Total Charge and Drive time vs. speed

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Michael Bornstein

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Oct 29, 2012
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280
In the past, Tony posted a Range Chart ( http://www.myrav4ev.com/forum/viewtopic.php?f=2&t=67) that gave the expected range of a new battery vs speed. For those taking long trips, what is also important is the time you have to cool your heels while your car recharges. The chart below assumes a 100 mile journey and gives the total drive time, charge time, and their sum for both a public L2 charger and a home 40A charger. Unfortunately, there is no free lunch. the faster you go, the longer the total trip takes, although the difference on a 40A charger is small from 45mph to 65mph. The difference is greater with the 30A public charger. This means that you should look for NEMA 14-50 plugs whenever you can.

Total time for Driving and Charging (Obviously you can't go 100mi at 85 mph in the RAV4 EV)

Speed (mph)______________________45____50_____55____60______65____70_____75____80_____85

Time for 100mi (hours)____________2.22___2.00___1.82___1.67____1.54___1.43___1.33___1.25___1.18

miles/kWh_______________________4.7____4.3____3.9____3.6_____3.4____3.1____2.7____2.4____2.0

kWh/100mi_____________________21.3___23.3___25.6___27.8____29.4___32.23___37.0___41.6___50.0

Charge time @ 208V 30A (hours) ____3.90___4.26___4.70___5.09____5.39___5.91___6.78___7.63___9.16

Total time for Public Charger (hours)__6.12___6.26___6.51___6.75____6.93___7.34___8.12 ___8.88__10.33

Charge time @ 240V 40A (hours) _____2.53___2.77___3.05___3.31____3.50___3.84___4.41___4.96___5.95

Total time for Home Charger (hours)__4.76___4.77___4.87___4.97____5.04____5.27___5.74___6.21___7.13

According to the chart, there is only a 17 min difference between 45 and 65 if you have a 40A charger, but a 49 min difference with the 30A charger. The 30A charger also takes 1h:55m longer to charge than the 40A charger. These calculations are all based on a 87.5% charger efficiency. I hope this data will be helpful for those planning long trips.(I apologize for my inability to format the table correctly)
 
This is really useful, but I'm going to point out two caveats here...

87.5% charger efficiency rate, this seems to take a real dive after 80% SOC, especially in the heat. To use the Baker problem as an example, you can't necessarily stop at 80% and jump back in the car. Baker is far enough out from the rest of electrically-equipped civilization that you will probably want the extra cushion (I did) and the heat in Baker is very extreme during the summer months. Plus, there are only so many Baklava Milkshakes you can pound back at the Mad Greek before you start to turn into the Mad Greek yourself!

The other catch is that the total "time-spent-getting-there" index is valuable for a trip with only one charging stop, and less valuable for trips with >1 charging stop. If you want to minimize charging stops then you will want to be able to squeeze 150 miles from every charge (not impossible by any means). Why minimize charging stops if the chargers are there anyways? One reason is that the addition of each charging stop will add 20 minutes of overhead on average. Some require a much greater deviation from your route, and then you have to find/pay people at RV parks and get your EVSE set up. You may also find that you have to use a 208V/30A EVSE as a mid-point somewhere and will want to minimize time spent at that location in favour of 240V/40A locations.

Some sort of calculation that could factor in the penalty for additional charge stops would be good. Something like (in minutes)... T = Drv + Chrg + [(Dist / Rng) x 20]

Still a handy little chart nonetheless! Thanks, Michael!
 
DevinL said:
If you want to minimize charging stops then you will want to be able to squeeze 150 miles from every charge (not impossible by any means). Why minimize charging stops if the chargers are there anyways?

I use 150 miles as the "goal" between charge events, and adjust speed accordingly. With a new battery on flat terrain, 55mph is about right and will match the speed of the big-rig trucks in California.

The other issue that you rightly point out is that the charge rate drastically lowers above about 85-90%. So, the absolutle fastest charging would be to stop at about 80% and drive 80% of 150 miles at 55mph.

I've got a little surprise for tomorrow that I know you guys will like in the "long range" driving game.
 
DevinL said:
87.5% charger efficiency rate...
Everything I've seen points to a charging efficiency of roughly 80%, throughout the normal charge range. The charger itself might be 87.5% efficient, but there are other losses in charging (TMS, for one) that contribute to the overall 80% efficiency figure.
 
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