Determining the amperage of an unknown transformer
in [Design]
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From: Scott on 10 Aug 2010 11:32 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: Jan Panteltje on 10 Aug 2010 11:34 On a sunny day (Tue, 10 Aug 2010 08:32:06 -0700 (PDT)) it happened Scott <smbaker(a)gmail.com> wrote in <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? Wire diameter?
From: Tim Wescott on 10 Aug 2010 12:16 On 08/10/2010 08:32 AM, Scott 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? Weigh it, then look in the Digi-Key or Mouser catalog for toroidal transformers of similar weight -- that'll come close to telling you the VAC rating of the thing overall. For output current, measure the resistance of the windings, then find the currents for the two secondaries that seems to make them equally efficient from an open-circuit vs. loaded condition. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From: John Larkin on 10 Aug 2010 12:29 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. John
From: GregS on 10 Aug 2010 13:05
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 |