Why An Alternator And 16-Volt System Are Beneficial For Drag Racers

One of the common debates among racers, largely bracket and drag-and-drive competitors, revolves around the charging system and storage devices (aka, the battery) that supply the power to the cars’ vital components. This includes whether or not to use an alternator, and whether 16-volt batteries are better than one (or two) 12- or 14-volt batteries. To help us answer those questions, we turned to the teams at Powermaster and XS Power to lend us their expertise.

Racers in heads-up categories rarely drive their cars to and from a run, are intent on preserving every last horsepower, and for obvious reasons, are obsessed with weight. For drag-and-drive racers traversing hundreds of miles and racing without the aid of a tow vehicle, an alternator is, of course, a no-brainer. For bracket racers, however, the alternator is both an inessential, but nevertheless valuable, asset. It is a choice. The loss of a few horsepower and the extra weight are easily chalked up as fair tradeoffs to the peace of mind of having a charged battery — especially if they get into a late-round situation where there isn’t time to charge it up at the trailer. But many still don’t run one.

Our 15:1 compression big-block demands some strut cranking power, which a 16-volt battery can supply.

What about the other half of this equation: the battery voltage and amperage? It turns out, a battery is not a one-size-fits-all decision, and your application, uses, and requirements will dictate your selection.

The example we’re going to use in this story is a relatively typical, 5-second (1/8-mile) full-bodied door car, with a 604 cubic-inch, 15:1 compression big-block. We’ve run a single 12-volt battery on this car, then we used a pair of them, in each case without an alternator. Such an engine combination obviously demands some cranking power to fire, which a higher voltage battery can deliver. But we also don’t want to have to rely on fully charging the battery between runs, especially if we get late into the night and time is of the essence. A 16-volt battery and an alternator are both perfectly suited to our needs.

Enter The XS Volt

One product that has helped to simplify this decision, at least for us, is Powermaster’s relatively new XS Volt series of one-wire alternators. No longer must you choose one system or the other, but instead, the XS Volt is a one-and-done purchase, allowing you to run 12-, 14-, or 16-volt setups (also handy if you need to swap out a battery with whatever you can find at an auto parts store in a pinch, as we have). The XS Volt is adjustable from 13.5- to 18.5-volts, to cover 12- and 16-volt systems (or the 14-volt, which has proven popular in drag-and-drive racing). 

Powermaster put a lot of engineering time into the XS Volt to ensure a nearly bulletproof product that offers plenty of flexibility and features to racers. The voltage adjustment feature allows the racer to change the set point of the voltage system while the unit is running; a small potentiometer at the back of the unit is adjustable from the aforementioned 13.5 – 18.5 volts. To that end, there’s also a power-saving mode, with two operating levels designed to conserve horsepower loss depending on the amperage being drawn from the alternator (we’ll get to that in a minute).

Powermaster also utilizes a large MOSFET transistor and heat sink to ensure the unit can handle increased loads with capacity to spare. It’s also short-circuit protected, has loss-of-ground protection, and is sealed with epoxy to keep contaminants out and isolate vibration.

What Misconceptions?

A common misconception of alternators is the amount of horsepower that is lost at the crankshaft to turn it — something Powermaster’s Ed Law believes may be overstated or misunderstood.

“A lot of people think they’re building Pro Stock cars or NASCAR Cup Series cars…that’s the mentality.There’s a vast difference in technology, in dollars-per-cubic-inch, with those cars. Normal people like us who run bracket-or Drag Week-style cars need to have an alternator. The horsepower difference between running one and not, at top-end, might be 3-5 horsepower depending on the amperage of the alternator. You get a lot of dragster guys that run the small Denso alternators, and they might only lose two horsepower. So, unless you’re going out there to set a national record or every horsepower counts in your efforts to win the race, there’s no reason not to have an alternator. It’s better for the charging system, and better for the ignition system. It gives you more spark energy going down the racetrack, because you’re not relying on a storage device (the battery) to supply power to everything. You’re filling that storage device, making sure the battery stays topped off at maximum amperage and voltage.”

We had to revert to an alternator bracket from Powermaster that we already had and make some minor tweaks in order to fit the XS Volt with our factory-framerail car.

To help alleviate concerns with horsepower consumption, Powermaster built an optional power-saving feature into the XS Volt. When activated, this circuit can temporarily drop 1.25-volts from the set point. For example, if the unit is set at 14.9-volts, when this circuit is activated, the output will drop to 13.65-volts. This reduces the parasitic drag of the alternator to a minimum level, saving as much as 2 horsepower (depending on the amp load of the vehicle, the size of the battery, and the size of the alternator). At times when extra horsepower is available (such as braking or other deceleration moves), the alternator can safely take horsepower and charge the battery at a faster rate. It is safe to say that this feature is a bit overkill for the majority of racers. 

