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Quantifying The Effect Of Additional Loads On The Powertrain In Regards To Range??

Discussion in 'Model S: Battery & Charging' started by RaySuave, Aug 8, 2013.

  1. RaySuave

    RaySuave Member

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    I've been working on a couple of ideas to increase the range of EV vehicles with a primary focus on smooth steady level freeway driving (over 55mph speeds), when increased range is needed the most. Since the
    Tesla Model S represents the current state of the art in EV battery technology, I'm using this vehicle as the basis for the majority of my research. I have developed a range calculator for the Tesla Model S which takes into account speed, battery capacity, and a list other factors that are introduced by my own range extending concepts. In efforts to improve the accuracy of range calculation, I cant seem to find any information on exactly how the Model S range will respond to additional loads on the powertrain introduced at the output prop/drive shaft. For instance, take a Model S going 55mph in optimal range conditions, if an additional 5 HorsePower load was added to the the prop/drive shaft, how would this effect the 300 mile estimated range? How would this additional 5 HorsePower load effect the 275 mile estimated range of the car going 60mph?
    I would like to be able to calculate these effects for varying additional horse power loads and increased speeds.

    Any links or information on this would be much appreciated.

    Thanks in advance.

    Ray
     
  2. Lloyd

    Lloyd Active Member

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    You could try the calculator on the Telsa website:wink:
     
  3. RaySuave

    RaySuave Member

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    I didnt see a calculator that lets you input additional loads on the powertrain... Can you provide a link?
     
  4. captain_zap

    captain_zap Electron tamer

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    Ray:

    The effect of an extra drivetrain load can be estimated as follows. Your 5 hp load would be a real range killer.
    Since hp converts to watts at 746 w/hp, this would add a continuous load of 5*746=3730w.
    Assuming a drivetrain efficiency (inverter*motor*transaxle), say 85%, then the battery power required to the inverter is 3730/0.85 = 4388w.
    Since we know that the MS consumes roughly 308 Wh/mi at EPA rated mileage, let's assume this can happen at 60 mph so in one minute of driving you cover one mile and consume 308 Wh.

    With your extra 4388w load over one minute you would consume an additional 4388/60=73 wh, bringing the total to 308+72=380 Wh. This is an increase of 23.4% in energy consumption.

    We know the usable capacity of the 85 kW-h pack is about 81.62 kW-h. So EPA range would drop from 265 mi to 81.62 kW-h/380 Wh/mi = 214.7 mi.
     
  5. RaySuave

    RaySuave Member

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    Thanks for the detailed explanation walk through....really appreciate it.
     
  6. schueppert

    schueppert Member

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    It's a bit of a downer the impact on range is so big. I totally thought attaching a 5HP generator to the battery and using it to charge the battery was going to work as a range extender!
     
  7. RaySuave

    RaySuave Member

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    I dont believe you can charge a battery and discharge it to feed the vehicle motor at the same time....not yet at least. Also keep in mind, the most common generators/alternators need to spin around 2,000 to 3,000 RPMs to produce the rated power.

    I knew the range would take a hit when applying extra load but not this much...plus in my other calcs, I have the inverter/powertrain being 80% efficient which will give even worse results.
     
  8. schueppert

    schueppert Member

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    I solve that problem by having two batteries: one for charging and one for discharging. Plus they can charge each other which is awesome. I also have a gearbox to match the generator speed to the motor. The biggest problem I'm having now is all the manual gear changes; I may need to investigate how to make this automatic :)
     
  9. Lloyd

    Lloyd Active Member

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    Sorry, You are correct. The calculator on the website does not allow calculation for additional load. I thought it did.
     
  10. RaySuave

    RaySuave Member

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    Your looking to match the generator speed to the motor speed, EV motors spin pretty fast, the MS has a 9.73:1 motor to drive shaft ratio. Check generator specs to see what their RPM limits are before bearings start to fail.
     
