In a message dated 06/11/06 09:06:10 GMT Standard Time, [EMAIL PROTECTED] writes:
The VW panel reads about 20V in full sun. When connected to Don Brown's low power controller, it drops to 12.75V (full sun). I have a few panels and tried them all....same results. Even paralleled two. :----------------------------------------------------------------------------- --------------------------- Hi Ken, I would think the VW panels are too puny to provide sufficeint power to fully charge a battery as they were designed only to trickle charge an auto battery in transit. The 20V you describe out of the solar panel is the open circuit voltage. Most 12V solar panels depending on type will give 17V to 21V under these circumstances. However, when you connect it to a battery, the voltage will fall to the charge voltage of the battery depending on it's current state of charge. Disconnect the controller and connect the panel direct to the battery if you want to check for sure. With most types of controllers the effect will be the same in that the readings will be identical less the current needed to run the controller. Unless you get hold of some solar panels with the necessary capacity the result is going to be the same in that you can only trickle charge the batteries. Apart from long term float charging where the controllers would only come into use after a long period of charge. For most cases with low power solar panels a controller is not needed unless the panel does not have a series diode fitted. Many more of the VW solar panels in parallel or a larger solar panel(s) to increase the power is the only answer if you need to use this facility in real terms. The VW solar panels will most probably have series isolation diodes fitted to prevent discharge of the auto battery back through the solar panel at night or when not insolated sufficiently As a quick test to see what your panel is capable of, remove the solar panel from circuit and place a current meter directly across the solar panel terminals. The current reading will be limited to the available capacity of the panel. This is how we checked the 15kW solar arrays at the workplace when they were originally commissioned. These were built up from about 200 of the 75W solar panels arranged in series/banks to provide the necessary voltage/current capacity and each individual one had to be tested to ensured that it met specification. Was not unusual to see 120A going into the 7500Ah 48V battery plant in the morning sun. For that we really did require multiple solar controllers of sturdy proportions! Regards, Bob, G3VVT (ex civilian desert rat) _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
