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Old 02-08-2009, 08:52 PM   #1 (permalink)
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Hybrid PWM/Contactor controller turbo-boost

Reading through one of the threads on here got me to thinking about an idea that was kicking around a while back.

A Hybrid PWM/Contactor EV controller.

The basic idea is that contactors are stupid, but work well and with variable voltages.

PWM controllers are great and smooth, but expensive.

Why not combine the both to get the control of the PWM with the speed and power of the contactor connection.

My basic idea would be to have a 72V max PWM controller hooked up to the motor and 6 (12V) batteries. One or two more batteries would also be in the car.

With some sort of a basic switch control, contactors would disconnect the controller from the circuit, and connect the spare battery or two into the circuit.

This would raise the system voltage by 12 or 24 volts and max out the available amperage - Turbo Mode!

I would think that a reversing contactor would work best for this. A reversing contactor is an A/B switch, instead of an On/OFF switch. By default, it completes one set of connections. When power is applied to its field coils, it disconnects the primary set of connections, and engages the secondary set of connections. This is a "break before make" kind of a switch.

The contactor could be engaged by either a big red button on the dashboard marked "TURBO". (Or maybe a button on the stick shift?)

Otherwise, it could be a microswitch attached to the potentiometer that engages when the pot maxes out. Press the pedal to the metal and the contactor kicks into overdrive.

What's the minimum number of contactors needed to create this configuration, make everything work right, and NOT fry my controller?

I'm not sure if I would need two contactors, or if I could get away with one reversing contactor.

Here is the motor, batteries, and controller as they are wired right now.

Here is how they would be wired in the higher voltage by-pass mode:

I would imagine having the reversing contactor located physically close to the PWM controller.

There are two cables going to the controller - one from the battery, and one from the motor. Would I need to break both cables?
For example, is there any reason why I couldn't leave a cable permanently connected between one end of the extra battery and the cable going to the motor? Without the other post of the battery connected at the same to anything, it's not sending any voltage to the battery or motor. (Imagine the little red line is a switch that can swing back and forth to connect the main battery pack string to either the spare battery or the PWM controller, but not both at the same time.)

Your thoughts on this?

It also just struck me that the bypass could also be used as a "limp-mode" to move the car in emergency if something happened to the PWM controller.

PS: Yes, you would have to make sure all the contactors are rated for high amperage....

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