  11. schueppert

    schueppert Member

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    Oh I just get rid of the existing gearbox in my design and replace it with a 3-way Y configuration gearbox. It matches the motor to the wheels, the motor to the generator, and the wheels to the generator for enhanced regenerative breaking!
     
  12. RaySuave

    RaySuave Member

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    #12 RaySuave, Aug 16, 2013
    Last edited: Aug 19, 2013
    Range Extender Calculator

    The screen shots below are from a website I'm developing for a range extender design. The calculator is my attempt to account for as many factors as reasonably possible to estimate some realistic expectations of my device. (deleted screen shots, will post again once the calculator is reviewed by others) The range extender utilizes an alternator driven by the existing drive train to charge the depleted battery of a dual EV battery bank...then switch to charging the other battery once it depletes. The switching process continues until both batteries have been depleted which results in the extended range. At the bottom of the calculator, a table is produced illustrating minute by minute, the miles driven and the switching of the battery charging status until the batteries are depleted.

    The calculations are based on Tesla Model S component capabilities. For simplicity, as a reference, an 85Kwh battery with a range of 300 miles at 60 mph is used in the calculations. Other assumptions and references are listed in the screen shots. Since the range extender is utilizing a rotating alternator driven by the existing drive train, I'm figuring the device would automatically engage after a speed of 60 or above is detected for a certain period of time as a way to determine freeway driving. The device will disengage when a speed under maybe 50 is detected for a few seconds to detect non-freeway driving.

    I have a complete 3D model of the device and a patent pending status on the range extending and power supplying methods that it embodies. I'm currently looking for an established professional to sit down with and review the device design and all of my supporting documentation to determine feasibility since up to this point, me and a patent lawyer are the only ones that have reviewed it. After I get some more opinions on the whole idea, I will post the website address so everyone can see it. Since I know a lot of people are working on ways to extend EV range, hopefully my work will help someone with their idea.

    Calculator Assumptions....so far
    :
    * Electric motor drive train and battery charging speeds used to calculate range estimations are based on existing Tesla Motors Model-S components
    * Battery pack range and range estimations reflect optimum driving conditions (non EPA): free-way driving, flat level road, 70 Deg. F
    * The 85 KWh 300 mile rated battery pack is used as baseline to calculate ranges of smaller packs
    * The effect of lighter weight battery packs is not accounted for
    * An 80% AC to DC charger efficiency is used to calculate charge rate
    - 19,200 Watts AC (240V 80A) for battery range increase rate of about 1 mile / minute
    - 15,360 Watts DC (19,200 x 80%) for battery range increase rate of about 1 mile / minute
    * An 80% drive train efficiency (DC battery power --> AC power --> motor --> drive shaft) is used to estimate range extender power consumption
    * An alternator RPM of 5,000 is the assumed requirement for rated alternator output
    * 20 Horse Power is the assumed requirement to rotate alternator at 5,000 RPM
    * Losses due to bearing friction from transferring rotational momentum to the alternator are not accounted for
    * Losses due to any necessary Alternator DC to Battery DC conversions are not accounted for

    Possible Alternator: 24V/28V 525A (SBC-24V-525).... Most powerful one of this type/size I could find. Still looking for one that requires lower RPMS and/or lower required horse power but still the same or higher output.
    product-181.jpg
    altgraph_zpsba043882.jpg
     
  13. woof

    woof Model S #P683 Blue 85 kWh

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    Well, on the face of it, this sure sounds like you are attempting to patent perpetual motion. Please explain to us how using a battery to drive a motor to drive an alternator to charge a battery results in extended range. It'd be like driving with the regenerative brakes on, resulting in increased Wh/mile out of the first battery in order to charge the other battery. Even with 0 losses in the system, you are taking energy out of the first battery in order to charge the second. In the 0 loss case there would be no extension of range as the original amount of energy available is fixed and just swapped between the two batteries. In the real world there are losses to consider.
     
  14. RaySuave

    RaySuave Member

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    #14 RaySuave, Aug 18, 2013
    Last edited: Aug 18, 2013
    Im just attempting to extend range. The calculator Im making is not finished as I dont have all the information I need to account for all the losses. I posted it primarily for just an example for other people who are working on range extenders.

