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Handy (and cheap) 1KW Isolation transformer.

 
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Handy (and cheap) 1KW Isolation transformer.

Post by Doz » Mon Jul 07, 2014 3:24 pm

These appear to be available on eBay for a few quid, and I was lucky enough to save mine from lining a skip!

It's a British Telecom MCU5A/1000 Mains conditioner.

It's a grey box, about a foot wide, and 6 inches tall, with 4 mains plugs on the front.

Inside, is an isolation TX , and some filter caps. As found it's not isolating, as the secondary neutral is coupled to the earth, but two seconds later with a pair of snips, and a nice isolation unit is created!

I'll post some pictures up when I get it home :bba

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by neil29 » Mon Jul 07, 2014 3:59 pm

I've already got a tool isolation transformer :aab but it's not really up to the job of supplying a large tv set :bbd . so it would be good to acquire something more suitable as on many an occasion I've found myself touching the live chassis of various TV's :ccf :aaj .

Cheers
Neil.

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Valvebloke » Mon Jul 07, 2014 6:08 pm

ppppenguin wrote:The audiophools might be on to these: http://www.pinkfishmedia.net/forum/show ... p?t=106442 :ccf ...


To be fair Jeffrey there are more posts in that thread saying "Don't bother with isolation transformers, just fix the noise at source (typically the fridge motor, the C/H boiler controller, the noisy switch-mode supplies in your cheap IT and entertainment gear, etc)" than there are claiming that the isolation trannies helped. And there are also two or three saying "Beware, they hum". Which they often do IME, making them hardly compatible with hi-fi, obviously :cch .

VB

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Doz » Mon Jul 07, 2014 6:13 pm

ppppenguin wrote:The audiophools might be on to these: http://www.pinkfishmedia.net/forum/show ... p?t=106442 :ccf

Neil, I'm susrprised a tool isolation transformer won't power a TV. Even the smallest are rated at 1kVA. The real snag is that you need 2 of them, as they are 110V output.


Tool transformers are 55-0-55

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Lloyd » Mon Jul 07, 2014 6:31 pm

Is this similar? If so I might grab one :aad

Regards,
Lloyd.

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Doz » Mon Jul 07, 2014 6:36 pm

Pictures, including details of which earth to remove. FAILURE TO REMOVE THIS EARTH MEANS YOUR OUTPUT IS NOT ISOLATED!!!

You have been warned.
20140707_181502 (Mobile).JPG
20140707_181502 (Mobile).JPG (43.14 KiB) Viewed 2846 times

20140707_182502 (Mobile).JPG

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Doz » Mon Jul 07, 2014 6:38 pm

Lloyd wrote:Is this similar? If so I might grab one :aad

Regards,
Lloyd.


... yeah, but only half an amp.... good for radio work I suppose.

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Lloyd » Mon Jul 07, 2014 6:42 pm

I won't bother with those then!! I'll wait for one of the bigger ones to come along :bba

Lloyd

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Doz » Mon Jul 07, 2014 6:44 pm

Just ordered one of these to adorn the front...

http://www.ebay.co.uk/itm/231183950928? ... 1497.l2649

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Doz » Mon Jul 07, 2014 7:02 pm

ppppenguin wrote:That transformer in Doz's photo doesn't look big enough for 1kVA to me. Though I could easily be mistaken. Even at 500VA it's enough for any radio or TV.


20140707_182502 (Mobile) (2).JPG

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Terrykc » Mon Jul 07, 2014 7:27 pm

Something to be wary of is that this unit drives 4 output sockets. If more than one is connected at the same time the units are no longer isolated (from each other).

Three sockets should be disconnected. It would also be a good idea to remove the earth from the remaining, isolated, one as a precaution, although I wouldn't expect a unit needing isolation to be fitted with a three core cable ...

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Mark Hennessy » Mon Jul 07, 2014 8:32 pm

Terrykc wrote:Something to be wary of is that this unit drives 4 output sockets. If more than one is connected at the same time the units are no longer isolated (from each other).

Three sockets should be disconnected. It would also be a good idea to remove the earth from the remaining, isolated, one


Yes, exactly what I was about to say.

If you haven't seen it before, you might also be interested in this EGN regarding safety isolating transformers:

https://dl.dropboxusercontent.com/u/990 ... former.pdf

This document explains why the protective earth connection is not carried through to the socket on the front panel.

Cheers,

Mark

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Doz » Mon Jul 07, 2014 9:44 pm

I was just about to say the same thing!

I'm well aware of the risks involved, but forgot to re-iterate it for the benefits of others.

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Refugee » Mon Jul 07, 2014 11:55 pm

I have noticed over many years that almost all BT stuff with transformers in it buzzes all the time as did the earlier Telecom and GPO bits.

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Doz » Tue Jul 08, 2014 9:13 am

Refugee wrote:I have noticed over many years that almost all BT stuff with transformers in it buzzes all the time as did the earlier Telecom and GPO bits.


Reassuring isn't it! Saves on an indicator light I suppose :aad

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Doz » Fri Jul 11, 2014 7:43 pm

Added the meter on the front panel (separately fused, of course!). Found a 5A breaker and a switch to switch the output on and off, and added these too.
10469721_10152606784249224_2927959049149157313_n.jpg

Regulation doesn't seem too bad.
983737_10152606784939224_6012095226222351749_n.jpg


Very pleased with my little unit.

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Herald1360 » Fri Jul 11, 2014 10:38 pm

Mark Hennessy wrote:If you haven't seen it before, you might also be interested in this EGN regarding safety isolating transformers:

https://dl.dropboxusercontent.com/u/990 ... former.pdf



It also refers to a mysterious "safety electrolytic screen" between primary and secondary of an isolating transformer :ccb

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by turretslug » Thu Aug 07, 2014 8:25 am

Bearing in mind that safety isolation (as normally understood with a workshop isolating transformer) isn't explicitly part of the original brief of these transformers, is it OK to assume that they will still perform to the expected standards (leakage, creepage, kV of spike/surge withstand)? It struck me that even the 125VA version could have utility where one wishes to divorce an Class 1, earthed chassis mains radio from mains earth from the noise reduction/signal improvement point of view- but I'd want to know that it was pretty unimpeachable!

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by FIXITNOW2003 » Mon Jan 18, 2016 12:42 pm

just picked up a smaller 500w one of these from a skip had circuit inside have uploaded here in case its of use
Attachments
bt mains.jpg

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Red_to_Black » Mon Jan 18, 2016 6:38 pm

Mark Hennessy wrote:
Yes, exactly what I was about to say.

If you haven't seen it before, you might also be interested in this EGN regarding safety isolating transformers:

https://dl.dropboxusercontent.com/u/990 ... former.pdf

This document explains why the protective earth connection is not carried through to the socket on the front panel.

Cheers,

Mark



At least that BBC document is far more sensible and makes far more sense than the (or a) previous version of EGN 4 :qq1 , and which was basically what I was more or less saying in previous long, long, long thread. :aad

The diagram Vince (fix it now) has posted does not provide the protective measure of electrical separation at all, it merely replicates a TNC-S system with the combined N-E.

That type of set up (the one posted by FiN) does have it's uses, and may be configured that way for a variety of reasons, however a fully floating bench isolating transformer it is not! , at least as it stands

 
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Re: Handy (and cheap) 1KW Isolation transformer.

Post by Doz » Wed Jan 20, 2016 8:55 pm

That's how mine was originally wired.

I disconnected the earth from the neutral on the secondary side. I left the screen connected.


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