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Working with a local college – Accrington and Rossendale – we have a benefactor willing to fund the development of an electric car based on a vehicle conversion (using the existing gearbox) and with regenerative braking

The kerb weight of the vehicle 1600 Kg

As a top level question what size of motor and what battery size would be required to give a top speed of 60MPH and a range of 60 miles

Appreciate the specification of battery will be a key factor – please give options and approximate costs for the motor and the battery pack

Any help gratefully received - have to start somewhere !

Stephen
[email protected]
0779 556 5556
 

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Battery size

I suggest looking for typical energy consumption rates, which are typically expressed in kilowatt-hours per kilometre or per mile. When you have a plausible value, multiply that by range to get the required usable energy capacity... and since you can't use the entire nominal capacity of the battery, you will need it a little larger.

Regenerative braking reduces the total energy requirement, but all production EVs do this so it is already accounted for in their energy-per-distance performance.

People can give you a number, but it will be based on their requirements and their understanding of your project... not yours.
 

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Motor sizing

... what size of motor ... would be required to give a top speed of 60MPH ...
The details are dependent of the power-versus-speed characteristic of the motor and the available gear ratios, but if a motor is just able to keep the vehicle moving at 60 mph on flat ground, it take essentially forever to get there and will not be able to maintain that speed while climbing any incline or facing any headwind.

I suggest defining some performance scenarios, determining what motor power is needed to handle them, and then looking for a motor to handle all of those situations, such as:
  • maintaining a target speed up a moderate incline
  • maintaining a lower target speed up a steep incline
  • accelerating to a target speed in a suitable period of time
These will all depend significantly on the vehicle mass. You have a target of 1600 kg, but how was that chosen? Since the battery mass is significant, if you independently choose the vehicle mass and the battery capacity, you have no control of mass available for the rest of the vehicle and cargo.
 

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... and with regenerative braking
to add on to what brian mentioned above, I would suggest you reconsider the regenerative braking feature.

What it is a nice to have feature, it does not make or break an EV conversion.

To reduce the complexity of the project (especially if this is the first EV conversion by the college), then I would suggest using a DC motor first (which doesnt not have regenerative braking). The DC motor is much cheaper and simpler to use than AC.

I've dropped you an email because I seldom check this forum, but I'm willing to assist with further information for the conversion.
 

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I'm seeing all these awesome college projects and I'm very envious that this a thing you can do.

and with regenerative braking
If it is fun for you, the do what you want.

For most DIY projects, this means a higher expense and a higher amount of effort than they care to put in.

It's trendy to fantasize about regenerative braking, but realistically you're adding ZERO miles to your highway range, and only 5-10% to your city driving range. Generally, on the cheaper side, you're better off ignoring regenerative braking and just adding that extra range as more batteries.

Though if you're using an AC/BrushlessDC motor and a controller that can do regenerative braking, there's no reason not to.

Regenerative Braking severely limits your DIY options, especially the cheap ones.

The kerb weight of the vehicle 1600 Kg
Weight only matters in an electrical sense (ignoring handling and all that), for the energy you spend getting it up to speed, and, correspondingly, the energy you waste when you stop it. It has (nearly) no impact on your range when driving a steady speed.

http://www.enginuitysystems.com/EVCalculator.htm <-- Here is a calculator.

Punch in your weight and target speed, and then read the top "Inertia" result. (Aerodynamics has no impact on this, ignore that stuff). That tells you how much energy you waste stopping from a given speed. Note that it is not linear.

For a 1600kg car:
- At 100km/h: 171 watt-hours
- At 50km/h: 42 watt-hours.

That's a quantity of energy, and amount. Every start and stop from a given speed wastes that much energy.

A single 18650 battery has about 10 watt-hours, so, roughly speaking, you're burning through 4 of those every time you stop at traffic lights, or, 17 of those every time you stop from highway speeds.

Weight isn't that big of a deal compared to aerodynamics.

