# Series Capacitor calculations

#### gilbey

Joined Jan 9, 2006
2
Really hope someone can help me here!

I'm really struggling to understand the formulae used to express the capacitance or resistance of series capacitors or parallel resistors. I know it must be really simple but i just cannot understand how the text books get to the final figures!

Say for instance you had 2 capacitors wired in series that were 10 μ F & 20 μ F how do i find the total capacitance for the circuit.

Please help this is driving me insane, i keep just staring at the formulae feeling pretty dumb.

Thanks

#### pebe

Joined Oct 11, 2004
626
Originally posted by gilbey@Jan 9 2006, 07:27 PM
Really hope someone can help me here!

I'm really struggling to understand the formulae used to express the capacitance or resistance of series capacitors or parallel resistors. I know it must be really simple but i just cannot understand how the text books get to the final figures!

Say for instance you had 2 capacitors wired in series that were 10 μ F & 20 μ F how do i find the total capacitance for the circuit.

Please help this is driving me insane, i keep just staring at the formulae feeling pretty dumb.

Thanks
[post=12970]Quoted post[/post]​
The formula for series capacitors is
1/Ctot = 1/C1 + 1/C2 + 1/C3 ....etc where Ctot is the total value.

In your case 1/C1+1/C2 becomes 1/10+1/20 which equals 3/20 . So Ctot = 20/3 = 6.66uF

Resistors in parallel use the same formula - just replace C with R.

#### gilbey

Joined Jan 9, 2006
2
Originally posted by pebe@Jan 9 2006, 07:15 PM
The formula for series capacitors is
1/Ctot = 1/C1 + 1/C2 + 1/C3 ....etc where Ctot is the total value.

In your case 1/C1+1/C2 becomes 1/10+1/20 which equals 3/20 . So Ctot = 20/3 = 6.66uF

Resistors in parallel use the same formula - just replace C with R.
[post=12972]Quoted post[/post]​
thank you, i knew it was simple but for some reason it just wouldn't sink in

#### mikeakarobinhood

Joined Mar 6, 2008
1
mad, thanx! my engineering test is tomorrow and this thread helped alot, its the only place i could find the capacitor formula in series. i registered just to say thanx, ill probly be on here alot more often now. ty

#### hgmjr

Joined Jan 28, 2005
9,029