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19th Mar 2016, 6:20 pm | #1 |
Pentode
Join Date: Jul 2014
Location: Northamptonshire, UK.
Posts: 135
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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
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19th Mar 2016, 8:34 pm | #2 |
Moderator
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 6,863
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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
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20th Mar 2016, 3:01 am | #3 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,553
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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 |
Dekatron
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
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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 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,843
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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 |
Pentode
Join Date: Jul 2014
Location: Northamptonshire, UK.
Posts: 135
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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
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14th Apr 2016, 9:12 pm | #7 |
Heptode
Join Date: Oct 2005
Location: Olympia, Washington, USA.
Posts: 664
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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 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,535
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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.
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25th Apr 2016, 11:00 pm | #9 |
Heptode
Join Date: Oct 2005
Location: Olympia, Washington, USA.
Posts: 664
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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.
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26th Apr 2016, 9:23 am | #10 |
Rest in Peace
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
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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! |