10 Volt Primary Winding, Function Of? - UK Vintage Radio Repair and Restoration Discussion Forum

percival007 · 16th Jun 2010, 8:26 am

Hi all,

this may be a silly question, i apologise in advance but i genuinely don't know.

Why is there sometimes a 10Volt winding on a Mains Transformer, the 'other side' of the 0Volt connection.
For example:- '10-0-110-220-240'

Is/was this to be able to 'make up' the different permutations of Mains Voltages in different countries, so if requiring 230Volts, the connection to the Transformer would be made across the 10-220 Volt tappings?

This seems like a logical explanation to me, but am not sure if correct. If someone can enlighten me i'd be gratefull.

James.

PJL · 16th Jun 2010, 9:39 am

Correct, it gives options of 110, 120, 220, 230, 240, 250. Not just for different countries as mains voltages are not consistent throught the UK 230 +/- 10% is allowed I beleive.

Andrew2 · 16th Jun 2010, 9:41 am

Quote:

Originally Posted by percival007

Hi all,

Is/was this to be able to 'make up' the different permutations of Mains Voltages in different countries, so if requiring 230Volts, the connection to the Transformer would be made across the 10-220 Volt tappings?

This seems like a logical explanation to me, but am not sure if correct. If someone can enlighten me i'd be gratefull.

James.

Yes, that's the reason. being able to 'add' 10v to all the values with one extra winding is a nifty idea instead of a load of extra taps.

Malcolm G6ANZ · 16th Jun 2010, 11:27 am

What they said. Its to make it easier to get the correct primary voltage from a fewer number of taps. On one of our machines we need to get an precise 5.5vac secondary on load. To this end the transformer primary is tapped at 10-0-200-220-240 and the secondary at 0-4-4.5-5.0-5.5-6.0. The secondary measured on load with a true RMS meter and the primary and sceondary taps adjusted to give the correct on load voltage. The process can take a long time to complete.

Malcolm

percival007 · 16th Jun 2010, 6:22 pm

Thanks Folks.

Simple when you know, isn't it?!?!?!

James.

Dave757 · 16th Jun 2010, 6:36 pm

Quote:

Originally Posted by Malcolm G6ANZ

What they said. Its to make it easier to get the correct primary voltage from a fewer number of taps. On one of our machines we need to get an precise 5.5vac secondary on load. To this end the transformer primary is tapped at 10-0-200-220-240 and the secondary at 0-4-4.5-5.0-5.5-6.0. The secondary measured on load with a true RMS meter and the primary and sceondary taps adjusted to give the correct on load voltage. The process can take a long time to complete.

Malcolm

Hi Malcolm,

The weirdest arrangement I ever saw was a transformer designed to give
up to 30 or so amps at various voltages between 10 and 20 volts. The taps were marked with the secondary voltages but were actually in the primary winding!

Kind regards

Dave G0ELJ

kalee20 · 16th Jun 2010, 6:44 pm

Just adding a (hopefully unnecessary) cautionary note:

Don't try running the equipment from 10V AC by connecting to the 10V primary taps. The wire it's wound with would not carry the current that would be necessary!

Herald1360 · 17th Jun 2010, 12:27 am

An interesting variation on the primary theme used to be on some of the small Farnell low power transformers- these had two windings, one 0-110-140, the other 0-110 only. This gave the options of 110V, 220V and 240V.

Tim · 17th Jun 2010, 1:24 am

Quote:

Don't try running the equipment from 10V AC by connecting to the 10V primary taps. The wire it's wound with would not carry the current that would be necessary!

Might be alright for small panal lamp or LED though

percival007 · 17th Jun 2010, 7:24 pm

Quote:

Originally Posted by Tim

........Might be alright for small panal lamp or LED though...........

That's an excellent idea, i may just do that on my next project. Thanks.

James.

Heatercathodeshort · 17th Jun 2010, 8:08 pm

A pilot lamp would be at mains potential... J.

Graeme Murphy · 17th Jun 2010, 10:28 pm

UK mains voltage tolerance is -6% +10% of 230 volts nominal.

glowinganode · 17th Jun 2010, 10:46 pm

Quote:

Originally Posted by Tim

Might be alright for small panal lamp or LED though

Rectified and smoothed gives around 12Vdc, ideal for supplying cooling fans on valve gear.
Don't forget you can use the primary of a large transformer as an auto transformer to feed a smaller transformer. Handy if you need a little boost for a heater transformer.
Rob.

Tim · 17th Jun 2010, 11:14 pm

Quote:

A pilot lamp would be at mains potential... J.

Yes and No. These windings are often as taps yes, but would be best placed at the neutral end(Given). No different to an AC/DC radio. Depending on the design of the transformer, it might even be possible to isolate the 10 volt winding. Viola!

kalee20 · 18th Jun 2010, 1:20 pm

Quote:

Originally Posted by Tim

Depending on the design of the transformer, it might even be possible to isolate the 10 volt winding. Viola!

It might, but it wouldn't be a good idea.

The 10V tap will be made by bringing out a loop from the winding to the 10V terminal, and then taking back in and continuing the winding. So, although you might be able to disconnect the terminal and separate the two wires, you'll still be left with a winding which is in close proximity to the rest of the primary, with the only insulation being the enamel on the wire.

This level of insulation, while it should comfortably pass a 500V test, would NEVER, not even in the deepest darkest days of the AC/DC live chassis heyday, be considered sufficient to protect the user from electric shock.

