Hi Lawrence,

All electrolytic caps are terrible when it comes to tempco, initial
manufacturing tolerance, and leakage. Perhaps you could use a larger R, and
a smaller C from a different capacitor type, such as polystyrene,
polycarbonate, or polypropylene. There may be some other types that are
good for tempco as well, I just took these from a table in Horowitz and
Hill. How long a delay are you looking for in your RC circuit? How much
tolerance is allowed. Also, I think that electrolytic caps won't tolerate
many repeated changes in temp from room temp to 80C.

Good luck,

Sean


At 11:57 AM 9/15/98 +0000, you wrote:
>Ok, so this time it doesn't have a PIC in it.  But my prototype IS on
>the same table as my ICEPIC, so it's remotely related.....
>
>
>I'm having trouble with an electrolytic capacitor (100uF, 85 C,
>50WVDC) that drops in  value as it gets hot.  It is in an RC
>timing circuit, so a change in capacitance is a problem.  The circuit
>has to work in an environment that starts at room temperature, and
>climbs to 80C.  I don't know how mush the capacitor drops, but the
>slope of the voltage on the capacitor gets steeper the hotter it
>gets.
>
>The question is:  Do all electrolytic capacitors change capacitance
>as they get hot?  If so, how much and what direction?  Is there a
>type that is more stable at higher temperatures?
>-- Lawrence Lile
>
>     "The ideal design has zero parts"  -
>            (attributed to Harold Hallikainen)
>
>Download AutoCad blocks for electrical drafting at:
>http://home1.gte.net/llile/index.htm
>
+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
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