…an alternator is designed to fill the bucket. The pump is filling the bucket, which is the battery and contains the reserve capacity, and the bucket hands out drinks to everybody. – Ed Law, Powermaster Performance

In regards to another misconception — weight — the XS Volt we’re using adds about 9.5-pounds to the car, including the bracket, belt, and pulley. For a bracket racer, there’s little consequence for adding that weight to the car. For anyone else who needs one, the utility certainly outweighs the additional weight (no pun intended).

“Most bracket racers and drag-and-drive racers are using alternators these days. And some classes are even now mandating alternators. But the drag-and-drive guys, they’re driving their car, stopping to cool it down for a little while, and then they start racing. The alternator world is changing, and it’s becoming a lot more prevalent. Guys with electronic fuel injection and engine swaps need an alternator. They have to keep the battery levels up, because they’re running multiple fans, EFI, fuel pumps, and everything else.”

Sizing Your Alternator

Selecting an alternator is a relatively straightforward process, not unlike buying a house with the right number of rooms for your family’s needs. Take inventory of all the electronic devices in the car, add up the total amperage draw of all of them, and you’ll arrive at the necessary total. In our case, it was 85 amps total. Powermaster can supply idle, cruise, and top-end amperage with its alternators. We of course need an alternator that could supply enough amperage, but conversely, can you buy too much alternator?

Because we repositioned the alternator, we would need a different belt than supplied. To measure, we simply cut the belt, measured the difference, and went online to buy a replacement.


“There’s no such thing as too much amperage. That’s the great thing about an alternator, is the regulator not only controls voltage, but amperage,” explains Law. “And so you could have a 220-amp unit on your vehicle but may only be using 40 amps to keep the battery topped off. That’s the key: an alternator is designed to fill the bucket. The pump is filling the bucket, which is the battery and contains the reserve capacity, and the bucket hands out drinks to everybody. The alternator will only provide what it needs to keep the battery topped off so it can supply the electrical needs of the vehicle.”

According to Law, if an alternator is sized appropriately for the vehicle, in a bracket racing application, where one is driving to the lanes, re-firing the car to move up, making a pass, and driving back to the trailer, should be fully charged or close to it.

On the left-hand column, you can see our complete amperage needs, a total of 85 amps.

“If the alternator is sized properly for the amount of current the vehicle is using, going down the track, it should be pumping as much electricity back into the battery as it’s using. The benefit there is, if you get into a round-robin situation, you don’t have to charge the battery between rounds. The guys with small alternators, who have to have an alternator for the class they run, usually size them too small. And the smaller the unit, the less amperage you’re going to get out of it, so they’ll have to charge them between rounds, but it doesn’t take as much to top it off, because they’re still kind of balancing them going down the track.”

In our example car, as is standard procedure, the power is run to the battery (through a kill switch) to the battery; from the battery to a distribution block on the firewall, and then out to the individual devices. This, Law says, is ideal because it cuts down on potential EMF and RFI interference.

We took the time to carefully route the cables back to the battery, running the line through the frame as much as possible to keep it away from the elements. Here, we cross over the four-link.

“Some people want to run electric fans off the alternator, and not take it to a distribution block, or they want to run the alternator to a distribution block and not to the battery. Electricity, like water, takes the path of least resistance. If the alternator can run two fans and not charge the battery, then everything else in line suffers.”

12, 14, Or 16?

The advantage of a 16-volt battery lies largely in the power delivered to the starter to crank a high-compression race engine. Remember, volts and amps are two different measures of electrical current — voltage is a measure of the pressure that allows electrons to flow, and amperage is a measure of the volume of electrons. Using a garden hose as an example, amperage is the flow rate through the hose, and voltage is the diameter of the hose (or the water pressure).

“In the drag racing world, high-compression motors need the extra voltage that 16-volt batteries provide,” XS Power’s Brady Basner says. “When running crank triggers or magnetos, you need a lot of flywheel speed. Back in the day, guys typically ran two 8-volt batteries, and figured out the faster starting speed was showing an advantage,” Basner says.

Some sources claim horsepower advantages (hotter spark, for example) from 16-volt batteries; Basner is aware of no data to corroborate that, but does say that if your 12-volt system is not providing enough amperage for your ignition system to perform optimally, then power improvements could be possible. That said, other benefits to a vehicle’s systems from a 16-volt setup have more factual basis.

“Fuel injectors are extremely happy with 16-volts,” Basner explains. “We’ve had manufacturers tell us how much more efficient they are…that from 16.2 to 16.4, there’s no drop in efficiency. But from 14.2 to 14.4, the injector became exponentially less efficient. So above 16-volts, they found efficiency flattened out.”

We mounted up a high-amp alternator shutdown relay from Painless Performance Products to protect us from engine run-on. Alternator feedback can keep the engine running even with the master disconnect turned off, so this will protect us in the event we need to shut down power to the car in an emergency.

Conversely, as voltage increases, amperage actually decreases. “A like-sized 12-volt battery has 1,100 cranking amps, while the D1600 (the XS Power battery we are using) only has 700. But, it’s hard to quantify with the faster starting, how much energy did you pull out of the battery by starting the car,” Basner explains.

