurements point to the transformer being OK. I checked the shore power cord, it is fine. I can power a small appliance from it, no tripping. This leaves me with the soft start unit. Mastervolt 13kw softstart

Soft Start 13 kW | Mastervolt Marine

The shore power inlet to this soft start has R=infinity measured between L1 and N (the two power wires from the shorepower), Measuring across the resistor on L1, I get 22 ohms which is OK (documentation says 25 ohm). But at the outlet of the softstart there is a resistance of 1.25kohm between the two "hot" wires. Ran out of troubleshooting time, but this seems strange. Why would I see anything but an infinity (Overload) reading between two hot wires? The softstart is a resistor that handles the surge current for a cycle (20 ms or so) and then closes some kind of relay to let the current pass without the resistor. These softstart outlet wires go to the inlet of the transformer but were disconnected from the transformer for this measurement. So as usual I am stumped.

[DeepFrz]

You are measuring across the coil of the relay.

http://images.mastervolt.nl/files/SO..._10_13kWNL.pdf

[goboatingnow]

Firstly European protection devices are residual current breakers usually also with overload protection known as RCBOs. There sense combined current in the line and neutral, they are not GFCIs. They typically have a 30ma residual setting.

( by the way never parallel European 230vac power , the RCBOs will always trip, never mind the phase problem)

Firstly are you sure your dockside supply can supply even the 10A inrush even after the soft start is engaged. Some marinas have quite low overload trip levels. Ie take something like an 230vac 2000W electric kettle and rig up a cable and plug it directly into the dock pillar.

How have you connected the boats earth lines. ( ie are the internal grounds separate to the shore power ground)

Is the shore power circuit from the dock pillar to the transformer free from leakage currents. Ie everything dry and clean.


Keep thinking, only two things are tripping the breaker. Current flowing back through a circuit other then the incoming live and neutral or your exceeding the overload amp trip.

Dave

[donpjr]

DeepFrz. I gather from your comment that the resistance I am measuring is OK. I should expect a reading across the two lines due to the relay coil, even if the relay is open? I'll have to read up on relays.

Goboatingnow. Thanks for the comments. The ground from the shorepower bypasses the softstart and is wired directly to the shore connection on the transformer input. This in turn is connected internally to the transformer (to the shield separating the transformer in and out I believe). The boat ground wire is then connected to the output ground on the transformer which is connected to the transformer case. The two ground wires (input and output) are separated totally (R=infinite). I have used the dock power to a smaller portable transformer that I have (1000W) and powered an electric 110V kettle (not sure of the wattage). It works fine. Also here the dock towers have multiple plugs for several boats. Others seem to have no issues but they are likely 240V boats to start with. I have tried several of the outlets in that tower without success. The tower itself looks in good shape, it is dry.

Back to the drawing board.

[DeepFrz]

Yes, you should see continuity across the coil of a relay. However there must be other circuitry involved in order to keep the relay from chattering. The picture of the cct. boards are two small to make out any detail. I would suggest you have at least a diode and a capacitor in the relay coil circuitry.

[s/v Jedi]

Ahem...

I pulled the manual for the softstart which lists the diagram. It is crazy, just a resistor and relay. The only delay I see is the relay.

According to the schematic, you should measure the relay coil on the input. However, you measure infinite resistance. Let me list the measurements you should see:

Li / Lo = Line in/out
Ni / No - Neutral in/out

between Ni and No : 0 Ohms (i.e. both neutrals are the same)
between Li and Lo : 25 Ohms
between Li and Ni : the relay coil
between Lo and No : the relay coil + 25 Ohms

I'm not impressed with this soft start device. I'm also not impressed with Charles isolation transformers. Wish you would have asked me before and got a Victron transformer which has everything built in and works as expected.

For now, the softstart is suspect imho.

cheers,
Nick.

[DotDun]

Nick,

The MasterVolt SS is a pretty standard design, a rate limiting resistor and a relay. The resistor will limit the current to 9-10a until the relay latches up, allowing enough time for a couple of cycles to get through to the transformer.

As Dave points out, one of two things is tripping the breaker, more than 16a or more than 30ma leakage.

A potentially dangerous test would be to disconnect the shore power ground from the transformer screen and see if still trips. Since the OP has never witnessed this transformer actually working, this would prove/disprove a short to the screen that only appears under power.

It would be interesting to measure the in-rush to see if it is actually exceeding the 16a.

[donpjr]

Thanks all again. To comment on s/v Jedi, I also wish I had asked. In any case the measurements are as follows:

Li / Lo = Line in/out
Ni / No - Neutral in/out

between Ni and No : 0 Ohms (i.e. both neutrals are the same) - YES
between Li and Lo : 25 Ohms - YES, well 22 ohms.
between Li and Ni : the relay coil - I get 1.24 something kohms. Does that sound reasonable number?
between Lo and No : the relay coil + 25 Ohms - YES. I didn't measure accurately whether Li and Ni give exact same reading as Lo and No, but they are close (rounded to 1.25 kohms)

DotDun. I don't know how to measure the current as the trip is instantaneous. I have an ammeter and could check if it would give a reading on the L1 input to the softstart in this short time. I can disconnect the ground and check that as well. Should be OK for a short test without frying anything, including myself.

Thanks. Don

[DotDun]

Originally Posted by donpjr

DotDun. I don't know how to measure the current as the trip is instantaneous. I have an ammeter and could check if it would give a reading on the L1 input to the softstart in this short time. I can disconnect the ground and check that as well. Should be OK for a short test without frying anything, including myself.

Thanks. Don

There are meters with in-rush functionality, you would know if your meter was capable.

Remember, when you disconnect the transformer screen from the shore power ground, if the breaker does not trip, you now have a hot transformer screen. Be careful!