isolation transformer needed

[sbnjhfty]

I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies. I see loads of them on ebay and some are
medical grade and inexpensive. Are these usable for what I want?
Other than that, any tips on where to get a good deal on one? I
don't want to spend a load as this is hobby work only.

 

[hr(bob) hofmann@att.net]

On Dec 1, 9:41 pm, sbnjhfty <fgsdf...@asfffwer.com> wrote:

I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies.  I see loads of them on ebay and some are
medical grade and inexpensive. Are these usable for what I want?
Other than that, any tips on where to get a good deal on one?  I
don't want to spend a load as this is hobby work only.

Do you want to power the 1000 watt supplies with the isolation
transformer, or use the transformer to power your soldering iron that
you use to repair the supplies?

 

[N_Cook]

sbnjhfty <fgsdfgrr@asfffwer.com> wrote in message
news:%llRm.94141$gg6.27160@newsfe25.iad...

I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies. I see loads of them on ebay and some are
medical grade and inexpensive. Are these usable for what I want?
Other than that, any tips on where to get a good deal on one? I
don't want to spend a load as this is hobby work only.

Try builders supplier for "site transformer" and also get a variac and a
RCCD/ELCB/GFCI .


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[GregS]

In article <%llRm.94141$gg6.27160@newsfe25.iad>, sbnjhfty <fgsdfgrr@asfffwer.com> wrote:

I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies. I see loads of them on ebay and some are
medical grade and inexpensive. Are these usable for what I want?
Other than that, any tips on where to get a good deal on one? I
don't want to spend a load as this is hobby work only.

Just an 'isolation transformer" means NOTHING for what
you want. Most all isolation transformers sold have the secondary tied to ground.
You need a service isolation transformer. You can usually get inside and remove a
secondary "neutral" connection.

greg

 

[Dave Plowman (News)]

In article <hf5ndl$4s2$1@news.eternal-september.org>,
N_Cook <diverse@tcp.co.uk> wrote:

sbnjhfty <fgsdfgrr@asfffwer.com> wrote in message
news:%llRm.94141$gg6.27160@newsfe25.iad...
I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies. I see loads of them on ebay and some are
medical grade and inexpensive. Are these usable for what I want?
Other than that, any tips on where to get a good deal on one? I
don't want to spend a load as this is hobby work only.

Try builders supplier for "site transformer" and also get a variac and a
RCCD/ELCB/GFCI .

Site transformers (UK) are 240 to 110 volt. And you pay for the rugged box
and outlets - not needed in the workshop.

I'm not sure if a similar thing is used in the US. Where I suppose the OP
is. Do wish people gave their location when asking about this sort of
thing. ;-)

A good quality 1000va isolating transformer isn't going to be cheap new.

--
*How many roads must a man travel down before he admits he is lost? *

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[Adrian C]

Dave Plowman (News) wrote:

GregS <zekfrivo@zekfrivolous.com> wrote:
Just an 'isolation transformer" means NOTHING for what you want. Most
all isolation transformers sold have the secondary tied to ground. You
need a service isolation transformer. You can usually get inside and
remove a secondary "neutral" connection.

That's interesting. I've never seen any transformer with the secondary
tied to ground - unless as part of an installation. The word 'isolation'
means just that. Sure you're not thinking of an auto transformer?

Seems to be a US safety requirement to ground one leg.
http://en.wikipedia.org/wiki/Isolation_transformer

I've got here a Farnell 500W 240V/240V isolating transformer that looks
and weighs similar to a typical building site transformer, the outputs
are floating.

--
Adrian C

 

[GregS]

In article <hf5svh$5gg$2@usenet01.srv.cis.pitt.edu>, zekfrivo@zekfrivolous.com (GregS) wrote:

In article <%llRm.94141$gg6.27160@newsfe25.iad>, sbnjhfty
fgsdfgrr@asfffwer.com> wrote:
I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies. I see loads of them on ebay and some are
medical grade and inexpensive. Are these usable for what I want?
Other than that, any tips on where to get a good deal on one? I
don't want to spend a load as this is hobby work only.

