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Know your Application

AGM battery technology is moving quickly into the trucking industry, bringing with it the benefits of a dry energy system. But even though OEs such as Freightliner have either adopted AGM technology or are considering doing so, there still...


AGM battery technology is moving quickly into the trucking industry, bringing with it the benefits of a dry energy system. But even though OEs such as Freightliner have either adopted AGM technology or are considering doing so, there still remains a fair deal of confusion about proper spec’ing and handling practices in the industry.

Brad Bisaillon, North American sales and marketing manager -commercial truck for Trojan Battery, did his best to set the record straight about AGM technology at the recent CFMS.

First, some basics about AGM batteries. They get their name from the fact they are designed to carry the electrolyte suspended in Absorbed Glass Mat separators. They are 95% dry and so can be integrated conventionally or on their sides. They can be installed inside of a truck’s side box or under the bunk. They have a service life of four to seven years when the correct application is considered and are not as susceptible to freezing issues found in conventional batteries.

Bisaillon pointed out that today’s batteries are application-specific, and so before choosing a battery, it’s important to determine what you need the battery to do:

• Does it need to start a vehicle?

• Does it need to deep cycle (for applications such as battery-powered APUs or air conditioners; power inverters or lift gates)?

• If multiple power sources are required, are the banks separated?

• What is the available recharge time?

• What is the recharge profile of the battery?

• Is the current alternator sufficient?

Batteries produced for starting or dual purposes are designed to deliver a large starting current for a very short period of time. They have a large number of highly porous thin plates made of a high lead content. The quantity of high porosity plates is what delivers high cranking ability. The initial reserve capacity of such batteries is close to 100%, but the capacity does decrease over time. Positive plate degradation is the leading cause of catastrophic failure, Bisaillon said, adding that cycling a pure lead, thin plate starting battery will quicken this process.

“When used for cycling, a starting/dual purpose AGM battery will generally fail after 50 to 200 deep cycles. They are only 85% efficient when cycling,” he pointed out.

Cycling batteries, meanwhile, are designed to be discharged to as much as 100% depth of discharge cycle after cycle. They are constructed with fewer but more robust plates, up to seven times the thickness of a starting battery. The lead content of the plates is blended with stronger alloys. Cycling batteries contain a higher density, controlled porosity paste chemistry to give the plate better structure and allow the current to be drawn more slowly for longer periods of time. This makes for less surface area, Bisaillon explained, which means they have less “instant” power than starting batteries. Batteries designed solely for cycling will typically have less than a 600 CCA rating, compared to 800 and up for starting batteries.

AGM batteries should be charged with an AGM compatible charger. AGM “bulging” is a result of improper charging causing heat. AGM and conventional batteries should not be charged together, Bisaillon warned.

Proper connections at the battery are critical to proper charging, but are all too frequently not taken into consideration, Bisaillon added. The battery stud is generally stainless steel, which has high electrical resistance. Connections reliant on the stud will produce excessive heat and thus poor battery recharge and premature alternator failure. The flat surface on the terminal should be used at the connection point. The lead metal there provides for the most reliable connection with the least resistance.

“All too often, an improper connection at the alternator is the root cause of a battery failure or misdiagnosed battery failure,” Bisaillon said.


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