Electronics > Beginners
Toroidal transformer modification
sureshot:
I was thinking of asking this in an existing thread, but thought it might be useful for other applications if it's a doable option. So I won't go it to the other thread details, other than I need a separate power source of at least 20mA to power a panel meter. My thoughts have turned to the idea of adding some suitable wire windings to my toroidal mains transformer. Then winding teflon tape over these windings. I haven't tried this yet, but think it might be a possibility for the 4.5 - 6 Volts I need. At around 100mA. Then current limit that with a 100mA fuse for safety. So does this sound a viable option for additional source of power for this low current application ? I would have asked this question in the panel meter thread I started. But feel it would be lost in there, as if it's viable, it could be useful to others that might need a separate low power source.
Thanks for reading, any thoughts appreciated.
capt bullshot:
Yes, that'll do the job.
Gyro:
Yes, perfectly doable. The primary winding is almost universally buried under the existing secondary, so there are no particular safety isolation issues. I've done it several times for auxiliary windings.
Make sure you use normal insulated transformer wire, never bare uninsulated (obvious I know, but some have tried - and failed!). You'll want to do a test winding to establish the turns per volt and then wind accordingly, spreading turns evenly around to core. Teflon / Kapton / Polyester tape should be fine.
P.S. Try to find a little bobbin for the wire, small enough to fit through the center hole, trying to thread long lengths of un-tethered wire through the hole is a pain.
JS:
Yes you could, wibd a few turns, let's say 10, and measure the voltage. Do the math to find out how many turns you need.
The caveat here is the original VA rating of the transformer should be remain unchanged, so from the load you had available you need to take this new out. You are only talking about 0.6W, you could be using about 1VA for that. So if you had a 100VA transformer and using 50VA from it you are totally fine, but if you had a 10VA transformer already tight to the requirements you can have some problems, the first one to appear would be lower voltage than expected in all windings I guess.
JS
sureshot:
Thank you for your replys. That's great, it means I don't have to add a separate small transformer. The toroidal transformer is 300 VA at 15 Volts twin secondary windings, the primarys are 2 x 115 Volts windings. Save a lot of hassle not needing a separate power source.the bobbin idea is great, saves threading and dragging wire through the core.
Thanks again much appreciated.
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