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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 23rd May 2020, 12:13 am   #21
joebog1
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Default Re: Rewinding a toroidal mains transformer

If you are going to voltage double it, make sure you use full wave rectification!!! If you use half wave the BH curve will be all biassed one way, the transformer will run hot, it will be noisy, and regulation will be horrible. A toroid must be closely balanced.

Joe
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Old 23rd May 2020, 8:16 am   #22
Diabolical Artificer
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Default Re: Rewinding a toroidal mains transformer

"OK, it's not pretty but £16 as compared to over £100 for a commercial unit looks good to me." Me too, well done. I recommend terminating the winding wire to your multi stranded wire somewhere where you can get to it in future, might be an idea to go easy on the varnish in that area too. I've had winding's break just there in the past, the thought of having to unwind does not appeal.

Andy.
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Old 23rd May 2020, 10:22 am   #23
Alan_G3XAQ
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Default Re: Rewinding a toroidal mains transformer

Quote:
Originally Posted by joebog1 View Post
If you are going to voltage double it, make sure you use full wave rectification!!! If you use half wave the BH curve will be all biassed one way, the transformer will run hot, it will be noisy, and regulation will be horrible. A toroid must be closely balanced.

Joe
Good point Joe. Yes, I'd already decided to use a full wave doubler, like in the simulation screenshot attached
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Old 23rd May 2020, 4:14 pm   #24
Electronpusher0
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Default Re: Rewinding a toroidal mains transformer

Quote:
Originally Posted by Alan_G3XAQ View Post
Quote:
Originally Posted by joebog1 View Post
If you are going to voltage double it, make sure you use full wave rectification!!! If you use half wave the BH curve will be all biassed one way, the transformer will run hot, it will be noisy, and regulation will be horrible. A toroid must be closely balanced.

Joe
Good point Joe. Yes, I'd already decided to use a full wave doubler, like in the simulation screenshot attached
Thats the same as used in the Armstrong valve Amp (see post 8 of this thread)

Peter
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Old 29th May 2020, 6:03 pm   #25
Alan_G3XAQ
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Default Re: Rewinding a toroidal mains transformer

The added HT winding worked out pretty much exactly as predicted by the circuit simulator. I'm using a full wave voltage doubler which seems to work fine with the more or less constant current drawn by the receiver it is powering.

The most time consuming part was waiting for the RS 199-1480 transformer vanish to dry after I'd given the whole transformer a good soaking in a tub of the stuff. I put about 8W DC through the mains winding to get the temperature up to hand hot (60C?) but it still took two days for the smell to dissipate.

Anyway, job done. Thanks for all the help
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