The series cycling charge controller is the easiest controller that averts the overcharging of the batteries by turning the solar panel’s current on and off based on the battery voltage. As the battery voltage rises to a preset point indicating that the full charge is nearly attained a mechanical relay or solid-state switch suddenly shuts off the charge. Simple! But if the battery voltage begins to fall…..if it gets low enough it will make the controller go back on. Battery voltage rises again and the cycle continues. On and off…… This results in battery voltage averaging somewhere between the high and low set points and that prevents your batteries from overcharging.

The constant voltage charge controller is most often what is considered 3-stage. What is 3-stage? A more precise control which gives you the  most charging that is possible for that day.

Bulk charge is the first stage. This is when the power is switched straight through from the solar modules until the batteries reach the preset maximum.

Absorption charge is the second stage. This is when the maximum battery voltage is held by reducing the charge current…….. enough to never exceed the target voltage. Reduced current is high speed on and off pulsing……when controlling on time versus the off time of each pulse determines the average charge current.

Float charge is the third stage. And this is when the battery voltage is reduced after the charge is completed. Avoids excessive evaporating of battery water and will extend your battery’s life. If you are using sealed maintenance-free, AGM or gel type batteries – then the three stage with float would be the safest method of charge controlling for you.

A Diversion charge controller does not mean that it is cut off from the charging source at all. What it means is that the battery charges to the maximum set voltage. Then the diversion control senses that voltage  which in turn causes it to absorb the excess current. That in turn will exactly off-set the excess charge. That will keep the battery voltage so it never goes over the preset maximum. This will be a small amount of heat in ceramic air heating resistors or water heating elements. Your control will adjusts its consumption rate to offset the excess charging exactly. Keeps the battery voltage at…. never exceeding the preset maximum voltage. When someone is  using a wind turbine or hydroelectric which does not have it’s own charge controller then they must use a diversion controller. Those particular  types of generators will be damaged by their charge not being absorbed into the batteries at all times. One diversion controller should handle the combination of solar, hydro and wind easily. Provided the total amps charged from all three together is within it’s amp capacity.

Our  charge controller is the Xantrex C-60 60 Amps, 12 volt and I think it sold for about $245. at Backwoods Solar in 2004. We have been very happy with it and have never had any kind of problem at all. Backwoods Solar will work with you, especially if you live off the grid! They have a great little catalog that is packed full of information. It is like a little encyclopedia for anyone that is trying to set up a system and they really go the extra mile if you know what I mean. Even if you live on the grid.

Copyright © 2009 Kathleen G. Lupole

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