Determining the amperage of an unknown transformer
in [Design]
|
From: Nunya on 10 Aug 2010 15:43 On Aug 10, 10:35 am, John Fields <jfie...(a)austininstruments.com> 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 > > --- > Hmmm... > > Since when are pounds SI units? > > -- > JF Not only that, but using weight as the rule is not going to be very accurate either.
From: John Larkin on 10 Aug 2010 16:02 On Tue, 10 Aug 2010 11:58:27 -0700 (PDT), Nunya <jack_shephard(a)cox.net> wrote: >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. Obviously. They seem to design for fairly high operating temperature, which saves copper. That requires better insulation and varnish. Every transformer designer has to make that tradeoff. John
From: Nunya on 10 Aug 2010 17:54 On Aug 10, 1:02 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Tue, 10 Aug 2010 11:58:27 -0700 (PDT), Nunya > > > > <jack_sheph...(a)cox.net> wrote: > >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. > > Obviously. They seem to design for fairly high operating temperature, > which saves copper. That requires better insulation and varnish. Every > transformer designer has to make that tradeoff. > > John Obviously and seem in the same reference. Hmmmm. Designing for high op temp does NOT "save copper". Insulation on mag wire is 1500 V/mil. They do NOT require "better insulation" They use standard single strength or double strength mag wire in ALL of their COTS designs. Nothing 'special' at all. As far as the varnish goes, they use ONE variety, and it is the same across the industry, and the only time it would be specialized is for a specialized contract. That would most likely be Dolph's AC-43. Sorry, John, but folks are not cutting corners the way you claim they are.
From: Martin Riddle on 10 Aug 2010 18:57 "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? I would try to get a measurement of the wire diameter. Use 600-700 circular mills to figure out the current capability. If it�s a small transformer then you can assume single insulation and get the wire size off the standard charts. Then you can load it and check for temp rise. Less guess work with the load selection. Cheers
From: Grant on 10 Aug 2010 20:25
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 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? 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 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. Grant. |