Isolation transformer use beyond test & measurement ?

[BravoV]

As topic's title, nowadays, is there practical use for an isolation transformer, if any ?

Examples ?

[BrianHG]

It got rid of that 'looping' ground buzz coming from the audio output of my old Sony HiFi VHS player.

Note that the buzz is because of the 'Y' capacitor and leakage in the switching supply transformer's crummy Hipot rating.

[bob91343]

You can hook it up to run 240 Volts gear from 120 Volts.  Or vice versa.

[BravoV]

It got rid of that 'looping' ground buzz coming from the audio output of my old Sony HiFi VHS player.

Note that the buzz is because of the 'Y' capacitor and leakage in the switching supply transformer's crummy Hipot rating.

Hmm .. noted, thank you. 

You can hook it up to run 240 Volts gear from 120 Volts.  Or vice versa.

Its not step-down/up transformer, as it has 1:1 winding ratio.

[bob91343]

It can be wired as step up or down.  For converting line power of 120V to give 240 V, just energize the primary and put the secondary in series.  You won't have isolation.

For the reverse, put the windings in series (be careful to get the phasing correct) and take output from one winding.

[tautech]

As topic's title, nowadays, is there practical use for an isolation transformer, if any ?

Examples ?

The same as it's always been, to reduce the rick of electric shocks from contact with phase and neutral or mains ground.
The outputs become phase and phase but only in relation to one another and with no relevance to mains ground.

I still use the ~20kg one my dad bought in the 60's after a near death experience with his skllsaw after lending it to a mate who left stored on the iron sand floor of his shed. Apparently it lit him up like a light bulb when he pulled the trigger and if it wasn't for the ol' girl watching and near the power point he wouldn't have lived another 30+ years.

[BravoV]

It can be wired as step up or down.  For converting line power of 120V to give 240 V, just energize the primary and put the secondary in series.  You won't have isolation.

For the reverse, put the windings in series (be careful to get the phasing correct) and take output from one winding.

Thanks, never thought of that wiring. 

Infact I already own similar thing, which is a variac/autotransformer, feel stupid now. 

[calzap]

Isolation transformers can be good at filtering noise, spikes and sags, and many are sold for this purpose.  Common use is for comm, medical and scientific equipment.  Be aware though that some of these, even though called isolation transformers, aren't really.  They may have one of the secondary output lines connected to the case and mains ground wire of the primary power cable.  This is usually stated in the specs.  Read the fine print!  An example is the Tripp-Lite Isolator series.  A test of isolation is to apply power and check for voltage between the output contacts and the contacts of a mains power socket.

Mike in California

[BravoV]

Isolation transformers can be good at filtering noise, spikes and sags, and many are sold for this purpose.

What kind of "filtering effectiveness" for these noise, spikes and sags ? Also noise such as like the one generated by crappy switching power supply count ?

About the sags, just curious how the "passive" transformer can withhold sags ? Its a 1:1 ratio winding. The sags here, cmiiw, example say like the kind of sag we experienced when the moment of a high powered devices (big wattage microwave oven, big rotary tool etc) was turned on right ?

[calzap]

You would have to read the specs for specific transformers to know the filtering characteristics.   For Tripp-Lite, go to tripplite.com.   There are numerous brands though.

I used "sag" to refer to a downward spike.  Most isolation transformers won't provide voltage stabilization for a prolonged decreased in input voltage.  However, some do provide long-term voltage stabilization and are usually advertized as line conditioners.  The Sola MCR series is an example.  I repeat that one must read the specs to determine if these are true isolation transformers. 

Mike in California

[bob91343]

Since it's a big iron transformer, it will afford some high frequency isolation as well.  It will depend on the details.

[vk6zgo]

You can use it to run AC/DC radios if you are a collector of such things.

[BravoV]

You would have to read the specs for specific transformers to know the filtering characteristics.   For Tripp-Lite, go to tripplite.com.   There are numerous brands though.

I used "sag" to refer to a downward spike.  Most isolation transformers won't provide voltage stabilization for a prolonged decreased in input voltage.  However, some do provide long-term voltage stabilization and are usually advertized as line conditioners.  The Sola MCR series is an example.  I repeat that one must read the specs to determine if these are true isolation transformers. 

Mike in California

Yeah, ideally, but the one I just recently scored is from local electronic recycler, cheap of course, but no reference nor spec. 

Shot with Fluke 189 for size comparison.

[BravoV]

Since it's a big iron transformer, it will afford some high frequency isolation as well.  It will depend on the details.

I'm assuming the HF isolation works both ways right ?

[Jeroen3]

With a isolation transformer you can create a system that allows for one ground fault. When system uptime goes first.
Operating rooms are an example of this. You do not want to troubleshoot a tripping RCD when you're working there. So the OR electrical system is floating with monitoring. When somewhere a problem occurs you are notified, and not put in the dark. You can troubleshoot later.

Also very often generators must operate since replacing is expensive and they aren't stock items. But a insulation failure somewhere in the system took out the original control system. When you add an isolation transformer you can tolerate this one fault.

There are still many use cases.

[helius]

The same as it's always been, to reduce the rick of electric shocks from contact with phase and neutral or mains ground.
The outputs become phase and phase but only in relation to one another and with no relevance to mains ground.

As an example, the UK uses "worksite power points" which are 120V supplied through a transformer with a center-tapped secondary. Each phase is only 60V to ground, making an electric shock much less dangerous.
This isn't an "isolation transformer" in the T&M sense but it is a similar way to reduce risk.

[station240]

Another use is to create a current limited AC supply.
The output current is limited by the saturation of the Isolation Tranformer's iron core.