Calculate mJ to kW?

[taahace]

Hey, I dont have any clue about electricity units at all.
I have the modular armor with an exoskeleton. I also have 4 Batteries with 20mJ. The Exoskeleton states it uses a maximum of 200kW.
Now I have 2 questions:
1. How long will the batteries in my armor last?
2. per which time will the 200kW be used? Per second? Minute?
Thanks :D

[Fel]

1W is 1J for 1 second.

20MJ / 200 kW = 100 seconds

But batteries are not producing power, they can only store it so the math is probably a bit more complex than that when you take into account the power generators you have in your armour.

[PunCrathod]

1 joule per second is equal to 1 watt.

[Dunhill]

1. Assuming you have no energy generation, they'll last for 100 seconds at full load.
2. Per second

If you do have energy generation (and you should), divide the battery capacity with just the power deficit (assuming there is one, but if there's not, they'll last forever) instead of the full power consumption. The actual power consumption will be quite a bit lower with exoskeletons than their max consumption, as you'll probably be walking maybe 50% of the time, rarely in very long intervals.

[Z0MBE]

1 killowatt is 1000 watts / kilo meaning 1000
1 megajoule is 1000 watts x 1000, or, one million watts / mega meaning 1 million
1 GigaJoule is 1billion watts, 1million x 1000 / giga means 1 billion


or giga Example: gigawatt 10^9
mega 10^6
kilo Example: kiloliter 10^3

[Fel]

Originally posted by mccafferty.max:

1 megajoule is 1000 watts x 1000, or, one million watts / mega meaning 1 million
1 GigaJoule is 1billion watts, 1million x 1000 / giga means 1 billion

Was this intended?
If yes it's hillarious but I can't be certain.

[jagholin]

Originally posted by mccafferty.max:

1 killowatt is 1000 watts / kilo meaning 1000
1 megajoule is 1000 watts x 1000, or, one million watts / mega meaning 1 million
1 GigaJoule is 1billion watts, 1million x 1000 / giga means 1 billion


or giga Example: gigawatt 10^9
mega 10^6
kilo Example: kiloliter 10^3

Once again, this time correct:
1. 1 kilowatt(1kW) is 1000 watt(W), kilo == thousand.
2. 1 megawatt(1MW) is 1.000.000 watt(W), mega = million
3. 1 Watt = 1 joule(J) / 1 sec(s), therefore 1 J = 1 W * 1 s
4. milli means 1 thousandths, and it is usually written as small "m". => mJ - millijoule, mW - milliwatt. Don't confuse this with mega-, which is usually written as big M ( MJ, MW ).

Joule is a measure of work/energy, Watt is a measure of power(energy per time unit).

PS. People also often use killowatt-hours (kWh) when measuring electricity. However this unit is somewhat misleading because it denotes energy, not power, even though it has "watt" in its name. 1 kWh = 1 kW * 1 h(hour) = 1 kW * 3600 s(sec) = 3600 kJ, which is an energy quantity indeed.

[AlexMBrennan]

However this unit is somewhat misleading because it denotes energy

It's as misleading as using "lightyear" for distance - you should be fine as long as you don't stop reading halfway through the word.

[Fel]

It's more misleading than that because we haver the bad habit to omit the "per" when talking about units in our everyday life (at the very least it's the case around here).
The biggest of such examples is with speed, we say kilometer hour or meter second (well, not in english).

At least for lightyears most people grasp it quickly but for watt-hours only a minority can tell with certainty if it's a multiplication or a division for the "hour" (especially since it's Joules, an unit that already exists as the base for watts).