Advanced Alternator/Battery Question

Hello guys. My first post. I am hoping that right off the bat somebody or even better, multiple somebody's with the knowledge and expertise can help out.
My buddies and I have an argument going about alternators and batteries. The basic question I have been required to ask is..." If you have a car with an alternator and no battery and, another car with both and alternator and a battery and, you also have a totally controlled "so-called perfect world" where no other possible mechanical or technical problem can arise except in the alternator. If both were started and then set free driving as usual with normal wear and tear in this perfect world to see what alternator failed first, which one will fail first?
Will the car with just an alternator last longer or will the car with both alternator and battery last longer in our perfect world?

Can you please explain your answers as well.
Also if any answers have to due with the resistance of the battery in the field can you explain that as well.

Also... Does a alternator vary its output of power due to the battery being some sort of resistance in the field?

Also ... If the battery is removed from the vehicle when running will it cause the alternator to surge and create full power, and will this wear your alternator and potentially damage electrical components?

Also...Do alternators work differently in modern times as they did 25-30 years ago?( I don't mean single vs triple coil either) I mean the basic all around function?

Also... Can an alternator work at different levels of internal stress that will LEAD TO PREMATURE FAILURE? Will an alternator that produces more power wear quicker that one that produces less?

Thanks alot to all that help/ you are settling a HUGE argument!!!!

One key element to this argument is the type of car (electrical load) since the load on the alternator is critical in determining how long the alternator will last. In a modern application the load on an alternator without a battery may cause the car to stall within several minutes, and you'll never get the car started without a battery. So in that case the alternator in the car with no battery will outlast the other because of the simple fact it will receive no wear since the engine won't run. Additionally, modern cars require the battery to filter off the noise from the alternator, so a modern car with no battery will allow enough noise to pass to the electronics other damage will likely occur that will prevent the car from running. I know you said to ignore these factors, but I want to point them out so neither of you get the idea you should perform a real world test on Mom's new Lincoln.

Even a car from the 60's with an alternator will not run forever on just the alternator. The alternator is not intended to supply enough voltage and current to meet the electrical demands from the ignition system and certainly the lights and radio. You need some method of storing the charge from the alternator. Having only an alternator in the car would likely overheat the alternator, both mechanically and electrically so I would put my money on the alternator lasting longer in the car with the battery. As the load on the alternator increases, the alternator places a larger mechanical load on the belt. Back before the days of self-tensioning accessory drive belts, if you didn't have a v-belt tight enough you might get a squeal when turning on the headlights. That was because as the electrical load increased due to the lights, so did the load the alternator placed on its mechanical input. That mechanical load will also place somewhat larger load on the bearings in the alternator, leading to increased wear and mechanical failure rate. The increased load due to not having a storage device (battery) will also cause increased heat, and heat is an enemy to electronics such as the stator, field coil, rectifier diodes, and voltage regulator.

-Rod

One key element to this argument is the type of car (electrical load) since the load on the alternator is critical in determining how long the alternator will last. In a modern application the load on an alternator without a battery may cause the car to stall within several minutes, and you'll never get the car started without a battery. So in that case the alternator in the car with no battery will outlast the other because of the simple fact it will receive no wear since the engine won't run. Additionally, modern cars require the battery to filter off the noise from the alternator, so a modern car with no battery will allow enough noise to pass to the electronics other damage will likely occur that will prevent the car from running. I know you said to ignore these factors, but I want to point them out so neither of you get the idea you should perform a real world test on Mom's new Lincoln.

Even a car from the 60's with an alternator will not run forever on just the alternator. The alternator is not intended to supply enough voltage and current to meet the electrical demands from the ignition system and certainly the lights and radio. You need some method of storing the charge from the alternator. Having only an alternator in the car would likely overheat the alternator, both mechanically and electrically so I would put my money on the alternator lasting longer in the car with the battery. As the load on the alternator increases, the alternator places a larger mechanical load on the belt. Back before the days of self-tensioning accessory drive belts, if you didn't have a v-belt tight enough you might get a squeal when turning on the headlights. That was because as the electrical load increased due to the lights, so did the load the alternator placed on its mechanical input. That mechanical load will also place somewhat larger load on the bearings in the alternator, leading to increased wear and mechanical failure rate. The increased load due to not having a storage device (battery) will also cause increased heat, and heat is an enemy to electronics such as the stator, field coil, rectifier diodes, and voltage regulator.

-Rod

Excellent response.!!

