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Isolating Transformer.


sailor0500
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20 minutes ago, Loddon said:

I thought the Thermistor wasn't within the potting compound.

 

Mine started life as one of these

https://airlinktransformers.com/product/enclosed-isolating-industrial-transformer-wm3602

So mine hasn't gone up in price as much as others. For 12 years it was in the shed next to the supply but since I moved moorings its  now housed with the soft start in an HDPE box , in a cupboard  at the back of the boat next to the inlet plug the inlet cable to the transformer is double insulated and in conduit just to be sure ;)

 

The thermistor was certainly potted. Yours  is basically the same as my new one except I overspecced the size and built my own casing. There doesnt seem to be any reason to pay extra for the marine version with all it's drawbacks unless you need it to be waterproof (e.g. if in engine room or chained up on the bank.)

 

1 hour ago, Loddon said:

https://www.ebay.co.uk/itm/402387460369

Still a thermistor but with a bypass relay and it works well.

 

These are sold for power amplifiers some of the ads say that they are unsuitable for an electric motor, I seem to remember that the washing machine was on when mine failed.

Edited by Phoenix_V
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2 hours ago, Loddon said:

The only downside to the Airlink transformer is the soft start, it is just a thermistor with no bypass relay, this is not ideal and they do burn out. I ran mine for many years with no soft start but it did mean sometimes the shore MCB would trip when the power came back on after an outage.

Two years ago I replaced the soft start with something like this

https://www.ebay.co.uk/itm/402387460369

Still a thermistor but with a bypass relay and it works well.

 

are you saying that the internal/encapsulated soft-start failed and then you added an external one? If so, where is it located, on the supply or output side? Thanks

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1 hour ago, Phoenix_V said:

These seem rather expensive do you have a link to anything suitable and reasonably priced

I was just passing on my own purchase which I think was app £180 delivered.

 

I always take the view with electrics that you get what you pay for and this was also wanted as a precaution against corrosion from permanent hook up to poor shore based electrics

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34 minutes ago, Halsey said:

I was just passing on my own purchase which I think was app £180 delivered.

 

I always take the view with electrics that you get what you pay for and this was also wanted as a precaution against corrosion from permanent hook up to poor shore based electrics

I couldn't find one at that price or near could you find a link please

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30 minutes ago, Phoenix_V said:

I couldn't find one at that price or near could you find a link please

Sorry don't know how to do links but if you go to RS components and put isolation transformer into the search engine then "safety site transformers" yellow boxes they are there 

Just done it - cant remember which one I had though sorry

 

Wife just found receipt! - their ref 122-6709 3kva portable isolation transformer £160 ish

Edited by Halsey
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1 hour ago, Markinaboat said:

are you saying that the internal/encapsulated soft-start failed and then you added an external one? If so, where is it located, on the supply or output side? Thanks

Soft start has to be on the mains input to prevent the connection surge, when you first plug it in, tripping the MCB or popping the fuse. So they do use power when nothing is plugged into them! Lots of it at first for the first few cycles.

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13 minutes ago, Halsey said:

Sorry don't know how to do links but if you go to RS components and put isolation transformer into the search engine then "safety site transformers" yellow boxes they are there 

Just done it - cant remember which one I had though sorry

 

Wife just found receipt! - their ref 122-6709 3kva portable isolation transformer £160 ish

https://uk.rs-online.com/web/c/power-supplies-transformers/transformers/safety-site-transformers/?searchTerm=isolation transformer

4 minutes ago, Tracy D'arth said:

Soft start has to be on the mains input to prevent the connection surge, when you first plug it in, tripping the MCB or popping the fuse. So they do use power when nothing is plugged into them! Lots of it at first for the first few cycles.

Did you have an internal/encapsulated soft-start that failed and just added the external one? Presumably, if the soft-start fails, there will be no power from the transformer? I ask as I have the airlink one with integral soft-start.

 

Edited to add: I think Loddon posted this.

Edited by Markinaboat
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6 minutes ago, Markinaboat said:

ht

19 minutes ago, Halsey said:

Sorry don't know how to do links but if you go to RS components and put isolation transformer into the search engine then "safety site transformers" yellow boxes they are there 

Just done it - cant remember which one I had though sorry

 

Wife just found receipt! - their ref 122-6709 3kva portable isolation transformer £160 ish

 

Not bad price but it is 1.5kva only the airlink one is supposedly twice the capacity. Though I notice that some of the RS ones are rated 3kva BUT only intermittent reduced to 1.5kva continuos, one wonders if the Airlink are truly rated for continuos use?

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19 minutes ago, Tracy D'arth said:

Site transformers are usually step down to 110v, rarely 240/240v

 

They are not intended for continuous duty and will overheat.

