Real-world EV Power Consumption

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photomac
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Real-world EV Power Consumption

Post by photomac » Tue, 15 Feb 2011, 01:58

Okay :D - be honest now - :)
What do you - the successful converter - actually achieve on the power consumption figures?
That's battery bank capacity and at wall-plug figures.
I'm chasing
car model
year
battery bank size and Depth of Discharge
or power used to achieve what distance. (eg you drove "x"km and used "y"kW between charges)
typical drive ratio (urban 60kph to highway 100kph)
and
with/without air-conditioning

many thanks in anticipation.

My reason for asking is the theoretical calculations vary from other gu'estimation techniques by up to 40% on some vehicles.
I know it's a bit like asking how many stars are in the universe but none-the-less, I haven't found many detailed figures to cross-check my calcs.

I have set up-up a spreadsheet where-by I can enter a car's weight, presenting area, Cd and transmission details to calculate, rolling resistance, Drag, Kinetic energy and ultimately, after typical power train losses and at various Depth-of-Discharge levels.

Your data will help me improve my gu'estimation techniques on my desired donor car.

Cheers
Matthew
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photomac
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Real-world EV Power Consumption

Post by photomac » Fri, 25 Feb 2011, 22:04

Okay - no taker's on the question above!
Mmmmm.
Do I conclude all converters are disappointed with "real world" results?

Thwot -wak -thwot -wak -thzzz   Come-on !!

So - here are some uneducated gu'estimations of range anxiety results.
How do your results compare?
I've used three "rules-of-thumb" guides and a calc using a series of formulae.

eg                               12.5 to 15.5        [13]      kW/100km
is read     "Rules-of-Thumb" range [Formulae] kW/100km

Holden Commodore - 24.5 to 27.5    [24.6]     kW/100km       [Sdn]
        Toyota Corolla - 18.0 to 19.7    [18.0]     kW/100km       [Sdn]
            Toyota RAV4 - 20.6 to 23.8    [24.6]     kW/100km
            Toyota Hilux - 23.5 to 28.0    [26.6]     kW/100km       [Tray 2dr 2WD]
                    Mazda 3 - 18.4 to 19.8    [17.4]     kW/100km       [wgn]
                    Mazda 6 - 22.2 to 23.8    [18.4]     kW/100km       [hatch]
              Mazda MX5 - 16.8 to 21.3    [18.8]     kW/100km
               Mazda RX8 - 19.5 to 31.5    [19.7]     kW/100km
             Honda Civic - 18.3 to 18.6    [16.8]     kW/100km
            Nissan Tiida - 16.7 to 18.0    [16.3]     kW/100km
[ figures above are battery pack size required at a DoD of 80% ]

In the rule-of-thumb guide the big unknown is the efficiency of their ICE engine. 20% is assumed

Which vehicle?
Oh bugger it! Build one of each LOL
I even checked out a Rolls-Royce calc !
But Rolls are releasing an electric prototype soon!
http://www.gizmag.com/rolls-royce-102ex ... cle/17929/
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woody
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Real-world EV Power Consumption

Post by woody » Sat, 26 Feb 2011, 18:28

Firstly, energy is measured in kilowatt-hours (kWh) these are the things on your power bill for 5-25c. This is also how you measure the size of a battery pack, analogous to the size of a petrol tank in litres. Joules is another way to measure energy, this is how town gas is billed. 1 kWh = 3.6 Mj.

Power, on the other hand, is measured in kilowatts. This is how fast you can use or deliver energy. E.g a car 100kW, a power point 2.3kW, a hair dryer 2kW.
Batteries need to satisfy your requirements of both energy + power.
The relationship between the 2 for LiFePO4 cells is approximately the 2/3 the C figure.
E.g markt's new pack is made of 450 10C capable 3.2V 16Ah batteries, total energy approx 23kWh, but capable of approx 173kW of power.

Secondly: possible reasons why EVers haven't replied to your post:
1. Measuring Wh/Km is hard - cheap meters aren't good at measuring battery chargers.
2. They've already measured it and published it somewhere else
3. Measuring range is dangerous to the pack
...
Planned EV: '63 Cortina using AC and LiFePO4 Battery Pack

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Real-world EV Power Consumption

Post by EV2Go » Sat, 26 Feb 2011, 19:47

Woody Mark T's pack is currently 400 cells not 450, the planned extra 50 cells are yet to make the car.

Think this has kind of been covered (maybe not in one place at one time) but essentially count your losses from in to out.

