Battery of Tests to Gauge SLA Battery Status
The rechargeable lead acid battery is a technology that was designed in 1859 by the French physician Gaston Plate. Today, it is still used to provide critical security system back-up power. Through the years, this technology has evolved into a cost-effective, low-maintenance storage device, which is today referred to as the sealed lead acid (SLA) battery.
Alarm service techs and dealers will tell you that servicing system batteries is at the top of their list. However, it is probably one of the least understood components in a modern-day security system.
This month, we will look at some key servicing and specifying points of the SLA battery. Understanding these operational and testing basics will make for a more profitable alarm dealer and a happier customer.
Make Cash, Keep Customers Happy
Dealer A receives a call from a customer who was awakened in the middle of the night by a beeping keypad indicating a “low battery.” When the junior technician goes to the panel, he takes his digital voltmeter (DVM) and reads 13.8V across the 12V battery and figures all is OK.
Since he is a newbie, he radios his supervisor who asks if he has removed the leads before testing. He had not and proceeds to test the battery again. This time it reads 12.7V on a 12V battery. The customer is told all is well.
The following night the tech is called back with another low batter alarm. The tech finds a spare battery in his service truck and replaces the bad one, billing the customer for a new battery. Next — you guessed it — the customer has another low battery, calls the alarm company and tells the dealer to remove the alarm system.
On the other hand, Dealer B has signed a new customer up for annual inspections. During the third annual inspection the battery is tested with a battery capacity tester analyzer, which indicates the battery is at 75-percent capacity. The tech shows the battery reading to the customer and gets replacement approval. No frustrating nighttime battery calls.
The situation with Dealer A might seem extreme to experienced techs, but it happens more than you might imagine. It is important to understand that using a DVM to test a battery charge level only works if the battery is placed under a load with no power source. In the case of Dealer B, new conductance technology testers allow techs to test the condition of a battery’s capacity to deliver backup current and inform the customer it is time to replace the battery.
Using Old-Time Testing Methods
The “Sparky” test method (see photo on page 20 of January issue) is one in which a short is applied to battery terminals. The theory is the brighter the spark, the better the battery. While this is a quick, convenient dynamic test, it places severe and damaging stress on the battery’s plates. It is not an accurate test and should not be used.
The “disconnected battery” test is a quick test in which a DVM is used to test the battery’s voltage after being disconnected from the alarm panel. Before disconnecting the battery, it should read about 13.5V. After disconnecting the panel’s battery lead, you should not see any noticeable voltage drop across the battery.
If the battery drops to say around 13.2V, then replacement or further testing should be done. If the battery quickly drops to 12V, a replacement should be seriously considered. This again is a quick test and is not dynamic in that an external load has not been introduced to the battery.
The “equipment load” test is done by removing the AC panel power and placing a DVM across the connected battery, using the existing alarm system as a load. A connected 12V battery should read around 13.5V before AC is removed.
Remove the AC power and you should immediately see only about a 0.1V drop, with only a few tenths-of-a-volt drop during the next 15-30 seconds. Again, if the battery quickly drops to 12V or less, a replacement should be seriously considered.
Activating the alarm system sounders will cause the greatest equipment load on the battery, but still should only cause less than a few tenths-of-a-volt drop in the first minute. Since you may not know exactly what the load is, this is another form of estimating a bad battery.
The “external load test,” which is popular with many technicians, consists of removing external power to the 12V battery and placing an external load — such as a 10-15 ohm, 25W wire-wound resistor — is placed with the DVM in parallel across the removed battery. You should not see the battery drop below 10V after a minute or so under load. This is a common dynamic test that many techs use to estimate if a battery is still good. CAUTION: Resistor is HOT!
Modern Analyzers to the Rescue!
Some of the above test methods are OK for estimating if a battery is still holding up. However, they do not provide an accurate method to test how long the battery may last. David Grant, managing director of Act Meters Ltd., comments, “The problem with these methods is that, unless the load and duration is relative to the stated Ampere-hour capacity, they can pass a low-capacity battery.”
An example of a “load-type tester analyzer” is Stone Technologies’ STC-612A (www.stonetechnology.com). This is a dynamic 6V-12V battery tester that will test both the battery charging circuit and capacity. It places a low 24ma current load on the battery. The tester has a simple good/bad display, which easily shows the customer the battery status.
A “conductance tester” tests the capacity of a battery by sending small signals through the battery’s plates. The measurement unit for conductance is mho (ohm backwards) and is displayed in testers such as the ELKBLTv2(www.elkproducts.com). If a battery capacity is displaying below 70 percent to 80 percent, a battery change is recommended.
Some manufacturers, such as Act Meters Ltd., have testers like the GOLD-IBT that display additional information (see photo) like the battery’s amp-hour (AH) capacity. ACT’s pulsing technology allows a battery’s capacity to be measured in seconds with no risk of arcing or sparking. Check out the additional battery test tips on the company’s Web site (www.actmeters.com).
Bad Batteries Cause False Alarms
According to the False Alarm Reduction Association (FARA), “If a customer has a false alarm after a bad storm, it may have been caused by a weak back-up battery.” FARA has a brochure at its Web site (www.faraonline.org/battery_bulletin.pdf) that can help enforce battery replacement and maintenance service suggestions to your customers.
New SLA batteries from your supplier should be fully charged. You should also make sure stored batteries are kept at around 70° F. Charge inventoried batteries every month as the internal discharge rate can beas much as 0.5 percent to 1 percent per day. A degragation process called “sulfation” will begin to take place on the plates of partially discharged batteries. Once this starts, the SLA battery will have a difficult, if not impossible, time achieving a new full charge. This is what happened to the battery used from dealers A’s truck.
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