solar options

chloe's ranch wrote:
Thanks again everyone for the help. Sounds like an adjustable controller might be a good idea. If I do go with option B(adding a third 120 watt panel to my current 240 watt system and using the Blue Sky 30 amp mppt controller) I have another question. Currently my two 120 watt panels are wired in parallel with 10 guage wire down a vent to the existing controller. Should I have the additional 120 watt panel run with a separate 10 guage wire down the vent and then spliced together with the current wire at the controller, and then 6 or 8 guage wire from controller to batteries?

A single 10 gauge wire can handle the 3 120 watt panels in parallel. Yes there will be some voltage drop, but that is usually not the critical voltage drop for your system. The controller (PWM or MPPT) will reduce the voltage even more as it does its work.

What is critical is the voltage drop from your controller to batteries - that is what can really slow down the charging. Short fat wire is needed from the controller to the battery to minimize voltage drop between them. What gauge wire is currently between your battery and controller? And how long is the wire run between them?

A great way to measure the voltage drop between controller and battery is to measure the voltage across the controller output and then across the battery posts when the solar panels are sending lots of amps into your batteries. The voltage at the battery terminals is what needs to be high to get the most amps into the batteries.

So while adding a 10 gauge wire from your new solar panel to your controller will help a little bit, it is more likely that adding that 10 gauge wire between your batteries and controller will provide you with more benefit. Note I said "adding" the wire between batteries and controller - you can add more wires between the two points or substitute thicker pure copper wires between them - whatever it takes to minimize voltage drop at the battery posts.

Ed