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4QD controllers
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Some controllers use a 3 wire potentiometer with a voltage input, some use a 2 wire resistive input. It is not difficult to convert the wiring of, for instance, the 4QD series controller to accept 0-5K instead of a potentiometer. 4, 5 and 6 are the pot connections on the 6 pin connector to the 4QD. Zero resistance will give zero speed and 5K will give full speed.
The circuit shows how to do this. R1 is a resistor, in series with the 0-5K variable resistor. Suggested values for this series resistor are between 4K7 and 12K: a value much higher than 12K runs a danger of operating the 'pot fault detect' circuitry at full resistance.
There is a small trade-off: the speed/throttle curve is made slightly non-linear. The lower the value of R1, the worse the linearity.
The first curve shows the response with a 15K series resistor (slightly too high a value to obtain full speed).
The second curve shows the response with a 4K7 series resistor. Although it is slightly less linear that the first, it is unlikely that an average driver would notice this - but that will depend on the motor and vehicle response.
Also, the higher the series resistor, the lower the available voltage swing. 4K7 will give 0-5.5v on the 4QD or 0-4.4 on the Pro and NCC controllers. 12K will give 0-3.2v on the 4QD series controllers which will easily give full speed.
However 12K will give 0-2.5v only on the NCC and Pro - which is not enough for full speed. Use a maximum of 6.8K with these.
On all controllers you will of course need to adjust the gain control for full speed.
The circuit also shows the 'top speed adjust' pot for the 4QD series. You cannot use this system for top speed adjust with the Pro-120 as the 'high pedal lockout' on these detects zero pot resistance at the wiper - you won't get zero resistance with a wiper series resistor!
Related to this page is our current loop interface. Indeed a variation of this interface could be designed to give a linear interface, but the small loss of linearity of the method shown here should not be a problem
If you have any problem with the recommendations here, or want a different scheme, then please contact 4QD.