isolation transformer

[Stu jaxon]

hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks,

[N_Cook]

On 22/11/2017 18:50, Stu jaxon wrote:
> hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks,
>

Does your ohmeter say there is a connection across both sides? ie an
autotransformer.

[pf...@aol.com]

On Wednesday, November 22, 2017 at 1:50:46 PM UTC-5, Stu jaxon wrote:
> hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks,

Most voltage-converter transformers are auto-transformers and do not provide isolation. As Mr. Cook suggests, see if you get continuity from the primary to the secondary.

http://www.electronics-tutorials.ws/transformer/trans28.gif This is an auto-transformer.

Peter Wieck
Melrose Park, PA

[J.B. Wood]

On 11/22/2017 01:50 PM, Stu jaxon wrote:
> hi group, does anyone know if i can use this= 750 Watt Voltage Converter Transformer Heavy Duty Step Up/Down 750W 110-220V as an isolation transformer, it does have output of 110v, ? thanks,
>

Hello, and do you have a particular make and model number of device in
mind? An marketed as an AC isolation transformers usually doesn't
provide voltage conversion with input (primary) to output (secondary)
energy transfer solely via magnetic coupling. There are also adjustable
autotransformers (e.g. the venerable Variac brand) that, for example,
takes 120 VAC at input and can provides 0-130 VAC output. The primary
and secondaries of these devices aren't conductively isolated (as an
ohmmeter test will confirm). There are also devices which combine both
isolation and adjustable autotransformer function in one enclosure. Or
you can simply take, say, a 120 VAC-to-120 VAC isolation transformer and
follow it with an adjustable autotransformer, keeping in mind the
maximum AC current/power ratings of the devices. Sincerely,

--
J. B. Wood e-mail: arl_1...@hotmail.com

[Stu jaxon]

here's the model Norstar ST-750.. it's on ebay for half price used. so more or less this just a surge protector.?

[Trevor Wilson]

**No. It's a step-down transformer, or autoformer. No way of knowing,
unless you can contact the manufacturer, or measure it yourself. I doubt
that it is an isolation transformer.

Which begs the question: Why do you need an isolation transformer?

--
Trevor Wilson
www.rageaudio.com.au

[Stu jaxon]

to protect my equipment, i picked up a new hobby.

[Trevor Wilson]

**An isolation transformer won't protect your equipment. An isolation
transformer is used to assist in protecting the operator (though that is
far from guaranteed).

Why do you imagine that an isolation transformer will protect your
equipment?
What sort of equipment?
What do you imagine the transformer will protect your equipment from?

--
Trevor Wilson
www.rageaudio.com.au

[bruce2...@gmail.com]

> to protect my equipment, i picked up a new hobby.

From what? And when you say 'surge protector', could you also have 'surge arrestor' (for much un-predictably higher un-controlled voltage input) in mind, as well?

To start with, your hobby device power processing should connect to an un-insulated copper or aluminum wire that should be in properly grounded and secured contact with your facility's (cold) water main.
Additionally, use specifically GFCI-advertized outlets when you think there is danger to people or property. It says that in the recent NEC- book rules, doesn't it?

[tabb...@gmail.com]

> to protect my equipment, i picked up a new hobby.

Your comments indicate that you most likely have several misunderstandings. It's your choice but would probably help you to say a lot more about what you're doing.


NT

[J.B. Wood]

On 11/22/2017 03:16 PM, Stu jaxon wrote:
>
> here's the model Norstar ST-750.. it's on ebay for half price used. so more or less this just a surge protector.?
>

That unit appears to be intended for those situations where, say a 120
VAC appliance sold in the U.S. is to be used in another country like the
UK on 240 VAC (also assuming the U.S. appliance can cope with 50 Hz vs
60 Hz). Vice-versa for using a UK-marketed appliance in the U.S. Most
likely it's a single winding transformer with a tap(s), which makes it
an autotransformer (no input-to-output isolation). But it could also
have separate primary and secondary coils. No way to tell from a
picture or not having a schematic. Sincerely,

[pf...@aol.com]

