Quote:
Originally Posted by Dwffy
Hi folks,
I want to throw in a quick question here to see what you guys think of this idea.
When pulling away from being stationary, the acceleration in the vehicle is reasonable and it would be nice to get an extra boost on occasions. Now here's my idea. What if I had a contactor connected from Motor - connection to B- connection of the pack and used a push button to engage it, but, only after the vehicle was already in motion. This should give full pack voltage across the motor without effecting the controller. Could this be a real idea to get a great boost on take off, or would it only let out the magic smoke?
-Doug
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Doug,
A 5 second blurb on how motor controllers work. They always apply the full pack voltage to the motor. What varies is the amount of time that voltage is applied. This is known as pulse width modulation, or PWM.
A motor controller at 100% PWM is exactly the same as your proposed contactor.
So all that is really needed is a push button to the controller and a small bit of code that sets the PWM to 100% when the button is pushed.
But IIRC this is usually the same effect as pushing the gas pedal all the way down.
Now there is one problem with both approaches. Generally when the car is at a stop and full power is applied, the current from the batteries into the motor (and all parts inbetween) shoots through the roof. So the controller measures the amount of current and cuts off power when an overcurrent condition occurs.
The problem with your pushbutton to the contactor is that if the current exceeds the contactor rating, it can cause the contacts to meld together and not be able to release. Same for frying the electronics of the controller.
So be careful if you take this approach.
ga2500ev