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| General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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21st Feb 2014, 5:54 pm
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#1 |
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Octode
Join Date: May 2010
Location: Worcestershire, UK.
Posts: 1,880
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Capacitive dropper calculation?
I've just done a calculation to find the value required for a capacitor to drop 240 volts AC mains to 115 volts at 125 watt load, I get 30µf. Just to confirm my maths is ok, is that correct?
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21st Feb 2014, 6:20 pm
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#2 |
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Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
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Re: Capacitive dropper calculation?
I think you forgot that the capacitor voltage and resistive load voltage are in quadrature, not simply added in series. Assuming 50Hz, I get 16uF.
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21st Feb 2014, 6:25 pm
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#3 |
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Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
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Re: Capacitive dropper calculation?
Agreed, using Paul Stenning's calculator I get 16.43uF, 16uF being the nearest prefered value.
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21st Feb 2014, 6:35 pm
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#4 |
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Octode
Join Date: May 2010
Location: Worcestershire, UK.
Posts: 1,880
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Re: Capacitive dropper calculation?
I did indeed forget that! Doh
 Good thing I checked, thanks guys
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21st Feb 2014, 6:37 pm
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#5 |
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Heptode
Join Date: Nov 2009
Location: Scarborough, North Yorkshire, UK.
Posts: 510
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Re: Capacitive dropper calculation?
I agree,resistance near enough, 105 ohms for the element, Xc 192 ohms Vc 208, Z 220 ohms and a 16 micro farad capacitor with a working voltage of 350. I use a similar arrangement to control my PV panels, heating our hot water via the immersion heater.Switching caps in and out.Ted
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