Experts on Solar Panel/Controller Question

[sailingabe41ds]

Hi,

Thinking about solar. Few simple questions. If you have an identical twin system with two sets solar panels and 2 controllers why would one controller not shut off when it senses the other controller is providing 14+ volts to charge the batteries ? The same question is why would both controller not shut off if you are charging from shore power or the engine running using the alternator? Finally, do you have an on off switch or do you always allow the solar panels to charge and let the controller take car of business regardless of if your alternator or shore power is charging the batteries?

Thanks in advance ...I may be over thinking this stuff.

Abe

[noelex 77]

Originally Posted by sailingabe41ds

Hi,

Thinking about solar. Few simple questions. If you have an identical twin system with two sets solar panels and 2 controllers why would one controller not shut off when it senses the other controller is providing 14+ volts to charge the batteries ?

A better question is why would it shut off?

If the controller is in the absorption or bulk phase it will be trying to maintain the programmed bulk/absorption voltage, which is usually 14.4v or higher. Thus if the batteries are at 14.0v because of input from another charge source, the solar controller will still be producing its maximum output to try and raise the battery voltage to the programmed bulk/absorption voltage.

If the battery voltage has been kept at the bulk/absorption voltage for the absorption time (usually around 1-3 hours), the solar controller will correctly (if the absorption time is correct) deem the batteries full and drop to the programmed float voltage, usually around 13.8v. Thus if another charge source is introduced and is maintaining 14.0v, the solar controller will supply no power because it deems the battery is full and the correct voltage at this stage is the float voltage of 13.8v. If the parameters on the solar controller are correct, the new charge source is overcharging the battery and the voltage of this charge source should be adjusted to match the solar controller.

If two charge sources are set identically trying to maintain the same voltage, often one will end up supplying most or all of the power if it has sufficient capacity to do so. In practice the set points will never be absolutely identical, due to minor measuring errors. As far as the battery is concerned this is of no consequence. The battery does not mind if the power is supplied by the solar controller or the battery charger, providing it is supplied with correct voltage. If you want one charge source to dominate (perhaps because shore power is metered and expensive) then adjust the voltage set points of the preferred source slightly higher.

Concern about multiple charge sources is generally unnecessary. There can be occasional minor conflicts, but these are usually of little consequence. The most common problem is slight overcharging (although surprisingly most people are concerned about the risk of undercharging, which rarely happens).

In some cases a minor adjustment to the charge settings (usually a reduction in the absorption time or a disabling of the tail current feature) is helpful to optimise the charge algorithm when multiple charge sources are regularly contributing, but making sure the fundamental basic settings are correct is more important than these minor alterations.

[sailingabe41ds]

Thank you
Abe