Just an 'isolation transformer" means NOTHING for what
you want. Most all isolation transformers sold have the secondary tied to
ground.
You need a service isolation transformer. You can usually get inside and remove
a
secondary "neutral" connection.

Futher explanation, if the transformer is raw unmounted, its
output is not tied to anything. A company who sells a transformer
mounted in a box with outlets to consumers, MUST ground one leg of the isolation transformer.
This also makes for what the transformer is mostly
used, to help cut down on noise, especially noise not in
common with ground.

I think you can buy service transformers ungrounded, but I never had one.

greg

 

[Dave Plowman (News)]

In article <hf5svh$5gg$2@usenet01.srv.cis.pitt.edu>,
GregS <zekfrivo@zekfrivolous.com> wrote:

In article <%llRm.94141$gg6.27160@newsfe25.iad>, sbnjhfty <fgsdfgrr@asfffwer.com> wrote:
I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies. I see loads of them on ebay and some are
medical grade and inexpensive. Are these usable for what I want?
Other than that, any tips on where to get a good deal on one? I
don't want to spend a load as this is hobby work only.

Just an 'isolation transformer" means NOTHING for what you want. Most
all isolation transformers sold have the secondary tied to ground. You
need a service isolation transformer. You can usually get inside and
remove a secondary "neutral" connection.

That's interesting. I've never seen any transformer with the secondary
tied to ground - unless as part of an installation. The word 'isolation'
means just that. Sure you're not thinking of an auto transformer?

--
*I'm already visualizing the duct tape over your mouth

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[GregS]

In article <50c36de762dave@davenoise.co.uk>, "Dave Plowman (News)" <dave@davenoise.co.uk> wrote:

In article <hf5svh$5gg$2@usenet01.srv.cis.pitt.edu>,
GregS <zekfrivo@zekfrivolous.com> wrote:
In article <%llRm.94141$gg6.27160@newsfe25.iad>, sbnjhfty
fgsdfgrr@asfffwer.com> wrote:
I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies. I see loads of them on ebay and some are
medical grade and inexpensive. Are these usable for what I want?
Other than that, any tips on where to get a good deal on one? I
don't want to spend a load as this is hobby work only.

Just an 'isolation transformer" means NOTHING for what you want. Most
all isolation transformers sold have the secondary tied to ground. You
need a service isolation transformer. You can usually get inside and
remove a secondary "neutral" connection.

That's interesting. I've never seen any transformer with the secondary
tied to ground - unless as part of an installation. The word 'isolation'
means just that. Sure you're not thinking of an auto transformer?

I have been thinking about it. The MAIN purpose of an isolation transformer
is to make it non isolated by making a NEW neutral close to the device
being powered. The main purpose of an isolation transformer is noise control.

Now we have us tecks who all our lives have learned isolation and that stuff.
I taliked to the people at Tripplite and verified ALL their isolation
transformers ARE grounded. Read the paragraph, and yet it says above, "Complete
line Isolation"
http://www.tripplite.com/en/products/model.cfm?txtSeriesID=325&EID=13703&txtModelID=230
Also look through
http://www.tripplite.com/en/keyword-search.cfm?q=isolation%20transformer
The isolator you buy from MCM is very unlikely to have the secondary grounded, but
I really can't verify that.



In reading PC Power Protection by Mark Waller, he
pointed out their is a NEC requirment for this grounding.
I have not found an exact description in the code. There is about 75 references
in that book, but no index marks. Man, I should sell that book !!!! Big Bucks.


greg

 

[GregS]

In article <7nnkudF3n27mkU1@mid.individual.net>, Adrian C <email@here.invalid> wrote:

Dave Plowman (News) wrote:
GregS <zekfrivo@zekfrivolous.com> wrote:
Just an 'isolation transformer" means NOTHING for what you want. Most
all isolation transformers sold have the secondary tied to ground. You
need a service isolation transformer. You can usually get inside and
remove a secondary "neutral" connection.

