Parasitic loads, hotel loads, safety loads: other than the emissions system, nothing on today’s trucks has changed more than the electrical systems
“You can’t work on a truck built in 2007 as you did on one built in 1957,” says Bob Dannenberg, chief engineer of Navistar’s electronics group. While his observation could apply to just about any part of a truck, he was referring to today’s electrical systems –– and was certainly on target. The electrical system of a truck of that era had basically two parts, a starting/charging component and a lighting circuit. And when the driver shut the truck down at the end of the day, there was nothing at all that needed power from the batteries, usually not even a clock.
How things have changed! Now we have many demands for electrical power even when the engine is shut down. And we’ve given them names that didn’t even exist just a few years ago. We call them parasitic loads and hotel loads.
Parasitic loads
In the last 20 years, vehicle systems have gone through a transition from mechanical to electrical devices. Take by way of example the instrument cluster. Then, air pressure gauges were purely mechanical devices driven through a direct connection from a pressurized component. Speedometers and odometers were driven by cables and spinning magnets.
In years past, electrical systems usually grew simply by adding more wires and connectors. That, of course, is no longer the case. Today gauges are driven by electrical signals — in some cases using just one or two wires carrying multiplexed messages to many gauges. That brings the size of harnesses down but the level of complexity up.
Every truck that comes off today’s assembly lines also has onboard computers. Dannenberg tells us that in the most basic International model there are five separate computers. In the company’s most sophisticated truck, there are upwards of 30.
Many of these computers need to be energized all the time because they must be capable of working even when the key is turned off. Paul Menig, chief engineer for mechatronics at Freightliner, tells us of one very popular feature on his company’s products. He says, “We have a body computer that is constantly monitoring for the door to be opened. When it opens, we have the instrument cluster come alive so the driver or maintenance technician can use the electronic odometer. It’s very common that a driver or technician wants to check the mileage when the truck is parked in the yard without turning on the ignition switch. To do this, we have to keep the computer alive.”
In doing so, it draws power from the batteries –– not very much, but some. Bruce Purkey, president of Purkey’s Electrical Consulting, says, “As more and more electronics are added to the vehicle, the key-off loads increase. Anything electronic that has memory will increase these parasitic loads. These loads are typically in the milliamp range, and while they have increased over the years, they are not much of a concern unless the vehicle sits for a long time. In a month of inactivity, these small parasitic loads will completely discharge a pack of four batteries.”
Truck manufacturers, of course, are aware of the concerns posed by parasitic loads and try to design out as many problems as possible. Dannenberg says, “To control parasitic loads, we try to make sure any electronic module draws less than one milliamp when the key is off. Five or 10 years ago there was much more quiescent current drawn by individual modules because of technology limitations, but there were far fewer modules on a truck. There could be as much as 15 milliamps drawn by a single module.”
Hotel loads
While parasitic loads would take days to cause any serious problems, hotel loads could run a battery pack down to a point that a truck would fail to start in just hours, indeed minutes. Sleepers have gone from a simple bunk behind a driver’s seat to walk-in hotel rooms with everything from refrigerators and microwaves to entertainment centers. Freightliner’s Menig says, “The biggest thing going on right now is the desire for air conditioning when the engine is off. There are electrically powered systems that look very promising, but they will require additional batteries on the vehicle. In any sleeper configuration we install a minimum of four batteries even though we need only two or three to start the engine. Customers want more and more stored energy on the vehicle.”
To avoid a no-start, Menig says that Freightliner all but requires the use of a low-voltage disconnect (LVD) on sleeper-equipped trucks. This is an electronic switch that monitors the state of charge of the batteries, and, if it decreases to a point that threatens a no-start condition, the LVD automatically turns off as many loads as possible. Menig says, “What gets turned off depends on the OEM and the customer. For example, it may or may not cut out the truck’s communication system. We won’t disconnect any safety related lights.”
