isolation transformer needed

[mike]

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.

You can certainly come up with a reason to have an isolation transformer.
But for most things, it's just a false sense of safety/security
that will let you convince yourself that it is reasonable to do
VERY UNSAFE things.

What matters is the DIFFERENTIAL voltage between two points.
If you float the mains, you still have that differential
and have gained nothing. To be safe, you still have to
put both hands in your pockets and leave them there.

So, you're bored standing there with your hands in your pockets.
Let's do some unsafe things! Let's make a measurement with the
oscilloscope. So, you grab the probe. Hey, what's this black wire
dangling from the probe? Let's hook it "here" in the circuit.
Doesn't matter where "here" is, you've now got a NOT FLOATING
power supply. What's worse, the normally isolated secondary side
may have a lot of common-mode volts on it. You're at risk of a
shock...AND...simultaneously blowing up your scope and anything
you're using for a load.

Well, we can't have that. Let's cut the ground pin on the scope power
cord. That'll fix it...wonder if they have WiFi in heaven so I can
report my progress???

If you want to work on power supplies, get yourself an isolated
scope probe. Or a portable scope with no metal parts designed
for that type of measurement.

Tektronix A6902 probe works well. I picked up mine at a garage sale for
a buck. I suspect they're substantially more from a dealer.

Using a DVM with well-insulated probes, you can tell if the
diodes are open or input
storage cap is defective or there's volts on the fet. Beyond
that, you really need more than an isolation transformer if you
expect to do it safely.

mike

 

[Phil Allison]

"mike the madman "

You can certainly come up with a reason to have an isolation transformer.

** Like being able to safety ground the chassis, speakers and tuner box of a
TV set that otherwise all sit at lethal voltages.

But for most things, it's just a false sense of safety/security

** Yep - never use one if the unit already has one.

What matters is the DIFFERENTIAL voltage between two points.
If you float the mains, you still have that differential
and have gained nothing.

** Pure insanity.

So, you're bored standing there with your hands in your pockets.
Let's do some unsafe things! Let's make a measurement with the
oscilloscope. So, you grab the probe. Hey, what's this black wire
dangling from the probe? Let's hook it "here" in the circuit.
Doesn't matter where "here" is, you've now got a NOT FLOATING
power supply.

** Any sane tech will simply ground the common ( negative line ) in the high
voltage part of the PSU.

Then proceed as usual for units that have internal isolation trannys.

What's worse, the normally isolated secondary side
may have a lot of common-mode volts on it.

** Totally insane BOLLOCKS.

Well, we can't have that. Let's cut the ground pin on the scope power
cord.

** Something only rabid lunatics like mike do.

Yawnnnnnnnnnnn........

If you want to work on power supplies, get yourself an isolated
scope probe. Or a portable scope with no metal parts designed
for that type of measurement.

Tektronix A6902 probe works well. I picked up mine at a garage sale for a
buck.

** Used examples sell for around $US1000 through on-line dealers.

More utter insanity.

I suspect they're substantially more from a dealer.

** Wot a posturing, bullshit artist.

Using a DVM with well-insulated probes, you can tell if the
diodes are open or input storage cap is defective or there's volts on the
fet. Beyond that, you really need more than an
isolation transformer if you expect to do it safely.

** Wot an obvious pile of crapology.

Typical of mug, 5V engineers way out of their depth.


...... Phil

 

[mike]

Phil Allison wrote:

"mike the madman "

You can certainly come up with a reason to have an isolation transformer.


** Like being able to safety ground the chassis, speakers and tuner box of a
TV set that otherwise all sit at lethal voltages.

But for most things, it's just a false sense of safety/security


** Yep - never use one if the unit already has one.


What matters is the DIFFERENTIAL voltage between two points.
If you float the mains, you still have that differential
and have gained nothing.

** Pure insanity.


So, you're bored standing there with your hands in your pockets.
Let's do some unsafe things! Let's make a measurement with the
oscilloscope. So, you grab the probe. Hey, what's this black wire
dangling from the probe? Let's hook it "here" in the circuit.
Doesn't matter where "here" is, you've now got a NOT FLOATING
power supply.

