NissanLeafCamper said:
GRA said:
If you look at Tony Williams' Range chart (you did print yourself out a copy for the appropriate battery capacity, didn't you? If not: http://www.mynissanleaf.com/viewtopic.php?f=31&t=4295&hilit=range+chart ), immediately below the Miles/kWh in the top box is the kW power draw used for speed in 5 mph increments. 35 mph on flat ground etc. requires 5.56 kW, 40 mph takes 6.78 kW. Drive for one hour at those power draws in those conditions, and you will have used 5.56 or 6.78 kWh, so 6 kWh would probably be around 37 or 38 mph. In other words, you aren't going to be doing that on a freeway (at least I hope not).
Hey thanks!
I actually had looked at the tables but I was having trouble understanding them
Now they make more sense now that I put 2 and 2 together.... So then every 4.3 miles going at 55mph drains about 2 hours worth of lv2 charge? That is, uh, that is a lot. I'm surprised it gets drained by that much. I do a 18 mile fwy trip to a location once a week. So if I go at 55 mph that is about 8.2 hrs worth of lv 2 charge??? I think I am still not understanding this right....
You've got that last statement correct
4.3 is the miles per 1 kWh @ 55 mph, so if you want to see how far you could go on 6 kWh at that speed, just multiply 4.3 miles/1 kWh x 6 kWh = 25.8 miles (kWh cancels out). You were originally asking something else, what speed you could go that would use 6 kWh in one hour. That's the next line down, which tells you the power draw at various (constant) speeds. In the case of 55 mph, the power draw is 12.79 kW, so (checking to make sure the above answer is in the right ballpark) it's fairly obvious that you'll be able to drive a bit under 1/2 hour at that speed and use 6 kWh. 12.79 kW x 0.5 hr is a bit over 6 kWh (6.395 if you want to be precise). Since one half hour at 55 mph will take you 27.5 miles, and per the above we figured that you can actually drive for a bit under 1/2 hour at that speed and use 6 kWh, 25.8 miles looks to be correct.
If you're still confused, remember that watts, W is the basic unit of electrical
power (for EVs we're usually using the kilowatt, kW, or units of 1,000 watts as it's a more convenient size*) , while the watt/hour, Wh (again, for EVs usually the kilowatt/hour, kWh) is the unit of
energy. If you use a power of 1 kilowatt (1 kW) for 1 hour, you've used 1 kWh of energy (1 kW x 1 hr = 1 kWh); use that same 1 kW of power for only half an hour and you've used just 0.5 kWh of energy (1kW x .5 hr); use that same power for two hours and you've used 2kWh (1 kW x 2 hr), even though you drew the same 1 kW of power in all three cases. Energy is rate (power in W or kW) x time (in hours or fractions of hours for EV purposes).
*For comparison, power plant outputs are normally rated in either millions of watts, megawatts (MW), or billions of watts, gigawatts (GW). Total U.S. electricity generating capacity is just over 1 terawatt or 1 trillion watts (1 TW), while yearly U.S. electrical output (energy) is something over 4 petawatt/hrs (4 PWh) , or 4 quadrillion watt/hours. As there are about 8,765 hours in a year, it's easy to calculate that not all power plants are operating at max. capacity 24 hours/day, as 1 TW x 8,765 hours would equal 8.765PWh, and we generate a bit less than half that. We have to keep power plants in reserve as some are always shut down for maintenance, accidents occur etc.
