Think Of It As A System

Think Of It As A System

Although the components of high-power electrical systems in today’s heavy-duty trucks - starters, batteries, alternators and cables - are very robust and designed to operate without problems for many thousands of miles,they are, unfortunately, not trouble free.

Although the components of high-power electrical systems in today’s heavy-duty trucks – starters, batteries, alternators and cables - are very robust and designed to operate without problems for many thousands of miles,they are, unfortunately, not trouble free.

“The first production electric starter was put on a passenger car in 1912,” says Paul Menig, Freightliner’s chief electrical engineer. “The failure rates of the major components are still too high, after nearly 100 years of development. The cost to our customers is considerable. We estimate the cost of a driver experiencing a “no start” is about $650, including the lost revenue, the logistics of getting a jump start arranged and any parts.”

Problems can result from excessive heat, vibration, voltage spikes or careless handling. Damage also can be a result of operational changes by a fleet or driver. For example, the addition of “hotel loads” in a sleeper ‹ a microwave, cooler or bunk heater - can result in components being damaged by excessive heat if they are forced to operate at continuously high output levels.

Unfortunately, problems with the vehicle¹s electrical system are often misdiagnosed. As a result, components are too often removed as having failed and replaced in error. Leece-Neville engineers say that industry studies indicate that approximately 55 percent of the alternators and starters returned under warranty to manufacturers and noted as “defective” are later discovered to be in good working order.

“There’s no question that diagnosing a problem in a vehicle’s electrical system can be tedious and time consuming,” the engineers say. “However, spending the upfront time required is much more efficient than having the vehicle’s driver come back with an uncorrected problem. Simply put, it’s important to take enough time to properly diagnose and correct the real problem.”

System checks

The industry’s basic guide, the Technology and Maintenance Council’s Recommended Practice RP-129, is intended to provide a procedure to be used for either preventive maintenance or troubleshooting truck electrical systems. Bruce Purkey, president of Purkey’s Electrical Consulting and a person who participated in the preparation of the RP, is currently lobbying for an update of the document.

“If you look at RP-129, we show people how to do a voltage drop test,” Purkey says. “The thing we never gave them was why it was important or the sequence to use when doing the tests. When you check these electrical systems, it’s really a ‘one-two-three’ process.

“For example, if you have a starting problem, the first thing to check is the battery,” he says. “The second thing to check is the ability of the system to deliver electrical energy between the battery and the starter. Then, you need to check the control circuit. If you do it in that order — battery, cables and control circuit — and it still won’t start, then it’s time to look for a problem with the starter.

“On the alternator side, again start with the battery. After making sure the battery is fully charged, make sure the voltage drop in the cables is within spec. Only then should you move on to the alternator.”

Too often, when checking out a starting problem, a technician will simply act directly on a driver’s complaint and go straight to the starter.

“If the battery isn’t any good or if the cables aren’t able to transmit power from the battery, he can’t really make a meaningful test,” Purkey says.

The battery is key

Much of this philosophy is echoed by Randy Andis, director of fleet operations at Remy Inc. “The state of battery charge is the most critical aspect of the system,” he says. “You really can’t start to diagnose problems of cables, alternators or starters until you are certain that the batteries are at a 100 percent state of charge. Technicians not properly trained on electrical systems tend to troubleshoot problems by starting at the starter or alternator — possibly even changing these components, only to have the failure repeat as a result of a misdiagnosis.”

A proper diagnosis starts by making sure the battery is completely charged. Then, check the cables between the battery and alternator.

“We look for no more than a half volt loss between the two components at the rated output of the alternator,” Andis says. “Then, look at the cables to the starter where there can be another half volt loss at 500 amps. If either of these values is exceeded, we recommend that technicians troubleshoot the lines, looking for frayed or cracked insulation and corrosion at the terminals.”

The weak link

The right battery spec is important. Purkey says, “Whenever people have issues with batteries, they often look for a battery with a larger cold cranking amperage (CCA) rating. That’s really not the problem with today’s trucks, especially when drivers live in them. A battery rated about 700 CCAs with 180 or 190 minutes of reserve capacity is usually the right size for most applications because it should have enough reserve. That battery is going to provide the power you need for cold-weather cranking and for loads that run when the truck is shut off during the night. Remember, the more you discharge a battery, the more you’re going to shorten its life.”

A slow crank is frequently the result of too much voltage loss in the cables, not a bad starter. It’s important to disconnect the cables and clean the terminals. If you still have problems, check the alternator’s output to ensure it’s stable at about 14 volts. “If it’s not stable, there’s trouble with its internal electronics, and the unit should be changed,” Andis says.

If all of this is OK and you still have starting problems, check the cables to the starter and the control circuit at the starter. Make sure there’s no more than one volt drop here, also.

