DC Alternator & Battery Charging

 

DC Alternator & Battery Charging

 

Alternator:

An alternator is a generator that converts mechanical energy into electrical energy via electromagnetic induction. The core components of an alternator are a rotator and an armature. The two common types are: one where the armature is stationary and the rotator spins to create a flux in the armature resulting in an alternating voltage, the other one is the stationary rotor and the armature rotates in clockwise and anticlockwise directions to create a flux. The former is most commonly used in cars; the rotor's shaft is connected to the engine via a belt. Since the alternator produces alternating current and most of the electrical components like radio, automatic locks need DC current. The alternators have a regulator that converts and maintains the output at a constant DC level even when the alternator's revolution per minute (RPM) varies.

The batteries in a car are DC and need to be recharged that’s where the alternator jump in. The batteries initially provide a huge amount of current for ignition, which results in battery drainage. As the cars start to move the alternator RPM changes, we have a regulated DC output that charges the battery. The RPM of the alternator normally ranges between 2000 to 5000 but may go as high as 12000 for some models, whereas the current ratings are between 40amps to 120 amps.

How To Select An Alternator For The Car Battery?

There are a couple of factors that go into the right choice for the alternator. However, the first thing that you need to lookup is the specification manual of your car.

The alternator's RPM affects the output it produces so if you are on a motorway, your battery is likely to charge quickly compared to driving in a busy city. At maximum RPM rating, the output is most stable.

Battery manufacturers recommend the charging current for the battery needs to be 1/10^th of the rating. So, if we have a 100Ah battery, it needs to be ideally charged at 10 amps, however, due to some losses the actual value needed is a bit higher than the ideal.

Say we have an alternator that charges the battery at a regulated value of 12A/h, and the battery rating is 100Ah so the charging time it would take is:

Time = 100Ah / 8A / h = 8.3 hours

Practically we have losses when it comes to charging. A nominal figure accepted in the

the industry is 40% so,

100Ah * 40%  =  40Ah

We have a total of 100Ah + 40Ah rating to charge; hence the charging time changes to.

Time = 140Ah / 12A / h = 11.6 hours