IN PRINT: Power Plays — Using the right battery opens up many fuel- and money-saving opportunities
Posted: November 30, 2017 by Jim Park
No longer are fleets stuck using the same old batteries for starting and lighting as well as hotel loads and auxiliary loads like lift gates. With several different types of energy-storing devices on the market, savvy fleets can spec’ the right component for the job and see potentially huge paybacks. But there’s a catch. You have to look at the electrical system as several sub-systems, each with a different purpose.
In bygone years, flooded lead acid batteries performed well enough in starting, lighting, and ignition applications. Because of their construction and chemistry, they are prone to degrading from deep voltage draws, over-charging, and physical damage. While this type of battery is reliable and inexpensive, it isn’t well suited to modern sleeper applications because of their hotel loads, and it can fall short in regional and Pickup and Delivery operations because of the high number of starting cycles without enough driving time to recharge the battery.
Absorbed Glass Mat (AGM) batteries are far more tolerant of deep discharge cycling in applications where power is drawn down slowly over long periods of time. They are great for powering invertors used for TVs and microwave ovens. They’re good for electrically powered climate control systems, too, but capacity can be an issue. On a full charge, a set of four AGM batteries will generally keep the system running for six to eight hours if the cooling demand is modest. However, if they aren’t fully charged at the beginning of a duty cycle, operating times can be considerably less. The AGM batteries will also start a truck, making them a good dual-purpose battery, but a bank of four may not have enough reserve capacity for starting if the demand from hotel loads is high. Low-voltage disconnects will protect the truck for starting, but electric HVAC performance can suffer.
About five years ago, ultra-capacitors appeared on the market. These are not actually batteries at all, although it’s easy to call them that, much to the chagrin of their producers. Ultra-caps, as they are called, do not produce energy as batteries, but instead store energy drawn from traditional batteries. Ultra-caps are used primarily for starting. They are very good at providing large surges of current for short periods of time. They are impervious to cold and can recycle their charge very quickly.
“With batteries it’s like pouring water out of a bottle,” says Jeff Brakley, OEM/distribution sales manager at Maxwell Technologies, a provider of ultra-capacitors. “With ultra-caps it’s like dumping water out of a bucket. You’re dumping a lot of power really quickly, and then it also recharges very quickly.”
Unlike batteries that rely on an electro-chemical reaction between lead plates and sulphuric acid to produce electricity, ultra-caps use an electro-static reaction to release stored energy. Ultra-caps use thin strips of metal separated by a non-conducting electrolyte material rolled tightly into spools and wired in series inside a Group 31 container.
When connected to a battery, random positive and negative ions in the metal align themselves into positive and negative, and build up on the charged metallic surfaces. The resulting imbalance of positively and negatively charged metal strips creates a strong electric field between them, separated by the electrolyte material. Once each of the metallic strips has reached its full positive or negative charge, the transfer of charged ions ceases and the electrical field keeps the strips in their positive and negative states of charge. This state can be maintained almost indefinitely.
The charge is released when a load is introduced and the circuit is closed, allowing the ions to flow between the strips, returning them to an electrically neutral state. This return to neutrality happens very quickly at a relative low voltage but very high amperage. This is what makes the ultra-cap an ideal power source for engine starters.
Brakley says ultra-caps – or Engine Starting Modules (ESM) as Maxwell calls them in this application – are no good for deep-cycle applications like hotel loads. “It’s for starting, and starting only,” he says. “The ESM handles all starting requirements, so you don’t need high CCA (Cold Cranking Amp) batteries to start your truck.”
The Maxwell ESM will provide enough current flow to turn the engine over for about 15 seconds. Once depleted, it can fully recharge in about 15 minutes. Interestingly, the ultra-cap doesn’t require great amounts of current (only 12 amps) or voltage to recharge, so it can be recharged by a battery that would be deemed dead for traditional starting purposes.
