All Set to make a Solar Panel. Require some informtion

[Naptown]

You appear to have a PWM type CC which just regulates the current flowing to the batteries but does not do anything to convert the voltage. As a result you are losing potential power from the panels because the panel voltage will be held very close to the battery terminal voltage whenever current is flowing.

Above is why you are getting that reading

I am checking the voltage at the end of wires. I mean near the Charge Controller. I did the same thing, first CC to Bat then CC to Panels.

[Sunking]

I was checking the panels today. I connected 2 panels, 72 cells configured at 18v, with 20 ampere charge controller. As soon as I connect the panels, the voltage drop at 12.7vol Open circuit voltage is 20.7volts. Why its happening?

It is normal and how a PWM controller works and is suppose to work. It will make your on paper 18 volt 20 amp panel (360 watts) 12 volts @ 20 amps or 240 watts.

PWM CC are just a switch that connects your panels to the battery. Al PWM chargers Input Current = Output Current. 20 amps in = 20 amps out. Solar panels are current sources, not power voltage sources. That it is why it is possible to say hook up say a 240 watt panel with a rating of 36 volts Vmp, 6.6 amps Imp (a typical Grid Tied 72 cell panel, and only get 12 volts x 6.6 amps output (79 watts) at best on a PWM CC. Surprise!

Just think you could have bought a MPPT charge controller and that same 18 volt 20 amp panel would output 12 volts @ 29.1 amps from the CC.

[mcc]

Friends, can you please suggest me which junction box should I buy? I see two types of JB, one with only two metal connecters and one with four metal plates.

[Naptown]

Friends, can you please suggest me which junction box should I buy? I see two types of JB, one with only two metal connecters and one with four metal plates.

Buy the one with 4 terminals and that is where the bypass diodes go.

[mcc]

Thanx !