A problem has only just emerged (May 2001) and we are on touch with Dan Danknick working out a best solution. In the meanwhile, here is the gist of our understanding!
The 4QD series controllers have an internal 12v supply line. This has available just enough current to work the controller and a pot. It was not designed to power external equipment.
When external equipment draws too much current, the internal supply line drops below 12v and the controller's protection circuitry detects a fault and switches off the controller.
The Team Delta interface draws 40mA max (with all LEDs illuminated).
The internal power supply of the 4QD delivers 60mA to drive the whole controller.
Clearly adding an external device which requires 40 mA current is going to cause a large problem!
The controller's current own internal demand is not constant, so the 'fault' is detected when the total current drain is too high. This may be temperature dependant, will vary with supply voltage (so a system may work on 24v, but not on 36v).
The fault condition may therefore seem erratic. The surprise probably is that it can work at all!
Clearly - you should not power external equipment from the controller's internal 12v line! It is best for the interface to be powered direct off the battery supply and not off the controller!
The internal current available in the controller could be increased. However this will result in components heating and the dissipations of all components must be safe, within manufacturers ratings, under all conditions. It is therefore not wise to nearly double the available current (and hence double the possible heating).