Alternators

Batteries provide power to start your car, run the engine, computer, radio, headlights, etc.  Anything that requires power is run off your battery.  Since batteries have a limited supply of energy they continually recharged by the alternator.  Alternators work by rotating a coil of wires (rotor) inside a magnetic field.  The amount of power produced is related to the rotor size, the strength of the magnetic field, and the speed at which rotor turns.

The engine turns the alternator (rotor) by a belt.  Years ago the alternator had a dedicated belt. Newer cars have a ‘master’ belt, referred to as a serpentine belt, which turns the alternator, a/c compressor, power steering pump etc.

The amount of power produced by the alternator is controlled by a voltage regulator which is located inside the alternator.  Since the voltage regulator cannot change how fast the rotor turns, it changes the strength of the magnetic field to vary the amount of power the alternator produces.  Based on the speed of the engine, and how much power is needed, the voltage regulator increases or decreases the strength of the magnetic field.

Starting your car requires a great deal of power from your battery.  Therefore, once your car starts the alternator goes to maximum to recharge your battery.  As the battery ‘charges-up’ the voltage regulator scales back the quantity of electricity produced, until the power into the battery equals the power out of the battery.

There are two reasons alternators need to be changed.  One, the alternator doesn’t produce enough electricity (measured in amps and in volts) to keep your battery fully charged.  Two, the alternator only produces maximum power.  If the alternator only produces maximum power, it will destroy the battery.  Also, a bad battery may cause the alternator go produce maximum power.  Since alternators are not designed to produce maximum power for a long period of time, a bad battery may destroy an alternator.

When I check a charging system I must check both the battery and the alternator.  If I have a bad battery I must replace it before I can be certain the alternator is good. 

I have seen cars towed here and the customer tells me, “They put in a new battery because they thought it was the reason the car would not start.  With a new battery the car started.  A few weeks later they had the same problem, the car would not start, so they replaced the alternator.  A few weeks later the car does not start.” At this point they bring the car to my repair shop.  The problem…. The alternator was bad and destroyed the battery.  When the customer replaced the battery it lasted until the alternator ‘fried’ the new battery (by continually producing maximum power).  The customer then replaced the alternator not knowing the alternator and the battery are bad.  The fried battery tells the new alternator that is needs “maximum” power, and the production of maximum power for a long time makes the alternator go bad. 

To prevent this from happening the battery and the alternator must be replaced at the same time.

One more item related to batteries

November 17, 2010

Batteries have two posts which are used to connect it to your car. One is positive, and one is negative.    The ends of the wires which connect to the battery are called “Battery terminals.”  Remember, these terminals are on the wires not the battery.  If the area where they meet is contaminated,  your car may not start.  I have had cars towed here which only needed to have the battery and the battery terminal cleaned to get them started.

When you battery is replaced, it is important clean the battery terminals and the battery.  Over time you might see a solid white mass around your battery posts.  This white substance is acid- be very careful.  This acid corrodes the wires and the battery terminals.  Sometimes you must replace the battery terminals because the acid has badly damaged the terminals, and sometimes you must remove a few inches of the battery wire because the acid “crawled up” the wire.  When a few inches of wire are removed you must also use a new terminal.

The battery terminals fit over a battery post or screw directly into the battery.  These connections must be tight.  If you can move the wire at the battery, you must tighten the connection or your car may not start. 

The negative wire goes to the engine.  The other wire goes to the alternator, and to the fuse box.  With over 26 years of experience, the ends at the battery are the only one which go bad. 

November 3, 2010 --- MORE about Batteries

November 4, 2010

More about batteries:

Batteries come in a variety of sizes and power.  Also, the positive terminal is sometimes on the left side, and sometimes it is on the right side.  When you choose a battery you need to have one that is correct for your vehicle.  If your battery is too big, it will not fit in the spot dedicated for a battery.  Forcing it into a tight space (and yes I have seen this) causes wires to be unusually pushed aside,  and because it’s too big the hold down strap cannot be used.  If the battery is too small, the hold down straps cannot hold the battery in place.  Therefore, when you get a battery you need to be sure you get the right sized battery. 

Batteries are measured in “Amps.”  A typical battery for a Honda is rated about 550 amps.  A battery for a large V-8 is rated about 750 amps.  Amps are a measure of ‘oomph.’  A bigger engine needs more oomph to get it to crank than a small engine.  When you buy a battery you need to get one with the right size and the right oomph. 

