Alarm Battery Question

[steveo44]

How do you work out the calculations for a 7.0 amp standby battery to last 12hrs please? I think i am right in saying that 15mins alarm time should be included in the calculation.

standby current 290 milliamps
alarm current 520 milliamps

is it

290 x 11.75 = 3407.5
520 x 0.25 = 130

3407.5+130=3537.5

3537.5/12=294.80

7000/294.80=23.74 hrs?

 

[TheAlarmMan]

Essentially yes.

Draw / Battery
290ma / 7000ma = 24.12hrs

However bear in mind when a battery ages it capacity can reduce, also alarm panels will only stay stable down to 11v ish. As the battery drains the voltage drops, so although there will still be current the voltage will disappear and the panel will become unstable.

So try not to put a 3.2aH battery in because it meets the 12hr min but rather stick a 7aH in.

I personally have 17aH batteries on my home alarm, even though mine is installed to BS regs which states 8 hour min.

 

[steveo44]

Essentially yes.

Draw / Battery
290ma / 7000ma = 24.12hrs

However bear in mind when a battery ages it capacity can reduce, also alarm panels will only stay stable down to 11v ish. As the battery drains the voltage drops, so although there will still be current the voltage will disappear and the panel will become unstable.

So try not to put a 3.2aH battery in because it meets the 12hr min but rather stick a 7aH in.

I personally have 17aH batteries on my home alarm, even though mine is installed to BS regs which states 8 hour min.

Good advice.

Another question, should the milliamp reading be only taken when the battery is fully charged as the charging of the battery would affect the reading?

 

[TheAlarmMan]

Which mA reading, battery current, battery load, aux load, battery charge current?

 

[steveo44]

Which mA reading, battery current, battery load, aux load, battery charge current?

battery load when mains is off.

 

[TheAlarmMan]

Yes in theory, although unless very discharged the current drawn from the battery should remain the same.

Remember testing load from battery when mains is off is only giving the current drawn, if you want to calculate how long that will last you need to know the current capacity of the battery.
Just because a battery is 7aH doesn't mean it actually is!

ACT do a range of battery capacity testers.