Sanity check

[pappaecho]

I want to confirm the logic involved with my solar panel

I used to have a second 15 watt panel used during the winter just to drive several 12 volt fans, to provide ventilation during the winter. This second panel did not have a charge controller so the fans only ran if there was a solar gain.

The winter storms carried this panel away. If I connect the fan system to the main solar panel before the charge controller, I am assuming that the blocking diode in the charge controller will stop the fans running on battery and will only run again if there is a solar gain.

Is this logic correct??

 

[William_H]

Yes you are right in that the blocking diode will stop the fans running on the ships battery. However you may have problems if the solar panel is big and is going through a reulator which will stop current from the solar panel when the battery is full.
A solar panel delivers around 18 to 20 volts no load. Attaching small fans to the panel without a regulator will deliver 20 volts to the fan possibly destroying the fans because the current drain is so low as to not reduce the voltage. With your 15w panel the power of the panel was so low that the voltage was pulled down by the fans.
Your presumably big panel without any other load will be too much voltage for the fans. The question then is whether the regulator on the big panel will waste excess power in a load resistor as some do or whether it will just switch off and on in pulses as some do when the ships batteries equire no more charge. In this latter case allowing the panel voltage to rise.
If you have doubt then measure the voltage of the solar panel output. If it is around 14 or 15 volts then the regulator is loading the panel so you can use your idea.
If voltage is higher then one fix might be to fit a 7812 regulaor before the fan to ensure fan voltage is always 12v. Another option being to fit diodes in series with the fan each dropping .7 volt until fan seems happy. Or run the fan off the ships batteries with a timer switch Or just buy another 10 or 15 w panel. good luck olewill