That's interesting. I've never seen any transformer with the secondary
tied to ground - unless as part of an installation. The word 'isolation'
means just that. Sure you're not thinking of an auto transformer?


Seems to be a US safety requirement to ground one leg.
http://en.wikipedia.org/wiki/Isolation_transformer

I just put that there. it was not there this morning.

I've got here a Farnell 500W 240V/240V isolating transformer that looks
and weighs similar to a typical building site transformer, the outputs
are floating.

Thats probably true, and correct. its up to the contractor to use
it in the right way.

greg

 

On Tue, 01 Dec 2009 22:41:38 -0500, sbnjhfty <fgsdfgrr@asfffwer.com>
wrote:

I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies. I see loads of them on ebay and some are
medical grade and inexpensive. Are these usable for what I want?
Other than that, any tips on where to get a good deal on one? I
don't want to spend a load as this is hobby work only.
Spending too little isn't cost effective either if you manage to fry a

scope probe or other piece of test gear. Still, the 30 KVa three
phase is serious overkill for your needs.

Give a little thought as to how you are going to be using this. If
you want to isolate the input side of the power supply from the line
so you can look at the control ICs a relatively low capacity isolation
transformer will suffice. If you want to isolate 1000 watt power
supplies while testing at full load, you'd better have an isolation
transformer rated at something over 1000VA.

I would say something rated at 250 VA is the minimum you want. The
medical isolation transformers or the BK Precision TR110 would be
better.

PlainBill

 

[GregS]

In article <hf6di4$97m$1@usenet01.srv.cis.pitt.edu>, zekfrivo@zekfrivolous.com (GregS) wrote:

In article <50c36de762dave@davenoise.co.uk>, "Dave Plowman (News)"
dave@davenoise.co.uk> wrote:
In article <hf5svh$5gg$2@usenet01.srv.cis.pitt.edu>,
GregS <zekfrivo@zekfrivolous.com> wrote:
In article <%llRm.94141$gg6.27160@newsfe25.iad>, sbnjhfty
fgsdfgrr@asfffwer.com> wrote:
I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies. I see loads of them on ebay and some are
medical grade and inexpensive. Are these usable for what I want?
Other than that, any tips on where to get a good deal on one? I
don't want to spend a load as this is hobby work only.

Just an 'isolation transformer" means NOTHING for what you want. Most
all isolation transformers sold have the secondary tied to ground. You
need a service isolation transformer. You can usually get inside and
remove a secondary "neutral" connection.

That's interesting. I've never seen any transformer with the secondary
tied to ground - unless as part of an installation. The word 'isolation'
means just that. Sure you're not thinking of an auto transformer?

I have been thinking about it. The MAIN purpose of an isolation transformer
is to make it non isolated by making a NEW neutral close to the device
being powered. The main purpose of an isolation transformer is noise control.

I think to a technician, ground isolation is whats important or really needed.
In some cases it may also include line isolation, but I have to think
about that for a long time.

greg

Now we have us tecks who all our lives have learned isolation and that stuff.
I taliked to the people at Tripplite and verified ALL their isolation
transformers ARE grounded. Read the paragraph, and yet it says above, "Complete
line Isolation"
http://www.tripplite.com/en/products/model.cfm?txtSeriesID=325&EID=13703&txtMod
elID=230
Also look through
http://www.tripplite.com/en/keyword-search.cfm?q=isolation%20transformer
The isolator you buy from MCM is very unlikely to have the secondary grounded,
but
I really can't verify that.



