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The Aptera electric car and calculations — Parallax Forums

The Aptera electric car and calculations

metron9metron9 Posts: 1,100
edited 2009-02-16 16:31 in General Discussion
http://autos.yahoo.com/articles/autos_content_landing_pages/857/exclusive-aptera-2e

Looking at this site http://www.windways.org/aptera/

It claims the new Apt era uses just 80 watt hours per mile.
12,000 miles on just $125.00 in electric at .13 cents per KW

Looking at a typical 1HP DC motor it uses 90 amps at 12V at no load 1080 Watts

Are they telling me this thing has a 1/10 HP motor?

If a 2 ohm resistor draws 72 watts at 12V (6 amps) they are telling me on that much power I can drive this thing a mile?

Did they really break the law of physics or am I missing something?






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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!

Comments

  • SRLMSRLM Posts: 5,045
    edited 2009-02-15 08:28
    Perhaps they use regenerative braking, and don't count that as part of the energy quota? There's also a solar panel...
  • metron9metron9 Posts: 1,100
    edited 2009-02-15 08:32
    Perhaps they did the calculations for going downhill, I guess then you could end up with more energy when you get there!

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Think Inside the box first and if that doesn't work..
    Re-arrange what's inside the box then...
    Think outside the BOX!
  • InstinctzInstinctz Posts: 18
    edited 2009-02-15 12:15
    Bleh I am a fan of electric powered vehicles. I have investigated alot of ways to produce or use "green energy". Despite the fact that I work in the oil field, its just a job right?

    But the thing is the overall technology to drive electric costs more. Even just a decent 72V 400-500A motor and controller will run around $1500. Which without a transmission is a very small car motor. 2.5K plus for a decent setup for a vehicle. You'll end up swapping batteries like you do brakes in a normal car. Ride it hard and it needs changed once a year, might get 3-5 if your lucky with depriciated performance. Thats not cheap, whether it be standard deep cycles or expensive battery array's.

    Sorry but it just starts me on a rant when I see those calculators which show $2000 a year upkeep for a gas vehicle, and $600 for an electric conversion. Its basicly taking the drive train out of the equation, as if electric never fails. You still have normal maintance, except you wont be able to find a shop in town which will "power cycle and normalize" the batteries. You'll have to do all the labor.

    Your average high output DC motor will draw about 200amps at 12-15HP @72V levels. Which is about average cruising. Most of the larger versions run around 140V, such as in vehicles.

    I dunno, electric has a long ways to go before its truly a viable option. You cant just stop in at a recharge station and 10 minutes later your on your way. And with only 400-600 recharges before your replacing batteries it definately isnt any cheaper.

    For the 10-20 miles per day driver it could possibly be a good choice.

    I am trying to figure out how they are supposily getting 80 Watt-Hours. But If they are truly describing it as Watt-Hours, its of course nearly absurd. Seems they added some quasi-math in there. Except they add their magic number per mile. So taken they are driving 60mph. Thats like 4800 watt's per hour. Or about 67 AH.

    Which isnt totatly fantasy. Its atleast plausible. Still means you'll need a trailer of battiers to drive more than an hour or so.
  • stamptrolstamptrol Posts: 1,731
    edited 2009-02-15 16:49
    The electric conversion vehicle I built used about 200 watt-hours per mile, but I drove it in normal traffic with the usual stops, starts and speeds. 80 watt-hours per mile could be doable on a special course( level, smooth, hard tires) , minimal stops, slow speeds, etc. Also, my 'Wattsun' weighed just under 2000 lbs.

    As was pointed out, the battery technology is still the kicker. We are still nowhere near low-cost, high number of cycles, light weight, compact battery banks. But, its lots of fun playing and better than hanging out at the tavern!

    I used a 19 HP jet starter motor. 36 volts, 400 amps max. Don't confuse instantaneous "watts" with "watt-hours". One is power, the other is energy.

    Cheers,

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    Tom Sisk

    http://www.siskconsult.com
    ·
  • W9GFOW9GFO Posts: 4,010
    edited 2009-02-15 18:47
    metron9 said...
    Looking at a typical 1HP DC motor it uses 90 amps at 12V at no load 1080 Watts

    Gah! 90 amps under no load? 70% efficiency when no work is being accomplished, I'd look for a different motor.

    Lets see, they claim 80 watt hours per mile. They mention 55 mph on their website. That is 80 * 55 = 4,400 watt hours or 4.4 kwh/hr. Assume 85% efficiency and that is 3,740 watt hours to the wheel OR about 5 hp. So, 5 hp to maintain 55 mph on smooth level ground with very good aerodynamics seems plausible to me.

    Now, did I screw up the math???

    Rich H
  • icepuckicepuck Posts: 466
    edited 2009-02-16 02:00
    DC motors have one other draw back, the replacement of the motor brushes, which is why most industries are switching over to AC drive motors..
    -dan

    http://www.sevcon.com/pages/productoverview.html
    http://curtisinst.com/index.cfm?fuseaction=cProducts.dspProductCategory&catID=8
    http://www.catlifttruck.com.sg/products/producttypes.php?product_category_id=3&product_type_id=9
    http://www.crown.com/usa/products/usa_electric_forklift/sit_down_counterbalance/FC_4500_Series/features.html
  • remmi870remmi870 Posts: 79
    edited 2009-02-16 04:04
    you can get more out of a motor using 3 phase than you can a dc motor, for instance, a 1hp dc motor at 230v will use 4.2 FLA, apples to apples a 230v 3phase motor uses only 3.3.

    however the curios thing is that dc motors pull more current at higher hp compared to a 3p ac motor. you could use a 10 hp 3ph motor in the two front hubs and they only would pull 22 amps a piece @230v, compared to dc at 28+ amps @ 230v, 3p motors also have the ability to use regenitve breaking so they can store braking force.
  • InstinctzInstinctz Posts: 18
    edited 2009-02-16 09:08
    The other thing is using a 3phase AC motor would require one "an inverter" at 85% eff you still loose alot, enough to probably counter the gains.

    Also is terribly harder to build a brake regen from 3phase ac, which inverts once again to loose even more gain.

    And you can get brushless motors right?
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2009-02-16 16:31
    This thread is being moved from the BASIC Stamp Forum to the Sandbox Forum.

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    Chris Savage
    Parallax Engineering
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