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Date:         Mon, 21 Jan 2002 02:33:18 -0500
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: AFM upgrade using 16 volt tantalum capacitor
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 09:14 PM 1/20/2002, Larry Alofs wrote: >It seems to me that the resistances in the AFM are around 1K. With a >capacitor of 10 MFD you get an RC time constant of .01 seconds, with 20 >MFD about .02 s. It appears that we could go to 50 or perhaps 100 MFD >and the signal would still change fast enough to follow the movement of >the vane in the AFM. > Whaddaya think?

Seems possible to me. Assuming 1K-ohm, and 5*RC for essentially complete response, that would give a tenth of a second for 20 uF, up to a half second for 100 uF. I have the feeling that half a second is pushing the envelope a bit, but it's just a feeling -- and you get 95% in 3*RC. The system has to be able to respond, for example, to the overswing of the vane when you open the throttle quickly (provides enrichment analagous to a carburetor acceleration pump). Watching mine idling, I have a feeling that the vane oscillates at around ten Hz, but I'm sure the system doesn't want to know that (and it's a while since I've watched it, could be off by factor of two).

Best I can say is it doesn't sound outrageous, why not try it and see what happens. I would recommend stopping short of those cute little 1-Farad caps from Panasonic, though. <g>

david

-- David Beierl - Providence, RI http://pws.prserv.net/synergy/Vanagon/ '84 Westy "Dutiful Passage" '85 GL "Poor Relation"


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