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| Why Are 3 or 4 Secondary Winding Toroidal Transformers Hard To Find? |
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| tautech:
--- Quote from: Alley_Cat_Jack on May 02, 2016, 01:58:01 am ---Yeah, I was wondering if I should go with a pair of transformers and if there is anything to worry about when doing so. --- End quote --- My first real PSU was built using 2 old 12VAC halogen transformers got for free, series'd or paralleled depending on output levels required and configured as Brumby has mentioned with correct phasing. LM338K to get 5A capability....easy build. |
| uncle_bob:
--- Quote from: Alley_Cat_Jack on May 02, 2016, 01:58:01 am ---Yeah, I was wondering if I should go with a pair of transformers and if there is anything to worry about when doing so. --- End quote --- Hi Quick and simple way to phase check the transformers: 1) Hook up the primary of each of the two transformers in parallel. 2) Hook up the secondary(s) in series. 3) Put a volt meter on the secondary series combo. You will either get: A) Secondary A + Secondary B on the multimeter -or- B) Secondary A - Secondary B on the meter As long as you are careful staying away from the line voltage, there isn't much risk in doing this. Once you know the phase, a couple pieces of colored tape is about all you need to preserve that information. The same process also works for "lining up" the phase on multiple secondary transformers. One caution: On multi primary transformers with unknown phase, start with only one primary connected. Be careful with the other primary since it will have line voltage on it. Generally the safest way to sort out unmarked primaries is to drive a secondary with (very) low voltage AC. You then sort them out just like the secondaries above. Bob |
| bill8n95:
--- Quote from: amspire on May 02, 2016, 12:53:03 am --- --- Quote from: Alley_Cat_Jack on May 02, 2016, 12:38:49 am ---I am trying to design my first linear variable power supply, but I am running into a bit of a problem. I am having trouble finding toroidal transformers with more than 2 secondary windings. The idea being of course to use relays to connect additional windings as voltage is increased. Does anyone know where to find these transformers. Or is there another way to do this that I have not realised yet? Sent from my HTC One_M8 using Tapatalk --- End quote --- If there is room to add more windings through the middle of the toroid, you can add your own extra windings. Also I would have thought that two centre-tapped windings are probably common. That gives you 4 different points to tap off which is usually enough. Add an extra low power winding or two to power the control circuit/logic and you are set. Just as an example, there is something like this: http://www.digikey.com/product-detail/en/triad-magnetics/VPM36-2780/237-2041-ND/5721760 Two 18V centre tapped windings. That lets you tap off 9v, 18v, 27V and 36V at 2.78A AC. It looks like this transformer has plenty of room to add a small extra winding to power the regulator circuit. An extra low powered winding doesn't have to go all the way around the transformer - you can just wind it over over 5 or 10 percent of the core, and it will still be fine. Add tape underneath and above to make sure it is well insulated. Finding out the number of turns is easy. Add 10 turns of any wire. Connect the primary to mains and measure the voltage across the 10 turns. Divide the voltage by 10 and you have the volts/turn. --- End quote --- I really don't understand how can someone tap to 9V (or 27V) on this transformer. I think that a transformer like this with 2x18V taps (4 wires) or 18V- 0V- 18V configuration (3 wires) , just lets you output 18V , or 36V . (All voltages in RMS) |
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