In reading PC Power Protection by Mark Waller, he
pointed out their is a NEC requirment for this grounding.
I have not found an exact description in the code. There is about 75 references
in that book, but no index marks. Man, I should sell that book !!!! Big Bucks.


greg

 

[Adrian C]

PlainBill47@yahoo.com wrote:

Give a little thought as to how you are going to be using this. If
you want to isolate the input side of the power supply from the line
so you can look at the control ICs a relatively low capacity isolation
transformer will suffice. If you want to isolate 1000 watt power
supplies while testing at full load, you'd better have an isolation
transformer rated at something over 1000VA.

I would say something rated at 250 VA is the minimum you want. The
medical isolation transformers or the BK Precision TR110 would be
better.

PlainBill

Could perhaps the figure of 1000W be taken from what might be repaired
as a hobby interest - surround sound home theater amplifiers, where the
actual power draw from the mains is considerably less than that hyped
1000W - and if it's that item, ye wouldn't really (if you value your
ears) be testing at full load/volume anyway after fixing something that
perhaps failed after moderate use.

--
Adrian C

 

[Dave Plowman (News)]

In article <7nnkudF3n27mkU1@mid.individual.net>,
Adrian C <email@here.invalid> wrote:

Dave Plowman (News) wrote:
GregS <zekfrivo@zekfrivolous.com> wrote:
Just an 'isolation transformer" means NOTHING for what you want. Most
all isolation transformers sold have the secondary tied to ground. You
need a service isolation transformer. You can usually get inside and
remove a secondary "neutral" connection.

That's interesting. I've never seen any transformer with the secondary
tied to ground - unless as part of an installation. The word
'isolation' means just that. Sure you're not thinking of an auto
transformer?


Seems to be a US safety requirement to ground one leg.
http://en.wikipedia.org/wiki/Isolation_transformer

Interesting.

I've got here a Farnell 500W 240V/240V isolating transformer that looks
and weighs similar to a typical building site transformer, the outputs
are floating.

Indeed. They used to be very common for feeding things like electric
guitars in a TV studio, etc. And grounding one leg of the secondary would
negate the whole purpose of them. These days it's more usual to do a quick
PAT (test) and supply the mains via an RCD.

--
*It's this dirty because I washed it with your wife's knickers*

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[Ron]

Adrian C wrote:

PlainBill47@yahoo.com wrote:

Give a little thought as to how you are going to be using this. If
you want to isolate the input side of the power supply from the line
so you can look at the control ICs a relatively low capacity isolation
transformer will suffice. If you want to isolate 1000 watt power
supplies while testing at full load, you'd better have an isolation
transformer rated at something over 1000VA.

I would say something rated at 250 VA is the minimum you want. The
medical isolation transformers or the BK Precision TR110 would be
better.

PlainBill

Could perhaps the figure of 1000W be taken from what might be repaired
as a hobby interest - surround sound home theater amplifiers, where the
actual power draw from the mains is considerably less than that hyped
1000W - and if it's that item, ye wouldn't really (if you value your
ears) be testing at full load/volume anyway after fixing something that
perhaps failed after moderate use.

A good source of pretty large 1 to 1 isolation trannies is old slot
machines. I used to be in that business and still have several. Find a
company who rents out gaming machines and ask, they scrap lots of
obsolete machines.

On the subject of earthing (grounding) the transformer frame and (if
metal) the enclosure is earthed, but neither side of primary or secondary.

Ron(UK)

 

[Baron]

Dave Plowman (News) wrote:

In article <hf5svh$5gg$2@usenet01.srv.cis.pitt.edu>,
GregS <zekfrivo@zekfrivolous.com> wrote:
In article <%llRm.94141$gg6.27160@newsfe25.iad>, sbnjhfty
fgsdfgrr@asfffwer.com> wrote:
I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies. I see loads of them on ebay and some
are medical grade and inexpensive. Are these usable for what I want?
Other than that, any tips on where to get a good deal on one? I
don't want to spend a load as this is hobby work only.

Just an 'isolation transformer" means NOTHING for what you want. Most
all isolation transformers sold have the secondary tied to ground.
You need a service isolation transformer. You can usually get inside
and remove a secondary "neutral" connection.