RS said OK for continuous use so long as they were well ventilated esp underneath it did get hot but they do have a safety trip and mine never tripped in an engine room

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40 minutes ago, Halsey said:

RS said OK for continuous use so long as they were well ventilated esp underneath it did get hot but they do have a safety trip and mine never tripped in an engine room

The spec of https://uk.rs-online.com/web/p/safety-site-transformers/1226709/ states RATING 3.0 kVA INTERMITTENT 5 MINS ON 15 MINS OFF

 

Probably okay for continuous use if you're not using it close to its limit.

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8 minutes ago, TheBiscuits said:

 

How often will it be at that power level?

 

Probably only when the kettle is on, as long as no electric heating is in use.  

It is sold as 1.5kva so presumaby that is the continuos rating very relevant if using an electric heater or washing machine  probably Ok for kettle as you say. What concerns me is that the Airlink only quotes one rating and does not state whether continuos or intermitant so anyone contemplating buying one needs to look at their potential usage and ask searching questions as to its continuos use safe rating, I cannot imagine that the encapsulation helps with cooling.

 

(If - as I suspect the- Airlink is more like 1.5 to  2kva continuos then the RS one would be a better buy.)

Edited by Phoenix_V
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19 minutes ago, TheBiscuits said:

 

How often will it be at that power level?

 

Probably only when the kettle is on, as long as no electric heating is in use.  

Hence my second sentence, which you didn't quote

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2 hours ago, WotEver said:

The spec of https://uk.rs-online.com/web/p/safety-site-transformers/1226709/ states RATING 3.0 kVA INTERMITTENT 5 MINS ON 15 MINS OFF

 

Probably okay for continuous use if you're not using it close to its limit.

How many reasons can I find for NOT using one of these.

1 underrated as @WotEver  said

2 if you look at the circuit diagram in the spec it shows a continuous PE through the transformer so not actually isolating in the way we would want it to be. There is more than one way to wire an iso transformer and for site use this is correct but not for boat use.

3 Neutral not connected to Earth on the secondary so voltage will be present between N & E not good for some electronics.

 

I could carry on but that's enough 

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Having looked a bit further at the Airlink site it appears that some of their ITs have a "safety earthed screen" which may explain the higher price. Others do not. Does anyone have any idea how essential such a screen is?

The metal cased 3500 va marine IT weighs in at 30kg and costs £80 more than the encapsulated waterproof one wheras there is an industrial 3500va IT which weighs the same as the encapsulated one and costs about £80 less

Edited by Phoenix_V
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2 hours ago, Phoenix_V said:

If - as I suspect the- Airlink is more like 1.5 to  2kva continuos then the RS one would be a better buy.)

My Airlink is 3.5kw continuos and has been run at more than that (20amps) for hours at a time when Aircon, Battery Chargers and Washing machine were all on at the same time  without a problem

5 minutes ago, Phoenix_V said:

Having looked a bit further at the Airlink site it appears that some of their ITs have a "safety earthed screen" which may explain the higher price. Others do not. Does anyone have any idea how essential such a screen is?

Depends on how lucky you feel in the case of a major transformer meltdown ;)

 

Edited by Loddon
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12 minutes ago, Loddon said:

2 if you look at the circuit diagram in the spec it shows a continuous PE through the transformer so not actually isolating in the way we would want it to be. There is more than one way to wire an iso transformer and for site use this is correct but not for boat use.

3 Neutral not connected to Earth on the secondary so voltage will be present between N & E not good for some electronics.

 

 

Presumably this could be modified?

13 minutes ago, Loddon said:

My Airlink is 3.5kw continuos and has been run at more than that (20amps) for hours at a time when Aircon, Battery Chargers and Washing machine were all on at the same time  without a problem

Depends on how lucky you feel in the case of a major transformer meltdown ;)

 

Comforting to know about your real world usage , but the one you say you have  does not appear to have an earth screen?

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4 minutes ago, Phoenix_V said:

Comforting to know about your real world usage , but the one you say you have  does not appear to have an earth screen?

Mine does have the screen as it was 14 years ago maybe its been changed.

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4 minutes ago, sailor0500 said:

Now I feel really confused. As usual on Forums one asks a simple question and it starts a discusion which produces no definate answer and even seems to confuse the experts.

Well, you had the direct answer to your question in post 2. The rest is ‘discussion’ as per the name of this forum. 

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2 hours ago, WotEver said:

Well, you had the direct answer to your question in post 2. The rest is ‘discussion’ as per the name of this forum. 

You have the fit and forget answer (post 2) and some alternatives which involve more study/work but may cost less and might work better

 

 

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3 hours ago, WotEver said:

Well, you had the direct answer to your question in post 2. The rest is ‘discussion’ as per the name of this forum. 

Agreed. But then even that was contradicted  by "Old Goat" in post nine who recons one is not needed at all.

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