Author Topic: Need an assist calculating KWH required for an Electric Car  (Read 3289 times)

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Offline GiveMeTheJuice!

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Need an assist calculating KWH required for an Electric Car
« on: March 04, 2014, 03:13:30 pm »
I have range anxiety and I'm posting to get help with an algorithm to determine how much battery (KWH's) I need stored in the battery to drive my Chevy Volt to a destination.

I've done some research such as reaching out to the local librarian, gathered areas of study that I would need and searched Gov sites, wikipedia and google as well, but failed to move forward in resolving this problem.

It sounds like this algorithm would be complicated, but that is probably because I don't understand how to do it :)

Factors I feel would give the best case scenario:

  • Weight (car, passengers, gas, cargo)
  • Elevation changes
  • Motor draw/usage
  • Stretch goal is to include wind and temperature (for battery efficiency) conditions
  • Stretch goal: Cabin heater/air conditioning usage

 I have or can get the input data for the listed factors. Excluding the stretch goals, if that increases likelihood of getting help here, what would the algorithm or mathematical formula look like? If that isn't available, tips, pointers, references, areas of subject matter to research would be immensely helpful!  ;D
« Last Edit: March 04, 2014, 03:18:33 pm by GiveMeTheJuice! »
 

Offline IanB

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Re: Need an assist calculating KWH required for an Electric Car
« Reply #1 on: March 04, 2014, 03:47:29 pm »
Doesn't the car itself have a range indicator on the dashboard? Using that and comparing it to the results you actually achieve is probably going to give you the best answer.

The biggest factor influencing the range you can get is how smoothly and slowly you drive. If you drive slowly with gentle acceleration you will achieve a much greater range than if you drive fast and accelerate hard. I note you don't have driving style in your list of factors above.
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Offline johnk

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Re: Need an assist calculating KWH required for an Electric Car
« Reply #2 on: March 04, 2014, 03:49:13 pm »
It's hard to calculate that absolutely correctly, because for example your aerodynamic drag depends (non-linearly) on your driving-speed. The average power consumption of your motor will also depend on what roads you use, how much you break and accelerate...
To make it easier you could just assume an average electrical power-consumption of your car (including air-conditioner, motor...). If you multiply this average power with the time you need to drive (which you can also calculate out of your speed and distance if you want to) you get the kWHs. ( E=P*(distance/v)/3600.000 <- /3600.000 because you asked for kWh not Ws) (I hope I did the maths right  :P)
 

Offline zapta

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Re: Re: Need an assist calculating KWH required for an Electric Car
« Reply #3 on: March 04, 2014, 03:53:35 pm »
Another approach is to collect data points and fit it to a model. Does your car has a port that allows you to collect data?
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Offline free_electron

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Re: Need an assist calculating KWH required for an Electric Car
« Reply #4 on: March 04, 2014, 04:22:39 pm »
there is a website that does that already.

it uses google maps and topological data to compensate for elevation. you select car and can set criteria even like windspeed.

Now, chevy volt ... range anxiety ? it's got a gas engine .... how can you have range anxiety ?
if you want to drive it pure electric , you bought the wrong car. the volt can merely do 35 miles on its battery.
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Offline GiveMeTheJuice!

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Re: Need an assist calculating KWH required for an Electric Car
« Reply #5 on: March 04, 2014, 04:26:04 pm »
Doesn't the car itself have a range indicator on the dashboard? Using that and comparing it to the results you actually achieve is probably going to give you the best answer.

The biggest factor influencing the range you can get is how smoothly and slowly you drive. If you drive slowly with gentle acceleration you will achieve a much greater range than if you drive fast and accelerate hard. I note you don't have driving style in your list of factors above.

There is a battery gauge with a miles label on the instrument cluster. This means nothing other than there is a battery icon and a number next to it. Its good eye candy and great for misleading customers. The number appears to be calculated by history data (but inconclusive input list) and I would guess the purpose of this icon and number, like you guessed, it is a range indicator. For example, when I leave a rest stop with 38 miles as indicated and head up hill at 70 MPH with a destination 20 miles away, I would need a tow (or use gas if I have some).
 