Maybe I'm reading it wrong, but in a car with alternator/battery, if the alternator can't provide all the power needed to run the vehicle's systems then eventually the battery would become depleted because the extra power needed is supplied by the stored battery power. The alternator must be able to provide all the power needed plus enough excess to keep the battery fully charged.

If the alternator died, the car would continue to run for a short time on battery power alone until voltage would be too low to run the lights, fire the plugs and the engine would quit.

If the battery died, the car would have to either be jump started or started by popping the clutch (manual transmission). Once started, the engine should run because the alternator can supply the power, but as stated, the battery would not be there to help filter any noise or power fluctuations as the engine speed changes. This is evidenced in most race cars that have no battery or starter. They are started externally and run solely off alternator power.

But the output from the alternator is not constant, it has the capability to provide more current as the rotations increase. The excess power is stored in the battery for the times when the alternator can not keep up, such as sitting at a stoplight for 3 minutes in the rain storm when the headlights, wipers, and brake lights are on. In this type of situation, the car would not run long with only an alternator. However, the prior 15 minute drive down the highway charged up the battery so that the battery is able to subsidize the alternator at the stop light.

-Rod

I'll agree there. Though I touched on it with my "power fluctuations due to engine speed" line, I didn't expand on it. An alternator's power output is dependent on engine speed to a point (worst at idle), then as RPMs increase the regulator kicks in to limit the voltage applied to the battery...to keep it from overcharging, overheating, and failing.

But even in a complete battery failure scenario, the alternator is (or should be) sized and the correct pulley diameter used to supply just enough power at idle to maintain operation...though you may have to turn off the kid's DVD and other ancilliary equipment.

The alternator on the car without battery will fail first for your comparison. The battery will act as a buffer knocking out the peaks and valleys. The average will probably be the same for both set-ups.

The output varies according to voltage. Resistance plays a small part in the voltage , but is insignificant.

Removing battery can cause surges and can cause damage.

I'm not sure about all alts , but I think they work same as they did when they first came out on cars/trucks.

If the two alternators are identical or nearly identical then the one that works the hardest will wear out quicker.

I disagree with Rod on this one. My alternator is rated to provide 70A RMS at idle and a peak of 150A before it fails. Therefor, it has more than enough power to run my car with music and ac blasting. Alternators have regulators on them, so the battery is not really needed to filter the power of the alternator. As a matter of fact, you can run a car without a battery and you can run a car without an alternator. I ran my car with no battery and just boosted the car externally. It got me all the way to the store no problem (4 Km) :).


In an ideal world, alternators shouldn't fail because if they can provide more current than is consumed, then no heat should build up and thus no failure. However, dirt buildup on the brushes or mechanical problems cause the alternator not to generate enough current. More current draw and less current generation causes heat build up. Heat causes failure.

When the car is running, the battery acts as a load on the alternator since the alternator voltage is 14.4 and the battery voltage is 12.8. The current required for charging a battery is another load that can push the alternator over the edge.

We can't really know for sure unless you test it out.

What year is your car? As mentioned above, cars with few electronics will fare better with no battery than cars with lots o' electronics. The regulator regulates the voltage but does nothing to filter noise. The battery is still needed to filter noise.

The RMS and peak ratings of your alternator are at some speed higher than idle. If you're sitting with no battery at idle with your headlights on, brake lights on, blower motor blasting, etc. your alternator will struggle to keep up.

If the battery is acting as so much of a load to "push the alternator over the edge" that's because either the battery is bad or because the electrical load is so high that the alternator cannot support it, exactly the reason you need the battery other than just to start the car.

If a car is newer than about 1980 I would not suggest you "test it out."

-Rod

That's why cars increase idle to maintain proper power from the alternator (just like they do for the AC). BTW, As long as the voltage of the alternator is higher than the battery, it's unlikely that the battery will ever act as a supplier. If your alternator is ever dipping below 14.4 volts, then it's under rated for the car or is dying. I really don't think it's necessary to have a battery because you can drive around with a dead battery just fine (increased load on the alternator). People do it all the time. The problem is people who drive around with dead batteries all the time need a boosting mechanism and wear out their alternator because now you need lots of current to charge the battery AND RUN THE CAR.

The idle speed increases when the A/C is turned on to keep the load from stalling the engine, not so much to increase the current output of the alternator. The IAC will also increase the idle when the hydraulic power steering is turned to lock to support the increased load. Yes, the PCM will increase the idle speed under large electrical loads as well, but the battery is still needed to 1) filter noise from the otherwise un-filtered rectified alternating current provided by the alternator and 2) to support large transient loads that the alternator cannot, such as starting the car, turning on a high-current electrical accessory. The alternator and engine idle cannot adjust to a transient load as quickly as a battery can.

