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Date:         Fri, 3 Jan 2003 14:26:42 -0600
Reply-To:     Larry Alofs <lalofs@ENTERACT.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Larry Alofs <lalofs@ENTERACT.COM>
Subject:      Re: Solar panel wrap-up
Comments: To: Ben McCafferty <ben@VOLKSCAFE.COM>
Content-Type: text/plain; charset=us-ascii

The 0.1 volt reading is meaningful as a voltage measurement.

When you set your DVM to an ohms range the meter uses its internal battery to apply a small voltage to what it assumes to be a completely passive component. From the resulting current and voltage values it calculates and displays the resistance ( R = V/I ). If the component being tested produces voltage on its own, the meter displays misleading results, perhaps even negative (!) resistance, assuming it isn't damaged.

Connecting an ohmmeter to a semiconductor p-n junction like a diode can tell you which end is which, if the meter uses a high enough voltage to overcome the voltage drop across the junction ( about 0.65 v for silicon). The reading in the conducting direction still should not be interpreted as resistance in the traditional sense of the word. A silicon solar cell has some resemblance to a silicon diode with the added complication of being a voltage source.

Larry A.

Ben McCafferty wrote: > > I followed the instruction from Jim to cover the panel so it would not be > producing any current, and the voltage output was 0.1. Would the reading > still be useful? > tx, > bmc :) > Ben McCafferty > ben@volkscafe.com > > Volks Cafe > 1823 Soquel Avenue > Santa Cruz, CA 95062 > 831-426-1244 > http://www.volkscafe.com > > > From: Larry Alofs <lalofs@ENTERACT.COM> > > Reply-To: Larry Alofs <lalofs@ENTERACT.COM> > > Date: Fri, 3 Jan 2003 11:43:38 -0600 > > To: vanagon@GERRY.VANAGON.COM > > Subject: Re: Solar panel wrap-up > > > > The readings will not be meaningful when you connect an ohmmeter to a > > component which is producing voltage and current. > > > > Larry A. > > > > > > Bill N wrote: > >> > >> Minus resistance? Is that like negative pressure? > >> > >> Bill > >> > >> ----- Original Message ----- > >> From: "Ben McCafferty" <ben@VOLKSCAFE.COM> > >>> > >>> As an aside, I did put an ohm-meter on a panel this morning, and the > >>> responses regarding diodes seem to be dead on. The resistance one direction > >>> was about 19 MOhms, and the other direction was about -4 MOhms. So I doubt > >>> we'll be seeing any glowing solar panels in the campground at night.


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