All the data bus modules (keypads, expansion I\O, etc.) use 12vdc power off the data bus, and the main board provides VAUX output power for devices like smoke alarms, as well as its own 12v digital outputs, etc. I’ve seen specs for fusing of different features, but I haven’t seen a spec. for the maximum output capacity as a whole, of the on-board 12v power supply. And what is the spec on maximum 12v draw per data bus? Output expanders have a potential of 330mA each, so two or three along a single bus is drawing a lot of DC power and I assume there’s a maximum capacity for the power delivery per bus line.
The M1 has 1 AMP of continuous Current available and during alarm 2.5 AMP with the additional current being drawn from the battery. The 1 AMP continuous is a combination of the +VKP, J16, +SAUX and +VAUX terminals. You can check the system current draw from a keypad Menu 8, 86-System Diagnostic, 2:Sys Volt/Curr. If the current during normal operation (not in alarm) is above 1 AMP you will need a secondary power supply.
Its possible I’m exceeding the capacity of the on-board 12v power. My calculated consumption is between 800mA to 1.3A (depending on number of active outputs). I might be right at the 1A limit during normal operation — I’ll have to check that out (P.S. I sent you the databus info via email). Would exceeding the capacity cause the symptom that I’m seeing? An I\O expander going “missing” on a data bus line? What’s odd is that its always the same expander every time. I would expect a power issue to be more systemic and cause random dropouts, if not across the board, then at least on the same databus branch.