Last Post 09 Nov 2012 03:43 PM by Niel. 1 Replies.
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New Member
New Member

09 Nov 2012 12:20 AM
    Would like to know how to determine the remaining power margin left in a battery after use. I have a 4Ah nicad battery that was at 30V with a 3A load for 750 seconds. At the end of the 750 seconds the battery voltage was 28.2V. Just want a rough way to calculate, not worried about heating or internal resistance of each of the cells.
    Basic Member
    Basic Member

    09 Nov 2012 03:43 PM

    You have use a total of .63Ah from the Battery (3A x 750seconds). This means that you have used approximately 15% of the batteries rated capacity. Unfortunately, the rating of batteries is usually based on a 10 or 20 hour rates, the 4Ah assumes that the draw on the battery is 0.4A (10 hour rate) or 0.2A (20 hour rate) at a current draw rate which would drain the battery in 1 1/3 hours you will not get the full rated energy from the battery.

    Still you can the voltage curve of a NiCad to make an estimate. Here is a website that describes the process for a particular battery. Curves may be available for your battery.

    Niel Leon