Electrical systems and batteries

Electrical systems and batteries

Strategies and devices to keep power available for cranking and other vehicle electrical loads

Nothing is more important than being able to start your truck and maintain electrical loads, says Darry W. Stuart, president and CEO of DWS Fleet Management Services. But modern commercial vehicles have never had so many accessories putting demands on the batteries essential to cranking the engine. To maximize the use of stored electricity on the vehicle, fleets have to control how much energy goes in and comes out of the vehicle’s entire electrical system. Managing that energy begins with spec’ing the right batteries, alternators and cables, and includes knowing your options for devices that can limit over-discharging and maintain sufficient battery-charging ability.

The right battery
The three main lead-acid battery types now used on commercial vehicles include traditional flooded-cell, absorbed glass mat (AGM) and gel-cell batteries. Where once batteries were needed solely for cranking the engine, they now are called upon to power a wide range of always-on electronics devices, liftgates and hotel loads. Bruce Purkey, president of Purkey’s Electrical Consultants, says the flooded-cell battery, while it is fine for powering intermittent high-drain loads such as engine cranking, is not designed for long-term, deep-discharge loads such as powering motors, A/C compressors and cab comfort electrical demands.

He notes the industry is moving toward AGM batteries that will cycle (a complete discharge and recharge) two to three times more than a flooded-cell battery. AGMs offer more run time because they pack more lead in the given space. However, Purkey warns that there will not be much of difference in the run time (how long the battery can continue to provide useable power to start and run hotel or sleeper loads) between an AGM and flooded-cell battery, maybe a 35% increase, according to his tests.

Jeff Coleman, director of OE sales, East Penn Manufacturing Co. Inc., explains that both acid-in-gel and AGM designs protect the plates during heavy, deep-discharges, but the properties of the gelled electrolyte make it even better suited for super-deep discharge applications like HVAC and APU systems. He adds that AGM batteries excel for high current, high power applications and in extremely cold environments.

Kalyan Jana, development support manager – specialty markets for EnerSys (makers of Odyssey batteries), says the main advantage of gel cells is their ability to cycle better than conventional AGM cells. However, he adds that thin plate pure lead (TPPL) AGM cells offer cycle life that is comparable with gel cells. In addition, TPPL cells can be rapidly recharged (more than 80% state of charge in about 30 minutes).

Maintaining charge
Managing batteries is really a very simple process to calculate as long as one has accurate numbers to use in the calculations, says Purkey. If more is put back in than is taken out, the battery pack should work well. The key to charging batteries is to have enough amps at the correct voltage at the battery pack. If there are voltage drops in the charge circuit, very little current can be “pushed” though the batteries even though there are plenty of amps available. You must have both voltage and amps available to be successful in charging, says Purkey. Enersys Odyssey Group 31 AGM battery

Powering liftgates
Liftgate batteries face real issues with voltage drop from the length of the circuit and the number of connections. Purkey says liftgate batteries rarely get charged correctly due to lack of voltage, resulting in short battery life and poor liftgate service due to discharged batteries.

To addresses the voltage-drop from running auxiliary equipment such as liftgates, Purkey helped to develop a controller that automatically chooses the optimal source of power to fully charge liftgate batteries without the risk of draining power needed to start the engine, run the refrigeration unit and maintain the integrity of the electrical system.

Marketed as the Permalogic Selector System from Phillips Industries,  Purkey describes the unit as a DC-to-DC converter that delivers the right voltage despite varying ambient temperatures. “Think of it as a voltage amplifier to compensate for drops from cold weather.”

The system automatically selects the tractor or the trailer’s reefer unit as the source of power to continuously charge the liftgate batteries to capacity. The system automatically shuts off if it senses a problem with the reefer’s electrical system. It will not cause issues with either the reefer unit or the tractor, says Phillips Industries.

Low voltage disconnects
Even when a vehicle is turned off, loads begin to run down the battery. One way to control the amount of power being drained is to use low voltage disconnects (LVDs). The main reason for using an LVD is to protect the starting power and life of a primary battery, says Geoff Schwartz, senior sales applications engineer for the Cole Hersee Co. As the battery runs down, the LVD shuts off power to non-essential (non-safety related) loads to assure that the battery has enough power to restart the vehicle. If the voltage goes above the reconnect voltage, the LVD reconnects the loads automatically.

Cole Hersee offers LVDs at various amperage ratings to work with inverters installed in sleepers, liftgate motors and electric-powered compressors.

Master disconnect switches
Master disconnect switches are designed to isolate the battery from the electrical system, primarily for safety. By isolating the battery, the master disconnect prevents injury to technicians troubleshooting or repairing the electrical system. It also will keep batteries from running down when a vehicle is parked for long periods. Cutting off the battery with a master disconnect removes all parasitic loads and small leakage currents that will kill a battery over time. When spec’ing a master disconnect, be sure that you are looking at both the continuous duty rating and the intermittent duty rating, says Schwartz. Size the continuous rating of the switch to the rating of the alternator, and size the intermittent duty to the CCA of your starting battery bank.

Battery isolators
Typically used in multi-battery bank applications, battery isolators allow you to charge multiple batteries from a single charging source without the risk that running down one battery will affect the other. The two basic types are one-way diode isolators and “smart” isolators or combiners. The former links a single alternator to two or three battery banks via a diode bridge. Advantages are no moving parts and it is always connected.

Smart isolators or combiners are a return to the solenoid/relay systems of the past, but improved with control electronics, says Schwartz. Because there is a direct connection, the alternator throws a full charge to the primary battery. Only when the primary battery has sufficiently charged does the auxiliary battery hook up to the alternator.

Smart isolators offer features you cannot get in diode isolators, such as start boost where a momentary switch hooks in the auxiliary batteries to aid in starting. Dual charging is valuable if the vehicle is set up for shore power. A smart isolator monitors the voltage in both battery banks, so if the auxiliary bank reaches 13.2 V, it will reconnect starter and auxiliary batteries, allowing the shore power to charge the starting battery bank.


Battery Safety Tips

East Penn, maker of Deka brand batteries, offers these charging tips:

• To avoid a battery explosion, never attempt to charge a frozen battery. Allow it to warm up to room temperature before placing on charge.

• Never overcharge batteries. Excessive charging will shorten any commercial battery’s life. Prior to charging, read the manufacturer’s instructions for proper charger hook-up and use. Turn charger off prior to hook-up to avoid dangerous sparks.

• If violent gassing or spewing of electrolyte occurs, or the battery case feels hot to the touch, temporarily reduce or halt charging.

• Gel and AGM batteries require a voltage-limited charger. Charging a gel or AGM battery on a typical shop charger may greatly shorten its life.

• Many common battery chargers are not fully compatible with AGM batteries; however, they will not ruin an AGM battery if used a few times over the battery’s lifetime in a commercial application. Large “wheeled chargers” must be avoided. Do not exceed 15.4 V at any point of its charge cycle.

 

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