micro1400 120vac blow up is internal powersupply

[Jeff23spl]

Hello
I have a micro 1400 blown and with a solid 120vac voltage, display isn't showing up and dc output read 0v

Sound like a 120v surge issue but is any of you heard about some weakness of these plc ? i goth others identical with issues out of the box ?

Can a temporary fix would work by forcing powering to the plc with a separate 24vdc power supply on the vdc out terminals of the plc?
I can't test it with the blown plc but it seem to work with a good one and it would give me time to replace it latter???

 

[Lancie1]

It sounds like you had a 120 volt voltage surge (lightning or large-device switching on same line). You probably need some surge protection, or a UPS power supplly, or and maybe a faster fuse on your PLC power supply input circuit.

 

[Ken Roach]

Do not attempt to "back feed" the 24V DC auxiliary supply on the MicroLogix controllers. That's not how they are designed to work and I do not expect it to function correctly.

The 24VDC "sensor supply" terminals on the AC-powered MicroLogix has a very small capacity (250 mA) and is meant to feed Input signals only.

If you are using it to supply output power or bulk power to other devices, you need to stop right away and re-design your circuits to use a proper, separate DC power supply.

 

[iant]

two things come to mind appart from the above.
- are you using the PLC's DC supply - there could be a field short.
- are you sure the AC side is blown - have you looked inside the PLC.
it may be other damage - water - Mouse or rodent PSS etc.

 

[Jeff23spl]

Do not attempt to "back feed" the 24V DC auxiliary supply on the MicroLogix controllers. That's not how they are designed to work and I do not expect it to function correctly.

The 24VDC "sensor supply" terminals on the AC-powered MicroLogix has a very small capacity (250 mA) and is meant to feed Input signals only.

If you are using it to supply output power or bulk power to other devices, you need to stop right away and re-design your circuits to use a proper, separate DC power supply.

I don't, the 24vdc internal source isn't used, there is a separate 120/24 for any other 24vdc supply but i'm 1000km away from this site. I was looking for a temporary fix to put it back in operation until it could be replaced and adding a surge protection...

I have tested the theory on a brand new ml1400 and it works just fine. It could work for them if the supply is only burned on the ac side, if not, the fuse will just blow and nothing more could happend...

 

[Jeff23spl]

On the other hand, since the begining, this plc is creating some issues...Some faults appears that need a power down and power up to clear and the customer is reporting a lot of problem with is site electric supply. But there is 2 identical panels and problems always happend to the same one...??? Maybe a new plc and surge protections will solve that.

To avoid that, i try to always use 24vdc plc powered by a separated 120/24 supply and usually the supply offer better protections than built in one or it's easier to replace a supply than a programmed plc...

 

[iant]

just be carefull it is not an electrical problem at the switchboard - it may well have a resistive joint / poor connection -
that could cause some of the problems you are seing.