[TowerTalk] Fw: SteppIR problem

[Ward Silver]

Just a thought...

It could be that the transients associated with pulsed currents to the 
motors is causing the controller or power supply to shut down.  The 
transients might not be large enough to cause disruption until the fourth 
motor is on-line.  If so, adding a fairly large electrolytic capacitor of a 
few thousand uF at the power supply connection to the controller might solve 
the problem.  To handle the high-frequency compoents of the transients, I 
would parallel the large electrolytic with a tantalum capacitor of 100 uF or 
larger.

A clue that transients are likely to be causing the problem is that it 
doesn't matter which of the motors is the "fourth" motor.  That pretty much 
rules out mis-wiring or faulty motors.  You won't see the transients with a 
voltmeter and the symptoms (power supply shut down) can be exactly the same 
as for simple over-current protection.

I would tack solder the large capacitor pair across the power supply 
connection inside the controller and see if the behavior changes.  That in 
itself would be a significant clue.

73, Ward N0AX