Capacitor Question

[lionelsoni]

A 1-megafarad capacitor charged to only 1 volt in a 50-watt toy train could power it for 2 3/4 hours.

[8ntruck]

Wow.  If I remember my basic electronics correctly, a farad is a sizeable charge.  I can't imagine what one would need a mega-farad size capacitor for.

[richhotrain]

lionelsoni

Well, what do you know?  I never heard of the "macrofarad".  However, I shall take refuge in the fact that I didn't strictly say that there was no "macrofarad", but rather that there is not a "macrofarrad".

LOL

I saw that it was misspelled when I researched it.   Bob, you can also take refuge in the fact that I know nothing about capacitors.  When Jim posted that thread, I had to Google "capacitor" to get a basic understanding of what a capacitor is and does.  That's when I read that there was such a thing as a macrofarrrad (sic).

Rich

[lionelsoni]

Well, what do you know?  I never heard of the "macrofarad".  However, I shall take refuge in the fact that I didn't strictly say that there was no "macrofarad", but rather that there is not a "macrofarrad".

[richhotrain]

lionelsoni

(There's no such thing as a "macrofarrad"!)

Sure there is:

http://www.websters-dictionary-online.com/definitions/macrofarad?cx=partner-pub-0939450753529744%3Av0qd01-tdlq&cof=FORID%3A9&ie=UTF-8&q=macrofarad&sa=Search#906

Rich

[Anonymous]

Thanks for the info.  I'll have to go to Radio Shack and get a replacement.

[Gray Cat]

lionelsoni

The proper symbol for microfarad is "µF".  To avoid confusion with "MF"--megafarad-- and "mF"--millifarad, it is common practice to replace the "µ" by "u" if Greek letters are not available, or "U" if lower-case letters are not available either.  So that capacitor should have been marked "UF" and probably would be if manufactured today.

The abbreviation "W.V.D.C." means "working voltage direct current".  It is the approximate voltage that the capacitor is actually meant to be used at, rather than an upper limit.  Electrolytic capacitors are moderately tolerant of and can actually adapt to overvoltage.  On the other hand, they can lose the ability to operate even at their specified working voltage if not used for a long time and then must be "re-formed" by increasing the voltage gradually.

(There's no such thing as a "macrofarrad"!)

 

Hi Bob, having rebuilt dozens of antique jukebox amps from the 50's and 40's that way of marking capacitors was quite common back then. You are correct on all points. Although reforming a capacitor is/was a common practice. I never truly trusted it on anything vintage, especially when dealing with lytics in a power supply section of an amp. Many of my friends in that hobby have done it. But to me it's much safer to just replace.

[lionelsoni]

The proper symbol for microfarad is "µF".  To avoid confusion with "MF"--megafarad-- and "mF"--millifarad, it is common practice to replace the "µ" by "u" if Greek letters are not available, or "U" if lower-case letters are not available either.  So that capacitor should have been marked "UF" and probably would be if manufactured today.

The abbreviation "W.V.D.C." means "working voltage direct current".  It is the approximate voltage that the capacitor is actually meant to be used at, rather than an upper limit.  Electrolytic capacitors are moderately tolerant of and can actually adapt to overvoltage.  On the other hand, they can lose the ability to operate even at their specified working voltage if not used for a long time and then must be "re-formed" by increasing the voltage gradually.

(There's no such thing as a "macrofarrad"!)

[Gray Cat]

That's a 100 jiggawatt Flux Capacitor. Only found in a 1957 DeLorean..

 

But seriously folks it's just a run a the mill 100 microfarad electrolytic (as denoted by the plus and minus signs). Not sure if Rat Shack (or Cell Phone Shack as it's now known) would have one with those specs but you can go to www.tubesandmore.com this is antique electronic supply (AES). The voltage rating shows 15 but you can go UP if there isn't a 15v available. You can always go up on voltage rating but never go below.

[Anonymous]

I have been troubleshooting the diesel roar in a Flyer 481 Silver Flash.  I've narrowed the issue down to a bad capacitor, but I am not sure if this is a 100 microfarrad or 100 macrofarrad.  Here is a picture of the cap:

Any help would be appreciated.