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Electronic Throttle for an Electric Car

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iss407

New Member
Hello!

I am finishing up converting a car to use and electric motor. I am using the Curtis 1231C controller. For a throttle input this controller requires a resistive input signal. From the manual:

0–5kΩ Input
The standard controller throttle input is 0–5kΩ. Any potbox that provides a nominal 0–5kΩ output (controller output begins at ≈300 ohms, full output is ≈4400 ohms) will work with the standard throttle input.

The normal throttle boxes us a simple potentiometer, but these wear out and develop "static" which results in jumpy control. Newer controllers now use an electronic throttle such as the Curtis ET103. The hall effect sensor won't wear out and works well in a dirty and harsh environment like under the hood of a car.

I would like to use the electric throttle with my existing controller. As the controller is usually isolated electrically from the rest of the car's electrical circuits (high voltage DC in the controller) I would like to maintain this isolation. I believe that the Fairchild H11F1M Photo FET Optocoupler will do the trick for me. I want a simple, robust circuit to convert 0-5V to about 0-5K Ohms.

It looks like the throttle input on the controller will be able to accept the minimum on resistance of 200 ohms since the throttle turns on at about 300, but it does say that the resistance without the throttle applied should be less than 50 ohms. I think I can do that by using a microswitch to short the output when the throttle is fully released. It also makes for a nice safety since releasing the throttle will mechanically bypass the electronic circuit. If the throttle input exceeds 7000 ohms the controller assumes the throttle box has failed and shuts down.

It doesn't have to be perfectly linear but the closer to linear it is the better. The driver is used to variables in throttle response. As long as it doesn't change quickly the driver will adjust. Just about every car is different to some degree.

I thought that I might need to add a DC bias to the throttle output to overcome the voltage drop in the emitter LED. Instead I can just adjust the throttle linkage so that a fully released pedal results in about 1.2 V or so, just below where the diode turns on. I'll need a POT to adjust so that 5V input is about 5KOhms output.

Am I right in thinking that this circuit may be as simple as a pot and this chip?

Thanks for your input.

-- Paul
 

Mr RB

Well-Known Member
If the hall sensor in the electronic throttle has a plastic 3-wire connector it will be insulated from any metal or grounds. If that is the case you don't need the opto-isolator you should be able to connect it direct to your controller, just keep the 3 wires insulated and away from vehicle grounds etc (of course).
 

iss407

New Member
I have no idea how the ET103 is wired. The 0-5V output shares a common ground with the supply voltage though, so I think I still need isolation.
 
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