Mitsubishi PLC and Power Supply, Wierd

irondesk40 · Oct 6, 2020

Have a machine that has a Mitsubishi fx32u-32m plc and a ABB Power Supply in the machine that is part number CP-E 24/0.75 It is a 120vac powered power supply.
The power supply is a switch mode power supply, class 2 power supply.
Need to add some 24vdc components to the machine so tried to replace the power supply with a larger 24vdc power supply.
INstalled a Allen Bradley 1606-xls120e. It is also a 120vac powered, 24vdc output power supply. Turned machine on and the Mitsubishi PLC will not power up. The plc has 24vdc but will not power up. Put original power supply in and the Mitsubishi will power up and operate. Very Strange, so tried a PLS power supply which is part number PIC240.241D, which is also a 120vac, 24vdc ouput power supply. Same thing, there is 24vdc measured on the plc but plc will not operate. The PLC does not power up.
Really confused, anyone have any idea why the machine will only work with the original ABB power supply?
Have to admit, has me scratching my head.
Thanks

parky · Oct 6, 2020

I have used a lot of different PSU's on Mitsubishi PLC's and never had a problem with any of them, we are talking about in the region of a couple of hundred (both new installs, replacements & upgrade power requirements).
The only two times I thought I had a problem was the printed cct. cracked on the terminal connection to the main board, I put the original back & it worked for a while it confused me too, the other was due to the retrofit PSU was not giving out enough voltage, even though it was brand new I had to tweak it from 21v to 24 before the PLC worked. I assume you have checked these though.
I do tend to use 120-240v supply type for PLC's in the last few years, I prefer to keep the 24v for control not power to equipment.

jdbrandt · Oct 6, 2020

irondesk40 said:
Have a machine that has a Mitsubishi fx32u-32m plc and a ABB Power Supply in the machine that is part number CP-E 24/0.75 It is a 120vac powered power supply.
The power supply is a switch mode power supply, class 2 power supply.
Need to add some 24vdc components to the machine so tried to replace the power supply with a larger 24vdc power supply.
INstalled a Allen Bradley 1606-xls120e. It is also a 120vac powered, 24vdc output power supply. Turned machine on and the Mitsubishi PLC will not power up. The plc has 24vdc but will not power up. Put original power supply in and the Mitsubishi will power up and operate. Very Strange, so tried a PLS power supply which is part number PIC240.241D, which is also a 120vac, 24vdc ouput power supply. Same thing, there is 24vdc measured on the plc but plc will not operate. The PLC does not power up.
Really confused, anyone have any idea why the machine will only work with the original ABB power supply?
Have to admit, has me scratching my head.
Thanks

As always, we need more information. Off the top, this sounds like a wiring problem....specifically a COMMON problem, as in the commons are connected unusually. The biggest clue is MITSU, which the default design would be sourcing inputs and sinking outputs. So, that might be someplace to check. After that, of course, we need to confirm GROUND is not somehow messing things up.
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"Diagnostics are great, so long as the designer of the diagnostics knew in advance every thing that could ever happen to the system."

Ronnie Sullivan · Oct 6, 2020

The only thing I have had similar is an fx** 24v dc supply where the dc to dc converter inside the plc went on the blink.
I took the 24V supply wires out of the terminals and put them on the 24V and 0v output terminals.
It was supposed to be a temp measure to get them going. It got forgotten and lasted forever.

alive15 · Oct 6, 2020

With the "bad" power supply, is everything else also off, or only your PLC is not coming on?

irondesk40 · Oct 15, 2020

thanks to everyone for suggestions. Just got back on this machine today been putting in some robot stations and got some time today to work on it again.
Was strange, could not find anything but adjusted the 24vdc power supply to give a output of 23.7 volts and the plc would power up and machine run. 23.8 or above and would not power up.
Put original back in and sure enough it measured 23.7 volts.
Tried multiple power supply units and had to adjust less than 23.8 volts.
Never thought of that as a reason, by default i always take a power supply out of the box and apply power to it and adjust the output to be exactly 24vdc according to my fluke power supply.
Anyone have any thoughts on why it has to be less than 23.8 volts?
Thanks

parky · Oct 16, 2020

I have never had that before one thing I learned when in pure electronics was to measure the power supplies, many people have been caught out looking for component failure on a board full of components but neglected to check the power supplies. I would be surprised if even 25 or 26 volts would crow bar the PLC power supply circuitry, the only conclusions I can come too is that either the PLC power circuit is faulty and crow baring on greater than 24v or the power supply you have has a large ripple on it so the peaks are causing the crow bar action (crow bar action is a protection in many power circuits that if the supply voltage rises above unacceptable limits it shuts down).

Mitsubishi PLC and Power Supply, Wierd

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