As a top level question what size of motor and what battery size would be required to give a top speed of 60MPH
Go back to that calculator I linked, and play around with the data. (Acceleration should be zero'd out unless you're testing acceleration, the calculator is a little odd to presume the values it does).

To know how powerful a motor you need, you need to know roughly the size of the vehicle, how much air it's pushing out of the way. That will tell you how hard it is to maintain a speed. Any extra power in the motor tells you how fast you can accelerate up to that speed.

Just to ballpark motor size to maintain 60mph:
- Around 8,000w, 11hp for a motorbike.
- Around 12,000w, 17hp for a small car.
- Around 50,000w, 66hp for a big van or truck.

Then, how long it takes to accelerate will depend on the weight. 0.2g is considered "aggressive" and 0.3g is considered "dangerous".

To figure this, the "acceleration" (also used for hill climbing) number for 1g is 9.8. So for 0.2g (0-60 time of 12 seconds, fast but not reckless acceleration), punch in about 2 there.

That changes your power to about 100,000 watts, or 136 horsepower to have "aggressive" acceleration. Most DIY electric vehicles will just have normal day-to-day abilities, not streetracing abilities. You decide.


The thing with electric motors is that their limits are generally only thermal. So you can overdrive them 3-10x what their continuous rating is for a couple minutes before heat builds up. That makes them well suited to most driving conditions because, as you can see, your power use when accelerating is about 8x your power use to maintain that speed, which only takes a few seconds. (17hp to travel at highway speed, 136 horsepower to aggressively accelerate to that from a dead stop).

If you want to go cheap, any 9" - 11" diameter DC forklift motor can do this. You can usually pick one up for Free-$200 if you're polite. It will weigh around 200lbs. Ignore whatever the label says it can do for power, if it's around 200lbs, you can get at least a hundred horsepower out of it. Duncan drives his to several times that, and it took him 7 years of actual racing before it took any damage. No regen though.

If you want to spend some high-hundreds or low/mid thousands of dollars, a Nissan Leaf motor is 120hp, a Tesla is 220-600 hp. Those can also do regen.

The motor will probably be rated for 36-48v, doesn't matter, you're going to give it at least 100, if not 175v or more. It will almost certainly be fine.

and a range of 60 miles
Go back to the calculator. Zero out acceleration. Punch in 60mph. Look at the "watt-hours per mile" result. Multiply it by 60 if you want to go 60 miles.

Anywhere from:
- 150 wh/mile for a motorbike.
- 250 wh/mile for a small and sporty car.
- 350 wh/mile for a normal sedan.
- 800-100 wh/mile for a van or truck.

You'll be looking for around a 20,000 watt-hour pack. That's what a Nissan Leaf has. Teslas start around 60,000, up to 100,000-ish.

Damien on his 1000euro build (including the price of the vehicle) said he can regularly pick up OEM lithium vehicle packs for $600. Damien has good luck, so, expect to pay 2-3x that perhaps if you're not as skilled a bargainhunter.

Do not use lead-acid batteries, they suck, and unless you can get them for free they are more expensive than buying used lithium ion batteries for equivalent performance. There is no reason to use them.

Any help gratefully received - have to start somewhere !
You'll need a controller too. You can build a big one yourself for around $600 for parts. Something salvaged probably isn't good enough. If you go OEM, that will obviously work fine.

Here are some nearly-identical threads with the same info:

http://www.diyelectriccar.com/forums/showthread.php?t=194601

http://www.diyelectriccar.com/forums/showthread.php?t=195105

http://www.diyelectriccar.com/forums/showthread.php?t=195706

http://www.diyelectriccar.com/forums/showthread.php?t=195826


Keep us updated with your questions and progress.
 

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You might want to take a step back and determine what the real requirements are. If you have assumed that regenerative braking would be best, that's a premature design decision; however, if learning about regenerative braking is a purpose of the project, then including it is a valid requirement.