Some basics:

a) Isolation transformers are designed to protect users under some conditions, and *certain* types of equipment under *VERY* limited conditions. Those latter applications are primarily under hospital and research conditions where an isolated ground is not enough. Generally, RF-shielded rooms use isolation transformers in their power-supplies, for example. But, no equipment protects against deliberate stupidity or carelessness. If one inserts oneself into the circuit, one will be stung.

b) Voltage adjustment transformers tend to be as inexpensive as possible per-watt. A true isolation transformer would have very nearly twice as much conductor in it as a simple auto-transformer. Not t mention more core material as well - I am careful not to use 'copper' or 'iron', as very cheap devices will use neither.

c) Any unnecessary equipment adds a degree of unnecessary complexity - and with it an opportunity for error. I have a 110/220 step-up/down transformer purchased in Saudi Arabia with no markings at all. It came with a Euro/US adaptor that could plug into either side. So, I engraved "High Side" and "Low Side" on. Imagine me going the 'wrong way' in actual use. Not so bad going from 110 to 55 volts. But 220 - 440 V, not so good either.

If you need to step up/down, check the equipment. A surprising amount of vintage audio equipment has multi-tap primary transformers that might require only a simple change in wiring, and a surprising amount of modern consumer electronics have smart supplies that do it all automatically. Otherwise, a brand-name surge protector (with a downline equipment warranty) will be your best option to protect your equipment.

[gregz]

Commercial isolation transformers get rid of common mode noise, and since
one leg of output is tied to ground, forms a new local neutral. This
prevents noise differentials between ground and output. There is always
voltage sag, so a120 vol output is at full load. More perhaps too much with
small load. Could be 10- 15% over 120 volts. This is not a test transformer
with isolated output from ground referenced mains. Some have voltage
regulation too.

Greg

[whit3rd]

On Tuesday, November 28, 2017 at 12:48:01 AM UTC-8, GS wrote:

> Commercial isolation transformers get rid of common mode noise, and since
> one leg of output is tied to ground, forms a new local neutral.

That's only true of SOME isolation transformers; the ones used for
bench safety when working on live equipment do NOT make the
neutral-ground connection.

[tabb...@gmail.com]

quite. And building site transformers earth the centre tap.

Re noise, there's the capacitance...


NT

[gregz]

All commercial isolation transformers must inform to code. All Tripplite
isolators are grounded. It worries me some think it's all the same. Easy
enough to examine or measure. Still can be a problem on equipment needing a
ground configuration for the circuitry.

Greg

[whit3rd]

On Wednesday, November 29, 2017 at 12:22:46 AM UTC-8, GS wrote:
> whit3rd <whi...@gmail.com> wrote:
> > On Tuesday, November 28, 2017 at 12:48:01 AM UTC-8, GS wrote:
> >
> >> Commercial isolation transformers get rid of common mode noise, and since
> >> one leg of output is tied to ground, forms a new local neutral.
> >
> > That's only true of SOME isolation transformers; the ones used for
> > bench safety when working on live equipment do NOT make the
> > neutral-ground connection.
>
> All commercial isolation transformers must inform to code. All Tripplite
> isolators are grounded.

Commercial isolation transformers are leakage-tested, but the ground-neutral
connection is not always present.

Tripplite also makes smart power strips that won't work if plugged into
an isolation transformer that doesn't strap ground-to-neutral. So, they
work with isolated (hospitals, sometimes) power only if you add a Tripplite isolator.

details are here, in the reviews section:
<https://www.tripplite.com/for-patient-care-vicinity-ul-60601-1-medical-grade-ps-4-15a-hospital-grade-outlets-safety-covers-15-ft-cord~PS415HGULTRA/>

[Michael A Terrell]

pf...@aol.com wrote:
>
> c) Any unnecessary equipment adds a degree of unnecessary complexity - and with it an opportunity for error. I have a 110/220 step-up/down transformer purchased in Saudi Arabia with no markings at all. It came with a Euro/US adaptor that could plug into either side. So, I engraved "High Side" and "Low Side" on. Imagine me going the 'wrong way' in actual use. Not so bad going from 110 to 55 volts. But 220 - 440 V, not so good either.

