Charging Raven Long Range on HPWC

[ajdelange]

Actually I'd be closer if I used .225% which is typical of what I actually get. But the object isn't accuracy. It's simple back of the envelope calculations without the envelope. If I start worrying about corrections for efficiency, temperature, coriolis effect... it isn't simple any more.

 

[Rocky_H]

Wow. That seems a bit more complicated than the method I use. Or at least trying to work out that conversion factor of .225% or whatever takes more estimations and inaccuracies. A fairly easy way you can do this is to take one known correspondence data point where you know the amps and the miles per hour, and then use a quick ratio to scale it up or down to other amp amounts. For example:

On my old Model S 85, they have a pretty solid known rate at 40A charging of 29 miles per hour. So then what if you want to see what it would be at 32 amps or at 48 amps?

40/29 = 48/X
Solve for X. This is middle school or high school math techniques with cross multiplying. 40 times X equals 48 times 29. So X = (48 times 29) divided by 40 = 34.8 mph (This works scaling only on the amps if you are comparing two situations with the same voltage. If you're having to compare a 240V situation to a 208V situation, it doesn't work as well, and I kind of fudge-factor it down a bit for lower voltage.)

So if you figure out one known charging rate data point for you vehicle, then you can work out others fairly easily.

 

[ajdelange]

I think you are missing the point. You DON'T work out any conversion factors once you figure out what your magic numbers are. For an X 100D they are 4 and 3. The % charge per Amp per hour is just the amps divided by the first number, 4. It may be easier to divide by 2 twice. Then the range added 3 times that. Looking at actual charge histories I find that this method gives me answers that on average are about 13% higher than what the car reports. My first number is really closer to 4.3 but dividing by that in my head is something I cannot easily do. If I am in the mood I can easily knock the 13% off (or at least 12.5% of it) with mental arithmetic but why bother? If I'm at home (72A charging rate) I know I'll get 72/4 = 18% per hour charge. If I want to add 40% I know that's going to take a bit over 2 hrs. At my summer place where I can charge at 40 A I know I get 10%/hr and I'll need about 4 hrs charging to get that same 40%. What is more important is knowing that I get about 3 mi/% in range. That makes it a simple matter to figure out my fuel condition at any point with a quick glance at the battery indicator.

This is so easy because the factors are 4 and 3 and that's because the 100D has a 100 kWh battery and its range is about 300 mi on a full charge. For other vehicles the numbers may not be so convenient and another more complicated method may be required but multiplying 40*48 and then dividing by 29 is certainly not easier that dividing by 4 and multiplying by 3. At least it wouldn't be for me. In your case, however, your magic numbers are also 3 and 4 but used differently. Divide the available current by 4 or divide by 2 (48/2 = 24) and then divide by 2 again (24/2) = 12. Now multiply by 3 (12*3) = 36. That's your estimate for miles per hour gained at 48 amps and is certainly close enough to 34.8 for me. (3/4)*32 = 24. In your case it is easier to go directly to miles gained.

If you have 208 volts as opposed to 240 you need to knock off 13.3%. To knock off 12.5% divide the answer by 2 three times. 36/2 = 18; 18/2 = 9; 9/2 = 4.5 and subtract that off so your estimate at 208 corrects to 36 - 4.5 = 31.5. This should, again, be close enough for government work:
(208/240)*(3/4)*48 = 31.2 and (208/240)*(29/40)*48 = 30.16