** Any sane tech will simply ground the common ( negative line ) in the high
voltage part of the PSU.

Then proceed as usual for units that have internal isolation trannys.


What's worse, the normally isolated secondary side
may have a lot of common-mode volts on it.

** Totally insane BOLLOCKS.


Well, we can't have that. Let's cut the ground pin on the scope power
cord.


** Something only rabid lunatics like mike do.

Yawnnnnnnnnnnn........


If you want to work on power supplies, get yourself an isolated
scope probe. Or a portable scope with no metal parts designed
for that type of measurement.

Tektronix A6902 probe works well. I picked up mine at a garage sale for a
buck.

** Used examples sell for around $US1000 through on-line dealers.

More utter insanity.


I suspect they're substantially more from a dealer.

** Wot a posturing, bullshit artist.


Using a DVM with well-insulated probes, you can tell if the
diodes are open or input storage cap is defective or there's volts on the
fet. Beyond that, you really need more than an
isolation transformer if you expect to do it safely.

** Wot an obvious pile of crapology.

Typical of mug, 5V engineers way out of their depth.


..... Phil


Creative snipping eh?

 

[Andy]

On Dec 2, 12:03 pm, zekfr...@zekfrivolous.com (GregS) wrote:

In article <50c36de762d...@davenoise.co.uk>, "Dave Plowman (News)" <d...@davenoise.co.uk> wrote:



In article <hf5svh$5g...@usenet01.srv.cis.pitt.edu>,
GregS <zekfr...@zekfrivolous.com> wrote:
In article <%llRm.94141$gg6.27...@newsfe25.iad>, 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.

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.

 

[Phil Allison]

"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 fuck up.

This is NOT an opinion forum for morons.

Despite appearances.....



.... Phil

 

[Phil Allison]

"Dave Plowman (Nutcase)"

If your mains supply has one side grounded, then touching the 'live' side
causes a shock. If you use an isolating transformer, you can touch either
leg safely.

** Not if **anything** is earthing one of them -
like a scope or other test equipment ground.

Or an unknown fault in the equipment.

That plus an RCD feeding it provides the best degree of safety
in the workshop.

** Appalling BULLSHIT !!!

Once you add an isolation tranny in the AC supply

- RCDs do NOT work anymore !!!!
---------------------------------------------

Wot an ignorant pommy turd to say otherwise.

I'm surprised you don't see this.

** No surprise to anyone that Dave Fuckwit Powman is full of SHIT up to his
eyeballs.

The notion he describes is 100% FALSE and totally discredited many decades
ago as a very DANGEROUS practice.




..... Phil

 

[Dave Plowman (News)]

In article <hhbs06$hvi$1@news.eternal-september.org>,
mike <spamme0@go.com> wrote:

You can certainly come up with a reason to have an isolation transformer.
But for most things, it's just a false sense of safety/security
that will let you convince yourself that it is reasonable to do
VERY UNSAFE things.

What matters is the DIFFERENTIAL voltage between two points.
If you float the mains, you still have that differential
and have gained nothing. To be safe, you still have to
put both hands in your pockets and leave them there.

If your mains supply has one side grounded, then touching the 'live' side
causes a shock. If you use an isolating transformer, you can touch either
leg safely. That plus an RCD feeding it provides the best degree of safety
in the workshop. I'm surprised you don't see this.

--
*Wrinkled was not one of the things I wanted to be when I grew up

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

 

[Phil Allison]

"Dave Plowman (Nutcase)"

If your mains supply has one side grounded, then touching the 'live' side
causes a shock. If you use an isolating transformer, you can touch either
leg safely.

** Not if **anything** is earthing one of them - like a scope or
other test equipment ground.

Or an unknown fault in the equipment grounds the incoming AC
or something linked to it.

That plus an RCD feeding it provides the best degree of safety
in the workshop.

** Appalling BULLSHIT !!!

Once you add an isolation tranny in the AC supply

- RCDs do NOT work anymore !!!!
---------------------------------------------

Wot an PIG ignorant pommy turd to say otherwise.