The other decision that I noticed is the use of the original transmission; there might be good reasons for that, or it might be unnecessarily constraining the design.

There's also the mass of 1600 kg. I had read that as a target, but I now realize that I probably misread it - it is likely the curb weight of the vehicle before conversion. After conversion it will likely be heavier, so be careful with assumptions about the post-conversion mass.
 

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Re: Battery size

I’d focus on what you want the students to learn and how many hours are they expected to put in on such a project. How many students will be involved? They will need to fill all the various roles that us DIYers do ourselves; project manager, parts and tools organizers, marketing (corporate donors of various components), project coordinator, schedule tracking, technical consultants, safety officer, CANbus programmer, etc.

Certain skills are learned using DC motors, slightly different skills with AC motors. Reused EV components from a junkyard are a third approach with skills developed that are most useful in the automotive EV world.

If your budget is tight with few corporate sponsors, go with a DC motor. What will be the disposition of the vehicle at the end of the project? One school near me raffles off the finished vehicle to pay for next year’s project. They usually do a classic vehicle restoration.
 

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Working with a local college – Accrington and Rossendale – we have a benefactor willing to fund the development of an electric car based on a vehicle conversion (using the existing gearbox) and with regenerative braking

The kerb weight of the vehicle 1600 Kg

As a top level question what size of motor and what battery size would be required to give a top speed of 60MPH and a range of 60 miles

Appreciate the specification of battery will be a key factor – please give options and approximate costs for the motor and the battery pack

Any help gratefully received - have to start somewhere !

Stephen
[email protected]
0779 556 5556

First of all you need a driving resistance curve to know how much power you need at a any point. Than you now the minimum power consumption to calculate a battery capacity.
Looking on motors you need to take account on rated and peak power/ torque and rpm.
I sendyou an excel sheet. Not finished. But gives you some help.
 

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Hello Everyone,
I am working on my college project related to conversion of Toyota Yaris (sedan)
the aim is to attain a maximum speed of 120kmph with a range of 150 km

These are the calculations I have done on my side.

I have assumed 10% gradient.
Mass of the vehicle is considered to be 1916 kg ( I have assumed the battery pack may weigh 30% of curb weight)
overall gear ratio=7.8066 (assuming car will run on 2nd gear)
wheel radius= 14"

Rolling resistance force= 187.026 N
Aero Drag= 517.477 N
Gradient Resistance= 1870.40 N

from above values Power= 84 kW
torque= 140 Nm

I am thinking of using HPEVS AC x 35 electric motor 144V and 500amps
Battery Back of 35 kWh and capacity of 200Ah


are these values correct? Please suggest corrections if any
 

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Hello Everyone,
I am working on my college project related to conversion of Toyota Yaris (sedan)
the aim is to attain a maximum speed of 120kmph with a range of 150 km

These are the calculations I have done on my side.

I have assumed 10% gradient.
Mass of the vehicle is considered to be 1916 kg ( I have assumed the battery pack may weigh 30% of curb weight)
overall gear ratio=7.8066 (assuming car will run on 2nd gear)
wheel radius= 14"

Rolling resistance force= 187.026 N
Aero Drag= 517.477 N
Gradient Resistance= 1870.40 N

from above values Power= 84 kW
torque= 140 Nm

I am thinking of using HPEVS AC x 35 electric motor 144V and 500amps
Battery Back of 35 kWh and capacity of 200Ah


are these values correct? Please suggest corrections if any

1870 N overall resistance at 120 km/h with a Yaris? To much.
But your rolling resistance should be around 375 N


I get with a VW T2 Camper a value of 1253 N = 41,78 KW + Drivetrain loses.

Do you have the CW x A figures of the car?
 

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are these values correct? Please suggest corrections if any
Please keep your build questions inside your own build thread(s). This thread is for a different person to keep track of their progress and ask questions about their build.

You already have 2 threads, no need to be cross posting tangents on other people's threads.
 
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