Just a quick question,
Whats the best way to wind another winding onto a toroidal power transformer?
Small bobbin and keep joining the winding or a long shaft?
I could just trial and error, however some must have done it..
Is it better to spread the winding across the whole core or limit it to about 2/3 of the way around the core?
Thinking about the tail outs from existing windings..
Regards
M. Gregg
Whats the best way to wind another winding onto a toroidal power transformer?
Small bobbin and keep joining the winding or a long shaft?
I could just trial and error, however some must have done it..
Is it better to spread the winding across the whole core or limit it to about 2/3 of the way around the core?
Thinking about the tail outs from existing windings..
Regards
M. Gregg
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if it's low VA then you need lots and lots of turns for required output voltage. That requires a lot of wire that is very long.
Best to wind that onto a long flat bobbin that fits through the eye of the toroid.
If it's high VA then you need a lot fewer turns but need thicker wire. That is again a hassle.
Use that long flat bobbin.
If you only need a low current winding from a high VA transformer then you can handwind,
But in all cases you have to calculate the length of wire required for the number of turns you have worked out.
Wind on a test winding by hand. Just try 10 turns. Power up from the mains, with the bulb tester and then measure the AC voltage available at the open circuit test winding.
The long flat bobbin can be a piece of plywood, 300mm long, by 5mm thick, by the "eye" diameter less 5mm. It has to be able to pass through after you wind on the second last turn. Round the ends of the ply so that you curve the wire around the ends and not create "kinks".
Best to wind that onto a long flat bobbin that fits through the eye of the toroid.
If it's high VA then you need a lot fewer turns but need thicker wire. That is again a hassle.
Use that long flat bobbin.
If you only need a low current winding from a high VA transformer then you can handwind,
But in all cases you have to calculate the length of wire required for the number of turns you have worked out.
Wind on a test winding by hand. Just try 10 turns. Power up from the mains, with the bulb tester and then measure the AC voltage available at the open circuit test winding.
The long flat bobbin can be a piece of plywood, 300mm long, by 5mm thick, by the "eye" diameter less 5mm. It has to be able to pass through after you wind on the second last turn. Round the ends of the ply so that you curve the wire around the ends and not create "kinks".
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It all depends on what purpose the winding is for. If its a supplementary winding for heaters then its relatively simple to hand wind onto the core using appropriately sized wire. Do 10turns and test what you get and then scale to what you need - testing at the end to fine tune. Bind up with insulating tape at the end.
I have done this a number of times to build a heater transformer.
Higher voltages are unlikely to be practical since feeding the required wire through the hole is unlikely to be practical.
Shoog
I have done this a number of times to build a heater transformer.
Higher voltages are unlikely to be practical since feeding the required wire through the hole is unlikely to be practical.
Shoog
Sometimes a gem of a story comes up and this is one of them. Thanks for posting.
Mac
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I take a long length of wire and fold it in half. Then put it on the opposite side for the other wires coming out of the toroid and tape the middle of the wire to the transformer and start winding one side at a time. This will get you in the ballpark. Take 5' or so and wind about 10 turns. Power it up and measure what you get. Take the desired voltage and divide into your voltage. Say 60V/10v if you got 10V out of 10 turns. You get 6 after division. Multiply that by 10 and you know you need 60 turns. Take a measuring device and see how long your windings are. Then estimate how tight your turns need to be spaced to stay even around the core. I've done this a bunch for filaments and bias.
Seems that 60V is going to take a few hundred turns from my experience. I personally wouldn't attempt it.
There is also the small issue of toroidals passing large amounts of hi-freq line hash.
Far better for you to find some small EI transformers to press into service - these can usually be hidden under the case without taking up to much real estate.
Shoog
There is also the small issue of toroidals passing large amounts of hi-freq line hash.
Far better for you to find some small EI transformers to press into service - these can usually be hidden under the case without taking up to much real estate.
Shoog
Besides the tedium of winding several hundred turns on the existing core there is also the distortion and rectifier harmonics from the filament windings if you are using dc for filament heating.
You might consider a small EI or toroid, were you here in the U.S. I would recommend one of the Antek line, some of them even have electro-static shielding. In terms of dealing with garbage (dust
) from the line you can always use a common/diff mode choke on the primary side.
Yes, 60V will require a few turns but if its fairly thin wire that's not a big problem.
As post 8 suggests, and many before it, make yourself a little bobbin that will easily pass through the centre of the toroid (allow for your extra turns). Calculate how long the winding will be and add a good few metres (its sickening if you are a few turns short). You don't need to be exact about spacing the turns around the toroid, close enough is good enough, just try to space them around the core.
HF "hash" passing through the core. Yes, it's true but I've never had any problem with it. A bit of filtering will usually get rid of it. Hell, you've got a toroid in there aleady.
As post 8 suggests, and many before it, make yourself a little bobbin that will easily pass through the centre of the toroid (allow for your extra turns). Calculate how long the winding will be and add a good few metres (its sickening if you are a few turns short). You don't need to be exact about spacing the turns around the toroid, close enough is good enough, just try to space them around the core.
HF "hash" passing through the core. Yes, it's true but I've never had any problem with it. A bit of filtering will usually get rid of it. Hell, you've got a toroid in there aleady.
Been there, done that: http://www.diyaudio.com/forums/tube...-5-v-secondary-antek-2t350-3.html#post2354966
It probably took me about an hour to add two 12 V windings to a toroid. I'm not sure I'd attempt it with a bias winding - definitely not without a bobbin.
~Tom
It probably took me about an hour to add two 12 V windings to a toroid. I'm not sure I'd attempt it with a bias winding - definitely not without a bobbin.
~Tom
#30 awg magnet wire is ample for bias winding....virtually no grid current flows, only in the voltage deviders...
you can wind say 10 turns to get your actual turns per volt....then you will get your actual turns for 60 volts...when winding, always add 1 turn at the end....
this is very doable....and a lot of fun...
I just added a winding to a tube preamp toroidal power transformer so that I could bump up the B+ by about 50 volts. It was incredibly easy, the trick is definitely all in making a really nice bobbin shuttle. Mine could have been a bit thicker, as I wound the wire around it lengthwise. I used a 26.5 inch long piece of aluminum. I notched the ends for the wire, and then rounded all corners and polished smooth. If I did it again I would use thicker aluminum so that the wire bends around a larger radius at the ends. Perhaps most important, I covered the ends with a shiny smooth liquid rubber that's sold for sealing scratches in vinyl-coated dishwasher racks. It goes on like fingernail polish, but is slightly rubbery, and not high-friction grippy. I should coat all the corners, perhaps the whole thing!
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