Voltage tripler behaviour

Thread Starter

user151281

Joined Jun 12, 2017
5
Hi all

I made a voltage tripler following this schema:
http://www.electronics-tutorials.ws/diode/diode52.gif
upload_2017-9-19_19-18-30.png

I used foil capacitors without fixed polarity and I didn't add an earth since I placed it in a hard plastic box.

I tried it and apparently it is working. Since I could not check the voltage at the maximum output I used it for few seconds then I discharged it and I checked with the tester the single capacitors, here I found something strange.
1) The capacitors do not discharge fully even if I drain all the remaining voltage from the output contacts.
2) C3 retains more charge than the others, more than 150 volts
3) C1 and C2 retain a small charge, but the opposite polarity of what I expected.
Actually I made many test and sometimes I measured the correct polarity in C1, but C2 is regularly reversed.

I checked the diodes and they seem to be working properly even though sometimes when I check D3 I can see a small resistance for a few seconds in the direction where there should be none.

What could be wrong with the circuit? Is it possible it is just a glitch caused by the current bouncing back when I disconnect it (although the diodes should prevent it)?
 

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DickCappels

Joined Aug 21, 2008
6,187
There is nothing wrong with the circuit. The reversing is not a pleasant thing with polarized capacitors, but shorting the output is not a good thing either :)

Apparently C3 has higher capacitance than C2 so that when you shorted the output C3 charged C2 in reverse.

If the input was connected to a transformer winding C3 would charge C1 in reverse through D1.
 

Thread Starter

user151281

Joined Jun 12, 2017
5
Thank you for the reply.
I thought about something happening after I disconnected it. Just I was mystified by the way I could reproduce it over multiple tests.
One difference I forgot to mention is that C3 has a smaller rating than the others, but the capacity should be the same.
 
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