If you've ever been involved in higher end car audio you might have noticed even moderate audio installs will incorporate 1 Farad or larger "stiffening" capacitors on the power lines. This is to support the large transient loads from the car audio (particularly during bass hits) because the alternator does not stand a chance of supporting such transient loads and even the internal resistance of the car battery cannot dump current quickly enough. For lower powered applications, the battery does just fine supporting the extra audio load. Take the battery out though and you'll quickly find the alternator cannot support these transients. If these capacitors are not used, the bass will be distorted and the alternator will not survive for long. This is somewhat of an extreme case, but helps identify that an alternator does not due well under transient loads. The drop in voltage from the alternator during transients will be hard on the alternator (including the regulator) and also on the multiple electronics in a modern vehicle.

I don't have anything old enough to demonstrate this for you with oscilloscope plots of the noise, but if you have a vehicle that you don't care about, you can hang a scope off the power cables, disconnect the battery, and watch the noise and transient voltage spikes as your car idles, then as you switch electrical devices on and off.

-Rod

I agree with you on that. But as you said, those are extreme cases. And can you honestly say that the noise is going to kill the alternator quicker than having a battery that's receiving trickle charge throughout the alternator's entire life? I think it's a tough call. One day I'll get a car just to test that out because it's an interesting question.

The problem with today's cars is that alternators are designed to meet the bare minimum that the car requires (cost effective). My police Impala had a nice oversized alternator. That alternator was never replaced (380000KM). It lived through 2 batteries that died from too many ignition cycles. I'm sure that alternator would have given more than enough power at idle for most purposes (not extreme sound applications). Now that I look back at it, I should have salvaged that alternator before scrapping the car...DAMN!!!

The idle speed increases when the A/C is turned on to keep the load from stalling the engine, not so much to increase the current output of the alternator. The IAC will also increase the idle when the hydraulic power steering is turned to lock to support the increased load. Yes, the PCM will increase the idle speed under large electrical loads as well, but the battery is still needed to 1) filter noise from the otherwise un-filtered rectified alternating current provided by the alternator and 2) to support large transient loads that the alternator cannot, such as starting the car, turning on a high-current electrical accessory. The alternator and engine idle cannot adjust to a transient load as quickly as a battery can.

If you've ever been involved in higher end car audio you might have noticed even moderate audio installs will incorporate 1 Farad or larger "stiffening" capacitors on the power lines. This is to support the large transient loads from the car audio (particularly during bass hits) because the alternator does not stand a chance of supporting such transient loads and even the internal resistance of the car battery cannot dump current quickly enough. For lower powered applications, the battery does just fine supporting the extra audio load. Take the battery out though and you'll quickly find the alternator cannot support these transients. If these capacitors are not used, the bass will be distorted and the alternator will not survive for long. This is somewhat of an extreme case, but helps identify that an alternator does not due well under transient loads. The drop in voltage from the alternator during transients will be hard on the alternator (including the regulator) and also on the multiple electronics in a modern vehicle.

I don't have anything old enough to demonstrate this for you with oscilloscope plots of the noise, but if you have a vehicle that you don't care about, you can hang a scope off the power cables, disconnect the battery, and watch the noise and transient voltage spikes as your car idles, then as you switch electrical devices on and off.

-Rod

It's not the noise that kills the alternator, the alternator generates the noise. What I feel would stress the alternator as a system (diodes, regulator, brushes, stator, field coil) is the transients due to switching loads versus the more constant, smoothed load when the battery is also in the system.

Ultimately, even if it were possible to start a car without a battery, I would not recommend running a car on the alternator alone. If you or others want to do so, that's up to you/them. I do not recommend it though.

-Rod

You can start a car without a battery...it's called popping the clutch, for manual transmission cars only. Done it many a time.

The battery weighs less and costs less to maintain though than the "heavy" that would need to ride along with you in the event you don't have a hill to roll down or another vehicle to tow you far enough to get the car started. ;)

-Rod

I'll agree with you partly there. A second person pushing to get it going is usually needed, but get it rolling abt 3-5 mph, drop it into second, pop the clutch and I was usually on my way to head to the nearest store for a battery.

Did the same with a motorcycle, though I didn't need a push for that.