That transformer would saturate and either blow a fuse, or overheat
if you fed 220 into a 110 winding, unless it is way over designed. It
would be a 220 to 440 transformer being used at a lower voltage if it
could handle 220 on the 110 winding.

[olds...@tubes.com]

On Wed, 22 Nov 2017 14:39:04 -0500, "J.B. Wood" <arl_1...@hotmail.com>
wrote:

>
>Hello, and do you have a particular make and model number of device in
>mind? An marketed as an AC isolation transformers usually doesn't
>provide voltage conversion with input (primary) to output (secondary)
>energy transfer solely via magnetic coupling. There are also adjustable
>autotransformers (e.g. the venerable Variac brand) that, for example,
>takes 120 VAC at input and can provides 0-130 VAC output. The primary
>and secondaries of these devices aren't conductively isolated (as an
>ohmmeter test will confirm). There are also devices which combine both
>isolation and adjustable autotransformer function in one enclosure. Or
>you can simply take, say, a 120 VAC-to-120 VAC isolation transformer and
>follow it with an adjustable autotransformer, keeping in mind the
>maximum AC current/power ratings of the devices. Sincerely,

I reaad on some website where someone took two 120 to 240 volt
transformers, connected both 240 windings together and ended up with 120
on the secondary, completely isolated from the AC line. This makes
sense, for someone who has two such transformers on hand. But would not
make sense to buy two transformers.

[Michael A Terrell]

tabb...@gmail.com wrote:
> On Tuesday, 28 November 2017 23:08:59 UTC, whit3rd wrote:
>>
>> On Tuesday, November 28, 2017 at 12:48:01 AM UTC-8, GS wrote:
>>>
>>> Commercial isolation transformers get rid of common mode noise, and
>>> since one leg of output is tied to ground, forms a new local
>>> neutral.
>>
>> That's only true of SOME isolation transformers; the ones used for
>> bench safety when working on live equipment do NOT make the
>> neutral-ground connection.
>

> Quite. And building site transformers earth the centre tap.


IOW, they convert the European 240volt system to the American
120V/240V system.

[tabb...@gmail.com]

On Thursday, 7 December 2017 21:17:18 UTC, Michael Terrell wrote:

They output 110v centre earthed, so nothing is over 55v ac from ground. It was the building site standard until RCDs made 110v not really needed.


NT

[Michael A Terrell]

Unless they didn't want to replace all their existing power tools?

The wiring is US, even if the transformer is only 50%. Not all of our
power tools are 120 VAC. Some are 240, and others are 480 VAC, three phase.

[olds...@tubes.com]

On Fri, 8 Dec 2017 01:14:00 -0500, Michael A Terrell
<mike.t...@earthlink.net> wrote:

>
> Unless they didn't want to replace all their existing power tools?
>
> The wiring is US, even if the transformer is only 50%. Not all of our
>power tools are 120 VAC. Some are 240, and others are 480 VAC, three phase.

I've always wondered why so many foreign countries have 240volts as
their standard voltage. We in the U.S. do just fine with 120v, except
for heating devices and some very large motors. So why do they continue
to use 240volts in these foreign countries? If for no other reason, it's
considerably more dangerous.....
I know all too well how getting shocked from 120v feels, and although I
have never gotten shocked by 240v, I know it's a lot worse. Both
voltages can kill a person, but I'd think that 240 kills faster...

[pf...@aol.com]

Very simplistic:

240 VAC Hot/Neutral is much more efficient than 120 VAC Hot/Neutral. Euro (residential) distribution is primarily three-wire ungrounded three-phase with varying phase-to-phase voltage. Grounding is done at the distribution transformer. Whereas North American distribution is 4-wire three-phase with single-phase 120/240 secondary distribution. Grounding in NA is done at multiple points.

Bottom line, Euro distribution allows either much more power on the same distance/size conductor, or the same amount of power to be transmitted twenty (20) times further for the same size conductor.

