240V isolating transformers

[Peter]

A week ago I posted a thread regarding 240V supplies. Part of the answers given was the need to fitted a galvanic isolator or isolating transformer. What I trying to find is where you can get isolating transformer from. Thanks for any help

Peter

 

[incognito]

Well, you can forget an isolating transformer - for the required electrical load, it will sink your boat, almost.

You need a galvanic isolator, takes little time to fit, if you can access the shoreline feed OK.

I think I got mine from Cactus.

 

[robp]

Re: Bright ideas dept

3 KVA transformers as ballast!

 

[incognito]

This is a verbatim exchange I had some time ago, before I fitted a Galvanic Isolator from Cactus, costing somewhere between £100 and £200, taking about half and hour, and weighing perhaps 10ozs. I was able to fit it right up under the gunnels where is very unlikely to get wet!!
I can supply the original email address of this supplier, who was most helpful, if you would like to go down that road.

----- Original Message -----
I am looking for a galvanic isolator for a boat. Do you supply such things? Or, if not, do you know UK based company that does?

--- First reply ---
Many thanks for your enquiry... the only sure-fire way to properly isolate an incoming supply on board is to use an isolation transformer, thus generating a true isolated earth point. Diodes are often used to achieve this and although they are smaller, cheaper and help inhibit electrolytic action a small amount of leakage current can pass back through the diode.
We can supply an isolation transformer rated at 16A (3500W)with a built in soft start for a list price of approx £520.00 -25% +VAT We can get isolation transformers in almost any size you want if you provide us with a spec, POA. Im obviously talking in the AC context.
We also supply 12V - 12V converters that can act to provide a true galvanic isolated 12V power supply rated at 8A for £149.00 -25% +VAT.
Are we getting somewhere near?
Please provide your contact details with address, telephone and fx number and we will be happy to send you the appropriate literature and price lists.
Hope this is helpful
Best regards
Sales Manager

--- Follow up from me ---
Thanks for your reply... sent at such an hour! I am more used to UK companies who can hardly be bothered to reply inside normal working hours, let alone outside.
I would like to use an isolating transformer, but the weight I have had quoted is really too much. I am not sure where I could put one.
I am not sure how I could use a 12V : 12V converter?
Yes, the diode solution (traditionally referred to as ‘galvanic isolators’ cannot totally isolate, due to the leakage current, but it seems the closest I can get. (Incidentally, some of my sailing friends take a risky route of never connecting the earth of the shore power to anything on the boat!).
I would still be interested, however, in looking at an isolation transformer if my pessimism about weight could be answered. I would have thought that 2 or possibly 2.5Kw would have been enough. I am not sure what the ‘take’ from shore power is, but it has to accommodate a battery charger, water heater, maybe an electric kettle and small electrical appliances. I may be able to measure it this weekend.
Are transformers rather conservatively rated? I used to know something about this, even designing and building small transformers about 35 years ago - but I have forgotten most of what I knew and the technology must have moved quite a bit since then. Is the limiting factor, which determines the power rating, the maximum acceptable heat loss in the core?
Please do supply any literature you have which may bear on my problem, address below.

--- First reply ---

Many shore supplies are rated / protected at 16A, it would be useful to check the rating of the main MCB or RCBO on your primary AC box.
The Victron transformer (the one for £520.00) isn’t the traditional double wound type (square laminated core with two windings), it is actually ‘torroidal’ - ring coil wound, therefore smaller, lighter and slightly more efficient than the traditional type.
Any other transformer we may be asked to supply would be the double wound type, in terms of £ per watt probably slightly cheaper, but physically larger and heavier. In reality if we had a 2 - 2.5KVA transformer made for you it would probably be bigger and heavier than the victron unit.
If you look at all your loads on simultaneoulsy you may find the total power consumption will probably total more than 16A - a domestic kettle takes over 2KW, water heater could be similar to the kettle etc etc.
The victron unit weighs 27.5 Kg, dimensions h x w x d, 445 x 300 x 240mm in a lovely blue lockable enclosure!!
Some factors that determine the transformer size and the possible need for oversizing are current draw (taking into account power factor), frequency, ambient temperature etc there are others... ratings of transformers are generally continuous at a given temperature.
Hope this is helpful, information will be posted to you today...
Best regards