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Re: [Amps] Resonant choke filter

To: Will Matney <craxd1@ezwv.com>
Subject: Re: [Amps] Resonant choke filter
From: R.Measures <r@somis.org>
Date: Sun, 1 Aug 2004 07:48:54 -0700
List-post: <mailto:amps@contesting.com>

On Aug 1, 2004, at 2:13 AM, Will Matney wrote:


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.

2kV will work. More doesn't hurt. Not enough WV results in shortened capacitor life. The 1500V screen PS in my current project uses a 10kV resonating cap.
end


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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Richard L. Measures, AG6K, 805.386.3734. www.somis.org

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