Purkey says, “LVDs came into being with the growth of irregular route carriers where drivers have sleepers in which they live. For any sleeper longer than 54-in. customers are pretty well required to have a LVD installed by the manufacturer. They work extremely well.”
Fleet managers should make certain that an LVD’s sensing point is at the battery pack and that it is connected only to hotel loads. It must not control safety or operational loads. Purkey says, “I’ve seen LVD installations that sense upstream from the batteries. This picks up voltage drops that fool the sensors. It has to see exactly the state of charge of the batteries to work properly.”
Low-voltage disconnects are available for aftermarket installation and should be located in series with any load you want to control.
Some fleets also spec load or battery disconnects. This is a mechanical switch that completely disconnects the battery from the truck’s electrical system and is normally used only when the truck is going to be idle for a prolonged time period –– say three or four days. Such a switch is often located on the truck’s floor next to the driver’s seat where it’s easy to reach when the driver gets out of the truck or for a technician standing on the ground. In any case it should be located near the batteries. Purkey warns, “Remember, they shut off everything. Anything with a memory will have to be reset. Drivers typically don’t like that.”
Handling hotel loads
Fleets that operate sleepers are constantly evaluating their various options, and manufacturers are responding to customer demands for higher onboard power in several ways. Caterpillar, for example, has its MorElectric product line that includes an auxiliary power unit (APU) that provides electric power to a dedicated HVAC module as well as the vehicle’s electrical system. The system provides a comfortable cab environment and power for hotel loads without idling the main engine. The APU shares coolant with the main engine to minimize cost/weight and keeps the engine warm for winter startability.
The new Kenworth Clean Power no-idle system is now available in production as a factory-installed option for the aerodynamic Kenworth T660 with 72-in. AeroCab sleeper. The system has the capability of providing engine-off cooling and heating, plus 120-volt power for hotel loads.
The system uses dedicated, deep-cycle batteries that power a thermal storage cooler, which fits under the bunk. As the truck is driven down the road, or if the truck is connected to a 120-volt AC electrical supply, the liquid inside the storage cooler is cooled to freezing. This translates to roughly 21,000 BTUs of cooling capacity.
Once the truck is shut off, a thermostat regulates the desired temperature and a variable speed fan circulates chilled air through a duct located near the bunk. Extensive testing has shown that, when the outside temperature is as high as 95 degrees, Kenworth Clean Power is able to keep the sleeper cool and provide accessory power for up to 10 hours. A convenient sleeper control panel is used to help maintain a comfortable temperature. To provide heat when temperatures dip, a small diesel-fired heater mounted under the bunk is also controlled with a thermostat.
The system is also packaged with high-output, low-current LED lighting and an enhanced sleeper insulation package for greater efficiency. Kenworth Clean Power may enhance fuel economy by as much as 8 percent for customers with current high idling times.
Inverters
Inverters can be used to provide power for hotel loads. Their use is growing in popularity with driver but causing problems to fleet managers. An inverter is a device that converts 12 volts DC to 110 volts AC –– the same signal that powers microwaves and electric blankets or televisions. They come in many power outputs and a full range of product qualities.
Many fleets have strict policies against the use of inverters that plug into cigarette lighters because of the potential danger of overloading that circuit and, of course, of discharging the batteries. But how can such a policy be effectively enforced? John Duffy, manager of advanced technology at Kenworth, says, “Drivers install inverters even though they don’t have sufficient knowledge of the truck’s electrical system. If they don’t do it right, they can drain the power out of the batteries. I would be very careful of such devices. A driver can very easily find a power lead and tap into it. Obviously, he could go to the cigarette lighter, but if he wants to hide it a bit better, he can tap into power anywhere. It would be very difficult to find.”
Purkey says, “Since it’s not possible to control the use of inverters by drivers even if you have a no-use policy, make sure you use qualified technicians to install connecting harnesses to avoid the propensity to have incendiary incidents.”
