CW multipliers
..., Mon Jul 31 2006, 02:43AMI have a question about Cockcroft Walton or Villard Cascade voltage multipliers....
In theory the caps only see a dc voltage... But as you draw current you get ac through them...
So I was wondering if electrolytics can be used? I want to use these 200v/820uf caps I have laying arround to make a 2 stage multiplier to take the 120v mains (160v p-p) up to 600v+ or so for an off line vttc. I calculate that with 800ufd I can give 500ma at 600v... But I worry that my caps will be looking at as much as 320vac, which they most definantly will not like.
So, how should I go about solving the problem? would it be 'safe' to put the 2 caps back to back to make a bipolar electrolytic? perhapse I need a diode in antiparallel with the caps? If I do that I will only have 400uf, but that should still be enough (I only need 200ma)
But then I am still running the caps at more than their rated voltage... But then I read somewhere that as you draw current off the multiplier you reduce the amount of voltage on the caps, so I think they might just be ok... So do I need to use 8 caps for each of the 4 caps in the multiplier for a total of 32 caps (a wooping 500J) That would be with the caps in a 2x2 arrangment for a 820uf/400v cap, then in antiparallel for a 400uf/400vac then the 4 caps for the multiplier.
Thanks!
Re: CW multipliers
ragnar, Mon Jul 31 2006, 03:17AM
Yup, if you want to make a bipolar electrolytic capacitor, connect the negatives together and place a diode across each capacitor with the cathode/stripe to the cap's positive.
I've been running a 10,000uF 63V electrolytic at 60V for a while now and he seems OK -- he's probably a quality cap though, and I suspect even if you go marginally over the ratings you'll get short-lived caps.
Personally I wouldn't rely on the load to keep the caps under their ratings... but hey, that's what dummy loads are for. =)
ragnar, Mon Jul 31 2006, 03:17AM
Yup, if you want to make a bipolar electrolytic capacitor, connect the negatives together and place a diode across each capacitor with the cathode/stripe to the cap's positive.
I've been running a 10,000uF 63V electrolytic at 60V for a while now and he seems OK -- he's probably a quality cap though, and I suspect even if you go marginally over the ratings you'll get short-lived caps.
Personally I wouldn't rely on the load to keep the caps under their ratings... but hey, that's what dummy loads are for. =)
Re: CW multipliers
dan, Mon Jul 31 2006, 03:17AM
Yeah that voltage rating seems a bit low. I have used electrolitics with pretty good results in a Villard cascade. I use it for charging. The caps don't seem to mind it but charging only takes a second or two. I would try to stay away from electrolitics for your application. I would probably look for some motor run capacitors but anything above 15-30uf is going to cost you if you buy them new. Never tired to make bipolar electrolitic with diodes before but it sounds like it would work. Since the capacitors really aren't in series(physically yes but electrically no) the new pseudo-bipolar capacitor should retian the same 800uf capacitance.
dan, Mon Jul 31 2006, 03:17AM
Yeah that voltage rating seems a bit low. I have used electrolitics with pretty good results in a Villard cascade. I use it for charging. The caps don't seem to mind it but charging only takes a second or two. I would try to stay away from electrolitics for your application. I would probably look for some motor run capacitors but anything above 15-30uf is going to cost you if you buy them new. Never tired to make bipolar electrolitic with diodes before but it sounds like it would work. Since the capacitors really aren't in series(physically yes but electrically no) the new pseudo-bipolar capacitor should retian the same 800uf capacitance.
Re: CW multipliers
..., Mon Jul 31 2006, 03:33AM
really I need electrolytics, since I need at lest 300ufd to get the necessary output power... A motor start cap of 300ufd would be huge... I am really tired of lugging that mot around (thus the offline coil-I was hoping that 4 little caps would work...)
I am thinking of using a little autotransformer to give me 240v, then use a full wave voltage doubler to give 700ish volts. Seems like a much more elegant solution requireing only 1/10 the caps
The coil would never have been truly offline since I needed the filament transformer...
..., Mon Jul 31 2006, 03:33AM
really I need electrolytics, since I need at lest 300ufd to get the necessary output power... A motor start cap of 300ufd would be huge... I am really tired of lugging that mot around (thus the offline coil-I was hoping that 4 little caps would work...)
