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Discussion Starter #1
Hi Everyone, I have been/am currently working on a project investigating the design of an electric three wheeled vehicle.

The outlines of this vehicle are as follows;

  • Should be less than 410 kg
  • Modest performance (0-60mph 10 seconds for example)
  • Aerodynamically very efficient
I have been working on specing the electric motor and batteries for it so that i can determine how much mass and volume allocation they will use.

I have chosen this motor http://www.azuredynamics.com/products/force-drive/documents/AC24LS_DMOC445ProductSheet.pdf
which i believe is also used by the aptera 2e, i would rather an even less powerful motor, but its the most decent one i could find.

Now i am trying to spec the batteries. I have calulated that over a urban,rual and motorway cycle that i can do an average of 100 miles (range) for a battery with a 10Kwh output.

Can someone help me in finding a suitable low mass/low volume battery for the purpose?


The aptera-2e used litium ion, but if there is something better (reliable, range and performace wise) i would like to know.

I would please like the insight of the forums users as you will all be very much more experienced in the practical aspects of spec-ing batteries/motors. My field of expertise is aerodynamics.
 

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Off hand I would say this is a good job for an HPGC ac-20 or ac-30 drive setup with 108v and Thundersky 100ah batteries

Guys?

BTW Robin, any pics of the project? I am building an aero trike of my own and would love to have a chat, perhaps compare notes. :)
 

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Discussion Starter #3 (Edited)
Off hand I would say this is a good job for an HPGC ac-20 or ac-30 drive setup with 108v and Thundersky 100ah batteries

Guys?

BTW Robin, any pics of the project? I am building an aero trike of my own and would love to have a chat, perhaps compare notes. :)
No pics at the moment, i am building a CAD model in CATIA. I have been working on a HPV (human powered vehicle as seen in my avatar) and running it in CFD for the past few months and now moving onto this. Would be great to chat about the technical aspects of this!

I also have some graphs and suchlike on how i calulated the power consumption and required torque etc.

Do you have a link for the specs of the setup?
 

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Discussion Starter #5 (Edited)
Thanks for the tip

I should have posted some of the specs of the vehicle;

0-60mph = 10 seconds (or just under)
Top speed = 100 mph
Max power required = 33.3 Kw (45 bhp) @ 5300 rpm (only one forward gear btw)
Max Torque = 100 Nm (probably 90 is better)

The target is not to exceed these at the cost of adding extra mass or volume. Obviously the main volume/mass will come from the battery to supply the motor so this is another reason to not have a motor which is overpowerful.
 

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Discussion Starter #6 (Edited)
From looking at the motor specs i dont think they match up to the task, my peak power requirement is at my max speed (100mph) an i need around 33kW to reach it in around 30s (from standstill). The AC-30 falls someway short of that, and for some reason they havent published the torque curve for it (which is crazy by the way).

The mass and volume of the AC24ls (the one im current using) isnt really that much more, though the controller is 10kg lighter!

If i am to use the AC-24 i have calculated i need around 12kwH of energy storage onboard for 100 miles range, which equates to around 80 Amp.Hrs for a constant 156v push of current to the motor. Does this sounds reasonable? It would mean that i only need one of the 100Ah batteries which kind of sounds wrong?
 

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I am also building a three wheeler which should be on the road within a month. I failed the MSVA test (neccessary to put it on the road in Britain) for the second time today, but next time it should all go OK. Even if your vehicle is very aerodynamic I don't think you will be going very fast if you are using only 120Wh/mile. My calculations suggest that my 330Kg trike will need at least 85Wh/mile at 40 mph. This does not include acceleration or hill climbing so I would probably expect to use >100Wh/mile cross country, at speeds mainly between 30 and 45 mph, with the odd bit of 50mph. I will post a full report as soon as I am road legal. Back to the workshop to do the fixes first though!

Andrew.
 

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Discussion Starter #8 (Edited)
I am also building a three wheeler which should be on the road within a month. I failed the MSVA test (neccessary to put it on the road in Britain) for the second time today, but next time it should all go OK. Even if your vehicle is very aerodynamic I don't think you will be going very fast if you are using only 120Wh/mile. My calculations suggest that my 330Kg trike will need at least 85Wh/mile at 40 mph. This does not include acceleration or hill climbing so I would probably expect to use >100Wh/mile cross country, at speeds mainly between 30 and 45 mph, with the odd bit of 50mph. I will post a full report as soon as I am road legal. Back to the workshop to do the fixes first though!

Andrew.
Hi andrew i did a recalc and came out with twice the number as before, so total 24000 KwH storage needed for 100 miles.

Ive posted the drive cycle here. Its seconds along the bottom and Kph on the y axis
 

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Don't forget that increasing the battery capacity increases weight and hence rolling resistance so doubling the batteries doesn't double the range.