Wall / charger to battery pack (x% charger loss)
How long the vehicle is stationary before use (x% loss in sitting)
Battery pack to controller (x% controller loss)
controller to motor (x% motor loss - variable)
drive train losses (x% gearbox, uni joints, diff etc)

peripheral power consumption i.e DC to DC convertor controller power consumption, headlights, indicators etc etc

If you count everything and don't be over zealous in efficency of everything i.e don't think peak efficiency applies across the whole motor range, you should be able to work out a fairly decent power in to power out ratio then apply your CdA, rolling resistance etc.
Last edited by EV2Go on Sat, 26 Feb 2011, 09:16, edited 1 time in total.

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Real-world EV Power Consumption

Post by photomac » Sat, 26 Feb 2011, 21:22

Dang!
I had kWh in this chart but some-one I talked to talked me out of it.
So I am really confused Image

Many thanks to this pointer too
[quote]The relationship between the 2 for LiFePO4 cells is approximately the 2/3 the C figure.
E.g markt's new pack is made of 450 10C capable 3.2V 16Ah batteries, total energy approx 23kWh, but capable of approx 173kW of power.
[quote]

Measuring consumption over a distance - is there a preferred method akin to ICE vehicles? Like petrol tank refill volume to distance covered between refills?

And thanks to the pointers about other losses too.
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Real-world EV Power Consumption

Post by photomac » Sat, 26 Feb 2011, 22:11

I'm now refreshing my poor understanding of kW/ kWh from this article

http://www.energylens.com/articles/kw-and-kwh
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Real-world EV Power Consumption

Post by woody » Sun, 27 Feb 2011, 05:12

EV2Go wrote: If you count everything and don't be over zealous in efficency of everything i.e don't think peak efficiency applies across the whole motor range, you should be able to work out a fairly decent power in to power out ratio then apply your CdA, rolling resistance etc.
I think you jumped from the real world into Spreadsheet world (Woody world?) there.

But you should be able to count battery amps in and out with one piece of equipment which should give you nice range answers. EV Works fuel gauge driver possibly could be extended to take a speedo pulse and output the data over serial link...
Planned EV: '63 Cortina using AC and LiFePO4 Battery Pack

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Real-world EV Power Consumption

Post by woody » Sun, 27 Feb 2011, 05:30

photomac wrote:
Measuring consumption over a distance - is there a preferred method akin to ICE vehicles? Like petrol tank refill volume to distance covered between refills?
I think the equivalent to the "6.6L/100km (combined/highway/city cycle)" is probably the Wh/Km or Wh/mile figure, but hobbyists can't just drive to a test track and see what they get over the "city cycle" AFAIK.

US EPA has some decent information on new car stickers for hybrids and EVs in the US, I'm not sure if Oz has something similar.

Different figures you'll find will be wall-to-wheel or pack-to-wheel or windmill-to-wheel depending on whether they take into account the efficiency of charging + balancing, power transmission etc.

I think wall-to-wheel is best comparison to L/100km, as you don't include the fuel used in refining and transporting your petrol to the bowser, buy you do pay for fuel which evaporates or splashes while you're filling up (charging?) :-)

I think mightyboyev was getting 90-110 Wh/Km.
A rough guide you may have seen is multiply the L/100km by 20 to get Wh/Km. I think that's pretty conservative though.
Planned EV: '63 Cortina using AC and LiFePO4 Battery Pack

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Real-world EV Power Consumption

Post by leadwings » Fri, 22 Apr 2011, 00:13

Funny, I was about to start a thread on exactly this and then found yours.

I have been measuring the perfromance from my car. I have a power meter on the power point that I charge at, and the odo from the car for km travelled.

Graph is below. I am averaging between 250 and 400 Wh/km. This includes charger inefficiency etc.

Another point is my Zivan tends to settle on a float charge of around 1A once the pack is full - so if I leave it on charge overnight (10 hours), but only do a small charge (say 5 kWhr), the pack charges in the first couple of hours and the 1A x 240V is waste - and distorts the power per km up.

I also note if I leave the car sitting, the number goes up. I suspect this is due to my 144V to 12V convertor running all the time, and a leak somewhere in the 12V system. Yet to chase it down. But the large spike was when I did few km and left the car sitting for a few weeks.

If I am not going to drive the car for a few days, I tend to disconnect the pack and 12V battery now.

I am also now clocking up more km now commuting to work, so will watch what the consumption does woth more data based on more km.Image

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