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.

On Dec 1, 9:41*pm, sbnjhfty 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?

On Dec 1, 9:41*pm, sbnjhfty 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?

sbnjhfty wrote in message
...
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/

In article ,
N_Cook wrote:
sbnjhfty wrote in message
...
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 London SW
To e-mail, change noise into sound.

In article , sbnjhfty 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

In article ,
GregS wrote:
In article , sbnjhfty 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 London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
GregS 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

In article ,
Adrian C wrote:
Dave Plowman (News) wrote:
GregS 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 London SW
To e-mail, change noise into sound.

In article , Adrian C wrote:
Dave Plowman (News) wrote:
GregS 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

In article , "Dave Plowman (News)" wrote:
In article ,
GregS wrote:
In article , sbnjhfty
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...txtModelID=230
Also look through
http://www.tripplite.com/en/keyword-...%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

In article , (GregS) wrote:
In article , "Dave Plowman (News)"
wrote:
In article ,
GregS wrote:
In article , sbnjhfty
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...D=13703&txtMod
elID=230
Also look through
http://www.tripplite.com/en/keyword-...%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

In article ,
GregS 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...txtModelID=230
Also look through
http://www.tripplite.com/en/keyword-...%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 London SW
To e-mail, change noise into sound.

On Dec 2, 12:03 pm, (GregS) wrote:
In article , "Dave Plowman (News)" wrote:



In article ,
GregS wrote:
In article , sbnjhfty
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=13...
Also look throughhttp://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

On an isolation transformer (single phase), the primary side is always
grounded because the neutral leg is always bonded in the distribution
panel. This is a code requirement. If the secondary is also grounded
(I am pretty sure this is also a requirement), the two sides are still
electrically isolated. The current leaving the secondary hot leg must
return to the neutral (grounded) leg of the secondary. There is no
path from the secondary hot to the primary neutral. The secondary has
to leave the hot leg and return on the secondary neutral leg. The
secondary current cannot go any where except through secondary loop.
Any noise on the high side (from nearby VFDs or other) must pass
through the primary winding in order to induce a current onto the
secondary. The winding itself is a low pass filter, so much of the
noise on the primary is dissipated as heat.

"Andy the Honky "

On an isolation transformer (single phase), the primary side is always
grounded because the neutral leg is always bonded in the distribution
panel. This is a code requirement. If the secondary is also grounded
(I am pretty sure this is also a requirement), the two sides are still
electrically isolated.


** No way is it a requirement for 1:1 mains transformers used for " safety
isolation " or electrical / electronic servicing.

When you have no clue - shut the **** up.

This is NOT an opinion forum for morons.

Despite appearances.....



.... Phil

In article , Andy wrote:
On Dec 2, 12:03 pm, (GregS) wrote:
In article , "Dave Plowman (News)"
wrote:



In article ,
GregS wrote:
In article , sbnjhfty
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=1
3...
Also look
throughhttp://www.tripplite.com/en/keyword-search.cfm?q=isolation%20transforme
r
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

On an isolation transformer (single phase), the primary side is always
grounded because the neutral leg is always bonded in the distribution
panel. This is a code requirement. If the secondary is also grounded
(I am pretty sure this is also a requirement), the two sides are still
electrically isolated. The current leaving the secondary hot leg must
return to the neutral (grounded) leg of the secondary. There is no
path from the secondary hot to the primary neutral. The secondary has
to leave the hot leg and return on the secondary neutral leg. The
secondary current cannot go any where except through secondary loop.
Any noise on the high side (from nearby VFDs or other) must pass
through the primary winding in order to induce a current onto the
secondary. The winding itself is a low pass filter, so much of the
noise on the primary is dissipated as heat.

I would agree with this except you also state then, there is no path from
secondary hot to primary neutral, which makes no sense in your
explanation. In electronic servicing you don't want to ground the
secondary making a new neutral. You got to get away from the code to do it.

greg

Dave Plowman (News) wrote:

In article ,
GregS wrote:
In article , sbnjhfty
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.

In article , (GregS) wrote:
In article , sbnjhfty
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

On Tue, 01 Dec 2009 22:41:38 -0500, sbnjhfty
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

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

Adrian C wrote:
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)

On Wed, 02 Dec 2009 19:35:30 +0000, Adrian C
wrote:

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.
Well, the OP said 'Power supplies'. I have a bad habit of taking
people at their word. The last time I worked on an amplifier I noted
the power supply was an classic 'heavy iron' design, with the AC line
feeding a transformer. Still, I wouldn't be surprised to find a SMPS
in something rated at a pretend 1000 watts.