Again, a benefit of learning from others. Post War Europe - when power-to-the-people became the norm rather than the exception was not rich in resources. So, a system that permitted more efficient distribution became a significant advantage.

Very simplistically.

[et...@whidbey.com]

I think that if 240 volts is really that much more dangerous it
wouldn't be so popular. And think of the advantages. The wires can be
much smaller. And for the same wattage resistive losses are 1/4 that
of 120 volts.

[Foxs Mercantile]

On 12/8/2017 2:25 PM, olds...@tubes.com wrote:
> I know all too well how getting shocked from 120v
> feels, and although I have never gotten shocked
> by 240v, I know it's a lot worse.

Working at Northrop Aircraft, I had to deal with
120, 240 and 480 volt systems.

To put it simply, 120 will get your attention and
you let go of it.
480 will knock you on your ass.
240 however with grab hold of you and hang on.


--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

[tabb...@gmail.com]

On Friday, 8 December 2017 20:28:25 UTC, olds...@tubes.com wrote:
> On Fri, 8 Dec 2017 01:14:00 -0500, Michael A Terrell
> <mike.t...@earthlink.net> wrote:
>
> >
> > Unless they didn't want to replace all their existing power tools?
> >
> > The wiring is US, even if the transformer is only 50%. Not all of our
> >power tools are 120 VAC. Some are 240, and others are 480 VAC, three phase.
>
> I've always wondered why so many foreign countries have 240volts as
> their standard voltage. We in the U.S. do just fine with 120v, except
> for heating devices and some very large motors. So why do they continue
> to use 240volts in these foreign countries? If for no other reason, it's
> considerably more dangerous.....

it's safer and cheaper
It's also barely practical to run a 3kW heating device on 110v. Our 240v 13A delivers 3.1kW per socket no problem.

> I know all too well how getting shocked from 120v feels, and although I
> have never gotten shocked by 240v, I know it's a lot worse. Both
> voltages can kill a person, but I'd think that 240 kills faster...

it sure does. Deaths from electrical fires greatly outnumber electrocutions, and less current reduces the risk of those.


NT

[Mike Coon]

In article <pusl2dhr24me0qssh...@4ax.com>,
olds...@tubes.com says...

>
> have never gotten shocked by 240v, I know it's a lot worse. Both
> voltages can kill a person, but I'd think that 240 kills faster...

If you prefer a slow death, stick with it!

Mike.

[gregz]

There was an old patent using two neon sign type transformers back to back.
The problem with isos, you get higher voltage with no load than normal, and
droop 10-20% with load..

Greg

[pf...@aol.com]

On Sunday, December 10, 2017 at 3:48:23 AM UTC-5, GS wrote:
make sense to buy two transformers.
>
> There was an old patent using two neon sign type transformers back to back.
> The problem with isos, you get higher voltage with no load than normal, and
> droop 10-20% with load..

Properly designed Isos are vastly over-sized for the rated load. Which is why a good isolation transformer is not cheap, and a cheap isolation transformer is not good. Can't have both - new, anyway.

The Iso in my Heath is rated at 4A, fused at 3A, weighs around 10 pounds and does not sag. Some of the hospital-grades units I have worked with in the past were heavy enough to be a major PITA to lift or move, and rated in the 8 - 10 A region.

[tabb...@gmail.com]

On Sunday, 10 December 2017 08:48:23 UTC, GS wrote:

> <olds...@tubes.com> wrote:

> > I reaad on some website where someone took two 120 to 240 volt
> > transformers, connected both 240 windings together and ended up with 120
> > on the secondary, completely isolated from the AC line. This makes
> > sense, for someone who has two such transformers on hand. But would not
> > make sense to buy two transformers.
>
> There was an old patent using two neon sign type transformers back to back.

I can't imagine how that could be worth patenting. Many patents have no value.

> The problem with isos, you get higher voltage with no load than normal, and
> droop 10-20% with load..

It would take an unusually tiny transformer to be that badly regulated.


