Necessary Equipments needed for SMPS development.

[jzaghal]

Hi Everybody,

This is my first post. Thank you for a nice and informative site. I want to share some knowledge, hoping it is useful for somebody.

A simple and useful idea on how to make an isolation transformer is as follows:

Using two identical transformers, such as a 500VA ,220V a.c to 12V a.c .

Simply connect the 12V a.c sides to each other. Applying 220V a.c power to one transformer will

give you an isolated 220V a.c at the output of the other transformer.

The idea is : the first transformer will step down the 220V a.c to 12V a.c ( the normal way),

and, the other transformer is used in reverse, i.e. having 12V a.c applied to its 12V side ( used inversely) ,

this will hopefully give you the isolated 220V a.c. output.

Care must be taken not to apply 220V a.c to the 12V a.c side !!! as this is dangerous, and will result in

destroying the transformer, as it will try to raise the output to 220 V a.c to 220V * (220/12) i.e around 4000V a.c .

But of course, the inter-winding insulation will break down, destroying the transformer.

Take care, and good Luck.

 

[envisionelec]

I don't understand why there is a warning to use only one input of an oscilloscope on an SMPS. I use two, three and four channels simultaneously on a regular basis....?

 

[Kanwar]

I don't understand why there is a warning to use only one input of an oscilloscope on an SMPS. I use two, three and four channels simultaneously on a regular basis....?

Because a rookie having non isolated channel oscilloscope can place the GND terminal of various probes at various potentials which can damage the scope as well as smps.

 

[mikile]

Hello people,
this is my first post here, but for some time I am reading some very cool stuf about diy smps, from very cool people who like to share...
do you connect only scope on isolation transformer , or scope and smps?

 

[MicrosiM]

I don't understand why there is a warning to use only one input of an oscilloscope on an SMPS. I use two, three and four channels simultaneously on a regular basis....?

Seems to me that you are using an ISOLATED oscilloscope.

Because most oscilloscope with multi channels, using one GND

 

[mikile]

@ MicrosiM

do you connect only scope on isolation transformer , or scope and smps? I am waiting some etd49 cores to start with some diy smps...any help will be valuable...

 

[MicrosiM]

@ MicrosiM

do you connect only scope on isolation transformer , or scope and smps? I am waiting some etd49 cores to start with some diy smps...any help will be valuable...

i am using isolation transformer for my Oscilloscope, because two times the internal Varistor blown (before using isolation transformer), I really cant tell why did that happen. I was measuring waves at the IGBT, then Booom.

Will help you into the SMPS

Regards

 

[envisionelec]

Because a rookie having non isolated channel oscilloscope can place the GND terminal of various probes at various potentials which can damage the scope as well as smps.

Hi Kanwar. That makes sense...I'm always careful where I stick my GND probe. ((@

 

[tartan5]

Hello,

Just purchased a TRIAD MAGNETICS 1000VA N-59MG Isolation Transformer from Ebay. Hot and Neutral are Isolated, and ground passes through. Do I need to float the ground of the scope to eliminate the ground reference?

Thanks!

 

[MicrosiM]

Hello,

Just purchased a TRIAD MAGNETICS 1000VA N-59MG Isolation Transformer from Ebay. Hot and Neutral are Isolated, and ground passes through. Do I need to float the ground of the scope to eliminate the ground reference?

Thanks!

Hi

a picture of the product will help to clarify things.

but if the 220VAC line is completely isolated, I dont think there will be any risk

but it wont hurt if you DISCONNECT the oscilloscope GND, in my case I am NOT using the GND, and USING isolation transformer

Trying to make SMPS without isolation transformer at first place, you may get nasty surprises, at least damaging the oscilloscope

Hope that helps...

 

[tartan5]

Here is a link to a pdf of the Isolation transformer:

http://www.mouser.com/ds/1/410/N-59MG-17182.pdf

My scope and supply will be running off 60Hz 120V.....

 

[MicrosiM]

Here is a link to a pdf of the Isolation transformer:

http://www.mouser.com/ds/1/410/N-59MG-17182.pdf

My scope and supply will be running off 60Hz 120V.....

