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Old 08-04-2009, 05:09 PM   #2148 (permalink)
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Power steering too?

I have been reading this thread for a couple months now and what attracted me here in the first place was a search for a power steering / accessory motor controller. There are a couple gasoline powered vehicles that have an electric-hydraulic power steering pump that can be scavenged, or new commercial solutions exist, but I see a couple problems with these solutions:

-If you are choosing a used electric power steering pump from an old vehicle (ex MR-2: Installing the Electro-Hydraulic Power Steering System) there is a limited supply and their availability at a good price is hit or miss

-New commercial versions are expensive. I had a quote for almost 800 buck from Power Steering Kit.

-Both solutions require sizing your 12V system to be able to handle the large peak current draws that can occur with those systems (~60A). Running off pack voltage would be better for efficiency sake.

I don't currently have an EV but I am planning a conversion next summer and I was thinking that why not take advantage of the power steering pump that came with my "glider" in the first place. All I need is a motor to turn the pump.

Perhaps a motor like one from an electric lawn mower or some other motor.

Then I thought that it would be nice to reduce the power steering boost when running above a certain speed to avoid wasting energy....I need a controller.

I was thinking that a single mosfet/diode/cap stage would probably be enough for the power steering pump motor. The 12V systems have a peak 60A = 720W. At 120V that current is only 6A for the same power. That should nicely fit into a single mosfet/diode/cap stage.

If the microcontroller was fitted with a main motor RPM sensor, and could output a second PWM signal to a separate mosfet driver circuit, there you have it - a power steering motor controller inside the main motor controller.

Those of you with an EV, what are you doing for power steering? Simply looping the lines is not an option for me as I would like my wife to be able to drive this thing, and I don't know if she could handle it without power steering.

Can the current micro-controller handle two PWM channels. Is there enough computational cycles leftover to handle the adjustment of the PWM of the power steering pump motor according to the motor RPM?

I have enjoyed reading these posts, all 2147 of them. Great work everyone. I can't wait until I can place an order for a kit.
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