AC capacitor question
in [Basics]
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From: lerameur on 24 Mar 2010 18:28 Hi, I believe it is possible but I would just like a confirmation. I would like to know if I can use an AC capacitor and make it behave like a DC cap, I would like to do a rail gun. Are DC capacitor better suited, do they perform better for a quick discharge.?? K
From: Tim Wescott on 24 Mar 2010 18:43 lerameur wrote: > Hi, > > I believe it is possible but I would just like a confirmation. > I would like to know if I can use an AC capacitor and make it behave > like a DC cap, I would like to do a rail gun. Are DC capacitor better > suited, do they perform better for a quick discharge.?? Um -- what the heck are you talking about? There are capacitors that are made primarily for service with zero DC bias, there are capacitors (polarized electrolytics) that are made for service _with_ a DC bias, and there are capacitors made for service attached to the electrical grid. Open a Digi-Key catalog and eliminate the half-dozen most popular dielectrics used to build capacitors with and you'll still have entries to spare -- and that's not including oddball dielectrics, nor is it taking into account the wide variation in ways that capacitors are constructed _using_ these dielectrics. I've seen a lot of different categories under which capacitors are sold, I don't recall ever seeing capacitors sold as "AC capacitors" or "DC capacitor". Perhaps if you said something like "I have very little practical knowledge of capacitors and I want to select the type that's best for a rail gun" then folks would be able to help you out. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: lerameur on 24 Mar 2010 19:25 On Mar 24, 6:43 pm, Tim Wescott <t...(a)seemywebsite.now> wrote: > lerameur wrote: > > Hi, > > > I believe it is possible but I would just like a confirmation. > > I would like to know if I can use an AC capacitor and make it behave > > like a DC cap, I would like to do a rail gun. Are DC capacitor better > > suited, do they perform better for a quick discharge.?? > > Um -- what the heck are you talking about? > > There are capacitors that are made primarily for service with zero DC > bias, there are capacitors (polarized electrolytics) that are made for > service _with_ a DC bias, and there are capacitors made for service > attached to the electrical grid. > > Open a Digi-Key catalog and eliminate the half-dozen most popular > dielectrics used to build capacitors with and you'll still have entries > to spare -- and that's not including oddball dielectrics, nor is it > taking into account the wide variation in ways that capacitors are > constructed _using_ these dielectrics. > > I've seen a lot of different categories under which capacitors are sold, > I don't recall ever seeing capacitors sold as "AC capacitors" or "DC > capacitor". > What I meant is that DC capacitors are polarized and AC are bipolar. I would like to charge a, AC Capacitor with direct current (electrolytic capacitor ) , there just need the positive to zero. From what I can read from you, I will be able to do what I need to do. I am just saying AC capacitor because you can see VAC on these capacitors. http://www.bridgat.com/files/CBB65_175uf_air_conditioner_capacitor.jpg cheers
From: Michael A. Terrell on 24 Mar 2010 19:31 lerameur wrote: > > On Mar 24, 6:43 pm, Tim Wescott <t...(a)seemywebsite.now> wrote: > > lerameur wrote: > > > Hi, > > > > > I believe it is possible but I would just like a confirmation. > > > I would like to know if I can use an AC capacitor and make it behave > > > like a DC cap, I would like to do a rail gun. Are DC capacitor better > > > suited, do they perform better for a quick discharge.?? > > > > Um -- what the heck are you talking about? > > > > There are capacitors that are made primarily for service with zero DC > > bias, there are capacitors (polarized electrolytics) that are made for > > service _with_ a DC bias, and there are capacitors made for service > > attached to the electrical grid. > > > > Open a Digi-Key catalog and eliminate the half-dozen most popular > > dielectrics used to build capacitors with and you'll still have entries > > to spare -- and that's not including oddball dielectrics, nor is it > > taking into account the wide variation in ways that capacitors are > > constructed _using_ these dielectrics. > > > > I've seen a lot of different categories under which capacitors are sold, > > I don't recall ever seeing capacitors sold as "AC capacitors" or "DC > > capacitor". > > > > What I meant is that DC capacitors are polarized and AC are bipolar. > I would like to charge a, AC Capacitor with direct current > (electrolytic capacitor ) , there just need the positive to zero. > From what I can read from you, I will be able to do what I need to > do. > I am just saying AC capacitor because you can see VAC on these > capacitors. > http://www.bridgat.com/files/CBB65_175uf_air_conditioner_capacitor.jpg > cheers It will cost you quite a bit more, for lower performance. DC electrolytics pack a lot more storage into the same space and cost a lot less. AC electrolytics aren't intended for DC applications. -- Lead free solder is Belgium's version of 'Hold my beer and watch this!'
From: Phil Allison on 24 Mar 2010 19:35
"lerameur" What I meant is that DC capacitors are polarized and AC are bipolar. I would like to charge a, AC Capacitor with direct current (electrolytic capacitor ) , there just need the positive to zero. From what I can read from you, I will be able to do what I need to do. I am just saying AC capacitor because you can see VAC on these capacitors. http://www.bridgat.com/files/CBB65_175uf_air_conditioner_capacitor.jpg ** That is an oil filled film ( likely polypropylene) capacitor with two sections, 5 uF and 17 uF. ..... Phil |