Tim · 18th Jun 2010, 2:19 pm

Fair enough!

geoff999 · 19th Jun 2010, 1:26 pm

I think Dave's weird device was an autotransformer, which has a single winding tapped in way he describes. Quite useful and economical but it provides no isolation as does a normal transformer with separate primary and secondary windings.

Geoff

glowinganode · 19th Jun 2010, 5:29 pm

Not weird and not necessarily an auto transformer.
Imagine a transformer whose secondary is wound to give 3.0 volts, tapped to give 2.9v or 2.8v if required. For practical purposes thes tappings are made on the primary rather than the secondary. The taps are marked with the voltage the secondary will produce when that tap is fed with 230v.
Rob.

Dave757 · 20th Jun 2010, 12:06 pm

Quote:

Originally Posted by glowinganode

Not weird and not necessarily an auto transformer.
Imagine a transformer whose secondary is wound to give 3.0 volts, tapped to give 2.9v or 2.8v if required. For practical purposes thes tappings are made on the primary rather than the secondary. The taps are marked with the voltage the secondary will produce when that tap is fed with 230v.
Rob.

Hi Geoff and Rob,

Yes, it was definitely not an autotransformer, and the taps
in the primary were factory marked. It worked fine, it just
seemed an unusual arrangement. I used it at the 12 volts tapping
to provide 12 volts AC to run a fridge in my old caravan which
would only run on 12 volts or gas, and there was no flue.
The 12 volts option was to allow for continued use whilst
towing, and took about 10 amps, but it seemed equally happy
on 12volts AC when connected to the site mains, as it was a
heated 'convection' system.

Kind regards

Dave G0ELJ

16th Jun 2010, 8:26 am	#1
percival007 Heptode Join Date: May 2005 Location: Oxfordshire, UK. Posts: 852	10 Volt Primary Winding, Function Of? Hi all, this may be a silly question, i apologise in advance but i genuinely don't know. Why is there sometimes a 10Volt winding on a Mains Transformer, the 'other side' of the 0Volt connection. For example:- '10-0-110-220-240' Is/was this to be able to 'make up' the different permutations of Mains Voltages in different countries, so if requiring 230Volts, the connection to the Transformer would be made across the 10-220 Volt tappings? This seems like a logical explanation to me, but am not sure if correct. If someone can enlighten me i'd be gratefull. James.

16th Jun 2010, 9:39 am	#2
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: 10 Volt Primary Winding, Function Of? Correct, it gives options of 110, 120, 220, 230, 240, 250. Not just for different countries as mains voltages are not consistent throught the UK 230 +/- 10% is allowed I beleive.

16th Jun 2010, 11:27 am	#4
Malcolm G6ANZ Octode Join Date: Feb 2006 Location: Bristol, UK. Posts: 1,042	Re: 10 Volt Primary Winding, Function Of? What they said. Its to make it easier to get the correct primary voltage from a fewer number of taps. On one of our machines we need to get an precise 5.5vac secondary on load. To this end the transformer primary is tapped at 10-0-200-220-240 and the secondary at 0-4-4.5-5.0-5.5-6.0. The secondary measured on load with a true RMS meter and the primary and sceondary taps adjusted to give the correct on load voltage. The process can take a long time to complete. Malcolm

16th Jun 2010, 6:22 pm	#5
percival007 Heptode Join Date: May 2005 Location: Oxfordshire, UK. Posts: 852	Re: 10 Volt Primary Winding, Function Of? Thanks Folks. Simple when you know, isn't it?!?!?! James.

16th Jun 2010, 6:44 pm	#7
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: 10 Volt Primary Winding, Function Of? Just adding a (hopefully unnecessary) cautionary note: Don't try running the equipment from 10V AC by connecting to the 10V primary taps. The wire it's wound with would not carry the current that would be necessary!

17th Jun 2010, 12:27 am	#8
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: 10 Volt Primary Winding, Function Of? An interesting variation on the primary theme used to be on some of the small Farnell low power transformers- these had two windings, one 0-110-140, the other 0-110 only. This gave the options of 110V, 220V and 240V. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

17th Jun 2010, 8:08 pm	#11
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: 10 Volt Primary Winding, Function Of? A pilot lamp would be at mains potential... J.

17th Jun 2010, 10:28 pm	#12
Graeme Murphy Tetrode Join Date: Oct 2009 Location: Blyth, Northumberland, UK. Posts: 62	Re: 10 Volt Primary Winding, Function Of? UK mains voltage tolerance is -6% +10% of 230 volts nominal.

18th Jun 2010, 2:19 pm	#16
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: 10 Volt Primary Winding, Function Of? Fair enough! __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

19th Jun 2010, 1:26 pm	#17
geoff999 Rest in Peace Join Date: Jun 2007 Location: Croydon Posts: 92	Re: 10 Volt Primary Winding, Function Of? I think Dave's weird device was an autotransformer, which has a single winding tapped in way he describes. Quite useful and economical but it provides no isolation as does a normal transformer with separate primary and secondary windings. Geoff

19th Jun 2010, 5:29 pm	#18
glowinganode Octode Join Date: Apr 2009 Location: Aylesbury, Buckinghamshire, UK. Posts: 1,522	Re: 10 Volt Primary Winding, Function Of? Not weird and not necessarily an auto transformer. Imagine a transformer whose secondary is wound to give 3.0 volts, tapped to give 2.9v or 2.8v if required. For practical purposes thes tappings are made on the primary rather than the secondary. The taps are marked with the voltage the secondary will produce when that tap is fed with 230v. Rob. __________________ We have done so much, for so long, with so little, we are now qualified to do anything with nothing.