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Power Supply Capacitors

Discussion in 'General Electronics Discussion' started by Y2KEDDIE, Jan 14, 2015.

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  1. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    I am building a variable DC power supply for experinenting with vacuum tubes. It will be 400Volts 150 mA output, full wave, semiconductor diodes, using a pi-filter with a choke, and possibly swinging choke.

    My plan is to use a Variac on the primary so I can vari the outpt to meet voltage requiremnts of various tube experiments. The Variac will be interlocked such that it will have to be set to zero before bringing the output up to load.

    I'm thnking I will begin by using 40ufd at 450 wvdc capacitors and a 10 hy choke. Either vertical can or axial type mounted beneath the chassis.

    My question is what type of electrolytic capacitors to use. I can mount vertical or horizontal, and about any reasonable size. I see all kinds of Series (styles) available and a huge price range.

    I realize there are certain types used specifically (Low ESR) for switching supplies and computer applications. I don't think for operating vacuum tubes ESR or low inductance are a big concern, but there are so many different types to choose from. general purpose may be fine but I also realise one usually gets what one pays for.

    I was looking at Nichicon capacitors: ( ALS40,PW,GU,GN,PM,PS, BT,VR Series, etc.) from Allied Electronics, CDE, Panasonic, etc are available as well.

    Thanks for your input!

    Eddie
     
    Last edited: Jan 14, 2015
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    Size and mounting style is completely up to you .... ie. whatever you case and circuit layout sizes permit

    For tube gear ... HV and low capacitance .... ESR probably isn't a big deal .... when I was repairing tube gear in days gone bye,
    I never heard anyone talking about ESR ratings
    In fact I never heard about ESR till after I joined this forum some years ago
    So for 30+ years I have been using caps in power supplies etc with an unknown ESR and nothing has ever failed as a result :)
    I sometimes wonder if it's given a too higher importance status ;)

    Dave
     
  3. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    I miss the "old days"; I wonder what the modern day equivalent is for a Spraque TVL2764.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    ESR won't be an issue but bear in mind that while the toobs are warming up there will be no load on the HT and the voltage could be as much as 50% higher than the final operating voltage, possibly even more than that, for 10~15 seconds. So I would be very generous with the voltage ratings of the electrolytics.
     
    davenn likes this.
  5. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    My transformer is 750V ct @ 150 mA. Using full wave rectifier 750 / 2 X 1.414 =530.25 VDC
    I would like to get as much voltage and current I can get at maximun output. Rather than series(ing) electrolytics which are rated at 450 WVVDC i was thinking of using Polypropylene Metallized AVX FFVE Series FFVE6C0476K-, 47uF 800v 100 Irms max A.. Or do you think thtis is overkill?
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    If you can afford them, then sure, use those!
     
  7. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    Like I said earlier I'm used to those old Spraque Aluminum cans. The packaging on the AVX,s threw me a bit. I'm hoping these are high quality , as might be reflected in the price. My project is one of a kind and experimental, I hope it will last the rest of my life, LOL.
     
  8. shrtrnd

    shrtrnd

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    Jan 15, 2010
    Want to add trivia to this thread.
    A lot of the old power supplies I've worked in tube circuits use the old oil-filled caps. They last longer than anything I've seen. I assume they went to electrolytics for tighter tolerances and ease of incorporating them on printed
    circuit boards. The electrolytics are going to be easer to find, and what I'd use. My concern with those these days, is to select a good quality manufacturer, and not cut corners on cost.
    I've got 30 year-old electrolytics that work fine, but they were well-made then. The new line of thought by manufacturers these days seems to be that consumer electronics is going to be discarded in less than 10 years anyway,
    so I question the quality of some of the manufacturers turning them out these days (ie: not expecting them to last much longer than that).
    Remember that electrolytics dry out. Watch where you install them, so that they're not exposed to continuous high-heat from the tubes. I think that'll give the caps longer life.
     
  9. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    I found this: CENEQ 97F5116 CAPACITOR PP FILM QC, NEWARK 13M4397. It's 40uF General Purpose DC Capacitor. Spec's say its dual rated: 440VAC/ 1000VDC. I wonder if this would work. There appears to be no plolarity markings. Is this a non-polarized device, possibly two 80 uF in series back to back. How would that work in a dc circuit? If that's the case, one could use AC motor start capacitors in place of standard electrolytcs. I''m a bit skeptical.

    The Polypropylene Metallized AVX FFVE Series FFVE6C0476K-, 47uF 800v 100 I found (above post) is only availabe in 16 pc lots. At $75 each, my budget is exceeded.
     
  10. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    I did it again, talked myself in a full circle. My question of the day: whats the differrence between AC capacitors ( types used in an electric motor for run and start), and that of an electrolytic type used in DC supplies? They are both capacitors, both designated in value as uF's, but one is polarized, the other not.

    I'm thinking the polarization is necessary because of the electrolytic chemical action( such as charged ion flow as in batteries.
    If a different material is used for a dielectric maybe polarity is not a concern.(?). Can AC capacitors be substituted in place of electrolytic if uF's and working voltages are considered. Maybe the DC equivalent voltage rating would have to be higher because of average current is greater. (?)

    I'm tempted to try it, but I hesitate (I don't want an explosion)
     
  11. Y2KEDDIE

    Y2KEDDIE

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    15
    Sep 23, 2012
    Update!!

    I tried using oil filled AC motor capacitors as filters for my supply. They work great! (proving Capacitance is Capacitance).
    I'm excited because these capacitors actually are less expensive than the Aluminum can capacitors that appear obsolete, or at least hard to find. Another plus is their higher voltage rating. With no connection polarity, and the fact the capacitor is electrically isolated from its housing, it makes it easy to wire in series to get a higher working voltage.

    The CENEQ 97F5116 CAPACITOR PP FILM QC, I ordered is rated for 440VAC / 1000 WVDC. I wonder (?) if this rating can be applied to other oil filled capacitors. I'm guessing the higher DC rating is attributed to the RMS output of a rectifier vs. the peak to peak output of the corresponding AC waveform. I have many 24uF @ 400 VAC capacitors for use in HID lamp fixtures. If I can use them at 400 x 1.414 =565 VDC (?) it would be great!
     
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