Mobility scooters generally operate at 24v and have a top speed of 4 mph on pavement (limited by law). Commonest motor is an EMD PM50 (about 250w rating). The controller will be capable of delivering about 50 to 70 amps peak. This gives them a hill climbing ability of about 1 in 4 and plenty of current for kerbs etc. If you do not require hill climbing, then less current is required. For road vehicles, which have a higher legally permissible top speed of 8 mph, proportionally more current will be required: these usually double up the motors, one for each rear wheel. If the controller has a ‘top speed switch’ to restrict speed to 4 mph or 8 mph, then a dual purpose vehicle is possible. Some older models used to have 12v motors, with inferior performance.
Controllers for mobility aids have, historically, become very complex and sophisticated. In part this is because the earliest vehicles were designed for very disabled people with poor motor control. The controllers therefore became very sophisticated to cope with the user’s disabilities. The second reason for this complexity is that early power semiconductors were temperamental and unreliable, so designs added more and more fail-safe protection circuitry. Then there are the commercial pressures of ‘Specmanship’ – selling a machine on specifications, to justify a higher price. This tends to lead to over-engineering.
4QD’s controllers started life for the Golf industry, which has started from the other end – very low technology gradually improving with time but always very price conscious. Golf vehicles need 100 to 200 amps which is much more than most mobility aids, except for high performance dual purpose machines. For these either our Pro-150 or our 4QD series is an ideal choice.
The other choice is our DNO-10 controller. This is fine for 4mph use.
The 4QD, Pro and DNO series have fail safe mechanisms built in and, although no one can totally predict all possible failure mechanisms, an uncontrolled failure to high speed is extremely unlikely.