By Paul Abelson
senior technical editor
Traditional batteries use technology that dates back centuries – back to iron nails in ceramic jars of salt water. Today, the automotive power crowd continues to scramble for ways to create a larger charge that lasts longer, travels better, weighs less, etc.
One industry guru says the next major development in batteries is absorbed glass mat technology, where the liquid electrolyte that normally floods the plates inside is trapped in the sponge-like separator material. Therefore, it’s non-spillable, even if punctured.
Bruce Purkey of Purkey’s Fleet Electric Inc. in Rogers, AR, is known as “Dr. Electricity” among his peers. At the September meeting of the Technology & Maintenance Council, Purkey and others discussed AGM technology and other gains in battery technology.
Purkey said AGM technology overcomes most disadvantages of flooded cells, but they “need more TLC” than the flooded cells. Land Line asked Purkey in late September to further explain AGMs.
“I truly think it’s the right move for the industry, but there’s one important thing we have to keep in mind about these AGMs. We have to service, charge and attach them properly. We have to learn how to take care of them,” said Purkey. “Because while they offer a lot, it’s a ‘starved’ battery and they are not going to be as forgiving as the old flooded cells.”
“Starved” means the battery contains just enough electrolyte to provide the necessary chemical reaction, as opposed to the older flooded design.
“We were never very good at taking care of the old flooded cells and they took a lot of abuse. These AGMs won’t. With an AGM, you can’t do something dumb like leave a boost charger on overnight. Remember, these batteries were really designed for the telecommunications industry, which has to have long standby power. These are built to much tighter specification than flooded cells are. That’s why they cost more.”
Why are Purkey and others so high on AGMs? The construction itself gives AGM batteries some serious plus marks. AGMs use fine-strand fiberglass mats to completely contain electrolyte and separate plates. The cases are completely sealed so the batteries will not leak acid, even when completely upside down. And there’s more.
Because the electrolyte is held to the plates by mats, separators and grids are not needed. More battery volume is available for plates, and for a given surface area plates can be thicker. So for a given measure of cold cranking amps, more reserve capacity is available.
AGMs weigh considerably more than flooded cells, because they contain more lead. While flooded batteries use alloy for strength, AGMs use almost 100 percent pure lead. That yields greater electrical density. The lead in AGMs doesn’t need as much structure. Room given to the reservoirs for flakes and electrolyte can now be filled with plates.
Because of their advantages, AGMs can last up to twice as long as flooded cells, while providing more amperage for longer periods. That’s why AGMs are used in most battery-powered, idle-reduction devices, such as the Bergstrom NITE system and Mack’s IdleFree.
Not all roses with AGMs
First, the AGM batteries are expensive – often three times the price of a flooded cell battery. Because they are heavier, revenue considerations may prevail if you’re hauling weight-sensitive loads.
As Purkey said, AGMs have special maintenance considerations, too. Special testing equipment is required. A common carbon pile load tester could burn out an AGM battery. Special testers are available through battery manufacturers.
Charging loads are different, too. Fully discharged AGM batteries require a three-step charge profile, with a rapid build-up from zero to 14.7 volts with a steady current followed by a longer absorption charge at a steady 14.7 volts with decreasing current. After that, a 13.6-volt low-current float charge will maintain the charge, provided the charger has automatic circuitry to protect the battery.
Ordinary chargers that immediately put up to 17 volts on a discharged battery will cook the insides of an AGM battery. As reported at TMC, untrained technicians have destroyed many AGM batteries by using the wrong equipment and wrong procedures.
Note this: Chargers that have output voltage less than 14.2 volts or more than 15 volts for a 12-volt battery should not be used with AGM batteries.
So, of the automatic chargers on the market, which is the best? Those that read battery voltage and adjust the charge rate accordingly – the type that brings the battery to 14.5 volts, then maintains a trickle charge of 13.6 volts indefinitely – are preferred over those that shut off, then charge again at full voltage after the battery drops below a minimum.