NT

[Foxs Mercantile]

"Neon sign transformer"
They are DESIGNED to be baldy regulated.
High voltage to strike the initial arc, then sag down to
a sustaining voltage.

Same design with fluorescent ballast transformers.

Both are designed for a specific purpose, not to be used in some
bastardized lash up.

[Foxs Mercantile]

On connecting transformers back to back to make an isolation
transformer.

A pair of 6.3 filament transformers, back to back, was a
popular kluge back in the '60s, but NOT for use as an
isolation transformer for testing radios.
Yes it was an isolation transformer, but it was to provide
an isolated 120 VAC for a B+ supply on small projects.

That 5 amp secondary at 6.3 volts translates to only 270 mA
on the primary side. Two transformers back to back is only
going to be good for about 200 mA load on the "isolated"
side.

AA5 "hot chassis radios from "back then" were typically 30
to 40 watts. That's 250-349 mA. This would be marginal at best.

It never fails to amaze me the number or ways people can come
up with to do things the wrong way. Then the amount of time
they waste trying to justify it.

[tabb...@gmail.com]

On Sunday, 10 December 2017 18:31:33 UTC, Foxs Mercantile wrote:

> On 12/10/2017 8:14 AM, tabbypurr wrote:
> > On Sunday, 10 December 2017 08:48:23 UTC, GS wrote:

> >> There was an old patent using two neon sign type transformers back to back.
> >
> > I can't imagine how that could be worth patenting. Many patents have no value.
> >
> >> The problem with isos, you get higher voltage with no load than normal, and
> >> droop 10-20% with load..
> >
> > It would take an unusually tiny transformer to be that badly regulated.
>
> "Neon sign transformer"
> They are DESIGNED to be baldy regulated.
> High voltage to strike the initial arc, then sag down to
> a sustaining voltage.
>
> Same design with fluorescent ballast transformers.
>
> Both are designed for a specific purpose, not to be used in some
> bastardized lash up.

which is one reason why no sensible person would use such a lash up


NT

[gregz]

In my experience 10% droop is pretty good. 15% more common. I'm just
talking transformers in general. A Feroresonant one will do good.

Greg

[gregz]

<tabb...@gmail.com> wrote:
> On Sunday, 10 December 2017 08:48:23 UTC, GS wrote:
>> <olds...@tubes.com> wrote:
>
>>> I reaad on some website where someone took two 120 to 240 volt
>>> transformers, connected both 240 windings together and ended up with 120
>>> on the secondary, completely isolated from the AC line. This makes
>>> sense, for someone who has two such transformers on hand. But would not
>>> make sense to buy two transformers.
>>
>> There was an old patent using two neon sign type transformers back to back.
>
> I can't imagine how that could be worth patenting. Many patents have no value.
>

I think I missed something in middle, like carbon trace resistors.

Greg

[tabb...@gmail.com]

On Tuesday, 12 December 2017 08:38:21 UTC, GS wrote:

Isolating transformers are not eh same animal as small appliance transformers. For the latter, you only need to get up to 12VA to get 15% regulation and 50VA to get 10%. Isos are more typically 500VA or more.


NT

[pf...@aol.com]

On Tuesday, December 12, 2017 at 3:38:21 AM UTC-5, GS wrote:

>
> In my experience 10% droop is pretty good. 15% more common. I'm just
> talking transformers in general. A Feroresonant one will do good.

Sola-type CV transformers put out a wretched wave-form. If your connected device is sensitive to mains noise, they will not work out so well. They will also back-feed noise in some cases.

It is important to understand that a purpose-made isolation transformer is designed not to sag, and is not-ever-never-ever operated at the margins of its theoretical design. They are operated at a limit well below their theoretical capacity for just this reason. Back-to-back kluges are the product of desperation or a McGyver type with a small brain, emphatically not any sort of long-term or permanent application.

[Foxs Mercantile]

On 12/12/2017 8:27 AM, pf...@aol.com wrote:
> Sola-type CV transformers put out a wretched wave-form.
> If your connected device is sensitive to mains noise,
> they will not work out so well.

Which is why I have one of their later "Harmonically
compensated" models.