Again, he offers a caution saying, “There is one area of concern with inverter use. Sleep apnea machines generally require a ‘pure sine wave.’ The typical inverter generates a modified sine wave because it’s easier to produce. If the sleep machine needs a pure sine wave, the driver needs to know that he is not going to be able to use an inexpensive inverter. Also look for UL approval on any inverter used in a truck. Without that approval, no one has ever done any testing on its ability to confine or avoid a fire.”
LEDs
The demand for lights, of course, never went away, but the quality of available lighting system components has improved dramatically. No longer is household wiring with twist-on connectors acceptable. A sealed harness powering LED lights is current state of the art.
Freightliner’s Paul Menig says, “I’d like to encourage the continued use of LED lights. Most fleets are spec’ing LEDs for lights high on the vehicle. They get a quick payback by having fewer accidents by technicians changing bulbs. I’d like to see that use migrate to lower lamps. We’re past the time of avoiding LEDs because of theft. I just don’t hear that complaint anymore.”
Maintenance
Wouldn’t it be wonderful if you could simply design or spec away the need for regular maintenance. That, so far, has not happened with electrical systems. Kenworth’s Duffy says, “The electronic systems on trucks are becoming more and more sophisticated. As a result they are more susceptible to loose connections. This is driving an increased need for regular maintenance on these systems.”
What should you do? International’s Dannenberg says, “Spec quality, wash off road chemicals to prevent corrosion and use dielectric grease in all connectors.” For more maintenance tips, read the sidebars in this feature.
Major causes of safety lighting failures & how to prevent them
Grote Industries LLC offers the following tips to prevent lighting failures:
Corrosion
Cause: Corrosion is the results of water, dirt and other environmental elements of the road and surrounding conditions.
Solutions: Corrosion around the bulb sockets cannot approach the bulb when it is sealed within a lamp housing. All electrical wiring connections should be sealed against moisture with a non-conductive, non-sodium based grease. Areas like electrical contacts, circuit switches and junction boxes. The purpose of this sealant is to totally encapsulate the area to protect it from the elements.
Shock & vibration/filament burnout
Cause: The constant road pounding caused when a tractor/trailer or truck is traveling down a highway is a major cause of shock and vibration. This causes filaments in the bulb to weaken and prematurely break.
Solutions: Install a lamp designed with shock-mounted mechanisms to cradle the bulb and absorb the effects of shock and vibration that otherwise would be transferred directly to fragile bulb filaments.
Advanced technology today includes baseless bulbs that are suspended and thus able to endure heavy-duty applications much more that the traditional S-8 non-shock -mounted bulb units or the standard J-slot bulb socket.
Inadequate wiring & cable
Cause: Cutting and splicing, or the merging of varying harness and wiring systems that are not designed to work together –– thus breaking the system’s modularity. Trying to cut costs with varying systems or scrimping on product quality.
Solutions: Suitable wiring can have a positive effect on product life and cost reduction. For example, a sealed waterproof wiring harness system should be selected based on the electrical load of the vehicle, applications and with regard to avoiding excessive voltage fluctuation. A larger gauge wire than required can be used in any circuit for minimal additional cost while at the same time offering reliable results.
The quality of the wire is very important. Stranded copper wire, which has a greater capacity to conduct electricity should be preferred. Galvanic action can form oxides at crimp connections in aluminum wire, limiting its ability to carry current. Copper wire can resist heat better than aluminum wire in the case of short circuits, thereby reducing the possibility of fire.
There are harness systems available that exceed industry standards, eliminate troublesome splices, seal out the elements, provide a common ground and last the life of a trailer.
Excessive voltage
Cause: It has been determined that as many as 60 percent of bulb failures are not in fact as they appear. Such deceptive indications have been the result of problems in the wiring system, either due to poor grounding or a problem inherent to the electrical system itself, that has produced a voltage surge and affected the lighting system.
Solutions: Voltage should be checked regularly to ensure the vehicle is operating within a safe range. Only one volt beyond the designed voltage will reduce the expected life of a bulb filament by more than 50 percent.
