# Battery Charging Sensors?



## John J (Dec 29, 2007)

How does a battery charger know the battery is charged?

How does a alternator know when to stop charging? 

Does it monitor the current of the charging circuit and then reduce the voltage?

Or is just a time issue? 

I use to know this stuff.


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## Curmudgeon (Jan 11, 2008)

Are we talking trains, models thereof, or automobiles, full sized versions thereof?


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## Greg Elmassian (Jan 3, 2008)

You are asking about a car battery and an alternator in a car? 

And a battery charger for a car battery? 

Buy a good battery charger from the car parts place, it will have a microprocessor and do it right, and what does it matter what the algorithm is, you are not going to reprogram it. It will sense terminal voltage under load to end the charge, but there's more complex stuff going on in the better chargers. 

In a car, the alternator charge rate is driven by a voltage regulator, and it runs on terminal voltage, will run up to 16 volts, newer cars have better smarts, but most just use a simple circuit that stops around 13.8 to 14.1 volts once the amps go down. 

Greg


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