Building an electric car, have techincal question?

Question

This will be the first in a series I'm sure.

A friend and I are converting a car to electric. We're thinking of using a single 9" 120V DC motor for the drive.

Question: Is it possible to attach two motors in series (say two 60V or a 94V and a 36V), to get the same power output of the 120V? The idea is to shut off one motor while cruising on the highway to increase range. If it is possible, any Ideas where I can find info about how to control the motors?

Thanks in advance.

I have no intention of running 120V through 60V motors. The Idea was both motors are getting 60V and I simply turn one off. Mechanical synchronization is accomplished by attaching the output shaft of one motor to the tail shaft of the other, then its output shaft to the car tranny. Weight, while important, in not in question here, only drive efficiency.

Answer 1

You would have a problem here because if you switch off one of the motors off the remaining motor would be getting 120V and it would burn it out
try using two different power motors of the same voltage
IE.
A 20A motor for town
and a 15A motor for motorway driving using differing gearing for higher speeds

Good luck with it I hope you succeed

Answer 2

Normally motors are not connected in series, but in parallel. If you had two 60V motors in series, there is no guarantee that each motor would see exactly half the 120 volts. Motors are not a purely resistive component and their resistance can change as the load on them changes. It might stay close to 60/60, but then again it might not.

Also, if you disconnected one motor to save power, that would open the whole series circuit, interrupting power to the other motor. If instead of removing one motor you shorted abound it, then all the 120 volts of the circuit would appear across the remaining motor, which would be bad for a 60V motor, or even it it wasn't it would not really save power, because a 60V motor running on 120 volts will use way more than rated power.

But you don't really save much power by using a smaller motor for low power cruise. I think just supplying one big motor with less electricity would be nearly as efficient.

Answer 3

It is mechanically a nightmare getting two motors to synchronize and drive together. It's better to have one larger motor for power. Also there is the consideration of energy loss due to mechanical conversion. Two motors would double the loss.
This application may be more feasible at a future time for racing when the amount of electrical energy storage is theoretically infinite. For now energy storage technology is way behind the rest of the car. The design of today's electric cars depend on high efficiency low power motors and short range driving. Two motors add much more weight with the associated parts. It's a great idea for future, but now not practicable.

Answer 4

I think you need to start looking for more answers at the library and web sites devoted to this technology than on Yahoo Answers. Here you may get some ideas and feed back but through real study you will get answers that involve the physics of power and design and learn from the successes and mistakes of others.

To start with putting motors in series is a bad idea as it doubles the current and voltage required to achieve the same rpm.

Second, are you talking about DC or AC motors and do you understand the pros and cons of both?

Third, there are many factors to consider for any vehicle design and how you balance the drive train to the balance of performance and stability is one of them. More is not necessarily better. In this case you really need to look at motors based on their *power rating* not their *size.* Shaft size is critical for them to handle the transfer of load to a heavy vehicle too but think kilowatts and horsepower not inches or even necessarily voltage.

There are DC hub motors out there to use in a small vehicle and the idea for an all wheel drive is to use one matched motor in each wheel so that they are automatically synchronized by running them with parallel power.

However it is possible to do exactly what you are talking about simply by switching. You run both motors off a single controller of sufficient capacity and then at cruise simply switch one motor off. The simplest way to do this is with a speed sensor that sends a signal to a relay that turns the second wheel on below a specified RPM and off above it.

Make sure your controllers are up to the task or they will burn out. Look for Curtis controllers that are made for golf carts and expect to operate in the 100+ range on amps.

Also learn about the difference between peak power, nominal or operating power, and continuous power ratings and the importance of temperature even for electric motors.

Answer 5

i'm thinking of two completely separate engines. it would be like mounting 2 engines in a front wheel force automobile. pass away one engine and transaxle interior the front. Mount the 2d one over the REAR wheels. do you recognize how prepare locomotives artwork? they have electric powered autos on the force wheels. A diesel engine produces electrical energy which powers the wheel autos. Now it truly is a hybrid. There are intense problems with working 2 engines on the comparable force shaft. many times you will want a viscous coupler (like a torque converter) to allow some slippage devoid of destroying your transmission or engines.

Answer 6

you may want to join the Yahoo ev group http://autos.groups.yahoo.com/group/diy_ev_cars/

2 motors used as you suggest will not be very efficient due to extra drag and other losses, even if open circuit.

You might consider putting them in the wheel hubs, as a friend of mine is doing with two lynch motors; but not switching one in & out due to synch & meshing and other transmission problems.

Answer 7

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