capacitor comparison

[jaison]

Hai sirs, how we can compare capacitor mfd and capacitor voltage , if we have capacitors 20 mfd 220v, 40mfd 110v these capacitors can give same effect. If we have three capacitors 10mfd,20mfd,15mfd all having 220v these capacitors conncted in series what is the after effect?, if we connected in parallel how is the after effect?any body can answer my request.

[Brian_UK]

Using Google, as a lot of us do, finds a lot of information on capacitors.

May I point you here -
http://tpub.com/neets/book2/3e.htm
to make a start.

[Electrocoolman]

if we have capacitors 20 mfd 220v, 40mfd 110v these capacitors can give same effect.
What do you mean by this: same effect ?



If we have three capacitors 10mfd,20mfd,15mfd all having 220v these capacitors conncted in series what is the after effect?, if we connected in parallel how is the after effect?

Capacitors in parallel:

Total C(tot) = Ca + Cb + Cc.... Voltage remains the same and = LOWEST working voltage

Capacitors in series is more complex:

Total V = V1 + V2 + V3......
Total C(tot) is given by formula

1/C(tot) = 1/Ca + 1/Cb + 1/Cc.....

So if you have 10,15,20 mfds 220V this will give

1/C(tot) = 1/10 + 1/15 + 1/20

...with a common denominator = 60

( 6 + 4 + 3 )/60

1/C(tot) = 13/60

inverting to find C(tot) gives

C(tot) = 60/13 = 4.6mfd
V = 220 + 220 + 220 = 660v

Basically when in series, Capacitance REDUCES and working Voltage INCREASES .....OK?

[jaison]

HAI BRIAN, your point web site doesnt open can you hint me any other please

[jaison]

ELECTROCOOLMAN, same effect i mean, what is the after effect if i use 220v 20 mfd absence of 40 mfd 110v, how voltage related to capacitance and frequency, capacitor series i am ok , if we put different voltages what will happen. also can you explain parralel connection of capacitors same and different voltages. thank you .,

[Brian_UK]

HAI BRIAN, your point web site doesnt open can you hint me any other pleaseSorry, it works for me in both Firefox and Explorer

[Electrocoolman]

Hi Jaison,


what is the after effect if i use 220v 20 mfd absence of 40 mfd 110v

So do I understand you want to use a 220v 20mfd inplace of a 110v 40 mfd capacitor?
.....well you will still only have 20 mfds ....in order to get the required 40 mfd, you will need to connect x2 capacitors (each 20mfd) in parallel. This will give you 40 mfd with a voltage of 220v.

If on the other hand, you want to use 110v 40 mfd capacitors to replace a 220v 20mfd capacitor, you will need to connect x2 110v 40mfd capacitors in SERIES....this will give you an equivalent value of 20mfd with the voltage shared equally across the two capacitors...i.e each capacitor in series will have 110v across it.

Beware that if you connect capacitors of different capacitance in series, the voltage across each capacitor will NOT be equal ....so you need to be careful that you do not exceed the working voltage of each capacitor.



how voltage related to capacitance and frequency?

Voltage (normally termed WORKING VOLTAGE) is not related to the capacitance and frequency, HOWEVER the REACTANCE 'Xc' (expressed in Ohms) of the capacitor is given by..... Xc = 1 / (2 x Pi x f x C )
(Pi = 3.142...)
This reactance acts like a resistance and thus Ohms Law can be applied across the capacitor (E=I x Xc)
The reactance decreases as the frequency increases, and thus the voltage measured across the capacitor will fall if the current is constant (or the current will increase if voltage remains constant).

So if you have a simple series circuit consisting of an AC voltage source, a light bulb and a Capacitor....the 'voltage' across the capacitor will decrease as the frequency increases....thus the bulb will get brighter as the frequency increases. (I've tried to keep it simple...in reality it is more complex)


can you explain parallel connection of capacitors same and different voltages.

When you connect anything in parallel...you have the SAME voltage appearing across all the items.....thus each capacitor MUST have a working voltage greater than the voltage of the circuit. So you can connect different working voltage capacitors in parallel provided the working voltage of each capacitor is greater than the circuit voltage.


Just a point to note....motor starting capacitors are only rated for INTERMITTENT use, motor run capacitors are rated for CONTINUOUS use.