I Have recently found in one site, the batteries box fitted far away from the fire alarm panel, say 25-30m, the question is:
1- Would that distance affect the batteries capacity calculation?
2- Would that distance cause volt drop?
I also found in some other different sites, the batteries box fitted in the basement while the main panel fitted in ground floor entrance, the distance is about 60m
This has no apreciable effect on the battery capacity calculation.
There are obviously
some volt drop issues. However fire alarms take relatively small currents and 60m of, say, 1.5mm cable would add very little volt drop even on full load. Obviously all volt drop on full load needs to be taken into consideration but it is likely to be a small problem in most cases.
The big problem with remotely sited batteries is the volt-drop affecting the charge circuit monitoring. This is not a problem on remotely sited batteries that also contain the charging circuit. The voltage of a battery is critical in the decision of how an automatic charging circuit will decide on how to continue charging it.
For example,a nominal 24v fire alarm system, will charge it's SLA batteries to obtain a full charge indicated as something in the the region of 27.5V. i.e below this voltage the charger will continue to try and charge them to reach that voltage and when it reaches it, the charging current rate will reduce to give them a trickle charge.
If you try to charge above trickle charge rate when the battery reaches it's fully-charged state (as indicated by a voltage of approx. 27.5V) then this will damage the batteries by overcharging them.
Therefore if your batteries are sited 60m away from the charging circuit, when the charging circuit monitors the battery voltage (to determine their charge state) it may get a reading of, say, 26.5V and decide it needs to continue charging the batteries at a higher than trickle charge rate. However if your 60m of cable is actaully causing a 1V volt drop due to the length of the connecting cable, then the batteries are actually at 27.5V (and fully charged). The false battery voltage reading due to the volt drop will cause the charger to carry on charging at a higher than necessary rate and damage the batteries.
In my experience, even a distance of a few metres between charging circuit and battery creates enough volt drop to affect the charging circuit and a 2.5mm or 4mm battery connection is required. You might find that 60m of cable requires a very hefty sized cable to get around the problem!
