Date: Wed, 24 Mar 2010 12:54:38 -0700
From: "Bill, W6WRT" <dezrat1242@yahoo.com>
Subject: Re: [Amps] ripple in B+ supply
ORIGINAL MESSAGE:
>> Just saying "1% ripple" with no qualifiers leads to
>> confusion.
>
>=====Absolutely wrong! In that writer's mind, I would
>suppose, but not in general. Certainly not my
>mind.
<snip>
>
>What is being overlooked here is that the ripple
>in the usual power supply is nearly sinusoidal,
<snip>
Bill you are a bright and knowledgeable fellow
but I think you should back off on this one. :-)
REPLY:
I appreciate your kind words Jim, but I have to respectfully disagree.
All of the PS ripple I have ever scoped looks more like a sawtooth
than a sine wave, having a sharp leading edge and a more gentle
trailing edge.
## Even Duncans PSUD shows a sawtooth. It peaks up every 8.3 msecs
when the caps charge up.. then slowly drops off in value... till it peaks
up again..8.3 msecs later. That's why it resembles a saw tooth.
Second (and most important) I still maintain that saying X% ripple
without specifying P-P or RMS just leads to the inevitable question
"Which did you mean?". All I ask is the author specify which. Either
way is fine as long as I know which is being used.
## Bill, EVERY arrl book I have, [back to 1960] plus Orrs'
books always references ripple to RMS. Every ARRL formulae
is referenced to RMS.
## Even if u measured P-P ripple on any scope, the 1st thing you
do is divide it by 2.. to give you peak. Then multiply peak x .707
[or divide by 1.414] Ok, now u have RMS. Take the RMS value,
and then divide by the LOADED B+ voltage. It will typ come out
like... '.029' = 2.9% ripple.
## what else are you going to do ? You can't take the P-P value..
and then divide by LOADED B+ voltage..... otherwise, if you do that,
you will end up with 8.20% ripple.
I was using a scope to look at ripple long before I owned a true RMS
meter so I might be prejudiced, but I suspect there are lots like me
out there.
## since it's a saw tooth wave form, the above arrl /orr method
is probably not exact. The simplest method is just to stick the
fluke 87 dvm across the lytic at the cold end of the string.... and
run a full bore cxr. The fluke has internal caps to block the dc
component, then u get the true rms reading. Even with a scope,
the results I get are virtually identical to psud.
## You can see 3% ripple, typ of amps with a 25 uf filter, plane as
day, on any rf monitor scope. It's plane as day on the Array solutions
wattmeter's too. The peak detector in that thing is very fast... fast
enough to easily show b+ ripple. [1200 w cxr]
## where psud falls down.. is with dynamic loads. I wish they could
simulate that. The original psud was for audiophile and stereo amp
fellows. I see the latest version will allow a cap up to 1 farad.
## Btw, in my latest experiment, P-P voltage dropped from 598v,
[2.95% ripple]..down to just 26 V [ .126%] That's at 120 hz. All the
harmonics of 120 hz are way down..... and no 150 lb chokes used any
where. Loaded B+ went up 106 vdc too.
later.... Jim VE7RF
73, Bill W6WRT
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