That looks perfect

Try with GND, I think its safe since the 110VAC lines are completely isolated

Regards...

 

[tartan5]

I'm having trouble understanding why the isolation transformer is used on the O'scope......

Not sure about elsewhere, but in the US residential 120 VAC the Neutral wire is bonded to earth ground at the electrical box. Putting the scope on an isolation transformer will isolate the Hot/Neutral from ground, but the scope probe grounds will still be tied to earth ground through the grounding plug, unless you float (pull or cut) the ground connection, in which case now your scope ground is tied to potentially lethal voltages.

It would seem to make more sense to run the power supply on the isolation transformer...... then all of the generated HV is not ground referenced, and you would be much less likely to get shocked. Also, you can then ground-reference any point in the circuit with the scope probe ground, and no current will flow, as long as you don't tie another ground lead to a different potential.....

Am I missing something?

Thanks!

 

[MicrosiM]

I'm having trouble understanding why the isolation transformer is used on the O'scope......

Not sure about elsewhere, but in the US residential 120 VAC the Neutral wire is bonded to earth ground at the electrical box. Putting the scope on an isolation transformer will isolate the Hot/Neutral from ground, but the scope probe grounds will still be tied to earth ground through the grounding plug, unless you float (pull or cut) the ground connection, in which case now your scope ground is tied to potentially lethal voltages.

It would seem to make more sense to run the power supply on the isolation transformer...... then all of the generated HV is not ground referenced, and you would be much less likely to get shocked. Also, you can then ground-reference any point in the circuit with the scope probe ground, and no current will flow, as long as you don't tie another ground lead to a different potential.....

Am I missing something?

Thanks!

This is 100% correct

You can Isolate the SMPS. But both ways will protect you!

regards

 

[tartan5]

i am using isolation transformer for my Oscilloscope, because two times the internal Varistor blown (before using isolation transformer), I really cant tell why did that happen. I was measuring waves at the IGBT, then Booom.

Will help you into the SMPS

Regards

Is it possible that you were running a grounded SMPS, with a floating scope? This might make sense, because if ungrounded, and the probe ground lead is connected to high power transients, the energy would try to return across the varistor to the Neutral line.....

 

[tartan5]

P.S. Thanks for the insights!!!! I want to make sure I don't blow up my Tek MSO-4032..... It belongs to my work, and I am doing this project on the side, I am sure they wouldn't be happy!!!!

Regards
Tartan5

 

[MicrosiM]

Is it possible that you were running a grounded SMPS, with a floating scope? This might make sense, because if ungrounded, and the probe ground lead is connected to high power transients, the energy would try to return across the varistor to the Neutral line.....

SMPS was not grounded at all

But there was no isolation transformer used.

 

[envisionelec]

An isolation transformer with a common ground is NOT correct. You must use a "balanced" isolation transformer so that the secondary ground is not tied to earth except through a RFI-coupling safety capacitor or RCD loop-breaker. You must be very careful to treat all secondary points as though the full potential exists. Secondary-side GND is now the reference, but it commonly NOT at zero volts. I cannot stress this enough.

Think of using a battery operated, portable scope and only on battery power (do not plug in to charge during tests).

 

[tartan5]

I understand why a battery powered scope would be useful, in fact I have access to one but unfortunately it's quite old, does not hold a charge well, and has very limited bandwidth.....

I looked up a balanced isolation transformer.....It looks like the neutral would be offset from the ground potential, whereas in typical use it would be (roughly) the same potential (as ground) when not run on the Balanced Isolation Transformer.....

You say that "An isolation transformer with a common ground is NOT correct"..... What are the potential problems?

Thanks!

 

[Malmir]

I might be the only one who is a bit confused. People talks about earth, GND, ground and common ground.
I do no know of US, but here, if one have a isolation transformer with EARTH passing through, there will be no danger as long as one do NOT touch both secondary leads and EARTH, but that has nothing to do with EARTH as touching both leads are lethal. Touching only one will put that lead to "reference" EARTH.
IF the scope power input are legal according to TÜV standards, the EARTH can be connected, but no connection between EARTH and one of the 2 secondary leads should be made.

Would there be any idea in "designing" a scope with diff input ?