“This is critical because the starter needs enough energy to have the solenoid properly move the lever that causes the gear to engage the flywheel,” Andis says.

Connecting cables are clearly the weakest link in the system.

“The ‘look approach’ doesn’t work when checking cables,” says Eric Karr, heavy-duty account manager at Mitsubishi Electric. “You need to use proper test instruments.”

For every volt drop in the cable between the battery and the starter, there will be a 30-RPM decrease in cranking speed. Therefore, for a good system with a 0.7-volt drop, you can expect a 24-RPM loss. It’s not likely you’ll ever notice such a decrease. A 2.1-volt drop, however, will result in a 63-RPM loss in cranking speed. This may or may not cause a problem. A bad cable system with a 5.4-volt loss will likely cause a no-start condition due to a 162-RPM decrease in engine cranking speed.

“Every PM sheet in the country says, ‘Check the cables,’” Purkey says. “Most guys take a quick glance and say, ‘Yup, the cables are there!’ That’s not what ‘checking the cables’ means. You have to put them under a predetermined electrical load and measure the voltage drop between terminals.”

Temperature effects

Temperature extremes, both high and low, can cause problems for starting and charging systems.

“If not properly addressed, high underhood temperatures can play a role in premature failures,” says Joe Scarnecchia, Mack Trucks’ powertrain sales manager. “This is why we have incorporated a number of key design and engineering features in our products to extend component life. Take, for example, the frame rails of our new Advantage highway and Cornerstone vocational chassis, which are flared around the engine compartment, and the engine sits lower in the chassis, allowing greater air flow under the hood for lower underhood temperatures.”

Freightliner’s Menig says, “Underhood temperatures tend to increase with each change in engine emissions regulations. Starter and alternator manufacturers are aware of this and have been improving their designs to make them able to work in the environment.”

Remy’s Andis adds, “Vehicle manufacturers have made significant strides in reducing overall vehicle weight, which has led to smaller, tighter engine compartments that see reduced air flow.

Additionally, the development of cleaner, exhaust gas recirculation diesel engines has resulted in increased underhood temperatures. These engines are extremely efficient and very reliable but produce more external heat than their older counterparts. And, increased heat can degrade the performance and reliability of conventional alternators.”

Remy responded to the problem with the introduction of its 35SI family of alternators, which are designed to perform in the highest ambient underhood temperatures (220 ºF) encountered in today’s emissions-compliant commercial vehicles.

Even more recently, Denso announced the availability of its 12V 5.0 Offset Gear Reduction Starter, designed specifically for use on heavy-duty vehicles with 10-to-16-liter diesel engines. The compact and lightweight design of its new 5.0 allows for easy installation, reduces vehicle weight and is designed to live and perform properly in the high underhood temperatures expected in 2007 EPA compliant engines, says Fran Labin, Denso’s vice president of group sales.

At the opposite extreme, cold temperatures present their own challenges, particularly with batteries and no-starts. Colder temperatures not only place more of a load on a battery but also make batteries more resistant to charge.

“Take a truck that’s been sitting overnight at 0 ºF with a battery that’s totally discharged, and jump start the truck to get it going,” Purkey says. “It will take an alternator regulated at 14 volts about 140 hours to recharge the batteries. Clearly, it will never happen in a 14-hour run. The only way you can get those batteries to take a charge is to raise the voltage.”

This can be done by using one of the newer alternators or accessory devices designed to automatically adjust alternator output based on the voltage measured at the battery terminals. Remy, for example, makes the technology optional on the 35SI alternator mentioned above. If an alternator with its “Remote Sense” feature senses that a less-than-ideal current is reaching the batteries, it will automatically increase output to compensate for the loss.

IMI also is marketing an aftermarket device called Smart Sense, which is designed to perform in the same manner. The company says there are several advantages to fleets using such technology, including:

• longer battery life and fewer replacement battery purchases;

• faster, more reliable engine starts;

• fewer no-starts, meaning more hours on the road;

• longer starter life;

• more time available for driver/sleeper appliance usage without the risk of no-starts;

• reduced engine idling time, resulting in lower fuel costs.

“We firmly believe that it is just a matter of time before Smart Sense technology is available as standard equipment on all new trucks," says Robert Fogel Jr., IMI president.

Remy’s Andis says, “A remote sensing option will compensate for line loss and increase the alternator’s output voltage so the batteries can be effectively charged. It’s an excellent option for cold weather or for operations in which a fleet has problems keeping batteries at a full state of charge.”

Maintenance technicians need two things to keep charging and starting systems in good working order: training and tools. Make sure your staff has both. Proper diagnostic tests are necessary when system problems are encountered.

Good maintenance practices will minimize downtime and enhance the service life of the components. “Remove and replace” maintenance is not acceptable for the charging and starting system because it’s too expensive.

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