How long will my battery last?

Good question.  Generally, the less you pay for a battery the shorter its life span.  Batteries age, and as they age they have less power to start your car.  I use Interstate Batteries because they guarantee (pro rated) their batteries for at least 75 months.  Additionally, if one of their batteries needs replacing within the first 24 months, they are replaced for FREE!  I could buy less expensive batteries, but I don’t want my customers to become stranded.  I have seen batteries that are only guaranteed for 24 months.  That’s not very long.

Most batteries are easily replaced, but as manufacturers shrink cars, they have come up with some unusually places for their batteries.  I have seen batteries in the trunk, under the rear seat and some are inside the wheel well.

Pre Winter Inspection

All summer and fall you get in your car, turn the key and it starts, gets you to your destination without any problems.  So why have it inspected?  Good question.  A good pre-winter inspection looks at over 7 areas that can cause cold weather, winter related problems.  The first I’m going to write about is your battery.

 For your car to start you need a battery with sufficient power to ‘crank’ your engine.  Just because your headlights, radio, wiper blades work does not mean you have a good battery.  These components take very little power to work (less than 10 amps).  Your battery needs to give your starter 250 amps or more for it to crank. Therefore, just because your headlights work, and your radio work does NOT mean you have a good battery.

Auto batteries use lead and acid.  Thru some magic of chemistry the lead and acid produce electricity to start your car and keep it running.  Once it is running the alternator recharges your battery.  The production of electricity is dependent on the outside temperature.  At approximately 70 degrees the battery has 100% of its available power.  At 32 degrees the battery only has 25% of its full power.

To make matters worse, the colder an engine gets, the harder it is to crank.  At 32 degrees, your engine is four times harder to start than a warm engine. 

As you can tell, all summer and fall a weak battery can crank your engine, and lead you to believe you have a good battery.  Once the temperature drops, this bad battery can no longer crank your engine.  If you notice that you car seems harder to crank, you may need a battery.

Batteries are easy to test.  We connect our battery tester to your battery and drain your battery at a rate of 250 amps.  After 15 seconds a good battery will indicate over 10 volts.  A weak battery will indicate over 9.6 volts.  Any reading under 9.6 volts is a bad battey and it must be replaced. 

Next week I'll discuss your alternator and how it is related to your battery.

Safe motoring

Eliot Silverman  B.S. Mechanical Engineering University of Michigan 1979

Owner of Eliot's Complete Auto Repair Shop

3658 N. Lincoln Ave.

Chicago, IL. 60613

Why get a Pre-Winter Safety Inspection

All summer and fall you get in your car, turn the key and it starts, gets you to your destination without any problems.  So why have it inspected?  Good question.  A good pre-winter inspection looks at over 7 areas that can cause cold weather, winter related problems.  The first I’m going to write about is your battery.

 For your car to start you need a battery with sufficient power to ‘crank’ your engine.  Just because your headlights, radio, wiper blades work does not mean you have a good battery.  These components take very little power to work (less than 10 amps).  Your battery needs to give your starter 250 amps or more for it to crank. Therefore, just because your headlights work, and your radio work does NOT mean you have a good battery.

Auto batteries use lead and acid.  Thru some magic of chemistry the lead and acid produce electricity to start your car and keep it running.  Once it is running the alternator recharges your battery.  The production of electricity is dependent on the outside temperature.  At approximately 70 degrees the battery has 100% of its available power.  At 32 degrees the battery only has 25% of its full power.

To make matters worse, the colder an engine gets, the harder it is to crank.  At 32 degrees, your engine is four times harder to start than a warm engine. 

As you can tell, all summer and fall a weak battery can crank your engine, and lead you to believe you have a good battery.  Once the temperature drops, this bad battery can no longer crank your engine.  If you notice that you car seems harder to crank, you may need a battery.

Batteries are easy to test.  We connect our battery tester to your battery and drain your battery at a rate of 250 amps.  After 15 seconds a good battery will indicate over 10 volts.  A weak battery will indicate over 9.6 volts.  Any reading under 9.6 volts is a bad battey and it must be replaced. 

Next week I'll discuss your alternator and how it is related to your battery.

Safe motoring

Eliot Silverman  B.S. Mechanical Engineering University of Michigan 1979

Owner of Eliot's Complete Auto Repair Shop

3658 N. Lincoln Ave.

Chicago, IL. 60613