Offline GiveMeTheJuice!

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Re: Need an assist calculating KWH required for an Electric Car
« Reply #6 on: March 04, 2014, 04:36:42 pm »
It's hard to calculate that absolutely correctly, because for example your aerodynamic drag depends (non-linearly) on your driving-speed. The average power consumption of your motor will also depend on what roads you use, how much you break and accelerate...
To make it easier you could just assume an average electrical power-consumption of your car (including air-conditioner, motor...). If you multiply this average power with the time you need to drive (which you can also calculate out of your speed and distance if you want to) you get the kWHs. ( E=P*(distance/v)/3600.000 <- /3600.000 because you asked for kWh not Ws) (I hope I did the maths right  :P)

This does feel hard, but doable. I did get road speed limits from Washington State DOT.

Another metric/data point is brake regen. When the brakes are applied, the electric motor is the other way by the wheels (somehow) and the resistance/load to spin the motor slows the car and produces electricity that is stored back into the battery. This is "brake regeneration" or some term close to that.

However, that adds more complexity which I planned to phase in after getting a "close enough for a starting point" algorithm going.

Because the battery usage tracking in the Volt is displayed by KWH, as is electrical usage when charging, KWH makes sense as a target number to determine how much battery I need. The volt will use 10.4 KWH before the engine fires to power a generator, if it has gas.

Thanks for the formula and idear :D
 

Offline GiveMeTheJuice!

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Re: Re: Need an assist calculating KWH required for an Electric Car
« Reply #7 on: March 04, 2014, 04:40:07 pm »
Another approach is to collect data points and fit it to a model. Does your car has a port that allows you to collect data?

:D

Yes! However, I don't have the hardware to connect to the car yet. Its over my budget right now.
 

Offline GiveMeTheJuice!

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Re: Need an assist calculating KWH required for an Electric Car
« Reply #8 on: March 04, 2014, 04:43:03 pm »
there is a website that does that already.

it uses google maps and topological data to compensate for elevation. you select car and can set criteria even like windspeed.

Now, chevy volt ... range anxiety ? it's got a gas engine .... how can you have range anxiety ?
if you want to drive it pure electric , you bought the wrong car. the volt can merely do 35 miles on its battery.

Link please :D

I have the right car :) It does drive on pure electricity and will do 100 MPH on juice alone. I tested this in Montana! The limiter kicks on at 101 MPH.
 

Offline Weez

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Re: Need an assist calculating KWH required for an Electric Car
« Reply #9 on: March 04, 2014, 04:57:58 pm »

If you just want to keep it basic, then you could just use the info available on Chevy's website.  It lists the battery as a 16.5 kWh lithiom-ion with a total range of 38 miles.  You don't say how far your destination is.  Some simple math indicates that 1 kWh of charge will get you 2.3 miles.

I haven't done much research on these types of cars, but you got me curious and I started reading through the FAQ section.  It takes 10-16 hours to fully charge a dead battery, using 120v.  Yikes.  Only 4 hours using 240v.  That'd be a no-brainer for me.

How long have you had the car?  Do you like it?
 

Offline GiveMeTheJuice!

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Re: Need an assist calculating KWH required for an Electric Car
« Reply #10 on: March 04, 2014, 05:26:24 pm »
I've had it for 1 year 6 months and 35k miles. I like it. It is high value with a great lease deal. In parallel, it is a pile of shit :) It has broke down twice and had countless substantial problems.
 

Offline Rigby

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Re: Need an assist calculating KWH required for an Electric Car
« Reply #11 on: March 04, 2014, 05:48:19 pm »
how can you afford to lease a vehicle but not afford an obd2 connector?  or is the data port not obd2?
 

Offline GiveMeTheJuice!

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Re: Need an assist calculating KWH required for an Electric Car
« Reply #12 on: March 04, 2014, 05:53:42 pm »
how can you afford to lease a vehicle but not afford an obd2 connector?  or is the data port not obd2?

Why do you ask?
 

Offline free_electron

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Re: Need an assist calculating KWH required for an Electric Car
« Reply #13 on: March 04, 2014, 06:01:57 pm »
i believe it is called evtripplanner.com
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Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 


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