I want to understand how calcutaing power draw works ?

Other Hardware General Electronics
1

I want to understand how calcutaing power draw works ?
I understand the concept of mAh . like 2000 mAh will give me 2 A for 1 hr , 4 A for 30 min and 1 A for 2 hrs .
Can anyone please explain ?

2

manveen_singh:
I understand the concept of mAh . like 2000 mAh will give me 2 A for 1 hr , 4 A for 30 min and 1 A for 2 hrs .
Can anyone please explain to me the power draw with the following example.

This is not exactly right. There is something called final voltage of the battery cell. For example:
If you are using rechargeable lead-acid battery of 6-cell 12V/60Ah, you can draw 60A current until the battery terminal voltage goes down to 11.4V (6x1.9) called final voltage. There is no guarantee on the usable life span of the battery if the battery is allowed to discharge below the final voltage which is usually specified by the manufacturer.

3

I understand the concept of mAh . like 2000 mAh will give me 2 A for 1 hr , 4 A for 30 min and 1 A for 2 hrs .

The above is not strictly true. The 2000mAh rating is done at a specific current draw. Capacity is reduced at higher discharge rates and increased at lower discharge rates. So, for instance, 2A for 1 hour, 4A for 20 minutes and 1A for 2.5 hours. Temperature also effects the real discharge curve. Consult the battery data sheet for the ratings. See here for more information.

4

manveen_singh:
I want to understand how calcutaing power draw works ?
I understand the concept of mAh . like 2000 mAh will give me 2 A for 1 hr , 4 A for 30 min and 1 A for 2 hrs .
Can anyone please explain ?

If i understand your question then the answer is this:

It is OHM's law. In DC you multiply the current drawn by the load with the voltage of the source and you get the power consumed by the load.

For example a 12V source is fed into a 12V fan and the fan draws 100ma Then the power consumed by the fan is 12V x 0.1A = 1.2Watt

5

Hi All,
With regard to amp-hour ratings:
common lead-acid, gell-cell, glass mat,
or nicad cells are rated in milliampere-hours
based on a 20 hour discharge rate at a
certain temperature, I think 25 degrees C.
The discharge test continues until the safe
limit of terminal voltage has been reached.
(This was mentioned before and is very
important!) So if you discharge a battery
faster than that, it will show a lower capacity.
Also, if you allow it to heat up, it will show a
lower capacity.
I hope this helps.
Herb

6

thank you for all your help