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| Why Are 3 or 4 Secondary Winding Toroidal Transformers Hard To Find? |
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| Alley_Cat_Jack:
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 |
| amspire:
--- 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. |
| Alley_Cat_Jack:
Yeah, I forgot to mention I was having difficulty finding toroidal transformers with additional taps as well. Clearly I wasn't looking hard enough, as I was looking on digikey. Either that or they don't exist at the specs I was looking for. Sent from my HTC One_M8 using Tapatalk |
| Alley_Cat_Jack:
Also, that transformer you linked to has the center tap on the primary, not the secondary. Sent from my HTC One_M8 using Tapatalk |
| uncle_bob:
Hi Some of the transformer outfits sell "extras" at some amazingly low prices on eBay. It's the real commercial transformer, from the real deal manufacturer. They might have an odd label on them from the (likely canceled) contract they were built for. Stacking a few 25VA / $5 transformers is a perfectly acceptable thing to do. It will take up a bit more room than a single 100VA device (that costs $56). All the usual disclaimers apply ... US dollars not Canadian. Shipping to anywhere not included on any of it. Bob |
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