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Get Powered Up! Certified Energy Manager Jeff Yago answers your alternative energy questions

Wondering about a great new energy-saving device
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Voltage regulator vs charge controller

Thursday, January 22nd, 2009

Hi Jeff,

I’m building a wind generator using an automotive alternator. The alternator has a voltage regulator in it. Do I still have to use a charge controller in my system? What, if anything, is the difference between a voltage regulator and a charge controller?



Automotive type voltage regulators are designed to regulate the battery charging current by varying the voltage to the coil winding of the alternator, with a limit of 14.5 volts. In other words, the voltage regulator in an alternator operates like a variable speed control with a constantly changing charging current based on battery voltage.

A solar/wind charge controller has three specific charging levels that change based on battery voltage and sometimes also based on time. To reduce charge time, the charge controller first goes into “bulk” charge mode which puts the maximum charging current into the battery bank. This usually lasts about 2 hours and can be programmed, unlike the alternator which has no programmable setpoints.

This really speeds up battery charging due to the high charging current. After about 2 hours, or when a programmed voltage setpoint is reached, the charge controller switches to “absorption” charging, which is a lower charging current which slowly tapers down as the battery nears the full charge setpoint which can be programmed based on the battery size and type.

Once this final setpoint voltage is reached, the charge controller switches to “float” mode which is a small constant charging current at a programmed level just to keep the battery at a full charge level and offsets any standby losses for a battery at rest. In addition, the temperature of any battery has a major impact on charging as the battery voltage which controls a chargers output is different at the different charge levels than a battery at standard temperature of 77 degrees.

Since an alternator has no temperature sensor, the alternator charging is base on the expected average temperatures a car or truck battery will be exposed to, and cannot maximize charging efficiency by adjusting the charging voltage based on battery temperature.

I think you will find the improved charging performance and shorter charging time makes a charge controller well worth the cost over any standard voltage regulator built into the back of an alternator.

Good Luck,

Jeff Yago



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