I have 2-80 watt & 2-120 watt modules 200 feet from C-40 controller. I am connecting them in series to get 86VDC to controller (max 125VDC). At the controller I want to add another module (175watt @ 43VOC). The system voltage is 24VDC.
What voltage can I expect at the controller?
Is this OK?
What can you expect from the controller – how about smoke?
The C-40 controller is not intended to be connected to a solar array that has a different voltage from the battery bank. The reason for the high 125 VDC nameplate limit on the input voltage for this controller is to protect the controller during no load and low temperature operation when any solar module will have an open circuit voltage that is much higher than its normal operating output voltage.
Think of it this way – this is a pulse-width design controller which means it is just acting as an on-off switch to turn on and off the flow of electricity from the solar array to the battery. Depending on how charged or dis-charged the battery is, the controller will cycle this switch to the “on” or “off” position for different lengths of time (pulse-width), but its just acting as a switch and does not “convert” the higher voltage from a solar array into a lower battery voltage. Putting this high voltage into the low voltage battery is not good and could either over-heat or dry out the battery bank.
You have two options:
1. Purchase a maximum Power Point Tracking (MPPT) solar charge controller which does adjust battery charging voltage and will allow connecting a higher voltage solar array to a lower voltage battery. It will check the voltage input of the mis-matched modules and adjust the output current and voltage to the correct levels.
2. Buy a second C-40 controller and put each solar module group on its on controller, connected to the same battery bank. They will work together.
Good luck, and buy a fire extinguisher.