I am thinking of using a little autotransformer to give me 240v, then use a full wave voltage doubler to give 700ish volts. Seems like a much more elegant solution requireing only 1/10 the caps
The coil would never have been truly offline since I needed the filament transformer...Re: CW multipliers
dan, Mon Jul 31 2006, 03:40AM
If you really want to make it run off-line you could use a voltage divider to power the filiment off mains. But a small filiment transformer isn't that heavy anyway..
dan, Mon Jul 31 2006, 03:40AM
If you really want to make it run off-line you could use a voltage divider to power the filiment off mains. But a small filiment transformer isn't that heavy anyway..
Re: CW multipliers
..., Mon Jul 31 2006, 03:49AM
I need about .5a for the filament, not something easy to take off the line directly...
I am going to build it arround the autotransformer for now and see where I get. I might rethink it later...
..., Mon Jul 31 2006, 03:49AM
I need about .5a for the filament, not something easy to take off the line directly...
I am going to build it arround the autotransformer for now and see where I get. I might rethink it later...
Re: CW multipliers
Sulaiman, Mon Jul 31 2006, 06:19AM
600V @ 200mA is 120W, say 150 VA transformer .. not too heavy.
Sulaiman, Mon Jul 31 2006, 06:19AM
600V @ 200mA is 120W, say 150 VA transformer .. not too heavy.
Re: CW multipliers
Electroholic, Mon Jul 31 2006, 09:24AM
lytics will be fine in a CW.
i have been using the same one as a charger for my CG for almost two years now.
no need to pair them with diodes to make "bipolar" lytics.
but increasing the voltage rating won't hurt.
say 330V?
Electroholic, Mon Jul 31 2006, 09:24AM
lytics will be fine in a CW.
i have been using the same one as a charger for my CG for almost two years now.
no need to pair them with diodes to make "bipolar" lytics.
but increasing the voltage rating won't hurt.
say 330V?
Re: CW multipliers
Tesladownunder, Mon Jul 31 2006, 12:40PM
100VAC in and 2000VDC out using electrolytics.
Peter
Tesladownunder, Mon Jul 31 2006, 12:40PM
100VAC in and 2000VDC out using electrolytics.
Peter
Re: CW multipliers
Steve Conner, Mon Jul 31 2006, 01:59PM
10kV @ 100mA from a MOT using series strings of cheap 22uF 450v electrolytics
I can't see how you arrived at a ripple voltage of 320V from 0.5A and 800uF.
Steve Conner, Mon Jul 31 2006, 01:59PM
10kV @ 100mA from a MOT using series strings of cheap 22uF 450v electrolytics
I can't see how you arrived at a ripple voltage of 320V from 0.5A and 800uF.
Re: CW multipliers
Marko, Mon Jul 31 2006, 04:31PM
I have acquired a bunch of 1uF 400V caps recently tending to build a prototype 6kV off-line CW, but still didn't get around it. (HV forum)
You will need to series the caps in order to get required voltage, or find some 400V rated.
It's just few caps and I don't think it would be some huge problem.
Marko, Mon Jul 31 2006, 04:31PM
I have acquired a bunch of 1uF 400V caps recently tending to build a prototype 6kV off-line CW, but still didn't get around it. (HV forum)
You will need to series the caps in order to get required voltage, or find some 400V rated.
It's just few caps and I don't think it would be some huge problem.
Re: CW multipliers
FaLLoUT, Thu Aug 03 2006, 10:59AM
What will be the best source to get HV caps
(e.g 1uF 400V or more) what good ones can be obtained in TV?
FaLLoUT, Thu Aug 03 2006, 10:59AM
What will be the best source to get HV caps
(e.g 1uF 400V or more) what good ones can be obtained in TV?
Re: CW multipliers
Marko, Thu Aug 03 2006, 01:01PM
I bought mine, they are about $0.1 and I doubt they could be more expensive somewhere in the world.
You can also find 400V electrolytics in range from 1 - 10uF from saver bulbs and small switchmode supplies (cell phone chargers etc).
Marko, Thu Aug 03 2006, 01:01PM
I bought mine, they are about $0.1 and I doubt they could be more expensive somewhere in the world.
You can also find 400V electrolytics in range from 1 - 10uF from saver bulbs and small switchmode supplies (cell phone chargers etc).
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