Determining the amperage of an unknown transformer
in [Design]
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From: John Fields on 10 Aug 2010 13:35 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 --- Hmmm... Since when are pounds SI units? -- JF
From: John Larkin on 10 Aug 2010 13:55 On Tue, 10 Aug 2010 17:05:25 GMT, zekfrivo(a)zekfrivolous.com (GregS) wrote: >In article <7hv266h4vj8k6vp6coppr51lg00ekk248m(a)4ax.com>, 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 >> >> >>Or just load it progressively and see how hot it gets. > > >Watching temp is good. > >I load down a transformer until the voltage drops 15%. This a bit tricky with multiple windings. >A great transformer is rated for 10% drop >A poor transformer is rated for a 30% drop. > >I still have a batch of old Signal Transformer Co. trans. >that seem to go by the 10% system. > >greg I always found the Signal transformers to be a bit soft. I think they used higher-temperature varnish and such to reduce the amount of copper. John
From: John Larkin on 10 Aug 2010 13:56 On Tue, 10 Aug 2010 12:35:06 -0500, John Fields <jfields(a)austininstruments.com> 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 > >--- >Hmmm... > >Since when are pounds SI units? Idiot. I post something useful, and you follow up with something useless. It's gotten to be a pattern. John
From: Tim Williams on 10 Aug 2010 14:39 Measure DCR. Assume 5% regulation per winding (including the primary, that's 10% total, i.e. ~90% efficiency). Current is then DCR / (0.05 * Vout). Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms "Scott" <smbaker(a)gmail.com> wrote in message news:d721ef17-ccf7-44b4-9cf2-b6e83883da51(a)t5g2000prd.googlegroups.com... >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?
From: Nunya on 10 Aug 2010 14:58
On Aug 10, 10:55 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Tue, 10 Aug 2010 17:05:25 GMT, zekfr...(a)zekfrivolous.com (GregS) > wrote: > > > > >In article <7hv266h4vj8k6vp6coppr51lg00ekk2...(a)4ax.com>, 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 > > >>Or just load it progressively and see how hot it gets. > > >Watching temp is good. > > >I load down a transformer until the voltage drops 15%. This a bit tricky with multiple windings. > >A great transformer is rated for 10% drop > >A poor transformer is rated for a 30% drop. > > >I still have a batch of old Signal Transformer Co. trans. > >that seem to go by the 10% system. > > >greg > > I always found the Signal transformers to be a bit soft. I think they > used higher-temperature varnish and such to reduce the amount of > copper. > > John You're a goddamned idiot. They use single or double strength, standard off-the-shelf mag wire, and ANY 'varnishing' takes place AFTER the wind. Got any more absolutely glaring non-sense? Nobody gets to cheat on copper. It comes down to core media, and winding particulars. Take an xformer made that way, and try to "cheat on the copper" and you'll find that you no longer have the transformer that you originally designed. All the varnish does is lock everything down mechanically and provide environmental segregation. Got any other segments of the scientific realm that you wish to insult today? Maybe a sport that you are to thick to grasp? |