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| Safest way to test unkown transformers with wire taps |
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| bsdphk:
"I have an old transformer that I believe came from a TV. One of the secondary windings is 150VAC." Did you overlook "Power that winding with low voltage AC from another transformer, a few watt should be enough." ? When you feed 12VAC and no more than a few watt into the winding with the highest DC resistance, it would have to be a very strange transformer indeed, if any of the other windings can hurt you. |
| queennikki1972:
I guess I had not thought that far. I have a few small transformers from alarm clocks and some of what i think are 12v and 24 v transformers. I realize now i should be looking at all of the advice above because i never know what size i might run into. I just thought on the very small transformers (LIGHT WEIGHT) it would be as easy as measuring across the secondary to see the output voltage. But you are all right, i first need to know the transformers primary and secondary and so fourth before lighting anything up and be more cautious. I will hold off on testing unknown things until i understand more clearly. I dove straight into building power supplies without even knowing all my symbols yet, lol. Cart before the horse. I am about the order a set of books called encylopedia of electronic components and already have the getting started in electronics by Forrest M Mims III. It would be great if i could find books specifically on transformers. MarKF Im paying attention, I will be making notes as you guys explain. |
| queennikki1972:
EXAMPLE Tiny transformer from alarm clock 2x red wires primary, I know because i clipped the wire myself. 2x black secondary unknown voltage unknown current red to red 1.479k ohm black to black 12.7 ohm black secondary to red primary 11M ohm. Made in china no markings plastic core Want to know output voltage and possible current |
| bob91343:
Back in college we used a big book on 'magnetic circuits and transformers' to work through some of the characteristics of practical inductive components. (I have a copy.) While I don't recommend this for the layman, I want to give a heads up that these things are anything but simple. First you need to realize that they are not linear. That is, as you increase the voltage applied, the current doesn't follow in proportion. Further, when you raise the input, there is a point at which the core saturates and the incremental inductance drops markedly, causing a rapid increase in current. That's why one needs to respect the ratings. This not only depends on applied voltage but on the frequency of that voltage. The heat generated comes from two main sources - the core and the windings. Heat is the worst enemy, as it can melt copper and cause smoke to come from insulation, etc. So if you are seeking a more profound education, realize that there is a lot to assimilate to appreciate these components. |
| MarkF:
--- Quote from: queennikki1972 on May 12, 2019, 06:58:59 pm ---EXAMPLE Tiny transformer from alarm clock 2x red wires primary, I know because i clipped the wire myself. 2x black secondary unknown voltage unknown current red to red 1.479k ohm black to black 12.7 ohm black secondary to red primary 11M ohm. Made in china no markings plastic core Want to know output voltage and possible current --- End quote --- If you can identify the primary winding, you can just plug it in and measure the secondary voltage. Current is harder. If it doesn't say, all you can do is guess based on transformer size and secondary wire gauge. Or If you can locate a fuse, you can go with its value as long as it hasn't been replaced with a bogus value. Or Wiring diagrams as in you giant transformer where each secondary had a fuse. |
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