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i just built a half-wave Crockroft Walton voltage multiplier, of 2 stages ( 2 x 1N4007 Vf=1.1v diodes , and 2 x 10nf 1kV caps each stage), the input is 120v ac at 60hz. I made a simulation of the circuit and the output is 675 volts. when i measure the output with a tester, it reads 240 volts. I dont know whats wrong:
why the simulation says one value and the tester another?
to calculate the load current (for Vdrop), do i have to put a resistor at the output node?
i made a lot of research but still i get some confusion.
what is the Vripple? does it affects the output voltage?
Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
Try putting a big capacitor from +HV to ground, and measuring the voltage it charges to. Dr. kV is right, you will barely get any power out of this setup as is.
i just tweakd the multimeter in the sim so the voltage resistance is 10M ohm, like my real tester. The result after running the simulation was around 308v, still not close to the 240v on my multimeter...
as for the reactance, does it has something to do with the load resistance for the time constant "tao" ?
im concerned that i did this thing backwards, with very few calculations on first place.
i just measure each cap , circuit conected to power source, and 3 of them measure around 150v . the close one to output measures 256v.
Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
Motor run caps at 4-10uF would probably work well for this application. You will likely need to balast the input on that though, to keep from blowing out the diodes.
how can i find the load current, do i need a resistor? if so, where do i put the resistor on the circuit?
i made some analisis in AC with a friend for positive and negative waves, where on each wave some diodes are open and others short. that is to find C equiv for each wave, bcuz he sugested me to do so to apply it in "tao".
for "tao"=RL*C, that it is the time of discharge, and T = 1/freq the time of each sin wave from 0 to 2*pi, there must be a RL*C>>T... or RL*Ceq>>T , where Ceq is the bigger value in boths half waves.
what i want to know is if these 10nf caps are usefull in this thing, cuz they discharge too fast i think. so i want to find a time constant large enough so they can not discharge too soon, if that can somehow fix it.
or find the optimum value of the caps if posible for this job.
Registered Member #191
Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
optimal capacitance value depends on the kind of output voltage and current you want.
VOUT = 2n*Vpk - VDROP VDROP = [Iload/(6fC)] * (4n3 + 3n2 - n) n is the number of stage.
For more power, i would use some 200V lytics, somewhere around 10 to 100uf. The caps don't see AC anyways, using AC caps in this circuit would be a waste.
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help, voltage multiplier newbie
