[Amps] Resonant choke filter

[Will Matney]

Richard,
Yea, I was shooting for the 3X (460Vdc X 3) but in the Allied catalog, 
there was a jump between 400V and 2 Kv. The X363 series from ASC goes 
from 100 to 400 Vdc. Then the next series is the X675, which starts off 
at 2 Kv and goes to 16 Kv. I guess they figure nobody will need anything 
from 500V to 1.9Kv? I actually needed 1.4Kv-1.5 Kv but they didn't show 
making it. Needless to say, I thought that odd myself. Since you 
mentioned trying that filter out, I looked around my shop and had a 5 
Henry choke. I figured just to build up a demo first using a 325 Vac 
transformer I had here just to see how much it would clean that up using 
a scope to check it. If I had a Polaroid scope camera to fit this 
Tektronix scope, I'd do a before and after pic. I'll try to get a pic 
with my digital camera if it will show the trace and graticule. Really, 
I'm building a new HV power supply for my bench using one of those 
transformers I have. It'll have an adjustable regulated screen and bias 
output. I'm wanting it to prototype other projects with. I've put off 
building the thing now for two years and just now thinking about 
starting it =) I need to find me a good deal on two panel meters in the 
500 Vdc range to go on the cabinet. Not found any yet without buying 
brand new. I might just modify a couple of surplus meters with a new 
face plate.

Will

R. Measures wrote:

>
> On Jul 31, 2004, at 1:30 AM, Will Matney wrote:
>
>> I had started designing a resonant choke filter for a supply I'm 
>> thinking about building and figured I would share the information 
>> here. I was looking at using a 5 Henry choke by Hammond Mfg. and 
>> needed to figure a capacitor for it. The formula is;
>>
>> C = 1 / f^2 x 39.4786 x L
>>
>> f = frequency in Hertz (Full Wave Rect = 120 Hz, 1/2 wave = 60 Hz)
>> L = inductance in Henrys
>> 39.4786 = 2^2 x pi^2
>>
>> So after calculating for C, I got 0.00000035 (3.5^-7) or 0.35 uF. 
>> Looking for a suitable capacitor, I needed one above 500 Vdc.
>
>
> Resonating capacitors are normally 3x the DC output V of the PS.
>
>> I figured on using a "metalized polyester" because they go up to 
>> around a 16 Kv rating. I found that in the 2Kv range was the highest 
>> that would have something close in value. 4Kv didn't have close 
>> enough really. Under 2 Kv, there was only a 0.33 uF so I need another 
>> to parallel which I found a 0.02 uf. Both together will give the 
>> required 0.35 uF. these caps sell for around $7 to $8 each from 
>> Allied Elect. which is not bad. Keep in mind though that even if the 
>> choke manufacturer says it's a 5 Henry, it may test to be something 
>> different. So, using a scope to test the DC output, adjusting the 
>> value of the capacitor(s) slightly may have to be done. If so, add or 
>> subtract enough C until the ripple goes as low as it can.
>>
>> Will Matney
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>>
>>
> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>
>
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