Powering Stand-Alone Electromechanical Locks

Stand-alone electromechanical locks require battery power to operate. Most network-capable, stand-alone electromechanical locks have a battery-condition indicator. As the battery in a networked lock begins to reach the level at which it should be replaced, the software typically can notify about this condition. This simplifies the process of battery replacement.

However, for non-networked locks, the story is very different. The average lock manufacturer designs locks with sufficient battery power for at least one year plus a margin of safety. Most lock manufacturers recommend replacing their batteries usually once a year.

Different electromechanical locks can have different sizes and numbers of batteries to ensure at least one year of normal operation. However, depending upon the actual number of operations (cycles), the batteries may need to be replaced sooner or last longer than one year.

Power draw and the resulting battery life is dependent upon the functionality and operational features of the electromechanical lock. For example, the Samsung EZON Digital Keypad Deadbolt has a stated battery life of 3,650 operations for the two AA batteries. The lock’s power requirement was designed around 10 operations a day for this touchscreen, motorized deadbolt lock. When the correct code is entered, a motor engages and retracts the bolt its one inch throw. When leaving and closing the door, the motor again engages and extends the bolt one inch. The motorized bolt requires a significant amount of power in addition to the power requirement of the touch screen and the electronics.

The Arrow Revolution is also a touchscreen operated lock. However, the Revolution has a battery life of approximately 20,000 cycles for the four AA batteries.

Note: Some lock manufacturers list the number of openings or cycles an average electromechanical lock can operate during the life expectancy of the batteries. Others indicate the number of years of operation using one set of batteries.

For non-networked locks, there are three general methods for determining battery replacement. The first method is checking the batteries at a regular interval by walking up to each lock, removing the batteries and determining their condition. This method requires a great deal of time and labor.

The second method is preventative replacement at a set time interval. A predetermined date is chosen for batteries to be replaced. If the facility has many electromechanical locks, preventative replacement may be the best method. Replacing all batteries at one time may prove to be fiscally and time wise the most practical.

The third method is to depend upon the “low battery” warning. The premise is that someone will notify you there is a sound coming from the lock and it is unusually slow to unlock. Or the other possibility occurs. You get an angry telephone call notifying you that people are locked out and cannot gain access and the meeting was supposed to start five minutes ago.

There are different methods devised by lock manufacturers to notify of low battery condition. The commonality is that when the batteries are in need of replacement, the lock will do something - flashing LEDs, beeps or tones, slow the lock unlock time, etc.

The Samsung EZON Digital Deadbolt Lock has an interesting method for notifying when the batteries need replacing. When unlocking the lock, the melody “Blues for Elise” sounds. This is the indicator the batteries have been depleted to the level of requiring replacement. The batteries must be replaced within approximately one week of hearing this melody. If the batteries are not replaced, the lock will continue to operate and play the melody until the lock fails to operate.

Most standalone locks have a key override that is used when the batteries are dead or the electronics are no longer operating. If there is no key override, most of these locks have contacts or a port to accommodate a backup (usually a nine volt) battery. Providing power should permit a User Code to be entered and to unlock the lock.

Battery Life Calculations

How long will the batteries actually last in a particular lock installed into a door? This can be determined by figuring out the number of times access is gained through the door. This can be the actual (or a rough guess) of how many times a year a particular lock will operate. Counters can be installed at the top of the door for a given period of time. Then multiply the number of days, weeks, etc. to come to one year.

Another option is to use a set of calculations to determine the average usage. High Traffic can be considered 100-200 openings per day; Medium Traffic can be considered 50 openings per day and Low Traffic (residential or limited operation) can be considered 25 openings per day.

To round out the traffic level numbers, the high, medium and low openings are for 365 days. Therefore, a 100- opening High Traffic door will have approximately 36,500 to 73,000 openings in a year. The Medium Traffic door will have 18,250 and the Low will have 9,125.

Using these numbers is a good way to gain an idea of the time a set of batteries will last in a particular lock once you know an average number of cycles. For example, according to Securitron, the six AA battery equipped SABL® has been tested for over 100,000 cycles, two year average battery life. Using 36,500 openings in a year provides a comfortable excess to insure two years of operation.

