Suppose I have a solar powered plant like this one below:
The solar panel charges the batteries and, when needed, the power is drawn from the batteries to power the load which in this case could be a DC motor or an AC motor depending on the application. For the sake of this example, let's say this is a 24V DC motor. Suppose the controller is just a switch.
By taking a look at the datasheet of some of the loads, most of them need a very high current at the start. For instance a centrifugal pump I took as example needs 78 A at the start.
From a theory point of view, if I consider the battery an ideal voltage generator, there is no problem. Furthermore, since 78 A are drawn for just a small time (suppose 1 second for the sake of argument) during the start up and then the load starts to draw the usual working current which is far lower than, 78 A, not that much extra-work is required from the battery after the startup.
However, batteries are far from being a perfect voltage generator, how can I understand if a battery is able to withstand such high current draw? A 120Ah battery in principle could easily do this since in theory it could supply 120 A for 1 hour (and in my case I just draw 78 A for a second) but I have some doubts that this reasoning could hold in practice.
Please address the following points in the answer:
- What is the technical parameter in the battery datasheet I should be looking at? (Max current draw??)
- What is an appropriate rule of thumb to address the start up current draw while not under/over sizing the battery package?
- Are the reasonings above correct? (at least in theory)