That insane notion will KILL someone !!!!

I'm surprised you don't see this.

** No surprise to anyone that Dave Fuckwit Powman is full of SHIT
up to his eyeballs.

The notion he describes is 100% FALSE and totally discredited
many decades ago as a very DANGEROUS practice.

Dave can go rot in HELL.



..... Phil

 

[Dave Plowman (News)]

In article <7pvmgqFv0bU1@mid.individual.net>,
Phil Allison <phil_a@tpg.com.au> wrote:

If your mains supply has one side grounded, then touching the 'live' side
causes a shock. If you use an isolating transformer, you can touch either
leg safely.

** Not if **anything** is earthing one of them -
like a scope or other test equipment ground.

Isn't that obvious?

Or an unknown fault in the equipment.

Err, no. The whole idea of an isolating transformer is to isolate any such
faults.

That plus an RCD feeding it provides the best degree of safety
in the workshop.

** Appalling BULLSHIT !!!

Once you add an isolation tranny in the AC supply

- RCDs do NOT work anymore !!!!
---------------------------------------------

But it won't do any harm...

Wot an ignorant pommy turd to say otherwise.

I'm surprised you don't see this.

** No surprise to anyone that Dave Fuckwit Powman is full of SHIT up to
his eyeballs.

The notion he describes is 100% FALSE and totally discredited many
decades ago as a very DANGEROUS practice.

You really should seek treatment. Preferably by connecting yourself across
any mains supply. Especially two phase.

--
*If you try to fail and succeed, which have you done? *

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

 

[mike]

Dave Plowman (News) wrote:

In article <hhbs06$hvi$1@news.eternal-september.org>,
mike <spamme0@go.com> wrote:
You can certainly come up with a reason to have an isolation transformer.
But for most things, it's just a false sense of safety/security
that will let you convince yourself that it is reasonable to do
VERY UNSAFE things.

What matters is the DIFFERENTIAL voltage between two points.
If you float the mains, you still have that differential
and have gained nothing. To be safe, you still have to
put both hands in your pockets and leave them there.

If your mains supply has one side grounded, then touching the 'live' side
causes a shock. If you use an isolating transformer, you can touch either
leg safely. That plus an RCD feeding it provides the best degree of safety
in the workshop. I'm surprised you don't see this.

You amaze me.

You're so bent on proving me wrong that you
are not open to the possibility that applying
logic to misguided advice might yield useful
information.

Normally, I'd not waste my time trying to train
internet denizens. But in cases where a plethora
of misguided advice presented vehemently and with
AUTHORITY puts people at risk of DEATH,
I feel compelled to speak up. This stuff hangs
around for years.

So, back to your statement...with logic...

If you "touch" only one thing, it doesn't matter
whether you have an isolation transformer
or not. Problem is that touching one thing
provides no information beyond what you could
get using an insulated tool. You really don't need
to "touch" anything.

Electricity finds it's way to touch you through
paths you didn't anticipate.

How many of you woke up on the morning of your
electrocution and said, "today, I think I'll electrocute
myself"? Raise your hands high...oh, those of you
who committed suicide by electrocution can put your hands down.

This is the important part...my contribution to the thread...
Pay attention now:

The primary reason to want an isolation transformer to
troubleshoot a power supply is to work on the primary side.
Now, the KEY word is TROUBLESHOOT. What that means is that
the power supply has a FAULT in the primary circuit.
What's the fault? You don't know, or you'd just fix it.
How safe is it to troubleshoot that particular fault?
You don't know, 'cause you don't know what it is.

You're gonna RISK ELECTROCUTION based on the misguided
assumption that an isolation transformer keeps you safe.
YOU'RE NOT SAFE. YOU DON'T HAVE ANY IDEA WHAT THE PRIMARY
CIRCUIT IS, BECAUSE IT'S NOT AS DESIGNED. IT HAS A FAULT!!!!!!!
The node that the designer called common may not be common
at all. IT HAS A FAULT!!!! You should not arbitrarily ground
ANY node. It has a fault!!! (I'm skipping over the obvious
question, "what is ground anyway?")

