Date: Mon, 25 Oct 2004 16:25:17 -0700

Author: "John Welch"

Subject: Re: low leakage capacitors

Post:

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Never mind everyone - I did some research and found capacitors that will =
do a little better than mine, but not much, because you just can't get =
below about .5 uA, so I'll just have to use a smaller resistor.=20
thanks anyway.
-John
----- Original Message -----=20
From: John Welch=20
To: tap-l@listproc.appstate.edu=20
Sent: Monday, October 25, 2004 3:30 PM
Subject: low leakage capacitors


We're doing a lab where students measure the voltage across a =
capacitor in an RC circuit, measure the time constant, etc. I'm using =
fairly large capacitors (220uF) to get a large time constant, but the =
ones I'm using are leaking enough that I'm getting a current and thus a =
measureable voltage drop across my resistor (100k), when the capacitor =
is "fully charged." I'm using electrolytic capacitors rated at 160V. =
Does anyone know if there is some type of capacitor that will work =
better for me in these circumstances? (i.e. will have a very low leakage =
current at around 10 V DC?)

I know that I could use a higher C and lower R to get the same time =
constant, and with a lower R I'll get a lower voltage drop at the R, but =
I still want to figure out what types of capacitors work the best for =
something like this.=20

thanks,

-John
Cabrillo College Physics Dept.
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Never mind everyone - I did some =
research and found=20
capacitors that will do a little better than mine, but not much, because =
you=20
just can't get below about .5 uA, so I'll just have to use a smaller =
resistor.=20

thanks anyway.

-John

style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
----- Original Message -----

style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black">From:=20
href=3D"mailto:jowelch@cabrillo.edu">John=20
Welch

To: title=3Dtap-l@listproc.appstate.edu=20
=
href=3D"mailto:tap-l@listproc.appstate.edu">tap-l@listproc.appstate.edu A>=20

Sent: Monday, October 25, 2004 =
3:30=20
PM

Subject: low leakage =
capacitors



We're doing a lab where students =
measure the=20
voltage across a capacitor in an RC circuit, measure the time =
constant, etc.=20
I'm using fairly large capacitors (220uF) to get a large time =
constant, but=20
the ones I'm using are leaking enough that I'm getting a current and =
thus a=20
measureable voltage drop across my resistor (100k), when the capacitor =
is=20
"fully charged." I'm using electrolytic capacitors rated at =
160V. Does=20
anyone know if there is some type of capacitor that will =
work better=20
for me in these circumstances? (i.e. will have a very low leakage =
current at=20
around 10 V DC?)

 

I know that I could use a higher C =
and lower R to=20
get the same time constant, and with a lower R I'll get a lower =
voltage drop=20
at the R, but I still want to figure out what types of capacitors work =
the=20
best for something like this.

 

thanks,

 

-John

Cabrillo College Physics=20
Dept.


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From wreitz@neo.rr.com Mon Oct 25 16:28:17 2004

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