UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

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.

Reply
 
Thread Tools
Old 22nd Feb 2021, 12:09 pm   #1
bikerhifinut
Octode
 
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
Posts: 1,888
Default wiring toroidal transformer primary in parallel

If I had a Toroidal transformer with 2 x 115V primaries, i.e. suitable for 115V Mains and 230V mains as most commercially available ones are, then is there any reason why I can't wire the 115V primaries in parallel on UK mains in order to double the output Voltage?
I was thinking about the commonly and cheaply available 2 x 55V secondaries that wired in series will give 110V and if the primaries were paralleled, logically you'd get 220V which becomes a useful Voltage for Valve Circuits.
If it's ok to do this, would it be advisable to de rate the VA rating?
I figured that the insulation must be capable of withstanding UK mains voltage when wired in series, so there shouldn't be an issue of insulation breakdown, and I am not advocating this practice to get a higher voltage from a high voltage secondary.
It's just that 2 x 55V toroids are freely and cheaply available, whereas high voltage ones tend to be "specialist" windings and as one offs expensive.
I know some here can wind their own but apart from one instance of modifying a low voltage secondary under advice of the Gent who made it (Thanks Joe Bog) and it was a right old faff on if very effective, I have no real ambition to get involved in transformer manufacturing.

Regards and Thanks in advance.

Andy.
bikerhifinut is offline   Reply With Quote
Old 22nd Feb 2021, 12:10 pm   #2
bikerhifinut
Octode
 
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
Posts: 1,888
Default Re: wiring toroidal transformer primary in parallel

I should add, I know I could use a voltage doubler, but that means extra stresses on transformer and capacitors that I would rather avoid.
A.
bikerhifinut is offline   Reply With Quote
Old 22nd Feb 2021, 12:38 pm   #3
M0FYA Andy
Nonode
 
Join Date: May 2007
Location: Preston, Lancashire, UK.
Posts: 2,178
Default Re: wiring toroidal transformer primary in parallel

You'll certainly be overstressing the transformer applying 230v to a 115v primary. Having two windings in parallel won't alleviate this.

Andy
M0FYA Andy is offline   Reply With Quote
Old 22nd Feb 2021, 12:54 pm   #4
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 6,711
Default Re: wiring toroidal transformer primary in parallel

Hi Andy, if it hase 2, 115v primaries they are meant to be wired in parallel FOR 115V ONLY, as otherwise the primary will be overloaded if only 1 is used.
Applying 240v to this 115 winding pair will push the primary well beyond saturation and cause mains circuit fuse blowing.

Ed
Ed_Dinning is offline   Reply With Quote
Old 22nd Feb 2021, 12:59 pm   #5
Maarten
Dekatron
 
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 3,165
Default Re: wiring toroidal transformer primary in parallel

You might be able to get away with it on a higher frequency, maybe 100Hz or 400Hz but that's very impractical.
Maarten is offline   Reply With Quote
Old 22nd Feb 2021, 7:35 pm   #6
Glowing Bits!
Octode
 
Glowing Bits!'s Avatar
 
Join Date: Oct 2011
Location: Wrexham, North Wales, UK.
Posts: 1,005
Default Re: wiring toroidal transformer primary in parallel

Me thinks this might call for a canister of CO2, it's good for putting out fires!
The primary should have two wires put together for 240v, not in parallel!
There is a way to up the output voltage using diodes but I can't remember how it's done, Japanese amps do things like this, it's 120v out to most valves except the output stage, diodes step it up to 350v.
__________________
Rick, the annoying object roaming the forum.
Glowing Bits! is offline   Reply With Quote
Old 22nd Feb 2021, 7:45 pm   #7
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 6,711
Default Re: wiring toroidal transformer primary in parallel

Yes, the voltage doubler circuit, but it does not have good regulation and at 50Hz and needing an amp or so of current will need pretty large caps.

Ed
Ed_Dinning is offline   Reply With Quote
Old 22nd Feb 2021, 7:47 pm   #8
Glowing Bits!
Octode
 
Glowing Bits!'s Avatar
 
Join Date: Oct 2011
Location: Wrexham, North Wales, UK.
Posts: 1,005
Default Re: wiring toroidal transformer primary in parallel

I can't remember what the caps are but 40uf springs to mind.
Me thinks it's time to dig out the circuit, the handbook has a nice A3 spread.
__________________
Rick, the annoying object roaming the forum.
Glowing Bits! is offline   Reply With Quote
Old 22nd Feb 2021, 9:08 pm   #9
bikerhifinut
Octode
 
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
Posts: 1,888
Default Re: wiring toroidal transformer primary in parallel

Thanks.
I knew there had to be a good reason why I have never seen it done!
OK thanks guys, we can put this one to bed. Be assured I WILL NOT try this at home!
Looks like the old voltage doubler from 110V if I go down this route.

Andy.
bikerhifinut is offline   Reply With Quote
Old 22nd Feb 2021, 9:30 pm   #10
kalee20
Dekatron
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 5,667
Default Re: wiring toroidal transformer primary in parallel

If you use 230V on 115V windings, the transformer core will saturate and the no-load current will, instead of being negligible, be sky-high.

The only way it can be done, is if the frequency is also doubled. But getting 230V 100Hz is going to be more expensive than buying the proper transformer!
kalee20 is offline   Reply With Quote
Old 22nd Feb 2021, 10:16 pm   #11
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 15,263
Default Re: wiring toroidal transformer primary in parallel

If you take care about VA loadings, you can use a couple of 230V:6V transformers back to back to give isolated 6.3V for heaters and (double) isolated 220V ish for HT.

A 25VA TX feeding a 12VA one would give you a couple of amps LT and maybe 40mA HT
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 11:25 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.