[SOLVED] 240vac rectification problem

[thebadtall]

Hello !!



I found some old transformers (with the good old transformers) 500ma 9v and 7.5v ac


wich back to back gave me 240vAC

and thought to use them and build a 4 tube preamplifier with around 300vDC B+ voltage.

but i dont know why, after the rectifier bridge, wheres the high voltage ? ? ? ? ?
look:


i did not use capacitor. can you tell me why there is so huge drop ?
because of the low power of transformers?

any suggestions to get >200v DC with those two ?

 

[KonstanU]

How can it be connected with power of transformator. Your output power equals zero.
I think can be 2 reason.
1. Your bridge is broken
2. Measurement tool is bad.

As a way put capacitance and look on the result.

 

[thebadtall]

unortunatelly, i cant understand your reply. but i will make a diode brg and measure again

 

[1206.sachin]

I think you should use O/P filter capacitor.
O/P of full wave rectifier hav lot of ripple so your meter on DC range will give you wrong reading.

 

[thebadtall]

that way you may be correct, since my meter is the cheapest. i will try in a couple of hours

 

[davoud]

I think as KonstanU said you should check your bridge.
- Please measure voltage before and after bridge when bridge is connected to your circuit .
rupture or short circuit maybe occurred.

 

[thebadtall]

yes you are correct, it was the rectifier failed.


now the new problem is where i will find caps ? I have 400v rated , but i will need of higher voltage... so i will stay on 230vDC


thank you for the interest !

 

[davoud]

Okay!
What do you want?
What power and current you need?
According to your circuit , it is a low power cir circuit thus I think you can produce high voltage by many caps and diodes and for higher power need to use other technique.
Please refer to these site my be useful :
https://www.edaboard.com/threads/255280/
https://www.edaboard.com/threads/205285/
Regards

 

[thebadtall]

my friend thank you for the interest, i dont want anything.. i was asking where i will find high voltage capacitors!
but then i said that will use lower voltage, around 240vdc because i dont want to overstress the 400v capacitors if i run the circuit at 380v

 

[1206.sachin]

my friend thank you for the interest, i dont want anything.. i was asking where i will find high voltage capacitors!
but then i said that will use lower voltage, around 240vdc because i dont want to overstress the 400v capacitors if i run the circuit at 380v

Use 350V electrolytic capacitos in series. Effective capacitance will be half the capacitor used.

You won't get electrolytic cap. more than 400V rated.

Capacitor value will be 1000uF for 1 Amp o/p current

 

[thebadtall]

i have bought a couple of months ago 10 electrolytic caps 20uf 600v (axial) and they where quite good at 480v.
what do you mean about 1000uf?
i guess to get 1000uf from caps in series i will have to use huge numbers

 

[davoud]

Yes you are right.
Unfortunately i didn't understand your purpose .....sorry.
As you said for provide 1000uf by 20uf , you need 50 pieces of this caps in parallel.
regards

 

[thebadtall]

today as I was dealing with Resistors and capacitor networking (with the transformers above) to cut the noise of the power supply, .. a capacitor exploded and it was a bad experience !!!!!