IMHO, it's a fool who repairs a power supply, then does not test it
with a dummy load BEFORE hooking it up to it's intended load. And
again, the OP has to decide if he wants an isolation transformer
capable of handling the full rated load. Personally, that is always
my recommendation. It avoids nasty surprises when one is in a hurry
to test and forgets to switch the power cord to an isolated source.

PlainBill

On Dec 1, 7:41*pm, sbnjhfty 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.

On Wed, 2 Dec 2009 17:13:20 -0800 (PST), whit3rd
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 wrote in
:

On Wed, 2 Dec 2009 17:13:20 -0800 (PST), whit3rd
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.

I have a 'short extension cord with a built in GFI'. I don't remember where
I bought it but you should be able to find such.
A google search for
extension cord with GFI
brings a bunch of hits.


--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

On Dec 2, 8:55*pm, mm wrote:
On Wed, 2 Dec 2009 17:13:20 -0800 (PST), whit3rd
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?

Yes, of course; more important, one can get a GFI socket and
wire it into a handy box (or a string of boxes with multiple
plugs) and make a power distribution panel. There are
(expensive, alas) sockets that offer 'isolated ground' so that
the metal case(s) of the distribution panel can be grounded
while the special sockets can be floated. Thus, you can
wire sockets with ground-optional to the isolation transformer
and have only the distribution panel on the workbench (the
transformer can live on the floor or wherever).

On Thu, 3 Dec 2009 13:57:06 -0800 (PST), whit3rd
wrote:

On Dec 2, 8:55*pm, mm wrote:
On Wed, 2 Dec 2009 17:13:20 -0800 (PST), whit3rd
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?

Yes, of course; more important, one can get a GFI socket and
wire it into a handy box (or a string of boxes with multiple
plugs) and make a power distribution panel. There are
(expensive, alas) sockets that offer 'isolated ground' so that
the metal case(s) of the distribution panel can be grounded
while the special sockets can be floated. Thus, you can
wire sockets with ground-optional to the isolation transformer
and have only the distribution panel on the workbench (the
transformer can live on the floor or wherever).

Very good. Thanks to you and bz.

whit3rd wrote:
On Dec 1, 7:41 pm, sbnjhfty 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.

This must probably again be a voltage US/UK thing - or maybe me - but if
I was working on 240V live equipment I'd rather it was ALL floating
through an isolation transformer than rely on the complexities and
effectiveness of a GFI/RCD to prevent shocks at the bench.

--
Adrian C

On Dec 3, 6:20*am, Adrian C wrote:
whit3rd wrote:
... *In terms of shock hazard, you can use a GFI to
the 1000W unit, and a small isolation transformer to run your
oscilloscope,

This must probably again be a voltage US/UK thing - or maybe me - but if
I was working on 240V live equipment I'd rather it was ALL floating
through an isolation transformer than rely on the complexities and
effectiveness of a GFI/RCD to prevent shocks at the bench.

Working on live 120V or 240V, you can always touch two points
and get a shock. Either an isolation transformer, or a GFI
interrupter, prevents the shock if one of those points is GROUND.

I'm not sure why you would distrust a GFI, but they have a test
button. Use it, and be reassured.

The main plan, always, is not to touch the live wires.

In article
,
whit3rd wrote:
This must probably again be a voltage US/UK thing - or maybe me - but if
I was working on 240V live equipment I'd rather it was ALL floating
through an isolation transformer than rely on the complexities and
effectiveness of a GFI/RCD to prevent shocks at the bench.

Working on live 120V or 240V, you can always touch two points
and get a shock. Either an isolation transformer, or a GFI
interrupter, prevents the shock if one of those points is GROUND.

If one of those points is ground touching the other gives you a shock. If
neither is ground you can touch either one without a shock. The whole
principle of using an isolating transformer for safety. Makes for better
odds.

I'm not sure why you would distrust a GFI, but they have a test
button. Use it, and be reassured.

The main plan, always, is not to touch the live wires.

That is the best safety advice. But have a backup plan for if you do.

--
*A snooze button is a poor substitute for no alarm clock at all *

Dave Plowman London SW
To e-mail, change noise into sound.

