Rebuild Tip Of The Week: Alternator Amperage

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A new development at Concept One that keeps the alternator cool even at high loads. See the new fan over the alternator.

If you are in the process of putting together a high-performance project build, there are a lot of components that need to receive attention. One thing that often gets over looked is the charging system. Many improperly-functioning components can have their issues traced back to voltage. For that reason, we talked to Kevin Redd at Concept One Pulleys, and JR Richmond at Powermaster Performance to get you the best insight so you can avoid this mistake.

1200-10“People always tell us that an alternator is just an alternator, and that they are all the same,” JR Richmond at Powermaster Performance told us. “This couldn’t be further from the truth.” The alternator is what supplies the electrical power to all of the components in your car. Back when most of our cars were built, the standard electrical system consisted of headlights, taillights, a simple radio, and in some cases an air conditioner or other powered accessories. Things have changed.

“If you put an LS3 in a 1969 Camaro, that means you are now running a computer, electric fuel pump, dual fans, and maybe even air conditioner and digital gauges,” explained Kevin. “All of these things are electrical.” With every accessory added, you are creating a greater amp draw on the alternator. If you put together an LS-powered ride like Kevin detailed, and use a standard 199-spec alternator, you are going to run into trouble really quick. Concept One developed a guide that details how to choose an alternator.

The guide gives amp estimates for all accessories, and details the alternators that you can order to supply the appropriate amount of power. The guide also details the size of charge wire you should use in a given amp range. Charge wire size is just as important as alternator output, so make sure you check that. Here is a sampling of the information they provide on alternator output:

  • Headlights / Tail Lights: 10 amp
  • Halogen Bulbs: 10 amp each
  • Dash Lights: 2 to 4 amp
  • Power Windows: 15 to 20 amp
  • Dash Lights: 2 to 4 amp
  • Air Conditioning: 19 to 22 amp
  • Electric Fans: 30 to 50 amp
  • Radio: 4 to  10 amp
  • Audio Amplifiers: 15 to  250+ amp
  • HEI Ignition: 10 to 12 amp
  • Electric Water Pump: 18 to 25 amp
  • Electric Fuel Pump: 8 to 10 amp
  • Air Suspension Compressors: 20 to 50 amp

If your build includes halogen headlights (20 amp), air conditioning (20 amp), a mid-range amplifier (75 amp) and radio (5 amp), electric fans (30 amp), an electric fuel pump (8 amp), an electric water pump (20 amp), and low-power air suspension compressor (20 amp), at any given time, your amp draw could be 188 amps total. If you were trying to power that system with a standard output alternator with roughly 120 amp peak and 95 idle amp output, it won’t last long.

2016-03-17_21-48-50When an alternator is rated at 120/95 amp, that means that 95 is the idle output, and the max rated 120 amps is sustainable for a short time, but not long term.  Richmond told us, “Shoot for meeting most or all of your amperage needs at idle.”  In other words, make sure that idle amp rating covers 100-percent of your estimated amperage requirement.

“When charging, a great deal of heat is involved,” Richmond described. “When an alternator is trying to keep up with demand, it does not reduce output and therefore the heat constantly increases until the laminations and windings burn up.”

The consensus from both Richmond and Redd is that more attention needs to be placed on selecting the proper alternator. Richmond added, “the entire charging system should be considered early in the build: size, location, wire size, and wire routing. Plan ahead for possible future upgrades, overkill is better here.”

MVC057F-vi

Using proper gauge wire is also essential.

Not only does an underpowered alternator kill your electrical system, but Richmond detailed how it could make your new hot rod into an unreliable driver. “The alternator will eventually fail trying to keep up with the demand. Engines overheating due to low voltage to electric fans is a very common thing we see.” He also told us that dim lights, burned up fuel pumps, and poor fuel mileage are side effects of an overdrawn electrical system.

1200-12So what can you do to avoid these issues? “Plan ahead. Make a chart with all of your electrical items and their placements. This will make alternator selection much easier.” Richmond also recommends, “Make sure you have clean ground connections with star washers. Terminal ends that are too large and terminal ends on painted or dirty surfaces will not cut it.”

The bottom line here is that the alternator is as crucial as any other component in your car. If you have any questions, err on the side of safety, and call the experts at either Powermaster or Concept One Pulleys, they can help prevent you from overworking your electrical system, and point you towards the right alternator.

Article Sources

About the author

Kyler Lacey

A 2015 Graduate from Whitworth University, Kyler has always loved cars. He grew up with his dad's '67 Camaro in the garage and started turning wrenches at a young age. At seventeen, he bought his first classic, a '57 Chevy Bel Air four-door, and has since added a '66 Plymouth Valiant and '97 Cadillac Deville to his collection. When he isn't writing for Power Automedia, he's out shooting pictures at car shows, hiking in the forests of the beautiful Pacific Northwest, or working on something in the garage.
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