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Old 9th Nov 2018, 2:41 pm   #1
Aub
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Default Toroidal Transformer with 220V or 240V Secondary?

Hello all,

I've been looking at various supplier sites, trying to find a toroidal transformer with 230/240 mains primary, but a single 230/240 v secondary at such a rating, that it would be bridge rectified and used in an H.T. power supply giving 300v DC at 150 mA.

I haven't looked extensively, but I can't see one listed anywhere. Preferably, it would have an open centre, such that an extra winding could be added to supply L.T. of 6.3v at, say, 3 amps, as i've seen done in some articles.

I know I could use a conventional ( non-toroidal ) transformer, but they do seem very expensive when compared with the price of a toroid.

Many thanks

Aub.
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Old 9th Nov 2018, 3:13 pm   #2
Ed_Dinning
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Default Re: Toroidal Transformer with 220 0r 240v Secondary?

Hi Aub, simplest way is to use 2, 240v to 24v toroids back to back. They would need to be at least 50VA rating.

As you say, a conventional transformer would be expensive as 150mA at 300v is much more than the average radio takes.

Mail me if all else fails as I may have a used/ tested conventional transformer.

Ed
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Old 9th Nov 2018, 5:00 pm   #3
Aub
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Default Re: Toroidal Transformer with 220 0r 240v Secondary?

Thanks Ed. I hadn't thought of doing it that way.
Aub
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Old 10th Nov 2018, 1:20 am   #4
Paul JD
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Default Re: Toroidal Transformer with 220 0r 240v Secondary?

Airlink Transformers do one that might be what you want https://airlinktransformers.com/prod...ange-cm0050172

I have bought from them in the past and they are very reliable.
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Old 10th Nov 2018, 4:45 am   #5
G8UWM-MildMartin
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Default Re: Toroidal Transformer with 220 0r 240v Secondary?

Thanks for the link. That's a very useful-looking transformer for adding heater windings to, and at a reasonable price. Bookmarked!
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Old 10th Nov 2018, 7:41 am   #6
Electronpusher0
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Default Re: Toroidal Transformer with 220 0r 240v Secondary?

I have successfully used these transformers with an overwind:
https://uk.farnell.com/triad-magneti...15v/dp/1785731
I usually add two wires simultaneously to give 2 X 3.15V which can be series connected and the centre tap grounded (I use them in audio amps).
I have bought a netting needle / shuttle to make winding easier.

Peter
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Old 10th Nov 2018, 8:56 am   #7
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Default Re: Toroidal Transformer with 220 0r 240v Secondary?

These lads - https://sklep.toroidy.pl/en_US/index do mains and OPT toroidal tfmr's at a very good price.

For myself I wind my own by hand re-using cores with primaries; small toroidal tfmr's are dirt cheap on ebay. If you wind two windings ( for the HT) at one go, it reduces the total amount of turns you have to do.

Andy.
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Old 10th Nov 2018, 11:05 am   #8
Aub
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Default Re: Toroidal Transformer with 220 0r 240v Secondary?

Wow! I've got a few options to think about now.

Thanks to all.

Aub
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Old 10th Nov 2018, 4:34 pm   #9
turretslug
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Default Re: Toroidal Transformer with 220V or 240V Secondary?

How much leeway is there as regards secondary voltage?- a trawl through the (decidedly heavy!) iron-ware box here has thrown up a NOS toroid with 200-240V tapped primary (approx 20V intervals) and a secondary producing 210VAC (presumably nearer 200V under load) when running with 240V into the highest tapping. I'm reluctant to suggest trying a lower primary setting as I gather that toroids run a bit near the edge anyway!

It also has 6V and 20V secondaries- I believe that it may have been intended for a run of monitor conversions of a standard '70s TV chassis for schools use (thus producing 200VAC to eliminate dropper sections as far as possible), so the 6V secondary was presumably intended for a CRT heater and so may not be capable of more than about an amp, perhaps the 20V secondary being intended for signal circuits. The size is approximately 115mm diameter (excluding terminals) by 47mm deep with a 30mm centre hole. The transformer gurus here might be able to give a VA guideline from that but to my layman's eye it looks good for 150VA.

If any use, it's yours for postage- it is quite big'n'heavy!- or otherwise I usually make it to Harpenden and Dunstable Downs, sometimes to Wooton Basset,

Colin
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