Emergency Lighting
Battery Chargers

The batteries of an emergency lighting unit must be kept in a ready state in order to provide emergency power during a power loss. This is done by connecting a charger to the battery to maintain the charge during stand-by mode.

The specific application will govern the type of charger and charging method used to keep a battery in a ready state.

There are three basic chargers;

1) Constant potential charger - This is the most common and is used where a long term charge is expected. It reduces overcharge current and prolongs battery life. As the battery terminal voltage rises, the current to the battery is reduced. When the regulated voltage is reached, a final trickle current of 10 to 100 milliamps is supplied to keep the battery at ready state.

2) Constant current charger - This is used where the battery will be cycled regularly with relatively short period of over charge. Normal charging is completed in 16 to 24 hours. A relatively stable current is used to charge the battery for a complete charge cycle. A voltage or time monitor is used to turn the charger on and off.

3) Dual Rate Charger - This provides rapid charging of a constant current charger and low float current of the constant potential charger. A relatively stable current is used to charge the battery during the first portion of the charging cycle. Once it reaches a predetermined voltage, the current begins to reduce until it reaches float voltage. At that point a trickle current is supplied to the battery to offset self discharge of the battery.

*** Note: In many cases if the indicator light stays bright on a dual rate charger for more than 24 hours it is likely the battery is bad. What is happening is the charger is trying to charge a battery that will not accept a charge.

Troubleshooting

Unit is Dead -

No AC Power Present. Apply AC Power

AC Lockout-

Most manufacturers have a standard feature called AC Lockout. This feature prevents battery discharge through the DC transfer circuit prior to the initial application of AC power. The AC Lockout feature allows the unit to be installed with the battery connected, completely ready for operation at any time prior to the availability of AC power. The purpose of the AC lockout is to allow the contractor the freedom to install the equipment when it is convenient for them and not have to return later to connect the battery after the circuit is energized with AC power.

*** Note - An important fact regarding AC lockout is that, in being a transistor controlled circuit, it is subject to the low leakage currents inherent with these semiconductor devices. In order to avoid battery damage it is recommended that unit be energized within 30 days after installation.

Battery has good voltage, but unit does not work.

Batteries must be checked under load. This means when you check the battery voltage you must disconnect AC power or hold the test switch. This will allow lights to come on and load the battery. Only now you will see the true voltage of the battery. If battery voltage drops below 87.5% of battery nominal ( 6V battery is 5.25V) the battery is bad.

*** Note - When a battery is bad, the battery voltage is likely to drop below the 87.5% mark very fast and rise back up to original voltage. This is the LVD doing it’s job.

LVD -

Low Voltage Disconnect -

This circuit is in most equipment using lead acid batteries and is required by the National Electrical Code for emergency lighting equipment. It is designed to disconnect the battery at aprox. 87.5% of battery nominal. It serves two main purposes.

1) Maintains a constant level of light during discharge. ( If battery would drop lower than 87.5% of nominal, lights would start to get dimmer and not provide the same level of light. )

2) Protects the battery from deep discharge. Lead acid batteries discharged below 87.5% of nominal will decrease in capacity and not perform properly.

Battery test’s OK but unit still does not work.

Check the light bulbs.

In cases of older unit or units that are frequently used it is possible that all of the light bulbs can be burnt out. Usually in cases where units are neglected and have not been serviced for quite some time.

Check voltage at PC board for DC voltage where lamps connect while pushing test switch or removing AC power. If no DC is present recheck battery connections. If all connections are good, it is possible the transfer portion PC board is bad. In many units this circuit can be damaged if battery was installed with polarity reversed even for a very short time. Check at lamp socket for DC voltage. If DC is present the bulbs are burnt out or the socket is defective. If no DC voltage is present check all connections.

If you need additional help in troubleshooting your Emergency Lighting Equipment

or need batteries or replacement parts, please Contact Us or Call 800-706-7009 for assistance.