    If I manage to extend range even 10%, I would be happy since the device I am working on has many applications other than extending EV range. Ultimately the thought behind my idea is to use the multiplied torque of the Model S transmission's output shaft to spin an alternator. What I still need to research and speak to vendors about is my approach to multiplying the rotational speed enough to reach 5,000 RPM for the alternator since I want to harvest the torque from the transmission output shaft which only rotates about 700 RPM at 60 MPH.

    As of now I believe I can get an RPM approaching 10,000 which could be reduced to feed 5,000 RPM to the alternator so it will require half the horse power to spin. In the screen shots, you will see that I am trying to account for the extra load on the batteries due to a range extender being engaged, currently, I figured a 300 mile battery range will be reduced to 190 miles, it isnt a guaranteed value but its a starting point. You will also see I am trying to account for inefficiencies in the normal operation of the vehicle. Also, consider the charge rate of the battery charger supplied with 19200 Watts AC which is supposedly to increase the battery range by 1 mile per minute.

    I realize that this is not enough information to get the full picture of my approach which is why I didnt make a separate thread about what I am attempting. Im going to delete this post since it is being perceived the wrong way. Yesterday I had a long argument about this same exact thing with someone on another board when I was asking for suggestions on similar alternators like the one I posted. If what Im doing is seen as feasible, I will make a new thread.
     
  15. woof

    woof Model S #P683 Blue 85 kWh

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    Well, there's only two ways to extend range--add external energy into the system, or use the existing energy more efficiently.



    Multiplying torque doesn't multiple energy, it also doesn't increase efficiency. The added load of the alternator will increase the amount of energy needed to move the car one mile. The amount of energy recaptured by the alternator will be less than just not using that energy in first place--in other words it does not increase efficiency, and instead decreases it with increased losses.

    Since it cannot increase the energy in the system, and since it doesn't increase the efficiency of the system, I fail to see how it can increase range.
     
  16. RaySuave

    RaySuave Member

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    Thanks for the input but the purpose of this thread was not to convince anybody of anything or ask for advice on range extending methods, it was only to gain advice on how an additional load to the system would effect battery range and thats it. I received an answer for this then posted results on how I used the information to serve as an example of an approach for other people to see. If I wanted my full idea analyzed, I would have posted all of my drawings of the device and made a totally separate thread asking for opinions. I know you have good intentions and dont want to see people wasting time and/or money working on things that will inevitably fail to produce the desired results which is fine but sometimes you have to let people fail. I have learned way more things in my life from falling short of expectations than from succeeding.
     
  17. NuclearPowered

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    #17 NuclearPowered, Aug 18, 2013
    Last edited by a moderator: Mar 13, 2016
    "The range extender utilizes an alternator driven by the existing drive train to charge the depleted battery of a dual EV battery bank...then switch to charging the other battery once it depletes."



    Your tool may be effective for quantifying additional loads on the drivetrain, but the overall idea is non-sense.

    Same concept as strapping a wind turbine generator to a Model S and using it to charge the battery.
     
  18. Yggdrasill

    Yggdrasill Active Member

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    One suggestion:

    Look *very* closely at the relationship between "extra power needed for rated alternator output" and "rated alternator DC output". I'm sure it's possible to find an alternator with papers showing that it needs 10 hp input for 14.7 kW output, but the papers will be wrong.

    You will need around 22 hp for 14.7 kW output.
     
  19. RaySuave

    RaySuave Member

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    I agree, which is why I plan to have an alternator gear/pulley ratio of 2:1 so the car will only have to experience an extra load of 10 or 11 HP. I mention this ratio in the screen shot.
     
  20. Yggdrasill

    Yggdrasill Active Member

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    Well, then the output will be more like 7.35 kW.

    An alternator is not a free energy machine, you only get out around 90% of the mechanical energy you input as electrical power.
     

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