Hello,

I am designing a hybrid vehicle drive system, which needs to use a brushless DC motor/generator (generator to charge battery, battery to apply electricity to motor).

The hybrid drive train consists of a fixed axle, which is connected by sprocket gears to the motor/generator, the axle is hand turned to demonstrate internal combustion engine torque (which is used to spin the unit as a generator).
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However, I am not sure on how to switch between operation as a generator and as a motor...this may be very simple but I am getting confused.

My thoughts are, when the battery is connected by a single path to the motor/generator, the battery will drive the unit as a motor, regardless of the torque applied to the axle by hand turning, therefore not working as a generator and charging the battery?

So my question is, how can I switch between the operations? and is this achievable?

Thank you in advance.

 

Conceptually, if you are applying torque to the motor in the same direction as the velocity, you are motoring. If you are applying torque in the opposite direction from the velocity, you are generating. The basic theory is that simple.

Now, you must have electronic hardware and logic/software capable of implementing this. You must understand how to apply torque to the brushless motor in the direction you want based on the rotor angle. This is significantly trickier than for a brushed motor.

The fact that you are asking such a basic question means that you really need to get some good basic background in motor & drive theory before you progress much. You have a long (but not insurmountable) learning curve ahead of you.

Good luck!

Curt Wilson
Delta Tau Data Systems

 

If the battery is fully charged and always connected to the motor/generator, it will cause the motor/generator to spin until the battery becomes discharged. You need to disconnect the battery from the motor/generator before you can start to recharge it. When recharging, you will need to reverse the flow of electrical current as compared to when you are discharging.

Simply reversing the wires between the battery and the motor/generator will do the job but the motor/generator will try to spin in the opposite direction. You will need to overcome this torque and add some more, in order to recharge the battery. The amount of reverse torque during the recharging cycle can be substantial, especially with a fully charged battery.

A double pole single throw switch or relay can be used to switch the wiring between the battery and the motor/generator, but it will be subjected to quite a large amount of current depending on the sizes of the motor/generator and battery. Also the amount of torque you can develop during the recharge cycle, if high enough, can produce large amounts of current that the switching relay needs to be able to carry.

Another scheme is to use two batteries. Discharge the first until it is at less than half charge and then switch over the the second battery. During a recharge cycle, reconnect the wiring but in reverse, to the first battery so it will recharge. Alternating between the two batteries this way will reduce the amount of load on the switches/relays and reverse torque in the system, during the recharge cycles.

If you incorporate regenerative braking it gets even more difficult. The troublesome part is how to regulate the amount of torque applied during a recharge cycle, to a battery that is in a variable state of charge. I assume you are interested in recovering kinetic energy while applying the car's foot brakes. It is necessary to have very exacting control over the amount of braking force generated. I believe this is where you are headed.

Since you are describing an internal combustion engine as the sole source of power to spin the motor/generator during a recharge cycle, the problem is fairly straightforward.

I hope this isn't too basic so that you've already made these assumptions yourself. If so, I apologize in advance. At least I'm not telling you that you need to learn more. If you didn't need to learn more, I'm sure you would not be asking.

 

I just found this thread, so I don't know if the original posters are still monitoring this site, but I have a similar question: I have built a pusher trailer for our tandem bike that incorporates a 400 watt 24 volt 10AH electric brushless motor, controller, chain, wheels, thumb throttle, batteries, and sprocket set from an electric scooter. When I push the thumb throttle, the motor pushes the bike, my disabled wife, me, and the weight of the trailer, batteries, and motor. It works wonderfully.

Since we also pedal, the motor's usual range is increased from 8 miles to 20 or even 30. I chose a brushless motor because of the lower friction caused by turning the motor shaft. I'd like to pick up some energy from all of that turning, especially when we are coasting down long hills and/or on long rides away from plug-in electricity. Is the amount of electricity generated worth the trouble of capturing it? Could I flip a switch to accomplish this? Does the motor have to turn in reverse, or can a switch accomplish the same thing? I can add more batteries if I need to, but I don't need regenerative braking. We live in Arizona part of the year and could use solar, as well.

Russ

 

hmm...if you use dc brushless, you can control your motor with pwm signal into the motor. but first you must know basic operation motor from motoring to generating..