### Author Topic: Battery Power Density / Energy Density and more...  (Read 3870 times)

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#### vidam

• Supreme Robot
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##### Battery Power Density / Energy Density and more...
« on: December 20, 2007, 09:28:40 AM »
I'm reading the specifications for a battery but can't say that I really understand them:

Energy Density: 400 KJ/kg
Power Density: 2500 W/kg
The battery is capable of  2000 J, 100 Watts and can deliver 100 W for short periods of time

I have been starring at wikipedia trying to understand the meaning of it all. Can anyone tell me how to interpret the meaning of these specs in layman terms.

• Supreme Robot
• Posts: 11,680
##### Re: Battery Power Density / Energy Density and more...
« Reply #1 on: December 28, 2007, 03:11:05 PM »
400 KJ/kg means that it holds 400 KJ of energy for every kg in weight

2500 W/kg means that it holds 2500 W of power for every kg in weight

Just multiply that value by the weight of the battery to get the final value you need.

I assume you read up on watts and joules in wikipedia?

#### vidam

• Supreme Robot
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• Robotronics.org
##### Re: Battery Power Density / Energy Density and more...
« Reply #2 on: December 28, 2007, 03:27:56 PM »
The battery weights 0.005 kg. So that means the battery has 2000 Joules in energy density.  The power density is 12.5 Watts. They claim that the battery can deliver 50 Watts instantaneously. How is this even possible if the maximum power density is 12.5 Watts. Am I completely confused?

• Supreme Robot
• Posts: 11,680
##### Re: Battery Power Density / Energy Density and more...
« Reply #3 on: December 28, 2007, 03:38:09 PM »
hmmm I just noticed you had:
Power Density: 2500 W/kg

are you sure it isn't 2500 Wh/kg? Notice h, meaning hours, where Wh/kg is power density.

Quote
They claim that the battery can deliver 50 Watts instantaneously
The total amount of energy a battery has, and the total amount the battery can supply at any given time, aren't the same thing.

#### vidam

• Supreme Robot
• Posts: 423