24V DC Back Up Supply

Last updated on 23/6/24

This part of Technical Section provides a guideline into setup of Back Up battery supply to your PA installations. Also highlighted are the precautions required to a proper and safe installation method in battery connections with relation to using Amperes BC9740 back up battery charging unit.

Minimum Battery Capacity Required

The battery capacity required is subjected to either the availability of these :

a. Building with back up generator :

The minimum capacity to maintain the system operation for at least 6 hours, after which it is able to operate evacuation broadcast in all zones for at least 30 minutes.

b. Building without back up generator :

The minimum capacity to maintain system operation for at least 24 hours, after which it is able to operate for at least 30 minutes.

Minimum battery capacity required :

Cmin = 1.25 ( ( T1 x I1 ) + D ( I2 x T2 ) ) Ah

Cmin - Min capacity of battery when new at 20 hr discharge rate at 20 deg C in Ah

1.25 - Ageing factor allowing 5% per year for 4 years

T1 - Battery standby period in hours

T2 - Alarm time in hours ( as 0.5 or 30 minutes )

I1 - Battery standby load in amperes

I2 - Batery alarm load in amperes

D2 - Battery de-rating factor ( Usually 1.75 for inefficiency of battery under load )

Source : BS5839-1 : 2013 : annex D

Connections of small loads

This is an example for connecting back up supply for small loads, typically less than 25A at 24V DC.

The power packs linked in series to form 24V, shall be terminated at BC9740 Battery Charger's BATT IN terminals and thereafter to PS9400 Power Supply's Batt connectors.

WARNING :

Ensure that the appropriate size of connecting cables are used to suit the total loading. In this setup, we recommend 2.5mm with high temperature PVC insulation cables.

Connections of large loads

For larger load which may exceed 25A, it is required to use external contactor to connect the DC back up supply to the amplifiers DC input. AC or DC contactor may be used with suitable contact rating.

WARNING :

Ensure that the appropriate size of connecting cables are used to suit the total loading. In this setup, we recommend cable size of 2.5mm and above with high temperature PVC insulation cables.

Cable size of back up supply

Cable size used to connect the battery bank and the loads ( particularly power amplifiers ) must be suitable to carry the amperage during full load. Failure to adhere or using undersize cable may lead to fire.

Proper connections with cable lugs is recommended and the route of the cable should not mix or should be separated from other cables such as signal or amplifier output lines.

The cable chart provides a guideline to selecting the proper size. It is important to note that the carrying capacity may differ subjected to how the cables are run and the ambient temperature.