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.

Dave:

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.

Jeff Yago

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Hey Jeff.

Matty:

Not sure what you mean by a “30 amp solar collector”. This is not usually how we reference their capacity. If you are talking about a “30 watt” solar collector (we call them solar “modules” if the generate electricity, and solar “panels” if the make hot water), but a 30 watt solar module would be about 10″ X 36″ in size so it would not need a trailer. If you are talking about a 30 kW solar array, this would definitely require a semi-tractor trailer to move around as it would be over 90 feet long.

If your interest is trailer mounted solar power systems in general, check the next issue of Backwoods Home Magazine (#108) as I will have a 2-part article on how to build your own using a 6 ft X 12 ft enclosed utility trailer.

Thanks,

Jeff Yago

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