Losing program with power outage - revisited

[ccdubs]

Hello,

I am experiencing some issues not unlike the other recent posting. I have a TriPLC being powered at 12V from a 24 to 12 V DC-DC converter which is fed from a 24V battery.

When the mains fails and the battery begins to drain the PLC code corrupts (goes into pause, loses ID and requires download password). I think this is due to the DC-DC converter which seems to cycle when it's input votage gets too low. According to the data sheet I thought the DC-DC converter unit would completely shutoff at 19V but it seems more like 10-12V input.

Can this cycling be causing the PLC code to corrupt? I have installed a 1000uF capacitor and it made no difference.

Short of buying a new converter are there any other recomendations to prevent this from happening.

The converter is a MeanWell SD-50B-12 which I would have thought was a reasonable product.

Any help is greatly appreciated.

Thanks

[support]

Simply powering up and down the PLC is not going to corrupt the EEPROM. Thousands of these PLCs are powered from standard switching power supply without such issue. The main trouble with battery-based system come from high energy transient that occurred when the power switched ON/OFF instead of smooth rise and fall of supply voltage.  I am not familiar with the converter and can't say what the converter put out during the power failure.

You mentioned that you have installed the 1000uF capacitor. Did you connect a rectifier diode before the capacitor to prevent the voltage from being drained out of the capacitor during power failure? Also adding a transient suppressor diode mentioned in the other thread before the rectifier diode can absorb large voltage transient spike from being propagated to the PLC. These measures should help.

[benb2000]

Good Morning,

CCdubs, have you been able to solve your problem, I am still having issues with my 12 vdc, driven T100MD888+ mobile units

Thank you

[ccdubs]

After my initial post I installed the cap and diode and the effect was the same. I believe that the PLC was being switched on and off too fast and eventually something would corrupt.

In the end I solved the problem by building an under voltage cutout unit. This depowers the PLC when the voltage drops to 10V and only powers on again when above 11.5V.