// #eevblog — 2019-04-23
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06:55:28 Topic Is: Official IRC channel of the EEVBlog - www.eevblog.com
06:55:28 Set By: (lego.jp.austnet.org) on: Sun Mar 17 01:18:37 2019
06:55:29 <!WebChatUser> hi everybody
06:55:29 <!WebChatUser> can anyone help me a little bit with a Cockcroft-Walton Multiplier
06:55:29 <!WebChatUser> i want to use it for my own power supply im building but i can't find anywhere what size capacitors i need for about a few ohms resistance
06:55:29 <T3sl4> you know how to calculate capacitance for a regular rectifier?
06:55:29 <!WebChatUser> i'm familliar with the 1 - e^rc equation if thats what you mean
06:55:29 <T3sl4> sort of
06:55:29 <T3sl4> do you know how to apply that for a rectifier?
06:55:29 <!WebChatUser> i wasn't sure how to use the equation for the multiplier
06:55:29 <!WebChatUser> so no
06:55:29 <!WebChatUser> i saw the video on youtube about the multiplier
06:55:29 <T3sl4> roughly speaking, you want something like 2000uF for a 12V, 1A load with 100Hz ripple
06:55:29 <!WebChatUser> the voltage collapsed with e few mega ohms load but i think he used a capacitor smaller than 0.1uf
06:55:29 <T3sl4> that's the baseline, then figure less C at proportionally higher V, more C at higher I, and less C at higher F
06:55:29 <!WebChatUser> oh thats a lot because i wanted to use 50hz
06:55:29 <T3sl4> so, 2000uF * (12V / volts) * (amps / 1A) * (freq / 100Hz)
06:55:29 <T3sl4> note 100/120Hz is for a full wave rectifier on mains
06:55:29 <!WebChatUser> oh yes of course you're right
06:55:29 <!WebChatUser> are you sure about the figures?
06:55:29 <T3sl4> Now, for a multiplier, you need N capacitors of at least N times the capacitance, but usually more like 2-3*N times or even more
06:55:29 <!WebChatUser> it feels like capacitors lose their capacitance with this trick
06:55:29 <!WebChatUser> then i don't think it would work
06:55:29 <T3sl4> the power factor is also awful, so if you're powering it from a transformer, expect 2-3*N times less output than nameplate VA capacity
06:55:29 <!WebChatUser> i wanted to make a 24 volts smps using a 230 to 12v transformer with a current rating of at least 20amps
06:55:29 <T3sl4> or, not N i should say
06:55:29 <T3sl4> ah, yeah, you'll need huge caps for that
06:55:29 <!WebChatUser> yeah i gues so
06:55:29 <T3sl4> like 40mF+
06:55:29 <!WebChatUser> not impossible though
06:55:29 <!WebChatUser> i recently bought 10mf 35v for only 3 euro's
06:55:29 <T3sl4> may not be great quality, but you don't need much at mains frequency, fortunately
06:55:29 <T3sl4> (depending on what kind of SMPS you want to put on it)
06:55:29 <!WebChatUser> not sure yet
06:55:29 <!WebChatUser> i already made a 555 time board to experiment with
06:55:29 <!WebChatUser> but i don;t have any education so it's not easy seeing through the forrest of the many ic's there are
06:55:29 <!WebChatUser> impossible for me
06:55:29 <T3sl4> indeed
06:55:29 <!*buffextras> [email protected] quit with message: [Quit: AustNet Web Chat - https://webchat.austnet.org/]
17:44:41 * steve30 purrs at Halcyon
17:52:03 <DogWomble_> damn, i miss my old kitty now
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