What is the formula for replacing capacitors

[navycop]

Trying to do electricity homework and I need to figure out what capacitor will replace a 35 picofarad run capacitor at 370 volts (dont want you to solve, just give my the formula).
The book gives an example of:
C1 x C2
C1 + C2 =c
but I only have one capacitor. Plus I don't see where the voltage goes.
Another example is:
2650xamperes
volts =microfarad
again I am missing something in the question==amps
Also is it different for a run or start capacitor?
Thank you..

 

[shippy]

I believe you are looking at a 35 micro farad cap, which should be replaced by the same value run cap. Start caps typically have a much higher micro farad rating and are only active very momentarily to start the motor. Be careful with capacitors tho, they can store a charge and give you a very unpleasant , if not dangerous, surprise if you happen to touch the terminals. With no power on the system, short across the termininals with a well insulated screwdriver to be sure the charge is bled off. If it is charged, it may pop and arc very quickly and you'll see why it's best not to touch the terminals of a charged cap! As far as the 370 volts, just don't go lower, but you may go hegher on voltage rating. Caps are cheap, 4 to 5 dollar range, so just replace it with the proper item. Grtainger, McMaster carr, or any local motor shop should be able to fix ya right up!
I changed out more caps in the last 3or 4 years than I did in total in the prior 20 years doing AC work, they simply aren't made as well as they used to be!

 

[PenMan1]

All I remember is c= q/v.

 

[PenMan1]

All I remember is c= q/v.

If you know the c=35 and v=370, then I THINK the formula is 35=x/370. I'm not sure this is correct, I'm hunting the book, now.

Edit:
I just found my book and the formula IS
C- capacitance = q - the charge divided by the voltage. Be careful of the decimal places, because c = farads ( you have picofarads).

I hope this helps!

 

[renowb]

E=MC Squared

 

[PTsideshow]

This is the circle of life for electricians, since you appear to have the formula you need. You will need a direct replacement as shippy said. They don't make em like they use to, I keep a couple on hand for the AC units. Between the insects and mice committing suicide. Always nice to keep the wifey happy and then just swap out the bad one for a good one with the ute's service person. They always seem to like the hour break.

I print it out and have glued it to some magnet stock, left over from the sign days and have a couple floating around works well inside the lid of the tool box.
:clown: