All controllers made by 4QD are generally wide voltage operating range: limits are the operating voltages on the MOSFETs and the relays, and the power dissipation in the current source transistor used for the internal supply. See Pro, Scoota and NCC series controllers. Internal power supply and protection circuitry for a description of how the powering works.
This means that essentially the same controller may be used on 12, 24, 36 or 48v with only relatively minor changes. However since the Scoota series include features such as undervoltage cutback and overvoltage protection, these 'relatively minor' changes do add up. Also the higher voltage versions may this require upgrading certain components so it is not necessarily acceptable to modify a controller to work on a voltage higher than that for which it was originally specified. This information may therefore be used for down-rating only!
In general the changes and components to check on all controllers are:
Other components
12v controllers use a 12v coil
Other controllers use a 24v coil
36 and 48v controllers have a resistor in series with the coil. This resistor can easily be bridged out by re-soldering a cut link just beneath the Relay resistor, on the copper side of the board. This 'Relay Resistor' is indicated on the drawing.
For 36v, use a 180 Ohm
For 48v, use a 390 Ohm
The relay coil resistance is specified as 93 ohms for the 12v coil and 330 for the 24v coil (but in practise they tend to be nearer 389-390 ohms), so a resistor equal to the coil resistance will effectively double the operating voltage.
This is a very technical subject as the maximum allowable voltage depends on ambient temperature. Also at high currents the contacts get hot and some of this heat gets transferred to the coils, reducing the maximum allowable operating voltage in a complex fashion.
Also, if the coil is hot, then the 'must operate' voltage rises, because of increasing coil resistance. So this value is dependant on how long since the relay last operated and on how much current the contacts were carrying.
This all makes it impossible for us to give a definitive operating voltage range but, for most purposes, the allowable operating range will probably be something like 80% to 150% of the nominal voltage at 40°C, so the 12v coil should work from 9.5v to 18v and the 24v from say 19 to 36.
MOSFET technology improves. So we use different MOSFETs as technology and prices alter.
MOSFETs most likely to be present are:
The current source on 12v, 24 and 36v controllers is a TO92 transistor delivering about 30 milliamps. At 36v this drops some 28v so dissipates about 700mW so gets very hot! On 48v it would self-destruct (over 1 watt) so we fit a TO39 (metal cased) transistor with a heatsink.
Commonly 50v, OK for 12v to 36v but not for 48v which requires 63v capacitors.
12v and 24v controllers normally have a clamping zener of 36v. 36v controllers use 47v and 48v controllers use 56v. This does not really need altering when down rating the voltage!
Generally on modern production other components are rated suitable for 48v operation but older controller hay have had transistors fitted which were not suitable for 48v operation.