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FX2N Battery replacement

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I have run across a Mitsubishi FX2N with a battery light on.  I have never worked with Mitsubishi before, but the manual describes changing the battery and indicates the controller must be powered down for the change.  You have to beat the clock and change the battery within 20 seconds.  Has anyone changed these batteries while powered?  Used to do that with PLC5's but I have never dealt with this processor before. 

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Hi PLCMentor.

With the Q-Series it is 3 Minutes but I guess a lot of it depends on the size of the Capacitors and Demand.

Officially; Mitsubishi have always stated to power the PLC off before replacing the battery, however I have changed the Q-Series ones for years powered on without an issue.

Just a slight note; If your code is monitoring the battery low latch, the PLC will have to be reset afterwards to clear this, if your PLC is monitoring the standard low battery voltage register, then it will clear automatically once the voltage reaches the minimum threshold.

 

Regards

Daniel

Edited by collinsd70

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Thanks - I have no idea how the battery is being monitored, but I am purchasing the software to make sure I have a backup so I can check that out. 

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Okay, basically if you have an alarm already (on your HMI etc) then chances are the the PLC bit is being monitored and you may need a power cycle.

The bits you will need to examine are: -

M8005- This is the battery low signal (taken from the PLC firmware), this should be a true reflection of the PLC state.

M8007- This is the PLC Battery Low Latch- ie this will stay high after changing battery, to clear this you may be able to toggle this, otherwise it will need a PLC reset.

So after a battery change...both bits should ideally be low.

Regardless of how you plan on doing this; make sure you take a backup of device memory (if you are in GX Developer then just upload "Device Memory", if your in IEC Developer you will need to use the "Device Edit"). Any latched memory not written to on startup means potentially you will lose all of this data in the event of a battery failure (things like HMI setpoints etc).

 

Regards

Daniel

Edited by collinsd70

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