Can I use the same Class 2 power supply for both DeviceNet and the rest of the machine control including outputs turning on relays and solenoids?
Answered by Bob Lounsbury, Physical Layer SIG, e-mail: relounsbury@ra.rockwell.com
A24) While it is technically possible for I/O to share the same power supply, it is generally not recommended. The main reason for this is that transients from the solenoids, relays and other large surge devices may cause transients in DeviceNet^s power bus. The transients could cause communications errors and even possibly bus-off conditions. If the inrush currents of the solenoids cause the power supply output voltage to momentarily drop below 11 volts, devices could generate an internal reset. If power supply sharing has to be done I would recommend that the two power buses be kept separate (do not take power from DeviceNet^s power wires V+ and V-). Make sure that the inrush currents of the loads do not cause the power supply to go into current limit conditions where by causing a momentary decrease in Vout.
How many 4-Amp power supplies/power taps do I need for 700-foot trunk line with (33) 15-foot drops, with each drop drawing 150 mA?
Answered by Matt Kuzel, Chairman of the Physical Layer SIG, e-mail: kuzel@voyager.net
A25) If I assume you are using separate power segments (red wire cut in the middle), and that you are using thick or flat cable, you are OK. I see close to 3 Amps supported at 350 ft (half of 700) on the charts in Volume I, Chapter 10 of the DeviceNet Specifications. This would be worst case distribution. If the loads are evenly distributed, all is even better. Two 4-amp supplies on a non-segmented power bus exceeds the Class 2 limit. That^s why the segmented assumption. You can also put the two supplies in the middle (NEC current boost configuration). I have seen a number of installations like this where one higher current supply is used for both segments with 4 amp fuses. Many inspectors may be OK with this. You did not mention the data rate. It is not important for power, but it sounds like you have a lot of drop 33 x 15 feet. You had better be at 125 Kbaud.
Is there a limit to how much a node can draw from the 24 VDC network power?
Answered by Ray Romito, DeviceNet Trainer, e-mail: raromito@ra.rockwell.com
A28) Thick cable and mini connectors can pass 8 Amps. Thin cable and micro connectors can pass 3 amps. There is also a turn-on delay in the Specifications for devices with switches that is based on current drawn.