We have to stop thinking of our start/charge systems as simply a handful of separate components, and start viewing them as a system. From alternators to batteries and starters, cables and regulators, and even add-on components like low-voltage cut-off switches and DC/AV inverters, each can impact the component next to it.
In electrical systems, weak components can manifest themselves in different ways, which can lead to misdiagnosis and mistaken replacement of perfectly serviceable parts. Start/charge systems are unique in their interdependence on various parts. What appears to be a failure of one part could actually be a very different problem.
Bruce Purkey, president and chief creative engineer at Purkeys Fleet Electric, says the scrap bins and warranty claims departments of this industry are overflowing with perfectly good parts.
“If people just followed troubleshooting charts, used the testers correctly and did a bit of basic electrical detective work, we’d send a lot fewer parts to the scrap pile,” he says. “For example, you can’t do an alternator output test until the batteries have been tested and found good. And then there’s cable. Have you done a voltage drop test? Is the alternator mounted correctly with proper belt tension? If your output test shows a bad alternator, the problem could actually be any other of these items, or a combination.
“Why spend $300 on a replacement alternator when the cables were really the problem?”
Cable is often the source of the problem, along with terminal connections – cheap, easy fixes that Purkey says are often overlooked because they aren’t always easy to access.
Does this scenario seem familiar? Ambient temperature drops and the truck won’t crank. Must be a bad battery. Change out a battery and the truck starts. Problem solved.
Maybe not, says Purkey.
“If you don’t do a load test, you’ll never know,” he says. “Chances are it was the cable. If that starter pulls 800 amps and I have a two-volt drop across the cable, I’ll lose about 60 rpm of crank speed but I’ll probably still start. If the starter is drawing 2,000 amps and I have a four-volt drop, I lose 120 rpm of cranking speed. There’s no way I’ll start. Is it a bad starter? A bad battery? No, it’s the cable or the terminal connections.”
You can have the best alternator in the world and the best battery in the world, but if you have a voltage drop and can’t charge the batteries you’re going nowhere. One of Purkey’s biggest pet peeves is the PM checklist that says “check cables.” What the sheet should say is “test the cables,” he says.
“In my experience, fleets hardly ever do voltage drop tests, but they are always doing battery tests,” he says “I know of a fleet with all kinds of starter problems but they never do voltage drop tests. I’ll guarantee they don’t have starter problems, they have cable problems.”
If you need guidance on doing such cable tests, look no further than The Technology and Maintenance Council of the American Trucking Associations’ Recommended Practice RP129A. It’s all there.
Voltage where it’s needed
Traditional alternators read their output voltage at the terminals, but don’t know what voltage the batteries are getting. The batteries could be getting a volt or two less than they need because of voltage drop across the cables and connections. A recent innovation called “remote sense” helps maintain 14 volts at the battery by increasing charging voltage at the alternator to compensate for voltage drops.
“Remote sense simply moves sense point of the regulator to the battery rather than the output of the alternator,” says Bob Jefferies, manager of fleet operations and services at Delco Remy. “Remote sense steps up the voltage to deliver what the battery needs, optimizing battery state-of-charge for improved efficiency and overall battery life.”
Inverters have proven a blessing and a curse for the industry. While they go a long way toward reducing the need to idle, they have placed quite a burden on electrical systems. Most of today’s industrial quality inverters include a low-voltage disconnect or they are wired into the system. Steve Carlson, manager of strategic sales for Schneider Electric/Xantrex Technologies, says the recommended disconnect voltage varies by OE between 11.8 and 12.1 volts.
That may not seem like a big difference, but if your charging system, through voltage drop, weak batteries or other cause, doesn’t maintain a healthy 14-volt output, your inverter isn’t going to stay online for long.
“Even with a healthy battery you’re going to see some voltage drop between the battery and the inverter, or you might get some surge demand that takes the system voltage below 12.1 and we get a nuisance shut-off,” says Carlson.
“Drivers are demanding these things today when they can’t idle, and we now have lots of drivers who need an inverter to run medical appliances like CPAP machines. A truck with a weak electrical system won’t support an inverter for long.”
Carlson adds that a well-maintained electrical system will support judicious use of an inverter, but if there’s any weakness in the system it will reveal itself the as soon as the driver starts the microwave.
Is bigger better?
When we’re talking alternators, size does matter – not in terms of output necessarily, but efficiency. A standard OE-spec’d alternator might be rated for 130 amps for trucks with 80- to 85-amp loads, but according to Jefferies, that alternator won’t be running at peak efficiency, and that costs money.
