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Thread: Goingbush's Electric Vehicle project

  1. #31
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    Logan
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    I'm only guessing, but wouldn't running an electric motor slowly drain less battery power than running it faster? Seems to be true with battery-powered tools.

  2. #32
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    Jul 2006
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    Tuross Head, South Coast, NSW
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    That's true, but wouldn't the same thing apply to a petrol motor? Wouldn't running it slowly use less petrol than running it fast?
    Even in low range, the motor still sometimes works fairly hard, regardless of whether it is electric or internal combustion.

    There must be someone with experience of an electric powered vehicle who can tell us what happens and why.

    1973 Series III LWB 1983 - 2006
    1998 300 Tdi Defender Trayback 2006 -
    - often fitted with a Trayon slide-on camper.


  3. #33
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    These people would know:

    World Solar Challenge 2017

  4. #34
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    Jul 2011
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    Yarrawonga, Vic
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    Electric motors work significantly differently to Internal Combustion engines. So much so that no comparison can be made on the power figures, the range can easily be doubled or tripled by going slowly , in Low range there is almost zero load on the motor = almost unlimited range, if thats how it translates in the real world we will see. I read a Tesla Model S recently did 1000km on a single charge by driving at 40kmh

    Tesla driver breaks 1,000km-single charge long distance EV record - SlashGear

  5. #35
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    I can't see how low range would help, the main gears would be spinning faster and creating drag. Teslas etc. don't have any gears. You would have to read a full set of efficiency vs revs vs load curves to find a sweet spot that overcame the extra drag.

  6. #36
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    Post

    Quote Originally Posted by bee utey View Post
    I can't see how low range would help, the main gears would be spinning faster and creating drag. Teslas etc. don't have any gears. You would have to read a full set of efficiency vs revs vs load curves to find a sweet spot that overcame the extra drag.
    With maximum torque at close to zero RPM , I don't think gear drag will be of any consequence. thats what I see when looking at the graph, but I'm no mathematician. We will soon find out. I just have the Iveco in the shed for more brake work and I'll be getting stuck into the Landy in about a week.

    Below is a graph of my motor at my chosen system voltage (144v) you can see that it hardly uses any power at low speed, compared with at 100kmh / 3700 with my 6.50-16 tyres .



  7. #37
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    Jul 2006
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    Tuross Head, South Coast, NSW
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    That graph is interesting, but I don't know if it includes a variable that I think is important. Is that created with a constant load?

    I know that some electrically powered devices benefit greatly from backing off the throttle even just a little bit.

    The chart below is for a Torqeedo outboard and shows that if you are prepared to go at about 40% of the speed, the range is over seven times as far and the running time is eighteen times as long. However, part of the benefit comes from the fact that the power required with a displacement hull is a cubic function of the speed. In other words, to go twice as fast, you need eight times as much power.

    Speed in knots (km/h)* Range in sm (km)* Running time in hours:
    Slow 2.0 (3.7) 20.0 (37.0) 10:30
    Half throttle 3.0 (5.5) 10.5 (19.4) 03:30
    Full throttle 5.0 (9.2) 2.8 (5.2) 00:35

    I can understand how a Tesla could increase its range dramatically by slowing down because it would have only a tiny bit of resistance at low speed. So as well as the benefit of lower revs that the graph shows, the motor would need to produce only a tiny amount of power to overcome the drag.

    My impression is that low range work includes trickling along with just a touch of throttle but also includes times when the motor has to produce a reasonable amount of power to climb hills or to push through sand or mud, or to clamber over rocks.

    So while I accept that electric motors produce maximum torque pretty much at any revs, I don't think a 4WD used for off-roading would benefit as much from slowing down as a Tesla on a smooth road.

    However, I might be wrong.

    Hopefully I won't need to wait too long for you to finish your project and either confirm or refute my theory.

    1973 Series III LWB 1983 - 2006
    1998 300 Tdi Defender Trayback 2006 -
    - often fitted with a Trayon slide-on camper.


  8. #38
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    Jul 2011
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    Yarrawonga, Vic
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    Quote Originally Posted by Lotz-A-Landies View Post
    I could be wrong, but to me the bolt pattern on the adapter plate replicates the bolt pattern on the engine block. This would mean that you have to use both the flywheel housing, the gearbox bell housing and the flywheel.

    The engine side of the flywheel is recessed to fit the crankshaft flange so you may not have a problem at all. I guess time will tell.

    It's a pity you're not up here in Sydney as we have a number of spare housings and flywheels that we could do test fits before you need to remove your old engine.

    Ive pulled the engine out and see I do have an issue , The face of the Flywheel adaptor is about 15mm too far back.

    As I see it here are my options
    1/ I need to make a 15mm spacer to sandwich between motor and adaptor plate
    2/ Remove a combination of 15mm from motor shaft and Flywheel adaptor .
    3/ modify clutch release - a combination of shortening pivot point to move throw out fork reward a few mm and/or make a new thrust bearing holder / get a thinner bearing.

    4/ a combination of 2 &3 above .

    I wont really even need a functional clutch , I could just install as without throw out mechanism .




  9. #39
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    Jul 2011
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    Yarrawonga, Vic
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    I can 'skim' 9mm from the back of the 21.5mm EV flywheel adaptor to bring it to the same thickness as the flywheel flange of the crankshaft .

    now I only have to find 6mm , rather than 'trimming' the end of the motor shaft I should be able to get a thinner thrust bearing or mod the bearing holder .


  10. #40
    Join Date
    Jan 1970
    Location
    Central West NSW
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    20,184
    Looking at the graph shown, it is quite clear, by looking at the current curve vs the power curve, that the electric motor efficiency is pretty much independent of motor speed. Which is what I would expect.

    This means that the power consumption will depend almost entirely on the resistance to movement of the vehicle and internal drag. The internal drag will be mainly from the bearings, seals, and gears in the transmission (plus at high speeds aerodynamic drag mainly from prop shafts). These will generally be more or less fixed for bearings and seals, but I'm not sure about gears - in the case of gears, I suspect power consumption will depend on the amount of power transmitted, and the number of gears used. (This suggests that gears should only be used where you need more torque than the maximum the motor can provide, and to match maximum speed to maximum power)

    The big one though is rolling and aerodynamic resistance to the movement of the vehicle. And hill climbing.

    Rolling resistance is the the power turned into heat in the tyres and shock absorbers, and would seem to be proportional to the the speed but also depends on the surface conditions.

    Hill climbing will use the same amount of energy regardless of speed, so its power use (power is energy/time) is proportional to speed. And if you have regenerative braking, you get most of it back when you go back downhill!)

    So these two factors will not depend, as a first approximation, on the speed of travel.

    The big one! Aerodynamic drag, however, depends on the square of the speed. Doubling the speed quadruples the power needed, but you get there in half the time, so the energy used is only double. But this is still the really big factor for realistic highway speeds, no matter how streamlined the vehicle or how small the frontal area. Crawling along offroad at <40k, it will be pretty small, but once above about that speed it becomes the dominant power requirement.

    Hope this analysis helps.
    John

    JDNSW
    1986 110 County 3.9 diesel
    1970 2a 109 2.25 petrol

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