# Microcontroller based controller Q's



## Qer (May 7, 2008)

In essence, that's all there is to it, yeah. Only one thing remains, you want to keep an eye on the current. If you're, for example, giving full throttle (bad word for an EV I guess) and the car is in an uphill, current will spike towards infinity which can kill both the controller and the battery pack.

So one way or another you have to make sure the controller limits the power if the current goes haywire. You might also keep an eye on the pack voltage so you don't run it too low, but that you can do manually by a volt meter. You don't have to do that in the controller if you don't want to.


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## hyper24 (Jun 13, 2008)

hmmmm.... I think I might give a shot at making my own controller.

Can you explain a bit more about the current limiting?
I guess I haven't read up enough about electric motors to know how they REALLY work.
I thought if you had a voltage hooked up to a motor it could only draw X amount of amps due to the resistance in the motor.
But obviously their is more to it if its possible to short the motor.

Could you explain more about how the current could spike in the uphill situation?


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## ga2500ev (Apr 20, 2008)

hyper24 said:


> hmmmm.... I think I might give a shot at making my own controller.
> 
> Can you explain a bit more about the current limiting?


Imagine a motor that is stalled, so it isn't spinning. Power is being applied to get it to start spinning. The motor will continue to pull more and more power in an effort to get started. Since the voltage is fixed, the amount of current continues to increase. Eventually the motor will burn out.

That's what current limiting is for. When the motor gets into a situation where it'll draw too many amps, the controller will cut power to the motor to keep both the motor and the controller from burning up.



> I guess I haven't read up enough about electric motors to know how they REALLY work.
> I thought if you had a voltage hooked up to a motor it could only draw X amount of amps due to the resistance in the motor.


But the resistance is quite small. So a lot of current can be drawn though the motor. Potentially thousands of amps of current.

In a stalled situation this power gets converted into heat. That's why the motor will burn up if you keep that kind of power applied for too long a time.



> But obviously their is more to it if its possible to short the motor.
> 
> Could you explain more about how the current could spike in the uphill situation?


The uphill situation is like the stall. The motor is working harder so it's drawing more amps. This can cause it to spike.

A current limiter will only let the motor draw up to the current limit, then power is cut off. With a PWM controller this is usually done by limiting the length of the power pulses applied to the motor. 

ga2500ev


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