Variable PSU from a dimmer switch ? - UK Vintage Radio Repair and Restoration Discussion Forum

clay shooter · 19th Mar 2016, 6:20 pm

Has any one constructed a variable power supply unit using a dimmer switch ?.

I'm guessing it's possible but suspect noise would be a problem, would it be possible to filter out the noise?.
I know a variac would be a far better option but they are far to expensive

Cobaltblue · 19th Mar 2016, 8:34 pm

We have been here a time or two before.

https://www.vintage-radio.net/forum/...ad.php?t=12241

Cheers

Mike T

Refugee · 20th Mar 2016, 3:01 am

I have seen power supplies with a pair of thyristors and two diodes in the bridge rectifier.
They were noisy and unreliable and still had to have a normal regulator as well.
I would not bother.

mark pirate · 20th Mar 2016, 11:52 am

Far better to save up and buy a variac, they do turn up at reasonable prices.
Maybe worth asking for one in the relevant section of the forum.

Mark

Nickthedentist · 20th Mar 2016, 12:00 pm

Yes, they turn up here all the time for not very much if you keep your eyes open.

Mine came FOC from a kind ex-forum member.

clay shooter · 22nd Mar 2016, 1:36 pm

I have found suitable variacs in China for only £9!! The trouble is that its almost £50 shipping , I shall keep looking, thanks for your input

FrankB · 14th Apr 2016, 9:12 pm

If you opt for a Variac (tm), get at least a 5 amp one. Then it will handle most sets, including TV.
Remember that one must DE-RATE the current available from it if you are using only a small portion of the winding. The rating is for the entire winding.

I had one here I got at an estate sale with a really crispy section that was only used across a small part of the winding. It went to the scrap yard. Not worth rewinding for the $25.00 it cost me. (I did get one over heated myself in that same manner, but no damage.)
On the new one I bought, the IM specifically stated the rating was across the entire winding.

Herald1360 · 18th Apr 2016, 6:19 pm

You don't need to derate the output current! That is related only to the gauge of wire used in the winding which cares not whether all of the winding is used.

You do need to remember that the output power it can deliver is only what is available at the actual output voltage and maximum rated output current so it (the power) will go down linearly with output voltage.

FrankB · 25th Apr 2016, 11:00 pm

I obtained my data directly from the manual that came with the new Variac ( tm) that I purchased.

Lucien Nunes · 26th Apr 2016, 9:23 am

That doesn't make a lot of sense - can you quote the manual? The current is usually fixed regardless of voltage, limited by the wire gauge and the brush resistance. Therefore the VA rating is proportional to output voltage, myabe this is what they meant to say but it was lost in translation?

And BTW returning to the original question, no, it won't work, it will do all kinds of nasty things too numerous to mention!

19th Mar 2016, 6:20 pm	#1
clay shooter Pentode Join Date: Jul 2014 Location: Northamptonshire, UK. Posts: 135	Variable PSU from a dimmer switch ? Has any one constructed a variable power supply unit using a dimmer switch ?. I'm guessing it's possible but suspect noise would be a problem, would it be possible to filter out the noise?. I know a variac would be a far better option but they are far to expensive __________________ If it ain't bust don't fix it

19th Mar 2016, 8:34 pm	#2
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,863	Re: Variable psu from a dimmer switch ? We have been here a time or two before. https://www.vintage-radio.net/forum/...ad.php?t=12241 Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

20th Mar 2016, 3:01 am	#3
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Variable psu from a dimmer switch ? I have seen power supplies with a pair of thyristors and two diodes in the bridge rectifier. They were noisy and unreliable and still had to have a normal regulator as well. I would not bother.

20th Mar 2016, 11:52 am	#4
mark pirate Dekatron Join Date: Mar 2008 Location: Worthing, West Sussex, UK Posts: 5,185	Re: Variable psu from a dimmer switch ? Far better to save up and buy a variac, they do turn up at reasonable prices. Maybe worth asking for one in the relevant section of the forum. Mark

20th Mar 2016, 12:00 pm	#5
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,843	Re: Variable psu from a dimmer switch ? Yes, they turn up here all the time for not very much if you keep your eyes open. Mine came FOC from a kind ex-forum member.

22nd Mar 2016, 1:36 pm	#6
clay shooter Pentode Join Date: Jul 2014 Location: Northamptonshire, UK. Posts: 135	Re: Variable PSU from a dimmer switch ? I have found suitable variacs in China for only £9!! The trouble is that its almost £50 shipping , I shall keep looking, thanks for your input __________________ If it ain't bust don't fix it

14th Apr 2016, 9:12 pm	#7
FrankB Heptode Join Date: Oct 2005 Location: Olympia, Washington, USA. Posts: 664	Re: Variable PSU from a dimmer switch ? If you opt for a Variac (tm), get at least a 5 amp one. Then it will handle most sets, including TV. Remember that one must DE-RATE the current available from it if you are using only a small portion of the winding. The rating is for the entire winding. I had one here I got at an estate sale with a really crispy section that was only used across a small part of the winding. It went to the scrap yard. Not worth rewinding for the $25.00 it cost me. (I did get one over heated myself in that same manner, but no damage.) On the new one I bought, the IM specifically stated the rating was across the entire winding.

18th Apr 2016, 6:19 pm	#8
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Variable PSU from a dimmer switch ? You don't need to derate the output current! That is related only to the gauge of wire used in the winding which cares not whether all of the winding is used. You do need to remember that the output power it can deliver is only what is available at the actual output voltage and maximum rated output current so it (the power) will go down linearly with output voltage. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

25th Apr 2016, 11:00 pm	#9
FrankB Heptode Join Date: Oct 2005 Location: Olympia, Washington, USA. Posts: 664	Re: Variable PSU from a dimmer switch ? I obtained my data directly from the manual that came with the new Variac ( tm) that I purchased.

26th Apr 2016, 9:23 am	#10
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: Variable PSU from a dimmer switch ? That doesn't make a lot of sense - can you quote the manual? The current is usually fixed regardless of voltage, limited by the wire gauge and the brush resistance. Therefore the VA rating is proportional to output voltage, myabe this is what they meant to say but it was lost in translation? And BTW returning to the original question, no, it won't work, it will do all kinds of nasty things too numerous to mention!