An isolation transformer is not inherently bad. It can
provide a layer of protection. What is bad is the FALSE
sense of security
that the transformer makes it safe to poke around inside
a supply WITH A PRIMARY FAULT.

I'll say it one more time.

I don't care if you design power supplies in your sleep.
A FAILED power supply DOES NOT have the circuit that
was intended. It has a FAULT. A safety analysis based
on a working power supply and an isolation transformer
DOES NOT APPLY. Maybe you've always been lucky.
That's no cause to suggest to another that they can do what
you've been doing and NOT DIE.

 

[Phil Allison]

"Dave Plowman Ignorant Fucking Nutcase"

If your mains supply has one side grounded, then touching the 'live' side
causes a shock. If you use an isolating transformer, you can touch either
leg safely.

** Not if **anything** is earthing one of them - like a scope or
other test equipment ground.

Or an unknown fault in the equipment grounds the incoming AC
or something linked to it.

That plus an RCD feeding it provides the best degree of safety
in the workshop.

** Appalling BULLSHIT !!!

Once you add an isolation tranny in the AC supply

- RCDs do NOT work anymore !!!!
---------------------------------------------

Wot an PIG ignorant pommy turd to say otherwise.

That insane notion will KILL someone !!!!

I'm surprised you don't see this.

** No surprise to anyone that Dave Fuckwit Powman is full of
SHIT up to his eyeballs.

The notion he describes is 100% FALSE and totally discredited
many decades ago as a very DANGEROUS practice.

Dave can go rot in HELL.



..... Phil

 

[Phil Allison]

"Dave Plowman Fucking Nutcase"

If your mains supply has one side grounded, then touching the 'live' side
causes a shock. If you use an isolating transformer, you can touch either
leg safely.

** Not if **anything** is earthing one of them - like a scope or
other test equipment ground.

Or an unknown fault in the equipment grounds the incoming AC
or something linked to it.

That plus an RCD feeding it provides the best degree of safety
in the workshop.

** Appalling BULLSHIT !!!

Once you add an isolation tranny in the AC supply

- RCDs do NOT work anymore !!!!
---------------------------------------------

Wot an PIG ignorant pommy turd to say otherwise.

That insane notion will KILL someone !!!!

I'm surprised you don't see this.

** No surprise to anyone that Dave Fuckwit Plowman is full of SHIT
up to his eyeballs.

The notion he describes is 100% FALSE and totally discredited
many decades ago as a very DANGEROUS practice.

Dave can go rot in HELL.



..... Phil

 

[Dave Plowman (News)]

In article <7pvq1iFek4U1@mid.individual.net>,
Phil Allison <phil_a@tpg.com.au> wrote:

If your mains supply has one side grounded, then touching the 'live'
side causes a shock. If you use an isolating transformer, you can
touch either leg safely.

** Not if **anything** is earthing one of them - like a scope or
other test equipment ground.

Then don't do that. People like you shouldn't mess with electricity.

--
*He who laughs last, thinks slowest.

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

 

[Dave Plowman (News)]

In article <hher8n$7cu$1@news.eternal-september.org>,
mike <spamme0@go.com> wrote:

If your mains supply has one side grounded, then touching the 'live'
side causes a shock. If you use an isolating transformer, you can
touch either leg safely. That plus an RCD feeding it provides the best
degree of safety in the workshop. I'm surprised you don't see this.

You amaze me. You're so bent on proving me wrong that you are not open
to the possibility that applying logic to misguided advice might yield
useful information.

Normally, I'd not waste my time trying to train
internet denizens. But in cases where a plethora
of misguided advice presented vehemently and with
AUTHORITY puts people at risk of DEATH,
I feel compelled to speak up. This stuff hangs
around for years.

And you still haven't learnt anything, obviously.

--
*There are two kinds of pedestrians... the quick and the dead.

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

 

[Dave Plowman (News)]

See our Oz retard is at it again...

--
*I wonder how much deeper the ocean would be without sponges*

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

 

[Meat Plow]

On Wed, 30 Dec 2009 12:51:35 +1100, "Phil Allison"
<phil_a@tpg.com.au>wrote:

"Dave Plowman (Nutcase)"

If your mains supply has one side grounded, then touching the 'live' side
causes a shock. If you use an isolating transformer, you can touch either
leg safely.


