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Battery Charge Controller


What Does It Do and How Does It Work

     Battery chargers vary a great deal in intelligence, the types of batteries they can charge, how they maintain batteries, and how long they take to charge. I'd recommend charging batteries at about 10% of their amp hour capacity. For example, an 80Ah deep cycle battery should be changed at a rate of about 8A.

     Different types of batteries require different charging regimes. SLA (sealed lead acid),  AGM (absorbent glass mat) and gel batteries are traditionally charged at a lower voltage than flooded lead acid batteries. This varies depending on the manufacturer. You should always check what charging voltage is required before you buy deep cycle batteries and a battery charger.


      A simple charger works by providing a constant DC power to the battery. A simple charger won't alter its output based on time or the charge on the battery. These type of battery chargers are usually cheap, but there's a trade-off in quality. Typically, a simple charger takes a lot longer to charge a battery, and a battery left in a simple charger for too long will be ruined by over-charging.

     If left in place too long, it will eventually boil the electrolyte out of the cells or damage the plates. Free hydrogen may accumulate and become an explosive hazard when sparked. 

     Timer based chargers operate much like a simple charger, but (as the name would suggest) they operate on a timer. The timing regime would be configured for a particular battery and then left. However, if batteries of lower capacity were charged they would be then overcharged, in addition if batteries of higher capacity were charged they would be only partly charged. Timer based chargers also have the drawback that charging batteries that were not fully discharged, even if those batteries were of the correct capacity for the particular timed charger, would result in over-charging.

Battery charger output

     Battery charger output current depends upon the battery's state. An intelligent charger may monitor the battery's voltage, temperature and/or time under charge to determine the optimum charge current at that instant. Charging is terminated when a combination of the voltage, temperature and/or time indicates that the battery is fully charged. In a sense, the batteries tell the charger when they are full.

     Some chargers use Pulse technology or pulse width modulation in which a pulse is fed to the battery. This DC pulse has a strictly regulated rise time, shape, pulse width, frequency and amplitude. This technology  works with any size, voltage, capacity or chemistry of batteries, including automotive and valve-regulated batteries.

Choosing the Right Battery Charger for Your System

     Here we go back to system design. What is our current input capacity to the charger from your solar panels, windmill, auxiliary gasoline generator, and/or the electric power grid? What is the  size and voltage of the battery bank? Will there be room and inputs for expansion of the current system? When the batteries are charged, will the output from the solar panels and/or windmill be automatically redirected to the inverter?

     Your battery charger has to match up with both your solar and wind generated energy outputs. The output of the
auxiliary gasoline generator may have to be adjusted to match up with the voltage of the battery charger input. When the batteries are fully charged the solar and wind energy should be redirected by the charger to the inverter for your use or for net metering.

     You may decide to charge your battery bank at night
using utility grid power when your max power load is small compared to daytime. This can insure your batteries are always topped off should you experience an unanticipated utility grid power failure, extended cloudy days, or calm winds. You can run your inverter during the hours of your peak daytime activity to reduce your peak daytime utility grid use.



Cost and Reliability



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Karl Kinkel - President
Karl Kinkel, President & Founder
Longsgap Services LLC
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Independence, VA  24348
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