**The importance of reducing small loads**

The small loads in many installations tend to be ignored on the basis that they don't really make much difference when compared to the effect of the larger loads.

This can sometimes be foolhardy. Once again, we have Peukert's effect to thank for the fact that the small loads can actually make an enormous difference to the available run time.

Let's look at a typical installation. It is very difficult to say what a "typical installation" is, but most that we come across (that have been specified and installed correctly) tend to give about 24 hours run time from a full recharge down to 50% state of charge.

The discharge on this battery bank will be a mixture of very heavy draw for short periods of time, medium draw for longer periods of time, and very small loads on for very long periods, or even on permanently.

Let's compare the effects of reducing a heavy current draw item to that of reducing a small current draw item. What is important here is that we do not consider reducing loads by a certain fraction or percentage. Reducing 2 different sized loads by, say, 25% will increase the available run time by the same amount in each case. What we have to consider is reducing a load by a fixed amount, say 1 amp, or 5 amps, or whatever.

If it wasn't for Peukert's effect then reducing the current draw of any item by a fixed amount (say 2 amps) would make no difference to whether the load was a heavy draw item or a small draw item. The effect on the available run time would be the same. However Peukert's effect is real, and the results of it are real. They are also extremely illuminating.

Due to Peukert's effect being exponential, the smaller the current draw, the more difference it makes to the available run time when this current draw is increased or decreased. Simply have a look at the graph on the Peukert calculator and you will see that small changes in current draw make a much greater difference to the available battery capacity at the left hand side of the graph.

Use the Peukert calculator and enter a battery capacity of 400 amp hours at the 20 hour discharge rate. Set Peukert's exponent to 1.3

In the user input box at the bottom enter a discharge current of 50 amps. You will see it calculate a total run time of 6.08 hours to 0% state of charge. Now change the discharge current to 49 amps (a reduction of 1 amp). You will see the run time has increased to 6.24 hours (remember these are decimal hours - not hours and minutes). This is an increase in run time of 2.6% for a reduction in discharge current of 2% (this can also be calculated by mutiplying the reduction in discharge current as a percentage by peukert's exponent i.e. 2% reduction * peukert's exponent of 1.3 = 2.6% increase in run time).

Now enter a discharge current of 5 amps. The available run time will be 121 hours. Reduce this to 4 amps and the available run time increases to 162 hours, an increase of roughly 34%