Hi Claude,
The GV300W outputs use a method common in electronic equipment. The output relies on external equipment to provide voltage and resistance.
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While writing this reply a thought occurred to me.
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An electronic circuit needs to be a loop. Current needs to flow through the circuit from the supply to the ground. If this does not occur the voltage is said to float; the results could be as you have experienced. It could also explain why it works with one output connected but not with 2 or 3.
How exactly is the Arduino connected to the GV300W ??
The GND of the Arduino needs be connected to the GND of the GV300W. (see pic below)
pin 7 OUT3 to Arduino pin
pin 8 OUT2 to Arduino pin
pin 14 OUT1 to Arduino pin
pin 6 GND to Arduino GND
When connected like this there will be a complete loop for current flow. The Arduino ground will be referenced to the GV300W ground. It will not be floating. (see UNO pic below, GND pins)
Regards
Jim
