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Measuring current draw
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elmegil



Joined: Mar 20, 2012
Posts: 2179
Location: Chicago
Audio files: 16
PostPosted: Thu Jul 04, 2013 2:02 pm    Post subject: Reply with quote  Mark this post and the followings unread
Osal wrote:
elmegil wrote:

I definitely do not know the overall VA rating of the transformer.
We can determine it. Just a few power resistors and a multimeter reading AC RMS voltage. In addition a K-prove or an infrared thermometer would be great.


I remember seeing you post about this in a previous discussion of a completely unknown transformer. I don't have an infrared thermometer or a K-probe... not even sure where to get the probe. I also don't have any power resistors handy; we'll see if Radio Shack has any, they did actually end up having one in-line fuse. My meter does read AC RMS....

Now that I've re-read that old thread, I realize I still made the mistake of not asking this seller for the Voltage Rating. Once again, probably not feasible to go back to them now.

No that is not the manufacturer's sheet, of course. Smile But it was the best I could get. googling the part number has never turned up anything, and right now it only turns up this thread Very Happy

AH, so here is a possible clue. The actual marking other than the TPZ number is:

Nippon Makisen NU3B3G-2029 5.11 (scratched off)

THAT actually does hit one other site:

http://www.olilio.com/file/detail/FQGS2.E68059.html

But that's all Sad
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elmegil



Joined: Mar 20, 2012
Posts: 2179
Location: Chicago
Audio files: 16
PostPosted: Thu Jul 04, 2013 5:49 pm    Post subject: Reply with quote  Mark this post and the followings unread
My sheet aluminum is 1/16" which is only 1.5mm....

So I'm guessing I'd either need to sandwich it, or find a commercial sink; most likely I'll do the latter.
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Osal



Joined: Aug 16, 2011
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PostPosted: Mon Jul 08, 2013 6:20 am    Post subject: Reply with quote  Mark this post and the followings unread
elmegil wrote:
not even sure where to get the probe.

http://en.wikipedia.org/wiki/Thermocouple
Most of the new DMM include a K-probe for temperature measurements. You can find one from about 20 euro. I think that we all should have this tool!

Quote:
I also don't have any power resistors handy; we'll see if Radio Shack has any, they did actually end up having one in-line fuse. My meter does read AC RMS....

To make it easier. Lets stay conservative and let's say that we want to output a maximum of 0.8A from this +/-15V power supply. You would need 2 resistor of 18 Ohms, power rating larger than 12.45W. Say the standard value 25W.
Just connect the resistors from the outputs of the power supply to the ground. Then, measure the actual voltage across the secondaries and the actual voltage in the mains electricity. Knowing the nominal mains voltage, we can estimate the nominal voltage rating of this transformer for this application.
If you don't have thermometer, just touch the transformer to be sure that it is not burning. For standard toroidal transformers we can expect about 50C of rise temperature over the ambient temperature, when it is delivering its current rating. Keep in mind that the transformer can last more than 5 hours to rise to its maximum temperature.
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