An application solution is to bring down the overall power consumption of your entire system. This can also be accomplished by utilizing the power economy levels of LED lighting.
Poor grounding
Cause: Open chassis grounding to elements and/or inefficient ground secure.
Solutions: Installing a lighting product and harness system that uses an internal ground will help assure an absolute ground –– forever. This internal ground also helps to eliminate rust and corrosion associated with chassis grounds.
Loss of bulb contact
Cause: In the traditional S-8 non-shock-mounted bulb units and the standard J-slot bulb socket, loss of contact is caused by corrosion and/or loss of spring tension.
Solution: With the inception of the sealed baseless bulb lamp and soldered connections, product life is further enhanced.
Physical damage
Cause: No protection to a lamp in an open area. Heat generation with no method to dissipate the heat. Housing or lenses made of inexpensive plastic compounds.
Solutions: A super-tough high-impact plastic that’s impervious to heat generated by the bulb and damage resulting from typical use answers this problem.
Both lenses and lamp housings should be manufactured of a space-age plastic. Using recessed mounts and branch deflector designs further protect lamps from impact damage. Lighting guards are also perfect protection for the physical lamp.
Preventive maintenance technical tips
Truck-Lite has outlined the technical procedures for troubleshooting lamps:
1. Never use a test probe to pierce wire insulation when troubleshooting lighting complaints. Wicking action takes place, which causes moisture to travel along the wire strands and corrode critical connections. If probing a harness or wire is necessary, make sure the puncture is properly sealed.
To correct voltage problems, discover the real cause. Under-voltage often is caused by poor electrical connections. To correct under-voltage, don’t just turn up the voltage –– find out what caused the under-voltage problem.
2. Detect lamp condition. Many discarded lamps are still in good condition. Play detective when solving lamp problems. First, test with either a meter, power supply, or battery. Then if you desire, open the lens on a discarded lamp and examine the bulb. It will tell you why it failed. For example:
A bulb with stretched or broken filaments was subjected to vibration.
A yellowish, whitish or bluish glaze on the bulb indicates a rupture in the bulb glass envelope.
A dark metallic finish indicates old age.
A black, sooty bulb indicates a poor seal in bulb.
Test all lamps one more time before you discard them. Truck-Lite’s warranty department reports that up to 20 percent of all lamps sent back are still in good operating condition. The ones that aren’t working can be turned over to your lamp supplier.
3. Help lamps run cooler. Dirt on the lens increases the heat, so keep them as clean as possible. Other people can see your rig, and that is one of the purposes of the lighting system –– to be seen. Certain lighting products generate heat. Care should be taken to avoid contact with flammable materials.
4. Treat the electrical system as you would the chassis. Lubricate sockets, pigtails, battery terminals and connections with NYK 77 "non-conductive" anti-corrosion compound. The purpose of the sealant is to totally encapsulate and protect against corrosion and water.
5. Inspect for improper ground connections. This is a major cause of lamp failure, especially when the trailer is used for a ground. When lamps are grounded through the lamp housing, make sure there is a clean connection (i.e., metal-to-metal). Also, a fifth wheel ground strap may be used for added protection on the chassis ground system.
6. Look for loose, bare or unsupported wire, and fixtures. Harnesses and wiring should be on the underside of top frame members rather than on the bottom where dirt and road splash collect.
Always replace wiring, trailer light cables, and harnesses with an equal or heavier gauge of wire than was used in the original specifications. If you don’t, you may cause unnecessary problems.
7. Lights out. On older trucks, you should never crank the truck when any lights or accessories are on. Also, never leave markers and hazard lights on when parked against a dock. Melted lenses are a sure sign that the vehicle has been parked against the dock while the lights were on.
8. Inspect the grommets that house the lamps. As they age, they eventually will deteriorate from sunlight, ozone and harmful chemicals. New grommets restore shock protection, security and improves appearance.
