Can I Boost My Alternator To A Higher Output?

Like today, I occasionally get this question, as some people need more output due to extra loads put on the alternator by adding other electrical equipment to a vehicle that did not come factory installed.

This is no simple question to answer, as too many variables enter the equation.  First I'll address what happens to the unit by ramping it up.  Most alternators are pre-designed to put out the maximum amps for their size, though some of them can vary and accept a small increase in output.  Also, alternators are only able to maintain constant output at 75% of their rated capacity, which means it you have a 100 amp unit, you can only expect to use 75 amps 100% of the time.  Taxing the unit for more will result in premature failure!

The real problem lies in the ability for the unit to put out a charge, in all the engine speed ranges or RPM"s.  If you have an OE 100 amp alternator, that was installed in a vehicle it was designed for, it will function properly at engine speeds from let's say 400 RPM's at idle to 3,500 RPM's top engine speed.  Now let's say you need to raise the output from 100 amps to 160 amps output out of the same unit, and for this purpose, let's say the parts are available to do such a boost.  What happens is, by putting the heaver windings to increase the output, you will also move the RPM range.  Since the unit wasn't pre-designed to run with these heavy components, you now have changed the range, to where it may only charge from let's say, 1,000 RPM's to 4,000 RPM's, so at idle speeds, it will drop out and no longer charge.  You will also have to run the engine faster to get the output you want.

For most applications, parts are not available to rebuilders to boost most units beyond factory specs.  Each unit is unique to the application and very few or none of the parts on these units are interchangeable anymore.  There are companies that build OE style units into high amp output units, usually for stereo amplifier applications, but these units are usually short lived as most consumers of these units, tax them to their limits.  For this reason, I personally do not market or sell these units, nor will I stand behind them either.

An exception to this, is in older units that came in a large amp range.  Take the Delco 10SI for example.  It was produced by Delco in the amp ranges from 37 to 63 amps and has been boosted to about 80 amps without any problems either.  So let's say you have a 45 amp unit and want to boost it to 72 amps, the parts are available to do the job and you won't be pushing the design limits.  It will still function properly in all the RPM ranges!

One other minor problem worth mentioning is if you increase the output, you will also tax the engine horsepower a little bit, which may decrease the gas mileage some too.  Is the trade-off worth it?

Bottom line is if you need a large boost in amp output, you need to use a larger alternator that is designed for that output.  If you need a large output alternator, but only have room for a small unit, then don't expect the unit to function at idle speeds and don't expect it to have a very long life if you tax it close to it's limit!