Power Transformer Output

crutschow

Joined Mar 14, 2008
27,714
To be conservative, it would basically be the summed total RMS current from all the outputs.

Note that, if you connect a full-wave bridge rectifier-capacitor to the outputs to get DC, you need to de-rate the DC current to about 60% of the RMS rating.
 

Thread Starter

Jonathan Foong

Joined Mar 13, 2021
27
To be conservative, it would basically be the summed total RMS current from all the outputs.

Note that, if you connect a full-wave bridge rectifier-capacitor to the outputs to get DC, you need to de-rate the DC current to about 60% of the RMS rating.
Noted and thank you very much for your advice.
 

michael8

Joined Jan 11, 2015
177
That works, assuming it's a current rating, until you see a transformer which says "5B". Then what?

Is there anything on the other side?

I'd trace out the windings via ohm meter as well as inspecting the wires on each terminal. The transformer core size
and wire sizes also give hints at the power & current level.
 

Thread Starter

Jonathan Foong

Joined Mar 13, 2021
27
That works, assuming it's a current rating, until you see a transformer which says "5B". Then what?

Is there anything on the other side?

I'd trace out the windings via ohm meter as well as inspecting the wires on each terminal. The transformer core size
and wire sizes also give hints at the power & current level.
The front side per picture attached
 

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michael8

Joined Jan 11, 2015
177
Ah. I'd guess that the 0, 6, 9, 12 are voltage taps on a single winding. And that it's maximum current 500 mA.
So perhaps the 5A on the other side is similar.

I've searched for MTH transformer and found a bunch of model train references but nothing which looked like this
transformer. Perhaps this transformer, though it looks unused, is really old? Also model train power "supplies"
do seem to use multiple taps on transformers (perhaps before they went solid state).

Still 5A * 32 volts is 160 watts (plus 12v * 500 mA or 6 watts for the other) so I'd check that the size of the core
matched an about 200 watt transformer. And I'd check the continuity to prove the taps really are taps on
each single winding (3 windings: primary 0 110 220 240, 500 mA 0 6 9 12, 5A 0, 6, 9, 12, 15, 18, 24 32).
 

Thread Starter

Jonathan Foong

Joined Mar 13, 2021
27
Ah. I'd guess that the 0, 6, 9, 12 are voltage taps on a single winding. And that it's maximum current 500 mA.
So perhaps the 5A on the other side is similar.

I've searched for MTH transformer and found a bunch of model train references but nothing which looked like this
transformer. Perhaps this transformer, though it looks unused, is really old? Also model train power "supplies"
do seem to use multiple taps on transformers (perhaps before they went solid state).

Still 5A * 32 volts is 160 watts (plus 12v * 500 mA or 6 watts for the other) so I'd check that the size of the core
matched an about 200 watt transformer. And I'd check the continuity to prove the taps really are taps on
each single winding (3 windings: primary 0 110 220 240, 500 mA 0 6 9 12, 5A 0, 6, 9, 12, 15, 18, 24 32).
Thank you very much for your detailed analysis, I get to know more about this transformer before my decision of its applications. I bought this during an electronic products exhibition trip to Indonesia, this booth also many other booths were selling many different types and sizes of transformers, I suppose this is a place that made a lot of transformers. At that time, before Covid 19 pandemic, I bought it because of its very wide range of inputs and outputs within one piece that interests me. Now I am thinking to make a simple linear power unit consist of various outputs for my future hobby projects maybe of 5V digital, 12V/24V security, 15V stepper, etc. but I am sort of no idea of its power rating to start with.
 

michael8

Joined Jan 11, 2015
177
as stated above:

If you don't know the maximum output power, measure the overall dimensions then look in a transformer catalogue for one the same size. It will have a very similar power rating.

What are the measurements, especially of the core? And the cross section of the core which goes down the middle.

Here's an old thread on figuring out the power rating of a transformer..
https://forum.allaboutcircuits.com/threads/assessing-an-unknown-transformer.38273/
 
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