# watts vs joules energy

Discussion in 'General Electronics Discussion' started by supak111, Nov 9, 2012.

1. ### supak111★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

327
4
Apr 29, 2012
Hey everyone. I'm building a coil-gun and I'm having some trouble understanding the amount power it will use. If anyone could help me clarify this I would very much appreciated it.

Lets say that I build an electric coil and use: 10amp at 12v and I leave it ON for 1 FULL HOUR, so that means it used 10amp X 12v = 120 watts. Now to get the joules I simple multiply the 120watts X 3600 (seconds in 1 hours).

So does that mean in 1 hours coil used 120w x 3600 s/h= 432,000 joules?

If so does that also mean the coil used 120 Joules per every second that it was ON?

Thanks guys

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,192
2,694
Jan 21, 2010
OK

No, that means it was using power at a rate of 120W (Or it was dissipating 120 Watts) for that hour.

Yep.

Yep.

Since a Watt is defined as 1 Joule per second, the answer must be yes.

However "using" bay be too strong a word.

Also, if the coil is highly inductive and has a low resistance (as it probably should be) then it may be using 120VA, but dissipating (or using) far less than 120W.

It all depends on whether the 120W is the real or apparent power.

Thanks guys[/QUOTE]

3. ### supak111★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

327
4
Apr 29, 2012

So this is what I'm getting at, if my coil-gun is powered by a single 120Joule capacitor, and I want the capacitor to fire once per second (60 times per min), will my 10amp at 12v power supply be enough to charge the capacitor? Or about enough I will take into consideration of the charging efficiency loses.

Actually this is my exact setup: 1 120v 120j capacitor (16666uf). Power supply would be batteries in series to make 120v at 1amp then right?

I'm also unsure how to calculate how long will it take for the above cap to recharge with the above power supply?

4. ### BobK

7,642
1,662
Jan 5, 2010
dV/dt = I / C

At 1A a 16666 uF capacitor will charge at a rate of 60V / second.

Bob  