Determining the amperage of an unknown transformer
in [Design]
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From: John Larkin on 11 Aug 2010 11:13 On Wed, 11 Aug 2010 03:48:01 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Tue, 10 Aug 2010 17:33:50 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Tue, 10 Aug 2010 19:13:01 -0500, John Fields >><jfields(a)austininstruments.com> wrote: >> >> >>>>>There is one thing though, which is up to the sloppy standards you >>>>>allow tyourself on this group; You didn't label the X axis, so who >>>>>knows what it could be? >>>> >>>>Uh, what do you call the blue label ---> POWER VA ??? >>>> >>>>What did you think the overall title VA RATINGS --- WEIGHT GRAPH >>>>might mean? >>>> >>>>Idiot. >>> >>>--- >>>Yup, mea culpa. >>> >> >> vvvvvvvvvvvvvvvvv >> >>>I thought it was just more of your usual claptrap, so I didn't think >> >> ^^^^^^^^^^^^^^^^^ >--- >So you criticize others for snipping out of context and then turn >right around and do it yourself? > >More hypocrisy, wouldn't you agree? >--- > >>>BTW, how did you generate the nicely parallel lines corresponding to >>>EI lams and toroids? >> >>Ruler and pens. > >--- >And yet more evasion. > >Why am I not surprised? > >--- >JF Still nothing to say about transformers? You bever talk electronics any more. Did you run the ball-knocker thing yet? Any data? Your setup, with the three single strings, looks unstable to me, sort of a chaotic oscillator. The commercial units have two strings per ball, to keep the balls centered. I was looking forward to data. My guess is in the 100 us range, from pulse leading edges. But the physics is messy. John
From: John Fields on 11 Aug 2010 11:35 On Wed, 11 Aug 2010 08:13:29 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >Still nothing to say about transformers? You bever talk electronics >any more. --- news:b5p466l0ggg5pu84umpehcgpum6f5cj214(a)4ax.com Just a few posts up from this one. --- >Did you run the ball-knocker thing yet? Any data? --- Today, sometime. Yesterday didn't work out. --- >Your setup, with the three single strings, looks unstable to me, sort >of a chaotic oscillator. The commercial units have two strings per >ball, to keep the balls centered. --- Yeah, but it doesn't matter since, for my purposes, I'm only concerned about what happens after the first hit. --- >I was looking forward to data. My guess is in the 100 us range, from >pulse leading edges. But the physics is messy. --- Duly noted. --- JF
From: Grant on 11 Aug 2010 11:43 On 10 Aug 2010 23:45:01 -0500, Xfmr Guy <nospam(a)aol.com> wrote: >On Wed, 11 Aug 2010 10:25:37 +1000, Grant <omg(a)grrr.id.au> wrote: > ><SNIP> >> >>I been wondering lately how to tell the power split between two >>windings on a nice looking transformer in the 'junk box'. >> > >A well designed transformer should have the same current density in all the >windings. It's not too hard to show that given a couple (or three) windings, >with one winding carrying a current I1 and with an output voltage V1, and a DC >resistance R1, and similarly, a second winding with I2, R2 and V2, the current >density in winding 1 is proportional to (I1*R1)/V1, and in winding 2, it's >proportional to (I2*R2)/V2. > >Then the currents in the two windings (for equal current densities) are related >like this: > >I1/I2 = (R2*V1)/(R1*V2) Thank you for that, only thing left is to guess at the capacity (VA) rating of unknown transformer? Assuming the thing is stable temp no load, one could load it until a drop of what 5%, 10% no load to full load voltage? Then monitor loaded temperature rise to make sure transformer is not going to cook with that load. What sort of temperature rise on load to use? I'd guess at max 40'C about ambient? I've seen many have a 130'C thermal fuse builtin, according to nameplate. Grant.
From: John Larkin on 11 Aug 2010 12:10 On Wed, 11 Aug 2010 10:35:37 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Wed, 11 Aug 2010 08:13:29 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > > >>Still nothing to say about transformers? You bever talk electronics >>any more. > >--- >news:b5p466l0ggg5pu84umpehcgpum6f5cj214(a)4ax.com > >Just a few posts up from this one. Ah. Ohm's Law. I think I've seen that somewhere before. John
From: XfmrGuy on 11 Aug 2010 15:20
On Thu, 12 Aug 2010 01:43:46 +1000, Grant <omg(a)grrr.id.au> wrote: >On 10 Aug 2010 23:45:01 -0500, Xfmr Guy <nospam(a)aol.com> wrote: > >>On Wed, 11 Aug 2010 10:25:37 +1000, Grant <omg(a)grrr.id.au> wrote: >> >><SNIP> >>> >>>I been wondering lately how to tell the power split between two >>>windings on a nice looking transformer in the 'junk box'. >>> >> >>A well designed transformer should have the same current density in all the >>windings. It's not too hard to show that given a couple (or three) windings, >>with one winding carrying a current I1 and with an output voltage V1, and a DC >>resistance R1, and similarly, a second winding with I2, R2 and V2, the current >>density in winding 1 is proportional to (I1*R1)/V1, and in winding 2, it's >>proportional to (I2*R2)/V2. >> >>Then the currents in the two windings (for equal current densities) are related >>like this: >> >>I1/I2 = (R2*V1)/(R1*V2) > >Thank you for that, only thing left is to guess at the capacity (VA) >rating of unknown transformer? Assuming the thing is stable temp no >load, one could load it until a drop of what 5%, 10% no load to full >load voltage? Or, as another poster suggested, find a similar size transformer in a catalog and use its power rating as a starting point. > >Then monitor loaded temperature rise to make sure transformer is not >going to cook with that load. What sort of temperature rise on load >to use? I'd guess at max 40'C about ambient? I've seen many have a >130'C thermal fuse builtin, according to nameplate. Transformers designed for general purpose use are usually Class A; see: http://www.stancor.com/pdfs/Catalog_2006/Pg_g.pdf This class allows a hot spot temperature of 105' C. If room temperature is about 20' C, then you can have a 65' C rise. Have a look at post #14 in this thread: http://forum.allaboutcircuits.com/showthread.php?t=38273 There is a discussion of how to determine temperature rise by measuring the change in winding resistance after several hours on load. > >Grant. |