How to test a pulse transformer

Thread Starter

Jotto

Joined Apr 1, 2011
151
The easiest way to test a pulse transformer is using your oscope. The people with a Fluke scope that has three different cal tests is probably the best one to play with. Others will have the 1 or 5 volts cal that can be used. But all work equally as well as the other. I just like playing with more then one.

Right now I am testing using a 1 vpp signal @ 1khz. You have to remove one of the terminals on the primary side to open the circuit. Apply your signal there and put the scope on the secondary. If you have amplification the transformer is good, if its flat or lower then the signal applied its bad. To get an idea of what a bad one looks like, put the cal on the secondary side and the scope on primary and you will get a idea what a bad one will look like. Also remember that you must disconnect the secondary if you wish to try that.

vpp input .488 output 2.28
acv input .172 output .808
freq input 5khz output 13.1khz
db input 13 dbm output .3 dbm

I am using the scope on the primary and secondary. Notice the change in frequency from the 1khz being applied and then changing to 5khz on the input.
 

Thread Starter

Jotto

Joined Apr 1, 2011
151
What do you get on the output with different duty cycle input?
That would depend on the signal your using. This is just a quick test to determine that the transformer is good.

Are you asking if your using a 5 vpp cal on the scope or using one of the extra ones that Fluke gives you? Or using a function generator. I can test the Fluke out tomorrow. I can take pictures also, but as I stated before the file size allowed here is too small for my pictures without cropping them.

The smallest file size for me using my camera is 2mb. The only other option I can think of is making a pdf file.
 

thatoneguy

Joined Feb 19, 2009
6,359
I've been interested in pulse transformers since I somehow got one and played with it.

It acted really differently between 5% and 50% Duty, that's why I asked. I think I tossed mine away since I didn't know the full ratings.
 

Thread Starter

Jotto

Joined Apr 1, 2011
151
I did a few more tests at different frequencies. This is using the Fluke scopemeter.

488hz
vpp .208 input 16.72 output
acv .07 input 5.90 output
freq 1.32khz input 2.44khz output
db -20.2 input 17.6 output

976hz
vpp .21 input 16.87 output
acv .07 input 5.9 output
freq 2.3khz input 4.88khz output
db -20.3 input 17.7 output

1.951khz
vpp .22 input 16.8 output
acv .08 input 5.92 output
freq 3.6khz input 9.76 output
db -19.7 input 17.6 output

Sine wave
vpp .06 input .11 output
acv .02 input .04 output
freq 102khz input 12.43khz
db -30 input -26 output

The only significant change is frequency, except on the sine wave which is not a good test for the transformer.
 
Last edited:

jimkeith

Joined Oct 26, 2011
540
There are numerous parameters that can be tested--each requires a different set-up:

*V-us rating (when does it saturate?)
*Leakage inductance (how tight is the coupling?)
*Inter-winding capacitance (how well does it isolate?)
*Turns ratio
*Phasing
*Winding resistances
*Hipot voltage test

Beyond that, there is voltage isolation rating that is inherent in the physical design
 

Lundwall_Paul

Joined Oct 18, 2011
226
The first thing that I do not see mentioned yet is the you need a copy of the specification for the part you want to test. Please post that if you have it.
 
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