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Pro-120 Mk2 History

In early 2003 we released a redesigned Pro-120 controller. However – in general it’s such a popular and good controller that not a huge redesign was possible. The main change is that it uses sub-miniature resistors, to give room to add alterations. This page gives the Pro-120 history

Etched in the copper of the Pro-120 Mk 2 is a number such as 30-3B-2-04, there the ’04’ is the Issue number of the circuit board.



The Pro-120 was originally available for 24v, 36v and 48v. When the Pro-150 was released, it was decided to discontinue the 48v version, which only sold in small quantity.The last Pro-120-48 was sold in late 2008.


In the early days a 12v version of the Pro-120 was available. However 12v operation at this sort of current is troublesome (see our faq pages on 12v systems) and we found that a high proportion of customers were simply using a bigger controller than they needed. Moreover the smaller controller (VTX-75-12) has been steadily improving its current output as MOSFET technology improves.The VTX has now been redesigned as the DNO which will operate from 12v through 42v batteries.

So in April 2010 the Pro-120-12 was discontinued, as sales of the 12v version had never been very high.

The issue numbers are listed below.

Pro-120 2 Issue 01
Released January 2003

  • Regen brake defeat: two pinstrips and headers can be adjusted to inhibit regenerative braking.
  • Dual Ramp reversing on/off. The feature may be turned off by a header to engage preselect reversing. This should be done if regen braking has been defeated, but can be done in any situation as desired.
  • High pedal lockout defeat: the feature may now be disengaged by a removable link.
  • Dead band at zero demand speed reduced (and adjustable to zero if required). There are two main events that happen when the speed pot is turned from zero: first the appropriate direction relay activates (Relay Activation Threshold = RAT). Secondly, modulation starts (Modulation Start Threshold = MST) and voltage is fed to the motor.
    • RAT preset added: this voltage was about 400mV on early Pro-120 controllers. It is now adjustable from 0 to 100mV. Factory preset will be about 50mV.
    • MST preset added: this voltage was about 550mV on early Pro-120 controllers. It is now adjustable from approximately between -200mV and 500mV. Factory preset will be approx 150mV.

    Factory preset values almost completely remove the present deadband (which is not beneficial in some applications) yet should suit almost all users.

Pro-120 2 Issue 02

June 2003. Most of the changes are minor tidying up of issue 1.

  • Ignition switch circuitry altered: there have for a long time been factory options on the ignition. These are now more easily accessible.
  • Current limit circuitry changed to new version (which has been in use on NCC and other controllers for a time).

Pro-120 2 Issue 03

September 2003. More tidying!

  • The direction relay catching diodes had been beneath the relays: this makes replacing them difficult (but they rarely fail). Now moved.
  • 100R added in series with top of pot – this will make the circuit even more tolerant of wiring faults back to the pot.

Pro-120 2 Issue 04
February 2004

  • Some rearranging to put the two regen defeat links next to each other. The links are now not fitted as standard to simplify production and because getting the links wrong can blow the controller.
  • Ignition circuit modified. See Pro-120 Ignition. The relay coil is now wired via a diode from Battery positive.
  • Components moved round to allow proper fitting of extra components for 12v version. See Pro-120 series, internal power supply.
  • Spacing between relays has been increased to allow fitting of a different manufacturer’s relays. Note: these new relays will not fit the earlier circuit boards.

Issues 1, 2, 3 and early 4 are now too old to qualify for factory servicing.

Pro-120 2 Issue 04 B In November 2005 the board was coated with green solder-resist and we no longer applied a varnish coating to them.

Boards after this date should have a date code written on them. This is a number for the year and a letter for the date. E.g. 10b would be February 2010. See the page Date Codes on 4QD controllers