Alternator Overload?

We sell batteries for your vehicle. If you choose to downsize your battery then the unintended clause kicks in and you only get a 6mth replacement - period. Most say then they just want to get it running and sell. Others are cheaping it. One guy asked if this would cause harder wear on the alternator (450coldcrankingamps when 600cca min is recommended). Thought this must logically be true - running more/harder/longer. What is the real scoop? thanks in advance

Reply to
neon
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Why? There's no evidence that a smaller cca battery than speced is going to wear out any faster just because greater starting demands are made on it.

Here's the real poop.

There's 3 major things that make car batteries die NATURAL death:

1) Vibration over time (years, that is) You can't do anything about this.

2) Extreme temp changes. You can't do anything about this either, save maybe move.

3) Age. Once again, you can't do anything about this either.

Now, there are 3 major things that make car batteries die before their time:

4) Overcharging due to a failure in the charging system, usually voltage regulator, or sometimes bad connections in the vehicle electrical system.

5) Chronic undercharging due to a failure in the charging system, usually alternator diodes or sometimes bad connections, voltage regulator, etc.

6) leaving headlights/electrical system on and draining the battery to 0 volts then leaving it sit fully discharged for long periods of time.

Now let me explain CCA ratings from a layman's POV

All batteries wear out due to items #1,2,3. Every month the battery capacity drops a small percentage. Thus, if a battery starts out life as, say, a 600CCA battery, after say 5 years it's capacity will have naturally dropped to, say 300CCA. Extreme vibration and temp changes will of course hasten this process. As the battery nears end of life, the battery capacity decreases in an expotential fashion until one day it won't start the car.

Larger CCA batteries have more and better and better designed plate material to allow higher short term current draw. Thus they have higher capacity, which means their age discharge cycle is going to last a lot longer than a smaller CCA battery. That is why they ususally have a lot longer warranties.

Now, as for using a smaller battery than the car spec calls for:

The auto designer when specing a battery basically designs the engine and after it's bolted together they put an ammeter on the battery and start the car, and observe the CCA demanded by the starter. Let's say it's 200amps for a smaller 4 banger. So they will spec a 300 CCA battery at minimum because at -20 degrees farenheight the 300CCA battery is only going to be putting out 200 amps. Then when the car is manufactured the automaker will install a 600CCA battery simply because they don't want the battery to fail during warranty so they don't have to replace it.

Also, as starters age, they can demand more power to generate the same amount of torque, if windings in the motor happen to short together.

So you can see here that the CCA spec is really all over the map. Everyone, from the automakers to the service people, to the owners to the auto parts people, all of them benefit from selling a far higher CCA battery to the customer than the engine really calls for. Thus the CCA specs are usually grossly inflated. You can see this for yourself by putting an ammeter on a few of the vehicles that come in the shop and starting the car and measuring how many amps are required.

Now, as for running the alternator harder:

The starter in a specific vehicle/engine is going to require a set amount of power. For example, lets' say in one car it demands 100 amps for 30 seconds.

Either the batter is going to supply the 100 amps or not. As long as the CCA rating is above this amount, the battery is going to start the car.

Once the car is started, the battery has been discharged a certain amount of power that the alternator must replace.

This power amount IS THE SAME regardless of the CCA of the battery. Fresh batteries that have been discharged after a starting cycle generally can happily accept as much power as the alternator can provide, up to 50-100 amps if available. Of course the alternator cannot provide that amount, it can only provide say, 10-15 amps charging current. So, for say a

20 second starting cycle at 100 amps, the alternator is going to have to provide, say, 10 amps at 3 minutes to completely replace all the lost power. And regardless of the CCA rating of the battery, that's all the alternator is GONNA provide.

So in summary, the load on the alternator isn't any worse for a smaller CCA battery in a given engine application.

Ted

Reply to
Ted Mittelstaedt

Stop and think....ALL the electrical power to run the car comes from the alternator anyway. The battery only supplies power when the engine isn't running or isn't running quite fast enough to carry the whole load. A smaller battery just means you can't run as long with the engine off, it doesn't make the alternator work any harder at all.

Reply to
Steve

Reply to
neon

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