Hi

 

How would you work out how long a battery will last?  I have a 3.2ah battery but id like to know if it will last 24 hours. 

 

http://www.actmeters.co.uk/alarm-advice/fault-finding-a-guide/

 

Using the act fault finding guide i have measured the standby current as 225 milliamps. so 3.2ah/225 = 14.22 hours. is this correct please?

 

 

Edited September 22, 20178 yr by Stephen Gibbons

yes you need a bigger battery. Also A/h is based on a 24hr discharge and only while brand new you will loose 10% in the first couple of years

13 hours ago, james.wilson said:

yes you need a bigger battery. Also A/h is based on a 24hr discharge and only while brand new you will loose 10% in the first couple of years

 

10% i cannot find anything to relate to that figure.

 

All seems a bit confusing. Looking on the net there seems to be a few different calculations.

 

What is meant by de-rating factor and aging factor? 

 

 

the capacity of the battery lowers with age and conditions etc

21 minutes ago, james.wilson said:

the capacity of the battery lowers with age and conditions etc

 

is there a recognised formula you guys use to calculate this please?

If the battery is a C20 (most likely) then Ah ratings are measured over a 20 hour period. If the battery is discharged quicker than that you loose out on amp-hours.

 

On a bells only domestic you would normally require a standby time of 12 hours with one (15 minute) activation. You also don't want to run close to that figure due to above and also ageing and environmental changes so therefore use the next battery up if within 10%. So you need the standby current and the alarm current for your calculations.

Unless your firing off lots of high amperage sounders, I would estimate a good quality 7Ah battery is required from your standby values.