He goes on to use the analogy, “If you had two boats with trolling motors, one has a 12-volt battery, one 16-volt, the 16-volt will take off quicker and be faster. The 12-volt, however, will go further, and at some point, the 12-volt surpasses the 16-volt and gives you more distance. That’s because the 16-volt has less capacity. In the racing world, it’s not an infinite distance, it’s racing to the 1/4-mile. In a car, with a specified distance, there’s no way to say which is better without looking at a specific application.”

Our D1600 battery from XS Power.

Basner offers a couple of key selection criteria for those on the fence.

“First, if it’s a pump gas car there’s really no need in most cars to go beyond a 12-volt system. Second, is what they’re trying to accomplish…if a guy just did a head and cam on the car, the timing is locked out, and it’s starting slowly, that pushes them right into 14 or 16 volts. Do you want to street drive the car? If so, we really lean toward the 14-volt system there,” Basner explains.

What If There’s Too Much Voltage?

Our electronic tachometer was one of the devices in the car we were most concerned with exceeding the voltage requirements of. It does, however, have an operating ceiling of 18V, which we intend to adhere to.

There’s a caveat, though, that we should point out about a 16-volt battery. That is, ensuring that you don’t introduce more voltage to any one device than it was designed to handle. With our car, we checked over everything from our MSD Power Grid, to the cockpit gauges, the delay box, interior and exterior lights, fans, and switch panels, and confirmed all were within an 11 to 18 volt operating range. To be sure we don’t harm any of those electronics, we will utilize a volt-meter and set our alternator to operate at a maximum of 18.0-volts. We will give up some charging speed in doing so, as the battery charges most optimally at 19.6-volts, but everything will stay within a safe range. If any devices had lower operating ranges, say 17-volts maximum, then we’d need to utilize a voltage step-down module for that item, which XS Power offers.

XS Power’s step-down module.

The step-down is essentially a big diode — or rather, two big diodes — with one input, and two potential outputs, depending on what you drop the voltage down to. With two items that only use 10 amps max, you could simply wire them both to the step-down. If, however, you have multiple devices with limits under the 18.5 volts from the battery, or higher amp draws, you would need a step-down for each. The device can drop 50 amps max, 25 amps continuous, and by either 3.6 or 2.4 volts.

Remember that while on an external charger, your 16 volt battery will be receiving somewhere around 19.5-volts. As Basner tells us, “On a lead-acid battery, you want 2.45 volts per cell charging for maximum charge speed. So a 12-volt battery would be a 14.7-volt charge current, a 16-volt is 19.6 volts.” However, if that voltage goes all the way through the system and reaches the devices in your car, it can inflict fatal harm upon them. So always be sure the power is off to everything in the car when you hook it up to top off your battery.

Fuel injectors are extremely happy with 16-volts. We’ve had manufacturers tell us how much more efficient they are…that from 16.2 to 16.4, there’s no drop in efficiency. But from 14.2 to 14.4, the injector became exponentially less efficient. – Brady Basner, XS Power Batteries

Because the alternator will run at 18.0 volts, we’d expect some need to top the battery off after a run. Nevertheless, the use of an alternator will give us a whole lot more peace of mind as we go rounds.

“We recommend charging the battery periodically, because it’s not going to get fully charged running at that voltage,” Basner says. “In a perfect world, you would charge your battery when you get home from work every day, because they are happier in a high state of charge. So whenever possible, always put it on a charger. Alternators are, at best, about 50-percent efficient, and you also don’t know how efficiently it’s working on the car, when you have belt slip and voltage drops due to wiring, you really can’t say how much of a charge there is. So put it on the charger and don’t leave it up to chance and risk your next round because the battery isn’t charged.”

For a bracket car, particularly big-inch, high-compression setups, a 16-volt system, and an alternator makes a lot of sense. As Basner tells us, drag-and-drive racers in particular have taken a liking to 14-volt batteries, for two reasons. One, it puts their ignition system and fuel injectors in a nice voltage range of around 16 volts. And second, using the above example, they can continually charge at the full 2.45 volts per cell without posing any risk to their other electronics, and without fear of the battery running down as they drive for hours at a time.

In our example, the cranking power after the change to a 16-volt system was immediately noticeable; the high-compression engine lagged to catch fire with the 12-volt battery, but was noticeably snappy once we dropped XS Power’s D1600 battery in the trunk. The additional weight on the nose of the further addition of the alternator is of little consequence to us given our use. But it does give us fresh confidence we can drive the car to and fro, with little worry of having enough juice to get back to the lanes.

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About the author

Andrew Wolf

Andrew has been involved in motorsports from a very young age. Over the years, he has photographed several major auto racing events, sports, news journalism, portraiture, and everything in between. After working with the Power Automedia staff for some time on a freelance basis, Andrew joined the team in 2010.
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