MadSci Network: Engineering

Re: Working power from battery? misc power questions

Date: Tue Jul 25 05:07:51 2000
Posted By: Jonathan Feldman, Undergraduate, Applied Chemistry, University of Technology, Sydney
Area of science: Engineering
ID: 961091678.Eg

To answer the first question, Yes, there is a difference between mA and 

mAh is the abbreviation of 'milli-amp hours'.  It is the product of current 
('Amps') and time (hours).  mAh is a measure of the total energy available 
from the battery.  If your battery indicated 1.5 mAh, that means that it 
will supply 1.5 mA for 1 hour, or 3 mA for 1/2 hour, or 0.75 mA for 2 hours 

Incidentally, you need to be careful with the use of the word "power", 
since power is the RATE OF ENERGY USAGE, ie. it is a function of time, and 
its standard units are Joules/Second or Watts.

This leads me on to your next question.  
I'm not quite sure what you mean by 'draining the battery better', but I 
take it to mean that it will drain the battery in a shorter time.

A certain amount of energy is available from your battery (in your case, 
1.5 mAh).  A bulb that draws more current, will drain the battery more 
quickly.  Now, a higher wattage bulb draws more current than a lower 
wattage bulb, so hence, the higher wattage bulb will drain the battery more 

As long as the bulb is rated at the correct VOLTAGE (3.0 V), it should not 
blow.  Using a higher VOLTAGE bulb, will not blow the bulb, but it won't 
glow as bright, using a 3.0V battery.

As for the battery re-gaining charge, that is a question for the chemists 
among us (which includes myself), but I'm not sure on the answer for that, 
so if anyone else who reads this knows why it happens, let us know!

I hope this answer has been useful,

Jonathan Feldman
University of Technology, Sydney

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