William_H
Well-known member
No typo. This statement was made assuming that the controller would stop current flowing from the battery to the PV panel. (if not then disconnect the panel) So if an amp meter is connected across the PV panel input leads then it would measure only pV panel (short circuit )current.Surely if set on amps the meter needs to be connected in series with the panel output, not across it in parallel, if in parallel the meter needs to be on volts. Edit:- If on amps it will probably damage the meter
Think maybe WH got a typo??OK for us that know these things but just thought post may have been a bit confusing.
Now an amp meter across any power source like a lead acid battery is usually a disaster. Very high current. Although it is a standard test for 1.5v for zinc carbon cells. (momentary test)
It is all about internal resistance of the battery or PV panel. The max current from a pV panel is typically around rated watts divided by 20. (volts no load) (so 20w panel 1 amp max.) Note some larger domestic panels may be 40 v max volts.
The max current will usually be stated on the rating data panel. Achieving the max short circuit current will depend on insolation (sun hitting panel) and condition of the panel.
This internal resistance dissipates the power in the panel itself. Without a problem. The internal resistance explains how a 20v panel can be connected directly to a 12v battery and the voltage of the panel will fall to that of the battery. The volt drop occurring in the panel. The panel will push the max current it can like about 80% of short circuit current. (varies of course) A PWM controller essentially does that connection until battery volts rise and this averts over charge. The 20v is achieveed by the number of ells in series in the panel. 20v chosen as a voltage which can fall with less sunshine to a voltage still able to push some current in to a 12v battery (ie 14v)
Here endeth the lesson. ol'will