For some reason, there are several systems in your average hot rod that seem to baffle folks. Electrical systems seem to be one of those, and at the heart of every street electrical system is a battery and alternator. Both are often forgotten, and are treated as an afterthought, when building hot rods. We’re here to tell you that falling into this habit will come back to bite you. There are several reasons to put real consideration into your charging system, the least of which is making sure you make it out of, and back into, your driveway under power.

One of the reason’s that electrical systems are such voodoo to some people is because they just don’t understand what is going on with electricity. Grounds? Power? Exciters? What the hell is all that stuff? We’ll go into more details on electrical systems in a later story, but for now lets make the assumption that your car’s electrical system is in pretty good shape, and you need to just focus on whether or not you have the right alternator in your system. We hit up Brady and the guys at Powermaster to help us give you all the right info. The info they shared is italicized below. If you want more information on Powermaster, visit them online at PowermasterMotorsports.com

So what IS an alternator? An alternator is a type of electrical generator that converts mechanical energy (a belt driven pulley) in electrical energy. As the name implies, an alternator creates alternating, or AC, current. As we all know, a battery is direct, or DC, current. An alternator uses a rectifier bridge to convert the AC current to DC in order to maintain your battery.

Okay, I know we said we weren’t going to go into electrical theory here, but you have to bear with us. DC current, like from your battery, has a power side and a ground side. Your house on the other hand is AC current and in reality the two main prongs on each of your outlets can be the power or ground at any millisecond. The Alternating Current that is traveling through them literally changes direction back and forth 60 times per second. That’s all, no more explanation…for now.

So the alternator just charges the battery? While most people would say an alternator charges a battery, the ideal and intended purpose is to maintain a battery. Alternators are unfortunately inefficient, as are most methods of creating electrical current. This inefficiency can create a great amount of heat when the alternator is asked to produce a large current.

There is a pretty drastic difference between charging and maintaining, with regards to your battery. Maintaining means that the alternator is matching, or nearly matching, the current draw being put on the battery so as to keep it at full capacity all the time. Charging means that the alternator is NOT matching the current draw being put on the battery, and therefore has to wait until current draw dips below the maximum amperage of the alternator so that it can “refill” or recharge the battery. If you have a Mustang with EFI, electronic ignition, a big stereo, electric fans, and electric fuel pumps, and your total system current draw is 110 amps, but you have a small 60 amp Autolite alternator on it, then the alternator will not be able to keep up. With the average battery that has a Reserve Capacity of 110 mins (at 80 degrees with a 25 amp load), your battery will fall below 10.5 volts in less than an hour. Clearly that’s an alternator that can’t maintain that battery. If you stop the car in 30 minutes and shut off the stereo, and the ignition isn’t working at full tilt, we’ll say that in theory the load goes down to below 60 amps and that allows your alternator to charge the battery back up. It’s not good for the battery, your electrical system, or the alternator.

How is an alternator different from the old generators that were on cars through the 1950’s? By the mid 1960’s most domestic vehicles had changed from generators to alternators. Alternators were able to offer many benefits that the generator could not match. Generators are very heavy, and inefficient. Weighing close to 30 pounds in many cases, with only 25-30 amps of total output, generators were replaced by alternators that were able to nearly double the output and cut the weight in half. Added electrical features in cars of the 1960’s also put much higher demands on the electrical and charging systems. Besides being lighter weight and having increased output, alternators were also easier to maintain. Instead of bushings the required periodic lubrication, like the generators were equipped with, alternators used bearings that had a much longer life.

What’s going on inside an alternator? Basically inside of an alternator you have a magnetic rotor spinning inside of a copper stator, or tube wound with copper wired, to produce an electric field. The energy produced is AC current that is converted to DC current through the rectifier. The rectifier is like a one way valve, that only allows electricity to travel through it in one direction, thereby getting rid of the alternating current flow of electricity. The alternator path is transferred through the positive and negative carbon brushes that ride on the slip ring at the back of the rotor shaft. This is the only contact between the stator and the rotor of the alternator, and is a common failure point f the alternator has oil or significant dirt or debris introduced to the inside of the case. On most alternators, (There is always something funky out there like the liquid cooled alternators on BMWs to make liars out of us.) air is pulled from the back of the stator windings to the front to keep the alternator cool. If you look at the fan on the front of an alternator, it’s actually pulling air THROUGH the alternator, not pushing it in. Thus, you’ll inevitably have a beer drinking buddy tell you the alternator fan on your engine is the wrong one.

How hard is it on the alternator to be the sole provider of electricity for a vehicle? Ie if you started the car using the battery, but then disconnected the battery and drove cross country using just the alternator for power. An alternator really needs the battery for proper output, but in theory, yes you could do this. As long as there is a completed circuit, the alternator should maintain just fine. However, I don’t know of anyone ever trying this on purpose, so the real world experience might prove different.

