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Author Topic: Parallel filter caps  (Read 5273 times)

matthias

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Parallel filter caps
« on: July 19, 2006, 01:43:32 PM »
Hey Forumites,
I'm re-capping my Slave and I ended up going with a Bank of capacitors to cover the needed value,
Well, I got into a conversation about it with this old timer at my work (not electronics related), He grabed a bar napkin and drew up something like this:

Now this is somewhat confusing to me because I thought that Selection C was the way to go.
Selection A kind of makes some sense but..............Selection B just seems out there.
He stands by what he says but I Just don't trust it, He is the know it all type who is "never wrong" if you know what I mean. help me out here is this guy just in some "parallel reality" or is this guy really dropping some Phat knowledge on me?
-Matthias


joecool85

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Re: Parallel filter caps
« Reply #1 on: July 19, 2006, 02:14:12 PM »
A is the one I would use.
Life is what you make it.
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matthias

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Re: Parallel filter caps
« Reply #2 on: July 19, 2006, 03:28:29 PM »
Crap!
I've been using C whenever this comes up!
Thinking about it A makes alot more sense. but still whats up with B?

RDV

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Re: Parallel filter caps
« Reply #3 on: July 19, 2006, 03:36:25 PM »
B is in series though the capitance is added together in parallel.

RDV

teemuk

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Re: Parallel filter caps
« Reply #4 on: July 19, 2006, 04:56:15 PM »
I would not use C since it might be interfered with rectifier noise. A seems better since the supply is taken from closer to the filters instead of rectifier. I reckon reading something about B being a good practice since it equalizes the wire lenghts and therefore resistances as well. Optimally both the first and the last cap have an equal wire lenght to rectifier and load. In my opinion B with supply and ground taken from the caps would be the best way.

Edit: I found it: "If the layout and each capacitor are not identical, the capacitor with the lower series trace impedance will see higher peak currents and become hotter (i2R). To promote this sharing, the form of the leads to both capacitors should be symmetrical." - Good Physical Layout Takes Black Magic Out Of Power-Supply Design, Marty Brown, Fairchild Semiconductor (http://www.techonline.com/community/ed_resource/feature_article/5430)
« Last Edit: July 19, 2006, 05:27:10 PM by teemuk »

matthias

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Re: Parallel filter caps
« Reply #5 on: July 19, 2006, 09:01:36 PM »
Thanks Teemuk,
That's some good reading, had to take some asprin after that.
Well, I went with Version A.
Got Brand spankin new 3055's and mica washers, all the other components checked out.
Its idle-ing on the Variac and light bulb limiter right now.
Bringing it up slowly it was thumping pretty heavy but  it slowed down fairly fast and the 40W bulb sank into its soft glow, a nice dim sunset orange. The heatsink is Ice cold. I'm getting anxious to run it full throttle.
I'll see what happens with it tonight.

I really want to thank everyone here for making such an open forum possible, It's a good thing.
I never have messed with SS to much before so thanks for the lessons.
_matthias


joecool85

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Re: Parallel filter caps
« Reply #6 on: July 20, 2006, 06:57:08 AM »
Well, it sounds like you're good to go.  Keep us updated!
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matthias

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Re: Parallel filter caps
« Reply #7 on: August 05, 2006, 12:19:43 AM »
well,
That didn't last.
got a bad cap in there and now it's making a HELL of a lot more noise than when I started.
o.k.
This time I buy caps from mouser.