learningsolar wrote:
wow quick reply...still working on pics....todays test condition are terrible...no sun visible and snowing...what should I be looking for for voc? for 12 system, I also have a 60 cell here that gives different numbers too, I could use either
panel
j box open
and internal wiring of panel
same panel split into 2 circuit was 28 volts each but each circuit contains 4 strings which overlap each other, so not too sure what that would show while wired up I would assume they would share voltage and balance out, don't know if I could even do that
To post a picture, you have the first two steps correct, put them on Photobucket and make the able to be seen by anyone.
Next when you make a post, use the "Advanced Post" and look for the little postcard looking image above this blank space that you are typing in. It is yellow with a little mountain on the bottom and stamp looking thing on the upper right. Click on that icon, then it will open a subroutine, paste the URL in there, and then add a height and width. I used 570 high and 640 wide. Do not exceed about 680 wide, it is to wide for most computer screens, and will take additional computer space.
Then hit enter a couple of times between pictures, and you are good!
As for the solar panels, 39 cells in series will make a 21 volt circuit voltage, and if you just used a on-off switch, it will be able to connect to a 12 volt battery and charge it effectively.
15 volts open circuit is not enough voltage to push much amperage into the battery, especially once the battery voltage is over 13 volts. You must have 13.5 volts to recharge the battery, and normally battery chargers are 14.2 to 14.5 volts to get it full.
My advice is get the correct MPPT controller. Or buy another panel, and sell this one to pay for the 12 volt nominal (21 volt open circuit) panel.
SunElec.com is one seller of panels in the near $1 per rated watt. They also sell controllers, both MPPT and PWM (Maximum Power Point Tracking and Pulse Width Modulation). PWM will only start and stop current flow with a very low wattage triac. So it might start current flow if battery voltage is less than 13.3 and panel voltage is higher than battery, then stop flow if panel voltage is over 14.2 volts (normally user adjustable) or stop flow when panel voltage is less than battery voltage.
MPPT controllers are a LOT more sophisticated. It will take in anything from 8 to 45 volts (in your case and models are available up to 600 VDC input voltage) and transform this with a high frequency transformer to 13.5 volts output (or what is required to charge the battery) so it can work earlier in the morning until there is almost no light outside. It will consume a little more power than a PWM, but can do something special a PWM can not, that is increase the output amperage to more than the input amperage from the solar panel. it does this by taking in say 5 amps at 21 volts and converting this to 12.5 volts output (if the battery just started charging and was only about 11.7 volts overnight) at about 7 amps. This "Can" happen because 12.8 X 7 is less than 100 watts, the amount available from the solar panel.
Fred.
