PLC with no mains supply

[Goody]

Today I was called to a customer with an electrical fault on a machine. I have specialized a little on this type of machine and I have also written a program to retro-fit these machines, so I was glad to go. (I smelled a plc sale)

When I opened the control cabinet, There was already a plc doing the biz in there. (ah well, never mind, just repair the fault) The PLC was an old Mitsubishi F1.

As I was tracing the wiring (not a drawing or nowt you know) I looked at this plc and there was no mains voltage to it.
There were inputs and outputs wired and the outputs had a common 240V supply.
The mains voltage terminals had options for 240V and 110V but there was no wires in those terminals at all.
The plc had no lights on as the problem was with the main power contactor not coming on.

I found the fault (mangled wire) and put the power on.
The plc sprang to life with inputs and outputs going on and off but still with no supply to the L1 N1 N2 terminals.

I then found that there was another 24VDC supply and this fed the plc's 24VDC service supply. (the one you use for inputs)

This must be able to supply the plc with what it needed through the back door, because it works fine and the age of the plc means it must have been working fine for years. Has anyone seen this before?

I scratched my head for a good while. I was sure either the plc was not used or someone had been messing..............

 

[rsdoran]

You may want to check the specs on that Goody, alot of the older models had the option of using ac or dc, when ac was used the dc side could be used as a power supply but you could use a dc power source to power them with no ac applied. I dont know mitsi but many other brands did this.

 

[Rick Densing]

I can second that. No direct experience with the F1, but I have seen (and used) AC/DC devices set up that way.

 

[Platootod]

Hi goody,
Sometimes Old better than New.
As I have use Mitsi F1 with a liitle High temp and dusty
still fine for nearly 10 years.

platootod