LITTLE RED BOOK OF BATTERIES

Choosing the correct size of battery

As mentioned earlier, batteries come in all shapes and sizes, from types no larger than a shirt button, to a battery system filling an entire room.

To find the size of battery you require you generally need two pieces of information battery load and back-up times. (Note; other factors may also have an effect).

Battery Load

Whether you power lights, motors, electronic equipment or a toy vehicle your equipment will draw a load in AMPS. If this is unknown then the equipment will have a rating expressed in Watts which may simply be converted to Amps by dividing the value by the normal voltage of the system.

Example You have chosen NPC for high cycle life and wish to drive a power tool rated at 120 watts 12 volts.

Load current = 120 divided by 12 = 10 Amps

Back-up time

This is the time you require the battery to support the load described above and is often called Autonomy or discharge time.

Example To power a cordless electric tool for a total of 3.0 hours before recharging.

With these two pieces of information use our selection graph to plot an intersection point from which you will determine a required size or capacity in Amp. hours (Ah).

Our figure No. 1 has been rationalised into rounded figures of capacity. If your intersection point falls between two lines choose the next highest value.

Fig No.1 NP Types

Always choose a suitable sized battery from the ranges appropriate to your application.

You may notice that the chosen capacity in Amp hours is often higher than the Value of Amps x Hours used, in our example using 10 AMPS x 3 HRS = 30 Ah and the chosen option being 38Ah. This is because the capacity 'cA' of each NP battery is stated at the 20 hour discharge rate. You will only get full capacity if discharged over that length of time.

Note:- This explanation is a simplified version, if in any doubt call our Technical department on 08708 500312