I HAVE MY CIRCUIT WIRED UP AS SUCH IN THE PICTURE, WHEN I TURN IT ON I GET 12VDC ACROSS THE CAPACITOR WITH NO LOAD CONNECT. BUT WHEN I CONNECT THE LOAD IT DROPS TO 9VDC, CAN SOMEBODY PLEASE TELL ME WHY THIS IR AND WHAT NEEDS TO BE DONE TO RECTIFY THE CIRCUIT TO GIVE 12VDC ACROSS THE LOAD?

 

what's the input voltage?
and what's the load on the Ckt.?
which diodes are u using?

 

Hello,

A 42 μF capacitor is a very low value for a buffer capacitor.
You will need about 1500 μF for each ampere.

Bertus

 

hi yes i was thinkin the problem was the the size of the capacitor alright, thanks for your help

 

If you really have 12 VAC, this should charge the capacitor to about 15.5 or 16 volts. You need to get picky about your measurements so they wil lead you to the error.

 

i put in a 1000uF capacitor and getting 11 volts across the load, but when i put in a 2200uF cap the voltage across the load begins to jump randomly up and down from 2v up to 6v down to 4v up to 7v??

 

i put in a 1000uF capacitor and getting 11 volts across the load, but when i put in a 2200uF cap the voltage across the load begins to jump randomly up and down from 2v up to 6v down to 4v up to 7v??

1000μf is good but it should be min. 25v(1000μF/25v)
just make sour that the capacitor voltage should be twice of the operating I/P voltage(secondary from transformer and after the rectifier diodes)

 

This'll answer some questions about what you'll need to get 12 v at load
http://www.hammondmfg.com/pdf/5c007.pdf

 

Thanks for the link http://www.hammondmfg.com/pdf/5c007.pdf
but whats the difference between these two
FULLWAVE BRIDGE Choke Input Load
FULLWAVE BRIDGE Capacitor Input Load

or whats the use of inductor (COIL/CHOKE)?
pl explane

 

Hello,

A 42 μF capacitor is a very low value for a buffer capacitor.
You will need about 1500 μF for each ampere.

Bertus

i have 4 lights installed with 12vdc battery.when i turn on the lights ,the get blink.i think voltage drop.can anybody suggent me what will the capacitor rating to use for it.?

 

What is the rating of the input source? It seems to not be able to supply enough current. There should be be at least 15v with no load, if the input is 12v RMS. 12v RMS should give 17v peaks. Maybe you need a heavier transformer. Or maybe your input is only 13.5 to 14 volts peak?

Anyway, once you have the correct transformer, you can calculate the capacitance needed:
Since i = C dv/dt we can make some assumption and get close-enough with C = i dt/dv where i is the maximum load current, dt is the time between charging pulses which is 1/2fmains, and dv is the voltage dip you want to allow, or the amplitude of the ripple voltage.

 

Zubair306, you're hijacking the thread. Start your own, describing your circuit and light ratings clearly.

 

but whats the difference between these two
FULLWAVE BRIDGE Choke Input Load
FULLWAVE BRIDGE Capacitor Input Load

or whats the use of inductor (COIL/CHOKE)?

The Capacitor choke filter was used for many years an amplifiers and radio recievers.
Often seen with a cap - choke - cap, it is known as a Pi filter because of the obvious configuration.
The capacitor stores energy, the choke has the effect of high impedance at the ripple frequency allowing DC to pass un-reduced, therefore filtering or removing the AC ripple .
Max.

 

I see it's a 18mo old thread!
Max.