DIYbanter - View Single Post - Tubes in broken spotwelder & other questions

Ralph Mowery

In article ,
says...

On Monday, November 14, 2016 at 4:13:07 PM UTC-5, wrote:
"Two caps in series must be calculated, but keeping it very simple, if two 20uF @ 450V are connected in series, the actual capacitance will be 5uF @ 900V. "

That's not what I "heard". It should be 10 uF.

(C1 x C2) / (C1 + C2) = Working Capacitance is the equation I have used these many years.

Example 1:

10 x 10 = 100
10 + 10 = 20
100 / 20 = 5

Example 2 (from the link):

10 x 22 = 220
10 + 22 = 32
220 / 32 = 6.875

At least where I come from.

Peter Wieck
Melrose Park, PA

If equal value capacitors are in series (same for resistors in parallel)
all you have to do is devide the value of one of them by the number.
That would be 20 devided by 2 for 10.

You can also take the long hard way and do the product over the sum as
in your example. You just need to LOOK AT THE VALUE IN THE EXAMPLE AS
BEING 20 INSTEAD OF THE 10 FOR EACH ONE THAT YOU USED.

For equal values of capacitance the voltage will add, if the voltages
are not equal then there are problems. Resistors are needed across the
capacitors when equal values of capacitors are used. This is mainly due
to the wide variation of capacitance in most of them. Helps to bleed
off the stored charge also.