MPPT vs. Shunting Solar Controller

[heritage]

I am also puzzled about one thing, probably something taught, when I had a day off in school: As your AMPs increase, so does the Voltage – which I can relate to on a common sense basis. Why do calculators generally show the reverse happening, ie. an increase in one factor leads to the decrease in the other?[/QUOTE]

No, you didn't miss a day of school. You are remembering the formula: Power (watts) = Amps X Volts. So if you increased the amps, the voltage would decrease if the wattage were to remain the same. In Mainesails examples the power increases allowing the voltage and amperage to both increase.

 

[Albanach]

Before finally installing my solar system, one last question, please. Would it be necessary to protect the circuit

a)leading from the solar panel (10W) to the 4.5A WMP Morningstar controller
b)from the controller to the battery bank.
​

The 2 batteries are connected via a Battery Switch: One On, Two On, All On. To avoid current backflow between the batteries via the direct positive solar feed wires to each of the batteries, I intend to incorporate a blocking diode in each of these wires. The wire is 4 mm.

My thinking: a) the current would never be enough to cause any problems, even with a short circuit and b) the diodes would eliminate any current flowing from the battery , except for the short connection after the diode to the battery.

Schematic attached.

 

[Albanach]

Sorry, attachment (XL,TXT) did not work

 

[Maine Sail]

Before finally installing my solar system, one last question, please. Would it be necessary to protect the circuit

a)leading from the solar panel (10W) to the 4.5A WMP Morningstar controller
b)from the controller to the battery bank.
​

The 2 batteries are connected via a Battery Switch: One On, Two On, All On. To avoid current backflow between the batteries via the direct positive solar feed wires to each of the batteries, I intend to incorporate a blocking diode in each of these wires. The wire is 4 mm.

My thinking: a) the current would never be enough to cause any problems, even with a short circuit and b) the diodes would eliminate any current flowing from the battery , except for the short connection after the diode to the battery.

Schematic attached.

This is not a recommended method for wiring a controller to two batteries.

1- You will add unwanted voltage drop to each battery after the controller. This can drastically cut your charging performance..

2- When the diodes are allowing current to flow and you hit the starter button you will likely blow the diodes. With a blocking diode for the panel you can't suck current from where it is not available. With batteries in parallel you can. Even the large very heavy duty "diode splitters/isolators" blow the diodes quite regularly and this is one of many reasons why they are no longer used.

3- Many of these charger controllers need to see voltage in order to turn on. Inserting diodes between the controller and battery bank will not allow some of them to even fire up. This is why "battery isolators" very often can not be used with solar controllers, wind controllers or modern battery chargers...

If you want a charge controller that does two banks use the Morningstar Sun Saver Duo. Alternatively a combing relay such as the Sterling ProLatch R can be used with your existing controller.

 

[Albanach]

Many thanks, MS, from preventing me creating a minor disaster. Really appreciated.
Shall now take the controller back for a refund and be looking at the dual controllers for RV’s. They sell for A$40-60 (WMP). I think they’ll do.The Morningstar is not available locally and would cost me over $160, including shipping, from the US, blowing my “Special” $40 project out to over $200. So, then my (hopefully) last question: Do I need fuses?