Off-road vehicles have always had their share of electrical accessories, such as extra lighting, winches, air compressors, and more. Today, you can add electric fans, fuel and cooling pumps, and EFI to that list. All of these components require even more electrical current to function at their full potential. Powermaster understands what it takes to keep a modern 4×4 charging, as the company has been designing and manufacturing alternators for over 30 years. One of their latest models, the HPR alternator, was developed to produce high current at lower RPM, where engines spend the majority of their time—at idle and mid-range cruising speeds. This story will explore the installation and benefits of the Powermaster HPR alternator and a set of high-performance cables on our early Ford Bronco.

We fit a 302ci-powered 1977 Ford Bronco with Powermaster’s high-output one-wire HPR alternator and a set of stout cables.

About Powermaster

The Powermaster brand was launched to support the specific needs of the performance and racing aftermarket by Machinery Components Inc., a manufacturer based in West Chicago, Illinois. Today, Powermaster’s facility encompasses over 140,000 square feet and continues to develop and manufacture what it claims are the strongest, most capable starters and alternators available. Its products are used on everything from monster trucks to land speed cars and Baja racing vehicles.

How To Select The Correct Alternator Output

The important thing to ensure when adding electrical accessories is that you have an alternator capable of meeting these increased current demands. The key is to understand your vehicle’s electrical needs, then select an alternator that exceeds those requirements.

For instance, if you have an electric cooling fan, an electric fuel pump, and air conditioning, you’re already looking at a draw of 75 to 100 amps—it adds up quickly. The solution is to choose a 140- or even 150-amp alternator. However, it’s important to note that most alternators are rated at their peak output when the engine is running at higher RPM, as the alternator spins faster. Therefore, it’s crucial to consider an alternator’s output at both idle and higher engine speeds.

The alternator on our 302ci-powered 1977 Bronco appeared to be original with a stamp indicating a 60-amp model – meaning 60 amps at best, almost 50 years ago! This would not be able to support a pending electric fan update followed by EFI and A/C.

A 1977 Ford Bronco In Need Of More Amperage

We found a mostly original 1977 Bronco that will soon be receiving some typical 4×4 updates, such as an electric cooling fan, fuel pump, and EFI. This means it will require some electrical upgrades. Powermaster’s Ed Law says, “Just adding an electric fan to your vintage truck can really tax a stock replacement alternator. For instance, this Bronco had an alternator rated at 60 amps—meaning its highest possible output! At idle and lower RPM, it’s likely closer to 20 amps, and most electric fans draw that immediately.”

Fortunately, Powermaster offers a direct-fit HPR alternator for the factory-issued 302 that will easily keep these new accessories operating properly.

About Powermaster’s HPR Alternator

Powermaster’s small-frame HPR alternator is capable of producing 150 amps at idle and up to 180 amps at high RPM. That’s plenty of current to support fans, pumps, EFI, and lighting while navigating technical trails or cruising slowly through daily traffic. It’s worth noting that Powermaster also offers a large-frame HPR unit that can support 195 amps at idle and 250 amps at the top end, though it’s not applicable for our Bronco.

The HPR alternator is a “hairpin”-style unit, which Powermaster says refers to the modern winding techniques used in the stator and rotor of today’s alternators. “We use a unique winding design, which allows us to increase the amount of copper wiring used in the rotor and stator, thus improving output,” the company told us.

Powermaster’s new HPR alternators are developed to support the current demands of today’s modern-equipped classic vehicles – especially at lower rpm. This small frame unit is a direct bolt-in for our Bronco and can produce up to 150 amps at idle and 180 amps at top end.

Powermaster’s specialized winding design creates a much more efficient assembly, capable of producing high current at low RPM while running cool and minimizing parasitic losses. The company’s HPR units also operate using similar six-phase technology. To convert this high alternating current (AC) into the direct current (DC) required by the vehicle, Powermaster incorporates a heavy-duty rectifier capable of handling the increased current and dissipating the heat generated.

Law says, “With the low idle RPM of modern engines, along with overdrive transmissions, we were tasked with supporting the current demands of today’s electronics-laden vehicles. Through the use of modern materials and winding techniques, we developed the HPR line, which provides great current output at low RPM as well as at the top end.”

While Powermaster does offer a direct plug-in HPR alternator that works with the factory connector and external regulator, we opted for a one-wire unit to simplify the wiring and it allows removal of the regulator.

Cables Are Equally Important

Another important aspect of keeping the charging system running smoothly is upgrading the charge cable and ground cable. There are two things to consider.

First, chances are your classic off-roader has a brittle old cable, or it has been replaced with a generic big-box substitute. When it comes to handling higher current levels—like those produced by Powermaster’s HPR alternator—you need to upgrade to a high-quality, multi-strand copper cable.

Second, you need to ensure the proper gauge cable is being used. For example, you must consider the distance between the battery and the alternator. If the battery is under the hood, you can use a 6- or 4-gauge cable, but if it’s located in the trunk or bed, you’ll need a 0-gauge cable.

Powermaster offers its own high-quality, multi-strand cable, which comes with hydraulically crimped terminals on each end.

Read On For Tips And Tricks

We followed along during the installation of the new Powermaster HPR alternator and cable on this Bronco and learned a few things along the way. Check out the photos below for a few tips and tricks. If you have any questions about your rig’s charging capabilities, give the Powermaster tech line a call at (630) 957-4019.

The installation of the alternator was straightforward—just two bolts. The supplied single V-pulley was the same diameter as the factory unit, so we were able to use the same belt, which Powermaster pointed out needs to be tight. As in really, really tight. Don’t judge by belt deflection; instead, get that belt seriously tight, as outlined in the alternator’s installation instructions.

With the increased output capabilities of the HPR alternator, it is highly recommended (i.e. mandatory) to upgrade the charge wire with a high-quality, multi-strand cable. Powermaster offers several pre-made cables in various lengths and gauges. With the battery in the factory location, we were able to use a short 6-gauge cable.

Powermaster’s higher output alternators also have a ground stud that should be connected to the engine block. Use the same gauge cable as charge wire just to keep the complete circuit congruent. When using painted, anodized, or powder coated brackets, the ground path of the alternator can be compromised and is another reason for the additional ground.

From the charge post of the alternator, connect straight to the battery with no interruptions along the way. Powermaster recommends that the alternator keeps the battery full then let the battery pass out the electricity through the vehicle wiring harness.

One important note on early Broncos and other classic 4x4s is that if you have a factory amp gauge, it will need to be disconnected due to the higher output of the alternator. We’ll be looking for a suitable volt gauge to add to our Bronco’s factory cluster and for now may simply run a volt gauge under the dash.

We did confirm the operation of the new unit by connecting our voltmeter, cranking up the 302ci V8 and turning on the lights and blower motor. The HPR delivered 14.6 volts as expected – just as noted on the Proof of Performance tag that Powermaster provides with every alternator.

Photos by Todd Ryden