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Inhibit switch / footbrake – 4QD series only [tour 16]


If a vehicle is fitted with a hand or foot brake, it can be useful to disable the controller.

This can be done with an interlock to ignition circuit on any controller. The problem with such a system is that you can’t do a standard hill-start on the hand brake, as the High pot lockout comes in. You could of course switch the potentiometer slider (speed input) line to zero – you’ll probably need to contact 4QD for assistance on the choice.

However the 4QD series have a special ‘inhibit’ input which doesn’t disconnect the ignition so won’t engage the HPLO. Connect this input to battery negative line and it will ramp the speed down to zero and the controller won’t operate until it is released. This was incorporated especially for one customer to work with a hand brake.

Hire Vehicles and Series wound motors

Undoubtedly a permanent magnet motor gives better control that a series wound motor, but the characteristics of a vehicle fitted with a PM motor are totally different to one fitted with a Series wound motor!

Riders in USA (and hirers in most countries) are used to driving series wound motor vehicles. It can be disconcerting to find that lifting your foot from the accelerator causes hard regen braking. This feature requires a new user to get used to it, and although the driver will prefer the one-pedal control once he is familiar with it, it causes a problem on hire vehicles.

So, to overcome this initial unfamiliarity, the temptation is to set the deceleration ramp to a slow response to reduce the effect of the regen braking, which now comes in slowly. The driver therefore uses the foot brake to slow the vehicle (inefficient: wastes battery energy. Regen braking is better!)

So the driver does a fast stop on the foot brake and, because the controller is ramping down slowly – it hasn’t reached zero when the vehicle stops – with a fairly obvious consequence!

Enter the latest FBI mod (Foot Brake Inhibit) on issue 10 4QD control boards: if the inhibit input is operated by a microswitch on the brake pedal, then it causes the controller to ramp down so that it is always braking, so it ramps down following the emergency stop and gets to zero speed as the vehicle stops.

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