I have not included doors that are in very high usage such as a large department store, office/manufacturing facility or entry door for a commercial building as most of these doors are operated using high energy operators with sensors. For these applications, the number of openings will probably range from 1,000 cycles per day and up.

Note: The ANSI/BHMA Standard A156.2: Locks and Latches, Series 4000 Bored Lever Handle and Knob Sets Cycle Test for  Grade 1 cylindrical locks is 800,000 cycles.

Most standalone, electromechanical door locks are powered using AA Alkaline batteries. A notable exception and possibly a look into the future is the Alarm Lock Networx Lock. Alarm Lock has increased the battery size for the Networx Locks to operate using four “C” alkaline batteries. As a result, the Alarm Lock Networx locks have a stated five-year plus battery life.

OK, so what about the batteries themselves? When we purchase batteries, is particular company you prefer? There are Eveready, Energizer, Ray-O-Vac, Duracell to name a few, as well as custom brands including Sanyo, Maxwell or Motorola. Most brands have reasonable quality batteries.

When buying batteries for a remote installation, it is probably a good idea to purchase a battery tester. This way the batteries installed into the lock can have the same voltage. The battery testers range in price from a couple of dollars up depending upon where you buy them. Note: Most alkaline batteries are considered dead when the voltage drops from fully charged at ~ 1.5 volts to 0.8 volts.

Choosing The Right Battery

All batteries are not the same. They vary by manufacturer, models and individual batteries. AA alkaline batteries are the recommended battery power for most electromechanical locks. Alkaline batteries, developed in the 1950s, have a higher energy density and a longer shelf life than the standard or heavy duty batteries. The difference between standard, alkaline and lithium batteries is the composition and the way the stored chemical energy is converted into electrical energy.

Points to consider:

• Batteries (cells) still in their packaging can lose upwards of 10 percent of their original charge every year. Some battery packages have a date stamp.
• Putting batteries in the refrigerator or freezer can slow this discharge rate. Not all batteries operate properly after they are frozen.
• Do not install a refrigerated (cold) battery until it is warmed to room temperature.
• When replacing batteries, make sure that all of the batteries are the same type, strength and age. Do not mix alkaline and nickel oxide or any other batteries. Batteries that have been on the shelf for more than one year should not be mixed with new batteries or used batteries in a lock.
• Do not mix rechargeable batteries with non-rechargeable batteries as rechargeable batteries have less voltage (approximately 1.2 volts instead of 1.5 volts).
• Do not use rechargeable batteries in electromechanical locks unless approved by the lock manufacturer. The lower (fully charged) voltage may cause problems as a four battery lock will have only 4-8 volts instead of 6 volts.
• Batteries wear out faster in warmer climates or if the lock is installed onto a hollow metal door facing east.

IMPORTANT: Lithium batteries are not recommended for use with electromechanical door locks for two reasons. Their life expectancy does not follow a calculable pattern, removing any timeframe for usable battery life. They operate and then stop almost immediately, providing no room for gauging replacement time or knowing when the batteries are loosing charge. Another reason is that Lithium batteries can have too rapid a discharge resulting in overheating, rupture, and explosion.

Overheating or leaking can also occur in alkaline batteries if there is too rapid a discharge or with rechargeable batteries that are too rapidly charged.

According to the All About Batteries web Site: http://www.allaboutbatteries.com, the average voltage for a “AA” alkaline battery is 1.5, the same as a “C” alkaline battery. Aside from the shape, the difference between the two batteries is the milli-Amp hours (mAh), the Watt-hours (Wh) and the Joules (J).

The milli-Amp hours for a “AA” battery is 2122 and for a “C” battery is 7800. The Watt-hours for a “AA” battery is 2.60 and for a “C” battery is 9.56. The Joules for a “AA” battery is 9360 and for a “C” battery is 34398.

The “C” battery has approximately 3.67 times more milli-Amp hours, Watt-hours and= Joules than a “AA” battery.

A battery’s voltage declines steadily during use. Alkaline batteries are optimal for intermittent of light load continuous duty. Electromechanical locks normally draw a light load when being operated.