Alexander Posted July 11, 2017 Share Posted July 11, 2017 Is there a way to verify an autotransformers that have nothing but the 0,2 & 5 markings? That is without say a scope and just a DVM? Quote Link to comment Share on other sites More sharing options...
mboxler Posted July 11, 2017 Share Posted July 11, 2017 My guess...a T10A autoformer, which will reduce the voltage by 9dB. You would need to pass a low voltage sign wave across 0 and 5 and measure it. The voltage across 2 and 5 should be equal to .3535 times the input voltage. You would need a true RMS meter to measure the voltage. Mike Quote Link to comment Share on other sites More sharing options...
djk Posted July 12, 2017 Share Posted July 12, 2017 . Quote Link to comment Share on other sites More sharing options...
Alexander Posted July 24, 2017 Author Share Posted July 24, 2017 Hmm was afraid of that, do not have any of that equipment to do that. Quote Link to comment Share on other sites More sharing options...
djk Posted July 24, 2017 Share Posted July 24, 2017 A cheap meter with LCR can measure the inductance, and then you can calculate the turns ratio. https://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=lcr+meter&_sop=15 Quote Link to comment Share on other sites More sharing options...
Alexander Posted July 26, 2017 Author Share Posted July 26, 2017 On 7/24/2017 at 6:42 PM, djk said: A cheap meter with LCR can measure the inductance, and then you can calculate the turns ratio. https://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=lcr+meter&_sop=15 Thank you djk, all we need now is a chart for all of the T?A autotransformer winding ratios and how to translate the mH values when found Quote Link to comment Share on other sites More sharing options...
mboxler Posted July 26, 2017 Share Posted July 26, 2017 This chart comes from Bob Crites web site... http://www.critesspeakers.com/3636atz.pdf As you can see, if you measure the inductance between taps 0-5, divide it by 2.833 (9db), you should get the inductance between taps 0-2. If you have a good DCR meter, I believe you can accomplish the same thing. I measured the DCR on a 3619 autoformer. .37 ohms between taps 0-5. .14 ohms between taps 0-2. .37 / .14 = .2.64. My meter only carries out to 2 decimal places, so this falls between 8 and 9 db attenuation. Would you agree djk? Mike Quote Link to comment Share on other sites More sharing options...
Alexander Posted August 9, 2017 Author Share Posted August 9, 2017 On 7/24/2017 at 6:42 PM, djk said: A cheap meter with LCR can measure the inductance, and then you can calculate the turns ratio. https://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=lcr+meter&_sop=15 Thanks djk for the link, picked up a LCR for about $20. Sure it isn't as accurate as the $100+ meters but I think it will do the job. Quote Link to comment Share on other sites More sharing options...
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