When spec’ing alternators for use with AGM batteries, consider including 20 amps for each battery in the bank. For example, a five-battery rack for a Mack or Dometic HVAC unit should have 100 amps more than a normal alternator. The old standard of 135 amps to 150 amps no longer applies. Alternators approaching 300 amps are available, and should be specified. LL
Seeking more electricity per pound
Truck batteries used to have only four tasks: to start your engines, light your lights, run your fans, and play your radios. Now, with increased anti-idling regulations and greater demand for driver comforts, batteries have additional jobs.
They run the refrigerators that replaced ice chests, the coffeemakers that replaced thermos bottles, and the microwaves that replaced take-out sandwiches. They run more interior lamps that light larger spaces, and they power computers and entertainment systems – including stereos, TVs and DVD players never imagined in trucks a generation ago.
And the greatest demand on their power and endurance is just emerging – providing creature comforts for increasingly longer periods with the engine off.
The most common batteries have lead positive plates and alloy negative plates, separated by inert dividers. Dilute sulfuric acid is the most common electrolyte. Research to find materials that store more electricity per pound or per cube is being stimulated by the development of hybrid cars and trucks.
Exotics such as nickel metal hydride and polymer technologies are effective, but still far too costly for traditional use. But variations of lead-acid batteries, such as gel cells and absorbed glass mats (AGMs), are offering improved performance and durability.
Many truck owners, fearing further restrictions on APUs and generators, are opting for hybrid (diesel-fueled heaters coupled with electric air conditioners) or battery-powered HVAC systems. A rack of five or six Group 31 batteries weighs about the same as one generator. LL
What’s next? Ultra what?
The next great advance in technology will probably be the ultra-capacitor, or UC. One Group 31-sized UC has the power to start any big bore diesel. In a nutshell, capacitors store electrons on their inner surfaces, rather than using electro-chemical reactions to release electrons. They can discharge rapidly – and recharge almost as rapidly – often within seconds, because of their internal carbon structure. Other noteworthy facts:
If spread flat, the Group 31 UC’s surfaces would cover the area of 13 football fields.
If the engine is slow to start, a capacitor can be recharged from any 12-volt battery, even one too weak to start an engine.
One ultra-capacitor teamed with three deep-cycle or AGM batteries in a standard battery box could handle starting loads and most hotel loads for a 10-hour layover. LL
The new Firefly Oasis? Promises, promises
A brand-new Firefly Oasis Group 31 battery was announced about a year ago, and there’s been some exciting talk at several industry events about this new metal foam technology. But, so far, nobody has actually seen one.
For those readers who have inquired about the Oasis and when that product will be available, we talked to Firefly Energy about the progress of its battery. Product Manager Dave Ginder reported that production validation runs have been completed. The company is expecting to deliver product for field beta testing at a number of truck fleets, truck OEMs, battery HVAC manufacturers and others. Ginder said the first production run is targeted for late this year. LL
– By Land Line staff
Alternators: the essentials
Electrical loads draw current from batteries. They must be recharged by putting current into the battery with greater force than the battery has. Each cell of a fully charged battery produces about 2.1 volts. A fully charged battery produces
12.6 volts. To recharge, alternator output is regulated to between 13.4 and 14.2 volts.
Alternators create current by harnessing the mechanical energy of the engine through belts and pulleys. When a wire is passed through a magnetic field, current flows in the wire. A pulley attached to the shaft of the alternator is rotated inside a set of windings, creating a magnetic field and current flow to the battery.
The flow of electrons into the battery reverses the chemical reaction on the plates, converting lead sulfate back to pure lead and strengthening the sulfuric acid in the electrolyte.
Alternator bearings fail because of contamination or pulley misalignment. Check for both during every service interval.
Alternators are now available with output approaching 300 amps to restore the large amounts of current used to provide hotel loads and HVAC from battery-powered idle-reduction systems. LL
– By Paul Abelson, senior technical editor