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  • MVP 2023
38 minutes ago, AlexUT said:

So if your power supply has load capacity less than 4A, than short time reverse polarity may activate power supply short circuit protection.

It is recommended to be careful with power supply polarity.

I'm sure my quick action is what saved me. The power supply I normally use in my office is 4.2 A (100W). Sometimes when setting things up for a quick test I get in a hurry and don't triple check the connections, but I've modified my bench with a bunch of pre-wired 5.5mm barrel connectors so that reverse polarity is no longer possible.

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  • MVP 2023

Inside V1210 we can see advanced power suply with TRANSIENT VOLTAGE SUPPESSOR DIODE on input side BFM marked on foto.


In my opinion, protection against reverse polarity is not provided in V1210 - because a symmetrical suppessor diode is used.

It only limits the maximum supply voltage to 33V (in normal and wrong reversed polarity) . Therefore, incorrect power polarity can cause problems in the PLC power supply.

If the PLC does not start in the normal polarity, I do not recommend changing the fuse or repairing the power supply.

Probably power supply board can be ordered separately from an official dealer.


P.S.  In V700 PLC implemented overvoltage protection and protection against reverse power polarity.

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  • MVP 2014

Hi Cveko,

I guess the golden question is, does it still work after you put the power supply back correctly?  Do you have any "known good" examples you can test with?  Was the CAN working before this mishap?

Also, I presume from the title of the post, you are referring to the -V and +V on the CAN interface on the V1210, not the main power supply.  I have spend a bit of time messing with Unitronics CAN.  I don't recall destroying any, and I probably crossed wires at least once somewhere along the way.

Hope this helps,

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  • MVP 2023

Then maybe useful to know that CAN  connector with 24VDC power supply has reverse voltage protection.


After analyzing the circuit and testing its operation in the correct polarity ... I decided to test it in reverse  :)

Thanks to the Unitronics developers of the circuit - in the reverse polarity - any dangerous voltage on the transceiver I did not find.

So by accidentally applying reverse voltage to the CAN port power PIN +V and -V, we probably will not burn anything - but the port itself will not transmit anything.

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