“At about 60% efficiency, it’s going to take about 600 gallons of fuel per year just to drive the typical electrical loads on the truck,” he says. “If you could make that alternator about 10% more efficient, you’d save about $300 a year in fuel cost.”
Jefferies says alternator efficiency is a combination of load, temperature, friction and output, and in general, the larger the alternator, the more efficient it is. Most alternators are only about 58% to 60% efficient because of losses due to belt friction, heat, internal drag and load. He points to a relatively new strategy of over-sizing alternators to get them into a more efficient range.
“If you can keep it operating at 35 to 50% of its rated current, that puts it down into the efficiency sweet spot, which saves fuel,” he notes. “That original 85-amp total connected load is less of a draw on a larger alternator, which makes it more efficient. And when we do need higher output it’s available, so you cycle the batteries less.”
And, he notes, alternators running lighter loads tend to last longer. As a percentage of rated output, lighter loads are easier on the bearings, it will produce less heat, and so on. But before you run out and grab a 435-amp alternator, Purkey warns that your cables have to be up to the task.
“If the OE wired the system for 130 amps, and you put a 200-amp alternator on there without upgrading the wiring, it’s like putting a 4-inch pump on a garden hose,” he warns. “You won’t get any more current through it, and while it probably won’t catch fire, the wire will become brittle and risk a short or a break.”
Replacement alternators need some consideration that will extend way beyond price. No longer will any old will-fit part do the job. Emissions changes over the past 10 years have driven huge change in onboard electrical loads, points out Keith Doorenbos, principal engineer at Kenworth.
“We have far more hotel loads than ever before, in addition to dozens of additional sensors and new electrically driven actuators, such as turbochargers and EGR systems. There are also urea system heaters; the list is a long one,” he says. “And to a lesser degree, there are new electronics related to safety systems, such as lane departure, stability controls, etc. Most are fairly efficient systems with low draw, but they are additional systems we have to consider.”
On top of that, Doorenbos notes, we now have very complex onboard diagnostic requirements. “In order to meet the very, very accurate demands of OBD, you need stable voltages for a reliable signal.”
Clearly, an underrated alternator puts at risk more than your batteries, but chances are they will be the seen as the culprit and junked before their time.
Time for a change
Cranking and charging systems as we know them today have been with us in much the same form and manner for about 50 years. While much has changed, much more remains the same. At this year’s Technology and Maintenance Council annual meeting in Nashville, Tenn., Carl Tapp, the now-retired maintenance chief at PAM Transport provided an interesting retrospective on such systems during the S.1 Electrical Study Group session on Challenges with Today’s Vehicle Charging Systems.
Tapp outlined the system’s evolution from the 1960s to the present, starting with a system that included a 50-amp generator/regulator and a 24-volt inertia-drive starter powered by a bank of four six-volt batteries run through a series/parallel switch.
“Anyone old enough to remember those systems probably still has nightmares about them,” Tapp said.
Systems evolved with the transition from generators to brushless alternators.
The series/parallel switch disappeared, and in the early 1970s we saw the first high-torque 12-volt starters.
Tapp’s presentation included photos of some of that early technology. Interestingly, the size and shape of many of those components remains much the same today, which is a testament to the engineering folks who have managed to cram a whole lot more performance into essentially the same envelope.
“We have 12-volt alternators out there now putting out 455 amps,” says Bruce Purkey, president and chief creative engineer at Purkeys Fleet Electric. “In the early ‘90s, a typical alternator on a new truck would be 135 amps. That went to 160 and now several OEs are spec’ing 230-amp output. The package size is essentially the same, but they are very different inside.”
Purkey says winding a stator with square wire rather than round has eliminated all the air spaces in the winding, which makes them much more efficient. “I’ve seen 230-amp alternators that are not much bigger than your fist,” he says.
So, what’s next? Purkey figures engineers have about reached peak performance with traditional technology in the current envelope, but Keith Doorenbos, principal engineer at Kenworth, speaking at the same session as Tapp, told attendees about evolution alternators and starters – the integrated starter/generator. He described it as a “flywheel-mounted electrical device that provides both fast starts by having a high torque output and very efficient power generation because of the wider diameter.
“This gets us around some of the challenge of demanding ever higher output from an ever smaller package,” Doorenbos said. “Because it’s integrated into the engine’s flywheel, we’ll have to make them very robust, but their performance and efficiency will be like nothing we’ve seen to date.”
Originally posted on Trucking Info