Not solar again ?
I ain't gonna do it , but I am Curious . In the course of a year I pull 3 different trailers and I was wondering : My pickup has a metal topper like the phone companies had in the past , if I put 3 o...
Forum Discussion
CA Traveler wrote:
Practically I agree, but this isn't proof. As soon as you connect a voltmeter there is a load and hence amps flowing even if it's extremely small.
Not sure how to "prove" it, any ideas?
Actually 2 checks are commonly used in full (or close) sun: Voltmeter and compare to Voc (open circuit) spec and ammeter and compare to Isc (short circuit) spec.
Typical DVMs will have input impedance of 1-10 megohm if not much greater, comparable to the olden days of VTVM (vacuum Tube volt meters) then the FTVM (FET transistor voltmeter) that replaced the VTVMs.
DVM will present a nearly immeasurable load than the lower impedance of the solar panels unless you have some access to laboratory quality picoamp meters.
Lets just say that the average cheap DVM isn't going to drop the open circuit voltage enough to be measured by even the best Fluke meter..
I mean if you really wish to get crazy you can buy lab quality meters which have GigaOhm impedances.. Like THIS which is rated 70 GigaOhm input impedance..
But reality is a DVM does not present enough "load" to alter your reading of a 18V panel so why make such a fuss?
A DVM simply PROVES that the panel is generating a output voltage (panel has no internal circuit damage).
And as you mentioned, the OTHER test is to use a short circuit test which is done by placing a ammeter across the terminals (standard ammeter looks like a short but also has a resistance). So one would have to use a very large ga wire to create the short then read with an indirect ammeter if you wanted to nitpick things this far.
