Alternator & Charging System Basics
(More tech articles on the Tech, Tests & Installs page HERE)

I had an electrical fire in the Dodge earlier this season. For those of you who’ve never had an electrical fire, it’s pretty scary. The Dodge was in my shop and I had just put my new motor in it. I had just started it up and had it running, getting some heat into it. I had my back to the car as I was getting my timing light ready. All of a sudden it just shut off, but I could hear the fan still running. I turned around and saw plumes of thick, acrid smoke billowing from the trunk, which thankfully had been open. I ran to the back of the car and found the alternator wire in flames and starting to ignite the other things I had been storing in the trunk while the engine had been out of the car. Being that the car had shut itself off, there was no more energy flowing through the wire so the fire went out pretty quickly at that point. Still, this was a wake-up call. What had happened was my alternator had a dead-short that I was not aware of, which sent way too much juice through the charge wire going back to the battery.

I spoke with my sponsor Powermaster Performance to learn more about what might have happened. Powermaster Performance specializes in starters and high-amp alternators for a variety of applications including drag racing. According to Brady Basner of Powermaster, one of the problems I had in addition to the dead-short was the size of the wire from the alternator to the battery; it was a 10 gauge. “The thing I always tell people is to look at it like plumbing,” said Brady. “From an alternator's point of view, it needs a clear path to the battery to charge properly, and a 10 gauge wire to the back of the car is extremely small. This will create a great deal of resistance (heat) in the wiring.” Too small of a charge wire will also result in a loss of voltage. Brady also informed me that they could repair my alternator even though it was not a Powermaster unit. They can fix up any starter or alternator regardless of manufacture.

So now I’ll be starting from scratch, rewiring the Dodge* and installing new components. How to begin? By doing some research. There’s an excellent resource in the Tech section of Powermaster’s website entitled “How To Choose A Racing Alternator." It details step-by-step the right way to choose and set-up the correct charging system for any application. Visit the page; it's great info. (*Note: see the rewiring job from start to finish HERE).

The challenge facing any charging system in a race car is that today's cars have more electrical demand than ever before. As a result, many of us run high-amp alternators but neglect to run a larger gauge charge wire to handle the higher amp loads. This was one of my mistakes. Furthermore, the pulley ratio has to be correct in order to keep the alternator charging at various speeds but without over-spinning it (the maximum RPM for an alternator is 18,000).

The first thing to do is make a list of all of the components of your electrical system: ignition, fans, lights, water pump, fuel pump, and so on. Then find the amperage draw for each component, and check with the manufacturers if need be. Total up the amps to get the amperage draw for the vehicle, and figure out the total length of charging wire you’ll need to get from the alternator to the battery. Now you can determine the size of the charging wire you’ll need in order for it to safely handle the draw over the distance.

Tighten Your Belt
According to Powermaster, the #1 reason for alternator failure including no output is a slipping belt. This has become a bigger problem with high-amp alternators because the higher the amps, the more resistance the alternator has and it takes more power to turn it. Signs of a slipping belt include:

  • Little or no output
  • Discharged battery
  • Pulley extremely hot and discolored
  • Rust on alternator shaft,
  • Belt dust on alternator fan and housing
  • Belt sticking to pulley
  • Glazed or cracked belt
  • Belt too deep in pulley groove
  • Bearing noise

So how can you determine if your belt is tight enough? Place a socket on the alternator pulley. Using a pull handle in the socket, pull on the handle clockwise. If the pulley slips, it’s not tight enough. The belt should be tight enough that it will try to actually turn the engine.

Next for the Dodge will be a complete re-wiring job. I’ll also be installing the alternator that Powermaster will rebuild as well as additional components that Moroso Performance Products suggested, such as their #74107 Alternator Shutdown Relay Kit, #74102 heavy-duty Battery Disconnect Switch and #74110 Boots for the battery disconnect switch. We’re also going to fuse the charging wire as an extra measure.

Choosing the right alternator and selecting the proper weight wire will not only improve the charging system’s performance, but it will make for a safer system. Going overkill on safety is always a good idea, especially with electrical systems.

Sources:
Powermaster Performance
www.PowermasterPerformance.com

Moroso Performance Products
www.Moroso.com


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