That's interesting. I've never seen any transformer with the secondary
tied to ground - unless as part of an installation. The word
'isolation' means just that. Sure you're not thinking of an auto
transformer?

My bench Isolation transformer, 2KW rating, has a 240v primary with a
centre tapped secondary that has provision to tie the centre tap to the
case which is also earthed. FWIW it weighs about 100 LB its also
marked as (Noise Suppressing) !

--
Best Regards:
Baron.

 

[Dave Plowman (News)]

In article <hf6di4$97m$1@usenet01.srv.cis.pitt.edu>,
GregS <zekfrivo@zekfrivolous.com> wrote:

That's interesting. I've never seen any transformer with the secondary
tied to ground - unless as part of an installation. The word 'isolation'
means just that. Sure you're not thinking of an auto transformer?

I have been thinking about it. The MAIN purpose of an isolation
transformer is to make it non isolated by making a NEW neutral close to
the device being powered. The main purpose of an isolation transformer
is noise control.

Now we have us tecks who all our lives have learned isolation and that
stuff. I taliked to the people at Tripplite and verified ALL their
isolation transformers ARE grounded. Read the paragraph, and yet it says
above, "Complete line Isolation"
http://www.tripplite.com/en/products/model.cfm?txtSeriesID=325&EID=13703&txtModelID=230
Also look through
http://www.tripplite.com/en/keyword-search.cfm?q=isolation%20transformer
The isolator you buy from MCM is very unlikely to have the secondary
grounded, but I really can't verify that.

It could be down to how power is distributed in our different countries.
Effectively in the UK as regards power outlets there is only one voltage
(240v) and all will be on the same phase. And the neutral is at ground
potential.
Without any form of protection, touching the neutral is safe. Touching the
live isn't. With an isolating transformer, you can touch *either* safely,
as there is no potential to ground.
The only power outlet allowed in a UK bathroom is a shaver socket - and
that is fed via an isolating transformer.

--
*Aim Low, Reach Your Goals, Avoid Disappointment *

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[whit3rd]

On Dec 1, 7:41 pm, sbnjhfty <fgsdf...@asfffwer.com> wrote:

I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies.  I see loads of them on ebay and some are
medical grade and inexpensive. Are these usable for what I want?

Yes, they are. In terms of shock hazard, you can use a GFI to
the 1000W unit, and a small isolation transformer to run your
oscilloscope,
and get the same kind of result. The best isolation transformers
are made for RF passthrough protection, or medical equipment
uses, and will work well for the less-demanding electronics workbench
even when they're 40 years old... so buying a used one makes sense.

 

[mm]

On Wed, 2 Dec 2009 17:13:20 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:

Yes, they are. In terms of shock hazard, you can use a GFI to
the 1000W unit, and a small isolation transformer to run your
oscilloscope,

Do they make plug-in GFI's? Like they make plug in surge supressors
and plug-in adapaters from 3 pin plugs to 2 slot receptacles, it
should be easy to make a plug-in, point of use GFI, but I havent' come
across one.

 

[mm]

On Tue, 01 Dec 2009 22:41:38 -0500, in sci.electronics.repair you
wrote:

I'm looking for an isolation transformer for repairing small (less
than 1000W) power supplies. I see loads of them on ebay and some are
medical grade and inexpensive. Are these usable for what I want?
Other than that, any tips on where to get a good deal on one? I
don't want to spend a load as this is hobby work only.

Now you've got me going and I want one too, but the biggest I saw
today was 385 va, and it's listed as new, not surplus (which is what I
thought you meant. They're 23 or 30 dollars plus 12 dollars shipping)

I see one for 8 dollars but it's only 100va.

Maybe I misunderstand your requirements, or my own .

I'll wait as long as you tell me to, and I'm not going to bid against
you, but you say there are loads of them. Can you give me a url or
item number so I can see what you're talking about.

I'd appreciate it.

Mike