It's difficult with a unique vehicle to estimate the energy use but here's how I have tried to estimate. Power needed is proportional to the square of speed so P=X*V^2 We can find the factor X by comparison with a similar ICE powered vehicle where top speed and power of the engine are known. For instance my first ICE trike used a 125cc Piaggio motor with CVT from a scooter. It gave 11hp and could reach 57mph on the flat. At this point it had possibly gone over it's power peak because scooters tend to be low geared for good acceleration, so lets assume 10bhp gave 57 mph. 10hp is 7460 watts so putting this in the equation give an X of 2.296.
So 40mph requires 1600*2.296=3673.6w Divide by 40mph gives you 91.84 Wh/mile.
Of course I'm hoping that my EV, though it may be 140Kg heavier is more aerodynamic and has a smaller frontal area. The inefficiencies between battery pack and rear wheel are less than those of an ICE with the CVT transmission which could rob me of 25% of my power easily. So all in all and making comparisons with other EVs such as the vectrix I reckon I need at least 85Wh/mile at 40! Once you've worked this out Wh/mile is proportional to speed so it's easy to find your energy use at any speed!

Andrew.

You can see my trike in the garage under Kirk EV or sparky. I'm also in EV Album which is easier to navigate.
 

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Hi Robin

it would mean that i only need one of the 100Ah batteries which kind of sounds wrong?


Don't forget each battery (cell) is only 3.3v (approx) so you will need 48 for your 156v

Also you should limit your discharge to 70 or 80% or battery life will be short
 

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Discussion Starter #12
Don't forget that increasing the battery capacity increases weight and hence rolling resistance so doubling the batteries doesn't double the range.
Yes, RR does increase but its fairly small compared to drag and inertial forces.

Doubling the battery size didnt double the range, it was a bit of a coincidence. My recalculation just showed my i neeeded twice the energy that i did before (more or less). I also forgot to add the mass of two drivers and luggage (increasing mass to 600kg), so again more energy required.

But would you agree that 24kWh of energy on board would take me the 100 mile distance.
 

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But would you agree that 24kWh of energy on board would take me the 100 mile distance.
at what speed? That sounds really tight unless your aerodynamics are astoundingly good.

back to batteries though. you are going to have to go Li, just choose between regular large format like Thundersky or SkyEnergy and the smaller a123 or something that would allow higher voltage in smaller space but more of an assembly challenge and be more expensive to boot. If you hvae lots of money, start looking at the kokams and other specialty units.
 

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Discussion Starter #15
Hi Robin

it would mean that i only need one of the 100Ah batteries which kind of sounds wrong?


Don't forget each battery (cell) is only 3.3v (approx) so you will need 48 for your 156v

Also you should limit your discharge to 70 or 80% or battery life will be short

Im not sure i understand the voltage concept entirely, im a bit rubbish at knowing what to do with these things. I know i need X amount of kWh of stored power, (or X amount of Amp hours). I dont really understand the voltage bit?

From what i saw one battery contains, say 100 Ah, how does the voltage come into this?
 

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Hi Robin

The voltage is the "pressure" (volts) the amperage is the "flow" (amps)

a Watt is a measure of "Power" (energy flow) (1 amp X 1 volt = 1 watt)

These give you the "Power" to drive your car

The next thing is how long can it drive - this is where Amphours comes in

1 AH (ampere-hour) is the ability to give 1 amp for one hour

A batteries consists of a number of cells (separate or all in one box)

Each cell has a voltage and an AH

a 100Ah lithium cell has about 3.3 volts so it can produce 100 amps for one hour at 3.3 volts

3.3 volts X 100 amps is 330 watts - less than half a horsepower -not a lot for a car!

so we put 48 cells together and get 48 X 3.3v = 158 volts

158 volts X 100 amps = 15855 watts or 15.8 Kilo-Watts about 21 horsepower for one hour

That is a more useful "battery"

158 volts X 100 amps X 1 hour = 15.8 Kilo-Watt-Hours

How much you need depends on

Size of vehicle
Speed it will be driven at - less obvious it takes a lot more energy to go fast
Range

kilo-watt-hours needed per mile can be from
0.15 Kwhrs/mile very efficient car (EV1)
0.3 Kwhrs/mile normal car

If you are making something like an electric recumbent bike these number can get a lot less
 

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Discussion Starter #17
kilo-watt-hours needed per mile can be from
0.15 Kwhrs/mile very efficient car (EV1)
0.3 Kwhrs/mile normal car
Thanks for that useful info Duncan. At the moment my calculations are coming out as 0.14 kWhrs/mile, albeit i havent taken into account efficiencys yet. That is also based on a 3 part drive cycle urban/rural/motorway at 10 minutes each, repeated until the distance reaches 100 miles. It is 'supposed' to be very efficient (Cd=0.15, very light, low rr tyres).

With constant motorway driving i need around 19500 Kwhrs to make 100 miles.

I also found that if doing performance tests 0-100mph, i can do only 5 cycles of 0-100mph before needing a recharge!

Can anyone quote me some efficiency numbers for transmission? I have a planned 1 gear transmission (just the diff) 1:5. The motor im currently looking at has 0.85 peak efficiency. Does battery efficiency matter as well??
 

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Its worth saying this.

When I said "There are likely other / better? sources of info on this drive setup," I in no way meant to disparage Thunderstruck, I have purchased from them as well and did get a first class experience.

Tom
 

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Discussion Starter #19
Can anyone quote me some efficiency numbers for transmission? I have a planned 1 gear transmission (just the diff) 1:5. The motor im currently looking at has 0.85 peak efficiency. Does battery efficiency matter as well??
 

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You may want to use aluminum pulleys and toothed belts with around a 7-1 gear ratio.This creates less friction and lessens the weight.You can also use the internal limited slip differential from a Honda.
 
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