On a similar note, for years there has been talk of how much power an alternator “robs” from the engine during use. At full output, a typical alternator can take as much as 14-15 horsepower from the engine in order to stay running at peak output. The more amperage an alternator is capable of, and in turn the more you ask it to produce, the more torque it takes to turn. With older alternators, guys at the drag strip would pull the charge wire to get it to free up that power. On modern alternators the alternator will actually full field, and put out as much power as possible, since it’s seeing an open circuit. This will actually cause more draw on the engine and damage the alternator in the process.

Voltage: Why do alternators charge at a voltage higher than 12 volts? Aren’t the batteries in passenger cars just 12 volts? And why are some race cars using 16 volt systems instead of 12 volts? In many cases, racers will use 16 volt systems for faster cranking during start up. Also on a fully discharged system, the 16 volt batter will still have more voltage and may keep the car running and starting. This is still not great for the battery, but a little more practical if the car is being used solely at the track. As far as why a battery wants higher voltage for a charge, it depends on the battery and it’s design. You’ll have to ask the guy at Optima for more specifics on that one.

How do you decide what alternator is right for your hot rod or race car? Selecting the right alternator for a hot rod or race car is pretty much just like figuring out a wiring harness.  Sit down, make up a good plan, and make sure you have enough amperage to cover the load.  We see tons of alternators, especially in custom vehicles, that are undersized.  Output is all about copper and steel, and the more amperage you want, the more copper and steel it takes.  A tiny 93mm style Denso alternator is never going to be capable of putting out the amperage that a Delco CS144 can produce.  There are really cool advancements in wire that are able to increase the surface area of current copper designs that increase an alternators output, but in the end, size does matter. 

How many amps do I need?  All of them! 

Are there ever too many amps? You can never have too much amperage.  An alternator will only produce what a vehicle is asking for.  However, there are other issues to consider.  A higher amperage alternator is bigger and heavier.  If you have 30 amps of total draw, there’s no reason to go to a 15 pound CS144, when a 6 pound 93mm Denso will do the job. 

What are the most common errors people make when choosing an alternator? Most often the improper selection of the alternator is simply choosing an undersized alternator.  Without enough amperage output to cover the load, the alternator won’t survive.

What are the most common mistakes people make when installing an alternator? Two issues arise on alternator installation exponentially more often than any other.  Improper grounds, and improper belt tension are by far the most common mistakes.  People forget that an alternator is an electrical item and the housing needs to ground. Painted or powdercoated brackets can keep an alternator from charging at all.  We recommend on any alternator that a belt be replaced with a high quality piece, and the belt be snugged up on install.  Gates has really good information on their website for proper belt tension and tools to check.  All of the “tricks” about belt deflection are really inaccurate.

Can an alternator make your car have more horsepower? Excellent question, and difficult to answer.  If you think of maximum horsepower draw at 14-16, what would you lose if your voltage went from 14.5 down to 12.5?  That’s a maximum draw, so real world conditions would vary quite a bit.

In theory lowering your voltage and/or amperage can free up some horsepower. But what if you go too far? What happens when the battery voltage drops down to 11 and your MSD stops sending out all the spark it can? Will it happen idling? No. When you’ll notice it will be at 1000 feet in a run when the car is under full load. Then that lack of amperage and voltage may be costing you a lot more.

Common misconceptions. We could probably get really deep into one-wire alternators, but I think everyone is just always going to have their opinions on the good and bad with them.  In a nutshell, not all alternators are created equal.  The guy selling a $20 chrome alternator at a swap meet is not selling a Powermaster, and it’s not going to do the same things a Powermaster will do.

The moral of the story is that if you care about your hot rod or race car, and it’s performance and longevity, you need to make sure that your build includes a high quality alternator and battery. Like Brady said above, figure out what you are going to have in your car, with regards to electrical draw, and plan your wiring and charging system accordingly. When we put together the 5 second S10, we were very particular on the alternator. I called Brady so early on in the project, that our Powermaster alternator was one of the first things that got to the shop. We planned for dual electric fuel pumps, dual electric engine cooling fans, an electric fan for the trans cooler, all the electronics running the engine, including a Racepak, Smartwire, MSD Grid, MSD 8 box, Boost Control, Fuel Tech EFI, coil drivers, injector drivers, headlights, tail lights, turn signals, trailer lights, and much much more. It’s a lot of stuff. And we could have went for the typical race small alternator. But instead we went for a bad ass Powermaster because we knew it would provide the amperage we needed when we were on the road in the middle of the night, hoping to get to the next checkpoint. Don’t skimp out on an alternator, it’s only going to cost you time, money, and aggravation.

And if your car is going to sit, disconnect that battery, and put it on a tender. Or at least put it on a tender. A good alternator will cost you far less than you might think, and then when you forget about your charging system and start taking it for granted at least you’ll have done the right planning so you can drive it back home and into the garage just like it left.

FOR MORE INFORMATION ON ALTERNATORS AND MORE FROM POWERMASTER, VISIT THEM AT POWERMASTERMOTORSPORTS.COM

We’ll have more electrical how-to, including hands on tech, tips, and instruction, in coming tech stories. If you have specifics you would like to see us cover, please let us know in the comments and we’ll make it happen.