Cruise Control

Just took delivery of a 2014 FFE and had to go to a dealer that was 91 miles from home, all highway. There were 2 ChargePoint stations 61 miles away so I thought I would charge at one of those. When I left the lot I had 78 miles left (or 17 surplus) according to the GOM. I figured I'd get on the highway and set the cruise control figuring that it would be the most economical. Well, that was a mistake. Within 20 miles my surplus was almost gone (2 miles) so I turned it off and handled the speed manually. Almost immediately I got some miles back although I did slow down to 55-60 versus the 62 I had set the cruise control at.

I was using the view with the bar showing how many miles left and surplus. While on cruise control the blue circle had the yellow outline almost all the time. When I switched it off it varied but the odd thing was one time I had a long downhill stretch and I put the car in neutral. Oddly, even when there was no power going to the drive the yellow outline appeared when the car was above ~60 mph. So it appears that yellow outlined can be triggered just by speed regardless if your using power or not.

Ultimately I got to the ChargePoint station with a 19 mile surplus, now I know why it is called a GOM. The station could not be unlocked via the mobile app (my cards have not arrived yet) and the help desk could not unlock it remotely either. I went to another about a mile away and same thing. Since the next closest one was 12 miles away I tried the first one again since I thought the first person I spoke to was learning on the job. In deed the second time they were able to unlock it remotely.

I find it odd that the cruise control does such a bad job conserving energy. I was happy though that I could rebuild the surplus by driving conservatively.

It is possible that, since your car was brand new, that it didn't have any history to go on and thus was even more unpredictable than normal or that since there were so few miles on it, and that they were probably all driven slowly the GOM value may have been an over estimate.

In addition just dropping the cruise down to 55 would have likely had the same effect.

Yeah, cruise control is far better than manual control, regardless of the speed you set. The speed you set in this case was most likely the biggest cause of battery drain. It's been proven that resistance has a huge impact on mileage when you get above approximately 55-60 mph.

Snowman said:

I find it odd that the cruise control does such a bad job conserving energy. I was happy though that I could rebuild the surplus by driving conservatively.

Click to expand...

That wasn't the reason you saw the difference, and the cruise wasn't doing a "bad" job. When you need to maintain a steady speed, the cruise is much better at doing so efficiently than a human driver.

The reason was simply that you were going 62 mph with the cruise and then dropped closer to 55 mph when you "switched to manual". There is a huge difference in the energy consumed between those two speeds. In an EV, small differences in speed can be very important in terms of managing energy consumption (and, actually, they are not minor differences in any car, but it is harder to notice the difference in fuel consumption with an ICE vehicle because they carry a relative "bounty" of fuel).

The reason minor differences in speed are so important is resistance... mainly wind resistance, but also rolling resistance of the tires. Wind resistance, and the energy required to overcome it, increases exponentially with each unit increase in speed, not linearly. In other words, increasing your speed by 5% will increase your energy usage by much more than 5%. This means that increasing your speed even by a few miles per hour will significantly increase the energy required to maintain that speed, and will reduce your maximum range in an equal proportion.

Increasing your tire inflation pressure by even a few pounds (I run mine at 45 PSI, versus the standard 38) will reduce their rolling resistance, and therefore the energy required to constantly overcome it. Several pounds (as mentioned, mine are +7) can reduce your energy consumption by perhaps even 10% (in my experience) and, as I've already said, increase your maximum range in equal proportion. (And, again, this is nothing special to EVs... the same technique can be used to increase the efficiency of any vehicle.)

As EV drivers, we must be much more sensitive to these realities, because we have so little fuel to work with. Think of it, driving around in an FFE is like driving around in an ICE car with no more than about three gallons of gasoline in the tank any any one time, and usually much less. If you had to make all your ICE trips under such circumstances (and assuming gas stations were few and far between, like EV charging stations) you would also have to become much more aware of how your fuel is being consumed.

I understand the resistance issue related to speed and agree that slowing down probably did more to save energy than anything else. However, the cruise control was very aggressive, meaning that when I started up a hill it immediately accelerated until I reached my set speed just like my ICE vehicles. When I was in control I did so more gradually. I know this is an N of 1 so more experience is needed. I just think in hilly terrain you might be better off handling the speed yourself.

My usage of the FFE will be very atypical I believe since I will be driving it just like I drive my ICE vehicles. The main reason is that I'll be driving on an interstate during rush hours and around Boston if you don't keep up with the speed (70 at a minimum) your a danger to yourself and others. My commute is only 15 miles each way so I'm not concerned about range. I'll also use the heater since I like it warm.