Voltage multiplier - Page 1
Forum section: electronics / beginners

author: Simon123
author_rank: Regular Contributor
timestamp: December 25, 2013, 11:30:44 am
content: Hello i built voltage multiplier-cockroft walton type.I connected secondary-12volt side to relay oscilator and primary-230v to multiplier.It works or some time, but then it starts producing small sparks.At start it can produce 6mm, but now very little.The capacitors are rated for 1kV, and diodes are BY133-1.3kV diodes.Could capacitors go bad?And they are polyester film caps.

author: Simon123
author_rank: Regular Contributor
timestamp: December 25, 2013, 11:34:31 am
content: And when i changed caps it worked fine for some tme, but now problems again.

author: Psi
author_rank: Super Contributor
timestamp: December 25, 2013, 11:37:38 am
content: When it sparks it's effectively a short, the energy in the caps gets discharged instantly.This high current usually damages the diodes before anything else but i guess it could be destroying the film inside the caps with every spark. Which would reduce their capacity.

author: Simon123
author_rank: Regular Contributor
timestamp: December 25, 2013, 11:39:15 am
content: But i checked diodes and they are fine, and are rated for 1A.

author: Psi
author_rank: Super Contributor
timestamp: December 25, 2013, 11:43:05 am
content: Do you have the datasheet for the capacitors?Check their max discharge current and add a resistor in series with the multiplier to limit the discharge current so its less.Depending on the number of multiplier stages you have you may want to use multiple resistors in series to make up the required value. Just so there's less voltage across each resistor.Also, what size are these capacitors?

author: Simon123
author_rank: Regular Contributor
timestamp: December 25, 2013, 12:05:22 pm
content: No, they are prety old by looks-i think they are from Iskra.They look like, they are from 90's.There is 1cm space betwen legs.

author: Zero999
author_rank: Super Contributor
timestamp: December 25, 2013, 12:08:54 pm
content: You're exceeding the capacitors maximum voltage rating.When the current in the 12V side of the transformer is interrupted, it will produce a high voltage, >100V which will be boosted by the the 240V winding to >2kV. With the correct duty cycle, it's possible to get 5kV when applying 12V pulses to a 12V:240V mains transformer but be the insulation on the 240V side could fail as it's not designed for high voltages.

author: Simon123
author_rank: Regular Contributor
timestamp: December 25, 2013, 12:16:26 pm
content: Ok, tnx so should i put some zener diodes on the primary side, to limit voltage?

author: Zero999
author_rank: Super Contributor
timestamp: December 26, 2013, 12:54:10 pm
content: It's back EMF so you need a normal diode connected in reverse parallel with the 12V winding.How many stages do you have?Have you tried to get sparks directly from the 240V winding?Rather than adding a diode, you could be better off connecting the diodes and capacitors in series and halving the number of stages but even then, the voltage could be too high.

author: Simon123
author_rank: Regular Contributor
timestamp: December 26, 2013, 02:14:30 pm
content: Yes, i get little sparks from 240v winding, i have 3 stages.And i have already made pcb for multiplier part, so i will proably use diode on 12volt winding, instead of changin multiplier.