A few questions regarding theory.

[simple295]

Hi, I am new here

I have a strange obsession with human generated power, such as using hand generators to power my everyday things. I'd like to roughly be able to figure out how many kilocalories(food calories) I would consume to charge a battery.

Lets use a 1000 mah 3.7 volt battery rated at 4 watt hours. Simply using google, I found that its 1.16 watt hours per kilocalorie. That seems like I can charge my cell phone with only about 5 calories, or one gram of sugar. Of course there are many inefficiencies, I know the human body is about 25% efficient, and the hand generator is probably 75% efficient, and the battery probably is about 75% efficient too.

Is my math correct though? In perfect conditions, should it only take 4 kilocalories to charge that 4 watt hour battery?

 

[Laplace]

Relevant conversion factors:

1 watt-hour = 3,600 Joules
1 food calorie = 4,186 Joules
1 gm sugar = 4 food calories

So, 4 watt-hr = 14,400 Joules = 3.44 calories = ~1 gm sugar

 

[simple295]

I had a feeling my calculations were correct. Its just amazing to me, I have a 1/10th scale RC car that is insanely powerful(hits 50mph, and 0 to 40 in about 2 seconds) and to think its only running on 30 calories.

Or my cell phone, which can create a LOT of heat, only uses about 5 calories.

I find it amazing how energy efficient these things are.

 

[daddles]

One of the most heavily-used programs on my computer is the GNU units program. It allows you to effortlessly convert amongst all the screwball units humans have come up with:

You have: 4 kcal
You want: J
        4 kcal = 16747.2 J

I recommend it because of mistakes like Laplace made -- 4 thousand times 4 is 16 thousand, not 14.4 thousand. And we humans often make arithmetic mistakes.

 

[poor mystic]

Another seemingly incurable human foible is refusal to standardise on units. The dieticians, for a glaring example, have their own name for a standard kilocalorie... they call it a calorie!
This has caused many people to gasp in amazement at the efficiency of biological processes.

 

[daddles]

Agreed; look at the thousands of silly units in the GNU units program. Most nontechnical people don't understand the problem -- they use whatever units people use locally and think everything is hunky-dory. But when you range over a wide field of technical problems, these silly units cause lots of problems.

And when someone says it's just a tempest in a teapot, you can point them to a NASA Mars mission that went kablooie and lost 100 million dollars or so because of a simple units problem -- and there have been cases where people lost their lives because of a unit problem.

If I was an all-powerful despot of the world, my first despotic act would be to mandate that everyone would use the SI system for measurement. Anybody violating this mandate would be beaten to death with a yardstick.

OK, truth in advertising requires me to say my first despotic act would be to kill off all the politicians. THEN I'd deal with the units.

 

[poor mystic]

Dieticians the world over are shaking with fear of Daddles Khan.

 

[daddles]

Careful, or I'll put a bug in your ear...

 

[Laplace]

I recommend it because of mistakes like Laplace made -- 4 thousand times 4 is 16 thousand, not 14.4 thousand.

Laplace said that 4 x 3,600 = 14,400

 

[daddles]

Laplace, I apologize -- I made the mistake. The bug goes into Daddles' ear.

 

[davenn]

Laplace, I apologize -- I made the mistake. The bug goes into Daddles' ear.

Hmmmm wonder what Sigmund Freud would have to say about some one bugging their own ear with a truth generating insect ??

D

 

[daddles]

Well, the bug is installed. The only thing the bug will allow me to say now is that my humility is only exceeded by my competence. Well, except where arithmetic with units is involved...