“We regulate the discharge, so that we deliver about 1,800 amps to get the engine turning over, and then scale back to about 1,600 amps to keep it turning,” Brakley says. “As long as you have enough charge in the battery to run the electronics that control the engine, which could be as low as 11 volts, the ESM will turn the engine over.”
Ultra-caps can be charged and discharged millions of times without ever wearing out; they are very light and contain no dangerous or toxic chemicals. Nor are they affected by low temperature. Cold will slow the electro-chemical reaction in a lead-acid battery, reducing its charge considerably, but the electro-static process in a Maxwell ESM is unaffected by temperature.
Ultra-cap & AGM
Combining an ultra-cap engine starting device with a bank of AGM batteries might be the solution to most electrical power needs. Some AGM batteries are now billed as dual-purpose, such as the Odyssey Extreme Series from Enersys. Bruce Essig, national sales manager for Odyssey Battery, says the construction of the battery and used materials give it the flexibility to deliver deep-cycle discharges for hotel loads, and high-current, short-duration discharges for starting.
“Aside from the hotel loads we see on highway trucks, even city delivery trucks can deeply cycle their batteries through multiple starting cycles on routes that don’t allow enough time to recharge the battery while driving,” Essig says. “Traditional [lead-acid] batteries don’t respond well to deep discharges, and will typically have pretty short lifecycles.”
While AGMs, especially the dual-purpose AGMs, are capable replacements for lead-acid batteries, there are still a few difficulties to be overcome – the capacity for hotel loads, and cost.
Essig says his Odyssey Extreme AGM costs roughly three to four times as much as a typical flooded lead-acid Starting Lighting Ignition (SLI) battery. An ESM ultra-cap can cost upwards of $1,000. Those are scary numbers when you’re used to paying around a hundred bucks for a lead-acid battery. There is, however, a pretty convincing business case for making the additional investment in migrating toward AGM batteries and an ESM starting system.
In an example related by Essig, Walmart Transportation recently switched from SLI to AGM batteries, and found that batteries were lasting the 1.5-to-2.4-million-kilometer life of the truck. The fleet was averaging three sets of lead-acid batteries in each truck over its life. That just about covers the upcharge of switching from lead-acid to AGM. On top of that, battery-related problems all but vanished. Essig says Walmart reported a huge decline in the number of jumpstart incidents.
“Walmart was spending something like (US) $1.3 million a year on jump-starts alone for its 8,600-truck fleet before the switch,” Essig says. “That doesn’t include the cost of possible tows, the cost of the replacement batteries, labor, downtime, driver and customer dissatisfaction, etc.”
As for reserve capacity, some fleets now double down on the AGMs, running two banks of four – one dedicated to starting, lighting, and ignition, with the other bank for hotel loads. You could dispense with the four AGM starting batteries and replace them with an ESM, but that would leave room in the battery box for only three hotel deep-cycle AGMs, and that may not be enough.
“At an 80% depth of discharge, even our Odyssey Extreme AGM only has 400 cycles,” says Essig. “In a year, you could potentially cycle a three-battery system right out, where you’ll usually get four to five years out of a four-battery system.”
Brakley says the ideal place for the ESM is the battery box, but it doesn’t have to live there. AGMs and ESMs can be stored inside the truck because there’s no danger of an acid leak or dangerous fumes, so there’s little to stop you from placing an ESM somewhere else on the frame, or even inside the cab or under the sleeper.
“The only concern is the length of the cable from the terminal on the ESM to the starter,” he says. “You would have to consider the gauge of the cable and make sure it has the proper capacity for the length of the run.”
Essig suggests fleets consider a bank of four AGMs with a super-cap starting system for maximum flexibility and performance. While pricing always varies with the vendor and manufacturer, such a system could easily cost north of $2,000. But when you think of all the problems you’re eliminating, including inconvenient jump starts, battery replacement costs, unhappy drivers, service calls, and additional shop labour, rolling the extra upfront cost into the price of your next new truck might be the way to go.