In article , "Dave Plowman (News)" wrote:
In article
,
whit3rd wrote:
This must probably again be a voltage US/UK thing - or maybe me - but if
I was working on 240V live equipment I'd rather it was ALL floating
through an isolation transformer than rely on the complexities and
effectiveness of a GFI/RCD to prevent shocks at the bench.

Working on live 120V or 240V, you can always touch two points
and get a shock. Either an isolation transformer, or a GFI
interrupter, prevents the shock if one of those points is GROUND.

If one of those points is ground touching the other gives you a shock. If
neither is ground you can touch either one without a shock. The whole
principle of using an isolating transformer for safety. Makes for better
odds.


Its also necesary to make certain differential oscilloscope measurments if you don't
have a differential plug-in.

I also tend to use a battery scope for that instead.

greg


I'm not sure why you would distrust a GFI, but they have a test
button. Use it, and be reassured.

The main plan, always, is not to touch the live wires.

That is the best safety advice. But have a backup plan for if you do.

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

"sbnjhfty" wrote in message
...
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.

So what do you want it for, to cut down on noise when you contact the "live"
when working on the PSU or to avoid shocks whilst working on the gear ??

Regards......... Rheilly P

Rheilly Phoull wrote:
"sbnjhfty" wrote in message
...
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.

So what do you want it for, to cut down on noise when you contact the "live"
when working on the PSU or to avoid shocks whilst working on the gear ??

Regards......... Rheilly P




To avoid shocks.

sbnjhfty wrote:
Rheilly Phoull wrote:

So what do you want it for, to cut down on noise when you contact the
"live" when working on the PSU or to avoid shocks whilst working on
the gear ??


To avoid shocks.

In which country are you?

--
Adrian C

Adrian C wrote:
sbnjhfty wrote:
Rheilly Phoull wrote:

So what do you want it for, to cut down on noise when you contact the
"live" when working on the PSU or to avoid shocks whilst working on
the gear ??


To avoid shocks.

In which country are you?


USA

In article , sbnjhfty 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.


One thing you don't hear mentioned too much about is voltage.
We all know transformers are rated for a voltage with load.
The same thing can apply to an isolation transformer. i
have ordered custom wired transformers, and its NOT 1:1 with
no load. They increase the voltage to make up for the loss.
In some applications the voltage may be too high after this.
Good to use a variac along with an isolation transformer and monitor
voltage and current.

greg

sbnjhfty writes:

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.



Buy 2 transformers with 120V primaries, and some voltage secondaries.
Hook them back to back.

The weirder the secondary voltage, the lower the cost. Try all the usual
surplus suspects.

Of course the secondary power rating will be the limiting factor.


--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

"David Lesher"

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.


Buy 2 transformers with 120V primaries, and some voltage secondaries.
Hook them back to back.

The weirder the secondary voltage, the lower the cost.


** That is a very unwise suggestion:

AC supply transformers are NOT intended to be operated in reverse - cos the
magnetising current is intended to be carried by the supply side winding and
NOT the secondary.

A standard 500VA transformer operating from 120 VAC may well draw 1.5 amps
with no load - no problem since as the primary winding has only about 0.6
ohms of resistance and hence loses only 1.35 watts in heat.

The iron core losses will far exceed that.

However, if you try to make it work in reverse to deliver 120 volts at 500VA
from the primary - things get nasty.

First, the secondary will have to be fed with a ** higher voltage** than
the **off load** voltage by about 4% to cover voltage drop under load.

Naturally this increases the previously mentioned magnetising current level
by about 30%.

So now it is say 2 amps, referred to the primary.

2 amps at 120 volts = 240VA and that HAS to be *continuously supplied* by
the first tranny in the pair.

So, the result is that the pair of trannys can only deliver half the VA into
the load that one is capable of.


..... Phil

"Phil Allison" writes:

Buy 2 transformers with 120V primaries, and some voltage secondaries.
Hook them back to back.

The weirder the secondary voltage, the lower the cost.


** That is a very unwise suggestion:

AC supply transformers are NOT intended to be operated in reverse - cos the
magnetising current is intended to be carried by the supply side winding and
NOT the secondary.

I've used this approach several times in the past, and never had
the catastrophe you imply. I recall doing it with a pair of plate
transformers [600V at 200-300 mA]; and later with some weird 60V@6A ones.

The idle currents were not egregious, and given the broad range of
"120 volt line" the loss unobtrusive. It was surely safer than working
on hot-chassis equipment without same.


--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433