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How do EVs handle unexpected bumper-to-bumper traffic slowdowns?

posted 12 years ago by mickeyone
5 replies | jump to latest

Recently I was on a pretty long trip driving down the interstate. As happens sometimes, the traffic started getting backed up. Things got real slow with bumper to bumper traffic (I eventually exited to make remainder of trip on local roads). And then I was wondering, how would this be in an electric car? Let's say I had beforehand estimated I could just get to my destination with the power contained in the battery with a little to spare. If I then had to endure say a trip that took twice as long, would I be penalized for it and end up running out of battery power? Of course, in an internal-combustion engined car, your car ends up idling and idling as you inch along, so in that case you know you are gonna use up something like twice the amount of gas on your trip. But with an electric vehicle, what would happen? I like to think that maybe an electric motor will use up the same amount of power to go from point A to point B no matter what speed the vehicle is moving at. Even if you have to stop and start and stop and start again. But I don't know. Does anyone know the answer to this?

I know one thing. On as hot a day as it was when I experienced this, if I am running the AC then THAT is going to use up a lot more power if the trip lasts twice as long.

[–] apeweek 12 years ago

...And then I was wondering, how would this be in an electric car?

Electric vehicles have two advantages in traffic jams, and one disadvantage.

The first advantage is that electric motors do not idle, and use zero power while sitting still.

The second advantage is regenerative braking. When the electric car inches forward, and then stops, a good portion of the energy used to push the car forward is recaptured into the battery when you stop again. So electric vehicles are very efficient in plugged up traffic.

The disadvantage, as you guessed, is running the heat or AC while stopped. Over the length of a typical trip, heat or AC typically uses just a few percent of the energy stored in the battery. If stopped for long periods of time in traffic, however, that heating or cooling energy adds up.

If the range of the EV is tight, the driver should consider turning off the AC, and run just the fan. However, whether this is a problem or not depends entirely on how long a trip the driver is trying to take.

I own a Volt, which I sometimes take to our local drive-in movie here in Michigan. It's open all year, so we go in winter also. For the cold weather, we'll roll up all the windows and run the heat and radio (to hear the movie sound) off the battery while we watch the movie. For every 10 minutes of movie watching with heat, I have observed 1 mile of electric range reduction.

This means that a 30-minute traffic jam with heat should only take around 3 miles off my driving range. I haven't tried the same experiment with AC, but it will probably be similar.

[–] mickeyone 12 years ago

Well, I should have never even mentioned the AC because yes, of course, that would be a disadvantage if you were to be so stupid as to use the AC if you were in danger of running out of power (if I was in that situation I would turn off the AC and open the windows - trouble is, it uses up power just to roll down the stupid windows). But anyway, I looked for an answer via Google and found this:

"This Automotive News piece, by way of Cnet.com, quotes a Nissan engineer as saying this about the 100-mile (160.9-kilometer) range Leaf: If stuck in stop-and-go traffic at about 15 miles per hour (24.1 kilometers per hour), on a cold day and with the heater turned on, it could go about 62 miles (99.8 kilometers)."

http://auto.howstuffworks.com/can-electric-cars-survive-major-traffic- jams.htm

Both you and this article point out about regenerative braking, which I admit I had forgotten about. But realistically, I doubt they would be much help in this type of situation.

"The first advantage is that electric motors do not idle, and use zero power while sitting still."

This I was wondering about, and now you've answered it. Thanks! Although I doubt that there is absolutely no power being used when stopped. If nothing else the control panel is electric and I assume that doesn't get shut off when the vehicle comes to a stop. But you are talking about the motor. I hope you are right that it really consumes zero power when stopped, but I wouldn't be surprised if even then it was drawing a very slight current.

[–] floyd-52 10 years ago

Some hybrids now have a solar panel array on their roof to power the A/C systems.

[–] NapoleonBender 12 years ago

The energy required to accelerate would be the same for gas and electric assuming equal weight. The real energy intensive thing is accelerating regardless of your fuel type, so stop and go would be just as bad for electric if not worse. It takes much less energy to maintain speed than to increase it in pretty much all circumstances.

[–] ShepherdSpy 10 years ago

I'm assuming you're talking about pure Battery Electric Vehicles (BEV's) as opposed to hybrids or plug-in Hybrids (PHEV's) that have an engine like the Volt or Prius..The range figures calculated for cars (and EV's) are currently carried out in rolling road tests indoors without using lights,heating,or A/C..real world figures will be about 10-15% worse off manufacturer's figures.Going super slow in an EV will extend the range into record breaking territory-borderline range should get you to your planned next stop.The slower you go,the better your range,but running wipers/lights/A/C will counteract that some.Unless you're driving a Tesla S,which is currently the only pure EV with long range capability built in with it's huge battery pack,Most other EV types are (for now) designed as commuter or city cars limited to about 100 mile range,so planning your next charge along a long route comes with the package.Unexpected is unexpected..but EV's have efficient electrical systems,regenerative braking to reclaim energy that would otherwise be lost as heat,thermal glass to reflect sunlight,less glass area to cut down the greenhouse effect..mine has a heatpump a/c system. (ZOE)

If Book was in Intelligence B4 finding God,does that mean He's a Shepherd Spy? (Thank You,Spike..)