EV on a mountain road?

No experience with EV, but for hybrid;

I gain and lose ~4000' at least five times per week and get 43 mpg in cold weather. Purely from empirical observations, the battery can only capture about 1000' of potential energy change (mg*deltaH) which is a damned shame, but it certainly doesn't prevent the car from getting good gas mileage. This does have me wondering how I can add more battery however...

If an EV does have enough battery to recover all the energy from the highest altitude change, I don't see why EV wouldn't work just as well.

 

A Prius requires about 0.15 kilowatt hours to drive on level smooth roads at 60 mph, or so I have read. For raising the car uphill, and neglecting any inefficiencies, we can use the following formula:

Potential energy (Joules) = kg * 9.8 m/sec^2 * distance climbed (meters)

A typical highway hill grade might be 6%, or 78 meters per mile. Prius may weigh 2890 lb. or 1314 kg

Potential energy = 1314 * 9.8 * 78 = 1004422 Joules

Divide by 3600 (seconds/hour) to obtain 279 watt hours, or 0.279 kilowatt hours.

Thus a Prius climbing a 6% grade requires about 3 times the energy as driving on level highway, assuming no mistakes in my math, and again neglecting inefficiencies in obtaining the climbing energy from gasoline. Data collected on the road could quantify those inefficiencies.

This can readily be recalcuated for other vehicle weights or heights climbed.

 

Hi Nomadic1,

Motor Torque is proportional to Motor Current. So, an uncoupled free spining motor will only require a very small current to maintain the speed that the applied voltage causes. Put a load on the motor, and the current required will go up to maintain speed.

A 175 A motor is rated to not burn out with 175 A. Find the torque constant in the motor spec, and multiply by the maximum current the batteries can supply, and you will get the maximum torque the motor will deliver with those batteries.

My recomendation would be to stay away from a wound-rotor motor for mountain climbing service. Like all DC motors the wound rotor motors have high low-end torque, but due to the suspended nature of the rotor, they tend to burn-out the windings in low-rpm high torque continuous service. At low vehicle speeds, the available ram cooling is small too. Additinionally, mechnical comutation is not ideal for low-rpm high torque (current) continuous service. A wound rotor DC motor usually uses a mechanical comutator. Although, I did see recently a motor company offering an electronically comutated, wound rotor motor. It had slip rings to get the field into the wound-rotor assembly, but then it has electronics on-board the rotor to comutate the windings.

I would recommend a motor with a stator winding. Windings on the stator can be more readily cooled in continuous duty high-torque application. My preference is for the socalled Brushless DC or Hybrid motors. Brushless DC motors have a permanent magnet rotor, which the stator windings act on. The Hybrid motors are a combination of the Brushless DC and the common Induction Motor (like is used in your furnace blower). They are called hybrid motors because the magnetic field is partially due to magnets imbedded in the rotor, and induction of currents that flow in the rotor due the applied fields from the stator windings. This is what is in the Prius. These motors have are economical, as the expensive magnets are smaller, although they do not have the super-massive low-end torque. Which is probably a good thing in automotive retro-fit application, as the drive train is designed for an engine, which has lower torque for the horse power. This type of motor is probably why the Prius HSD (gen II) has that 15 to 45 mph torque punch, and is a little slow up to 5 or 10 mph.


A variable frequency 3-phase drive and an induction motor might be a cheaper alternative to the hybrid or brushless-DC motor. As these motor drives might be found surplus. The state-of-the-art in induction motors is the Cast-Copper-Rotor induction motor, which Siemens just started to supply to the market. In typical induction motors, the induction bars are diecast aluminum alloy, that runs through the iron core of the rotor. This the socalled "birdcage" construction. Only recently has the ability to cast the birdcage bars out of copper been achieved, and even more recently offered for sale.

 

edit-vehicle sold

 

Maybe darell can weigh in. I can't speek with any authority. Even so, fFrom reading posts of the Rav4-ev list, several of the folks pull hills and it doesn't seem to be as tragic as you're making out.

 

I know nothing about conversions. But AC Propulsion drove its li-ion tzero from L.A. to Las Vegas on a single charge. I believe that involved going through mountains. The tzero is a tiny little sports car, so it weighs less than a conventional conversion car would, but still it suggests that the drastic drop in range you are talking about is exaggerated.

You would use more electricity on the uphills, but if you have regenerative braking, you'd re-capture a good deal of that on the downhills.