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Do you really need a high output alternator? Is there a big difference between alternators of the same output ratings? Are there versions that eat up more horsepower than others? In most cases, the answer to all of these questions is, "yes!"

Have you ever sat in traffic, idling, headlights on, cooling fans on and discover the amp gauge discharging or the signal lights very sluggish? That's because your alternator has not been keeping up while the excessive current demand has been draining your battery the past few hours. This is easily possible even if you already have a 100 amp alternator, however, one that may not be very efficient at lower rpm. You then shut your engine, and it doesn't want to start. If this is you, then you definitely need a larger, and more importantly, a more efficient alternator. A Reactor Alternator!

LOW RPM CHARGING: For the most part it's more a matter of  needing more output at lower engine RPM's, not necessarily more total output by itself. To accomplish this goal you need to pursue one of two options. The first option is to reduce the pulley size on the alternator to spin it faster at the same engine speed. While this may increase low RPM charge output, it also carries many negatives associated with that, which includes increased parasitic drag, decreased belt life and thrown belts at higher revs. Keep in mind, typically underdrive crank pulleys are used on high performance engines to slow down accessories, including the alternator's pulley speeds even more... making a bad situation even worse.

EFFICIENCY RATING: The other option is to upgrade to a  a more efficient alternator, not just a higher output one. The Reactor alternator will dramatically improves charge output at lower RPM's without the increased parasitic drag at higher revs that other brands see. That's the ticket to solve your problems! It just may so happen that the overall output ends up being a higher capacity, but that's not the goal, however, modern cars with high output electronic ignitions, electric fans, stereos, high out put head and tail lamp options, etc. can really use and benefit from the extra capacity on frequent occasions.

Considering this... you're sitting in traffic all day, really hot out, fans running full speed. Idling with most alternators can drain your battery before you know it!

SCOTTY, I NEED MORE POWER: Your full vehicular current load demand can exceed 40-50 amps EASILY even if the lights are not on, but at idle. Even some *Inefficient* 80 or even 100 amp alternators may only be putting out 20 or so at idle. That equates into a -30 amp draw right there, or the equivalent of 8 head lamps on without the car running. If you are in a parade, slow moving traffic, etc, it can eventually create problems like hard starting, etc. Many times people blame the starter because "it's hot" rather than realize they had the fans running and the alternator was not keeping up with them for the past hour. Now they shut their engine off and it won't start because the hot starter needs even more current to work.

Alternator Comparison

THE POWER GRID: If you look at the chart to the right, you can see just how wide spread low rpm alternator outputs can vary even though the total outputs can be very similar. It's how you achieve that output, that's most important.

THE DELUSION: You may also see 40 and 60 amp stock alternators put out MORE current at lower rpms than the same version that has been altered, "modified", or "amped up" (as some call them) to 100 amps in the same case and configuration. When you "hop up" a stock alternator, you have to sacrifice charge quality in the low end, just like a bigger cam sacrifices low end power in favor of upper end performance. If you need efficient low rpm charging qualities, it requires a whole new ball game to get there as far as alternator design and internal componentry.

WORST CASE SCENARIO: As a side note, consider the "worst case scenario" that is all to common being something like the following....

*   Sitting in extended stop and go traffic during rush hour on a city street.     
*   Idling at under 1,500 rpms for extended periods
*   Fans running during hot weather or Heater running during cold weather (25-40 amps)
*   Headlamps and tail lamps on using especially when higher wattage bulbs (12-20 amps)
*   Brake lights on, especially high output halogen styles  (8-18 amps)
*   Electronic Ignition system (5-10 amps)
*   Interior gauge and instrument lights (3-5 amps)

     Total amperage = 53 to 93 amps!!!!!! As you can se, it adds up QUICKLY!
     Now add a radio, CB, GPS, Stereo, etc, etc, etc... The power demand keeps going up and up and up.

DUTY CYCLE: Also, keep in mind a 60 amp alternator is not intended or designed to be running at 60 all the time... Nor is a 100 amp version intended to run at 100 continually. Alternators are designed for the most part to normally run at only 1/2 of it's rated capacity at best, if you want your alternator to live a long life. That's why it's common to hear of 40 and 60 amp'ers fail prematurely, as a direct result of each individual person's particular driving style, needs, traffic conditions, weather, temperature, etc... not to mention additional as well as revving alternators over their intended speeds that were not built for that.

CONSUMPTION: High Output alternators do not necessarily rob you of any more engine power needing to turn them. In fact, if you have two alternators, one a 40 amp and the other a 100 amp, they both require about the same power to turn them at the same output within their capacities. Only when an alternator is putting out higher amps on demand, is it needing more to turn it. In other words, you get out what you put in it. The only real difference is the efficiently in the rotating bearing, bushing and brush assemblies making the difference... and there is a big difference between cheaper alternators and well made-purpose designed units in that respect.

THE TRUTH: Alternators also do not use a lot of engine horsepower even when they are working their hardest... at about 1/10th the amount to turn a mechanical cooling fan. As you can see to the chart on the right, there is only about less than a single horsepower difference between a 40 amp and a 100 amp alternator to run at full output. And when they are not under full demand, they use about the same regardless.

Formula for calculating alternator power requirements...

((AMPS LOAD x VOLT CHARGE) / 745.7) +15%

The amperage multiplied by the voltage equals watts, and 745.7 represents the wattage equal to one horsepower.

UNDER DRIVE PULLEYS: It's not uncommon to see under drive pulleys being used in hopes to gain some precious horsepower, however, there is no need to under drive the alternator. Typically an under drive crankshaft pulley is used to under drive, or slow down the belt driven accessories on an engine, such as water pump, power steering, air conditioner, air pump, etc. This is done by using a smaller than stock pulley on the crankshaft, thereby slowing the accessories but up to 40%. This modification is intended for serious off highway performance, however, by slowing the water pump you will have diminished cooling at slow engine speeds, less power steering performance and diminished charging out put at idle and even freeway speeds while using your transmission's overdrive. This is the significant during sacrifice during typical street driving to gain that little bit in high rpm power, usually no more than the 10-15 hp range at most.

Even though it's common to see under driven crank pulleys, there is no need to under drive the alternator any further with an oversized pulley, thus slowing the alternator even further. What this does it turns the alternator up to 2 to 3 times slower than it otherwise might be. In other words, at 3000 rpm's the alternator could be spinning less than it would at idle, and when at idle it can be virtually non-functional. Since a 100 amp alternator even at full load only takes about 2 h.p. to run full tilt, there is very little gain to be had by under driving the alternator any more than necessary. Only when running extended high rpms where a belt might fly off at 8,000... 9,000 or more RPM's would an under driven (larger) alternator pulley be necessary.

Reactor Alternators will indeed perform better than others with under drive pulley's, however, the small gain of the pulleys may not be worth the sacrifice.

         ~ We hope this article assists you in understanding the intricate
                        details in alternator applications, needs and demands.

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