Determining the amperage of an unknown transformer
in [Design]
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From: John Larkin on 10 Aug 2010 20:33 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 ^^^^^^^^^^^^^^^^^ > >BTW, how did you generate the nicely parallel lines corresponding to >EI lams and toroids? Ruler and pens. John
From: John Larkin on 10 Aug 2010 20:45 On Wed, 11 Aug 2010 10:25:37 +1000, Grant <omg(a)grrr.id.au> wrote: >On Tue, 10 Aug 2010 09:29:53 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Tue, 10 Aug 2010 08:32:06 -0700 (PDT), Scott <smbaker(a)gmail.com> >>wrote: >> >>>I have a toroidal power transformer that I'm considering using for a >>>power supply project. It has two secondaries -- 18v-0-18v and 0-48v. >>>Part number is 7-40-0011 (already tried googling it, no luck). I'm >>>pretty sure I purchased it from one of the online surplus places, >>>maybe All Electronics, probably about a decade ago. >>> >>>What's the best way to determine how many amps the secondary is rated >>>for? Can I just throw a resistive load on it an measure the current? >>>or does this risk damage? >> >>This will get you started. >> >>ftp://jjlarkin.lmi.net/XfmrScatter.JPG > >Thanks for that. Quite useful, though our 50Hz xfmrs would be a >little heavier, I think. I think all these were 50/60 Hz transformers. All the ones we buy are. > >I been wondering lately how to tell the power split between two >windings on a nice looking transformer in the 'junk box'. You could measure the resistance and the open-circuit voltages. You could assume that each winding could be loaded to, say, 90% or 95% of its open-circuit voltage. > >Xfmr looks around 120VA with 9V and 33V secondaries. > >I was thinking measure no load, then load to 5% or 10% voltage >drop? Work from those results. Oops, yes. > >Tim's resistance measure would shed some light too. >> >> >>Or just load it progressively and see how hot it gets. > >Good double check of the other methods. Bit slow? > >This xfmr is a good quality E+I one with earth screen, got the >outside shorted copper turn and iron turn to reduce external >field, switch and fuse in a partial enclosure. Destined for >a bench power supply, I think. Once I have an idea where to >set the power limits. > > >Using SLA batteries for testing stuff has produced some fun >moments, watching the magic smoke escape ;) > >http://grrr.id.au/image/74HC74-let-go-magic-smoke-with-a-bang.jpg > I don't suppose it still works. >That was an odd situation where a line of five 'HCMOS chips >started emitting smoke from their middle pins, until the one >in the centre one popped its top. Didn't blow the 35A battery >fuse. Wirebonds make nice detonators, but don't pass a lot of I^2*T. The first atom bombs used exploding wires. Later ones used gold thinfilms. I spent the weekend blowing up DC/DC converters, not too bad at only $4 each. I unpotted one, but lost the transformer in the process. ftp://jjlarkin.lmi.net/VASD1_top.JPG Next project is to breadboard a current limiter circuit, and blow them up together. John
From: Nunya on 10 Aug 2010 22:35 On Aug 10, 5:25 pm, Grant <o...(a)grrr.id.au> wrote: > On Tue, 10 Aug 2010 09:29:53 -0700, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >On Tue, 10 Aug 2010 08:32:06 -0700 (PDT), Scott <smba...(a)gmail.com> > >wrote: > > >>I have a toroidal power transformer that I'm considering using for a > >>power supply project. It has two secondaries -- 18v-0-18v and 0-48v. > >>Part number is 7-40-0011 (already tried googling it, no luck). I'm > >>pretty sure I purchased it from one of the online surplus places, > >>maybe All Electronics, probably about a decade ago. > > >>What's the best way to determine how many amps the secondary is rated > >>for? Can I just throw a resistive load on it an measure the current? > >>or does this risk damage? > > >This will get you started. > > >ftp://jjlarkin.lmi.net/XfmrScatter.JPG > > Thanks for that. Quite useful, though our 50Hz xfmrs would be a > little heavier, I think. > > I been wondering lately how to tell the power split between two > windings on a nice looking transformer in the 'junk box'. > > Xfmr looks around 120VA with 9V and 33V secondaries. > > I was thinking measure no load, then load to 5% or 10% voltage > drop? Work from those results. > > Tim's resistance measure would shed some light too. > > > > >Or just load it progressively and see how hot it gets. > > Good double check of the other methods. Bit slow? I would load it up UNTIL it reaches max op temp AFTER all settling time. Then, all you need do is take note of those set-up parameters, and place your operating window inside of that at whatever cmfort level you want. > > This xfmr is a good quality E+I one with earth screen, got the > outside shorted copper turn and iron turn to reduce external > field, switch and fuse in a partial enclosure. Destined for > a bench power supply, I think. Once I have an idea where to > set the power limits. The op temp which YOU desire to run under with the fringe ranges you want will determine how hard you decide to push it, so one would think it best to simply "run it up" under observation, and slowly get to where you want the TEMP to be, then OBSERVE the set-up, then operate BELOW that plateau. > Using SLA batteries for testing stuff has produced some fun > moments, watching the magic smoke escape ;) Did you see the Siemens/Orange County Chopper E-bike episode? There was a guy there "touching" wires together after it failed to spool up on initial trial. It was funny, he jumped off several feet away, and when the camera went back on him, he had a huge burn on his fingers. 73VDC at a dead short on #4 copper cables! And those dopes get over $10k an episode! (the mechanics, not the family) > > http://grrr.id.au/image/74HC74-let-go-magic-smoke-with-a-bang.jpg You're a dangerous individual. > That was an odd situation where a line of five 'HCMOS chips > started emitting smoke from their middle pins, until the one > in the centre one popped its top. Didn't blow the 35A battery > fuse. Wild circuit connections then.
From: Nunya on 10 Aug 2010 22:36 On Aug 10, 5:33 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Tue, 10 Aug 2010 19:13:01 -0500, John Fields > > <jfie...(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 > > ^^^^^^^^^^^^^^^^^ > > > > >BTW, how did you generate the nicely parallel lines corresponding to > >EI lams and toroids? > > Ruler and pens. > > John You even define the word 'generate' differently.
From: John Larkin on 10 Aug 2010 23:09
On Tue, 10 Aug 2010 19:36:35 -0700 (PDT), Nunya <jack_shephard(a)cox.net> wrote: >On Aug 10, 5:33�pm, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> On Tue, 10 Aug 2010 19:13:01 -0500, John Fields >> >> <jfie...(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 >> >> � � � � � � � � � � � � � � � � � � � � � � � � � � ^^^^^^^^^^^^^^^^^ >> >> >> >> >BTW, how did you generate the nicely parallel lines corresponding to >> >EI lams and toroids? >> >> Ruler and pens. >> >> John > >You even define the word 'generate' differently. I didn't define "generate" recently. I did a manual 1st order curve fit, like they taught us in all our high school and college physics and chemistry and engineering labs. Don't you remember? John |