Author Topic: Fuses & Grounds for T100MD  (Read 10056 times)

cdenk

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Fuses & Grounds for T100MD
« on: June 03, 2005, 06:37:10 AM »
I have a T100MD-888+, MD-EXP4040, and a MD-HMI. The T100 manual shows a 1 amp fuse for the T100MD, but no fuses are shown for the other boards. Should the other boards be fused,? value?, parallel fuses?, or one larger fuse for all?  Of course all going to the same power supply, mine happens to be 12 DC.

On the T100MD-888+, the high current ground - all in/output grounds (returns) should go there, to an off the boards ground point (with short proper capacity (amps) wire)  with the exception of the TTL & Cmos in/out on the MD-EXP4040 which have their own grounds on the headers.
 :)

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Re:Fuses & Grounds for T100MD
« Reply #1 on: June 03, 2005, 10:18:19 PM »
The fuse for the T100MD+ is optional and if use, it should be attached to the +24V lead into the PLC's power supply input, not the 0V side. Since all the outputs are current sink type (i.e. they return current from the load to the power supply ground via the 0V terminal), the current drawn from the +24V terminal is mainly for powering the CPU and the inputs/outputs LED and this current (typically between 0.2 to 0.3A ) is independent of the current drawn by the NPN output load.

If there is a high current flowing into the +24V terminal it means something is wrong on the PLC circuit, probably a short circuit occurred  in some components.  If you have a fuse the fuse will blow to prevent further damage. However, replacing the fuse alone is probably not going to recover a failed PLC if there are permanent short-circuited components in the PLC. It just prevent more extensive damage (such as burning up of the PCB) so that the PLC would not become unrepairable due to extensively burnt PCB.

The two 10A PWM outputs on the T100MD888+ has two extra GND terminals to enable high load current to return to the power supply via the screw terminals instead of via the thin copper layer on the PCB.  Actually these two GND terminals are internally shorted with the power supply 0V terminal,  so if the load current is small you can actually omit to  connect these two GND terminals to the power supply. But for higher current load the connection of GND terminals to the power supply 0V is definitely required to prevent interference to the PLC's power system..

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