# Choose the best value of capacitor

#### BintarYudo

Joined May 6, 2018
6
Im currently working for college assignment and i intend to make a power supply, how do i choose the best value of capacitor for my project?
my power supply is 15Volts and 2 Amperes

#### ericgibbs

Joined Jan 29, 2010
18,865
hi Bintar,
Welcome to AAC.
E

#### BintarYudo

Joined May 6, 2018
6

here it is

#### bertus

Joined Apr 5, 2008
22,278
Hello,

That circuit looks like an overvoltage protection and not a powersupply.
What are you trying to make?

Bertus

#### BintarYudo

Joined May 6, 2018
6
actually this is an accu charger with overvoltage protection
trafo and the rectifier are outside of the pcb

#### ericgibbs

Joined Jan 29, 2010
18,865
hi,
Which capacitor in that diagram are you asking for guidance.?
E

#### BintarYudo

Joined May 6, 2018
6
the component with label C1

#### ericgibbs

Joined Jan 29, 2010
18,865
hi,
It looks as though the purpose of the capacitor is to add hysteresis to the relays operation, I would try a 100uF or 470uF.
Where did you find the circuit.?
E

#### BintarYudo

Joined May 6, 2018
6
is there any calculation for determining the capacitor value?
if i change the input to 18Volt, do i need to change the capacitor too?
sorry i forgot where i got this circuit

#### ericgibbs

Joined Jan 29, 2010
18,865
The 1meg pot sets the SCR trigger voltage, reset it when using the 18V input voltage level.
It make take a few attempts to get the 1meg setting correct, for say 18.5V as an example.
What is the value of D6.?

The C1 cap should be rated at least 25V working voltage.

#### BintarYudo

Joined May 6, 2018
6
D6 is zener with activation value 13V for now, and i'll change it to 16v for 18V input

#### ericgibbs

Joined Jan 29, 2010
18,865
hi,
If you want the voltage switch Off point to be say 18.5v , the 16Vz should give you enough range on the 1meg pot.
E