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

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Archive for the ‘Voltage regulator’ Category


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


Adding a secondary generator

Wednesday, November 26th, 2008


My question is about this article: Add solar power to your truck camper

The article is great for getting started with solar/battery systems. I never knew it was so simple.

My question is, how would one add a secondary generator for days when the batteries are dead at night? Basically, I want something that will combine the power of the solar, with the power supplied by the alternator in my car. That way each power source can charge the batteries.


Anthony Hildoer

Any boating supply store will have “dual” battery chargers, “dual” charge controllers, and “dual” voltage regulators. There are other solar suppliers you can check out, but for small 12 volt systems you can usually find these items at a local boating supply store. Almost all recreational boats have two identical batteries and a switch to allow changing from one to the other. This makes sure if you run down one battery while listening to radios or running lights while anchored out in the water, you will still have a fully charged battery to start the engine. The dual battery voltage regulators will charge the first battery then the second battery without connecting them to each other. That was the equipment used in the article.

On the other hand, if you wanted to also charge this battery from a separate energy source like a solar panel or small gas generator, just be sure to use the proper charge controller for each source which will allow charge to flow into the battery even if it is also being charged by other chargers at the same time. The charging current from the other charging sources will not “back up” into each other. As long as each charging source has its own charge controller, nothing will cause a problem with the other devices. However, if one of the charging sources has a much larger charge capacity or is set for a higher charging voltage than the others, it will take over all of the charging as the other charge controllers will “see” this higher voltage and assume the battery is fully charged and then stop their charging.

Good luck,

Jeff Yago



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