** Not if **anything** is earthing one of them - like a scope or
other test equipment ground.

Or an unknown fault in the equipment grounds the incoming AC
or something linked to it.


That plus an RCD feeding it provides the best degree of safety
in the workshop.

** Appalling BULLSHIT !!!

Once you add an isolation tranny in the AC supply

- RCDs do NOT work anymore !!!!
---------------------------------------------

Wot an PIG ignorant pommy turd to say otherwise.

That insane notion will KILL someone !!!!


I'm surprised you don't see this.


** No surprise to anyone that Dave Fuckwit Powman is full of SHIT
up to his eyeballs.

The notion he describes is 100% FALSE and totally discredited
many decades ago as a very DANGEROUS practice.

Dave can go rot in HELL.



.... Phil

Out of your Topamax again?

 

[Meat Plow]

On Wed, 30 Dec 2009 22:23:51 +1100, "Phil Allison"
<phil_a@tpg.com.au>wrote:

.... Phil

Yes you do give very bad advice.

 

[Dave Plowman (News)]

In article <hhfd8h$jdr$1@news-01.bur.connect.com.au>,
Phil Allison <phil_a@tpg.com.au> wrote:

"Dave Plowman Ignorant Fucking Nutcase"

If your mains supply has one side grounded, then touching the 'live'
side causes a shock. If you use an isolating transformer, you can
touch either leg safely.

** Not if **anything** is earthing one of them - like a scope or
other test equipment ground.

Then you end up with the same as plugging direct.

Or an unknown fault in the equipment grounds the incoming AC or
something linked to it.

That plus an RCD feeding it provides the best degree of safety
in the workshop.

** Appalling BULLSHIT !!!

Once you add an isolation tranny in the AC supply

- RCDs do NOT work anymore !!!!
---------------------------------------------

You use an RCD protected supply to feed the isolating transformer. To help
protect from a possible fault there.

Wot an PIG ignorant pommy turd to say otherwise.

That insane notion will KILL someone !!!!

Please state *how* either will make things worse. Of course a retard like
you can't cope with such a concept.

I'm surprised you don't see this.

** No surprise to anyone that Dave Fuckwit Powman is full of
SHIT up to his eyeballs.

The notion he describes is 100% FALSE and totally discredited
many decades ago as a very DANGEROUS practice.

No it hasn't. Isolation transformers are still used for many safety
related reasons. But don't expect you to understand why. Obviously.

--
*How do you tell when you run out of invisible ink? *

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

 

[D Yuniskis]

Hi Dave,

Dave Plowman (News) wrote:

See our Oz retard is at it again...

Hmmm... was this the Phil guy? I didn't see the post to
which you are replying -- and he is the only entry in my
killfile, here (though it could just be the original post
hasn't made it to my server).

I ask only because my filter was *supposed* to kill the
entire thread and not just his post (i.e., I shouldn't
have seen your followup to his post -- if indeed that
was the case).

--don

 

[Phil Allison]

" Dave Plowman = Ignorant Fucking Nutcase"

If your mains supply has one side grounded, then touching the 'live' side
causes a shock. If you use an isolating transformer, you can touch either
leg safely.

** Not if **anything** is earthing one of them - like a scope or
other test equipment ground.

Or an unknown fault in the equipment grounds the incoming AC
or something linked to it.

That plus an RCD feeding it provides the best degree of safety
in the workshop.

** Appalling BULLSHIT !!!

Once you add an isolation tranny in the AC supply

- RCDs do NOT work anymore !!!!
---------------------------------------------

Wot an PIG ignorant pommy turd to say otherwise.

That insane notion will KILL someone !!!!

I'm surprised you don't see this.

** No surprise to anyone that Dave Fuckwit Powman is full of
SHIT up to his eyeballs.

The notion he describes is 100% FALSE and totally discredited
many decades ago as a very DANGEROUS practice.

Dave can go rot in HELL.




..... Phil