SLC 500 Controller Memory Loss Problem

HI All,

I am experiencing one problem for few months which i would like to share with you experts. My SLC and Micro Logix Controller especially Micro Logix are experiecing this problem. The Power Supply of the Controller is powered up by an external 24V DC Battery Source which is charged by compressor alternator so that the battery doesnt get drained, but usually we found out during Preventive Maintenance of Compressor when the compressor is down and the alternator also. When we try to start the PLC after 7 or 8 Hours later its program is washed out from the controller which then needed to be downloaded again. The interesing part is this that i have tried several of time to disconnect power of controller by myself during compressor running then after power up it shows the program but i think when the battery get drain gradually it program is washed out from it. Does this assumption of mine is correct and what can we do to avoid it.

Regrads,
Sam Khan

I had this problem years ago with a slc 5/04.

during brownout conditions, the power would spike, the sag, then spike before stabilizing. the processor tries to do an emergency shutdown and power up at the same time, thus erasing the program.

the solution was installing a surge suppressor.
the processor has not shut down again in 20 years.

it is now our standard practice.
regards,
james

It's possible that during a short outage the capacitors in the internal power supply will hold the program (many PLC's do) to allow changing of the backup battery, it sounds like your internal battery for memory retention is either missing or dead.
I assume that you are trying to keep the plc up using external power (battery) during outage but to stop the loss of program then you should use the internal memory backup.
however if you are sure that the battery has not drained during shutdown then spikes could be the problem I know that the SLC500 can be prone to corruption on power spikes even with a good backup battery I tried a filter but still occasionally had problems then I fitted an EEprom for the program & not had a problem since.

James and Parky, good theories. When the compressor is cranked to start it could be dropping the battery terminal voltage to the point of the brownout / spike condition James mentioned.

I had a similar problem when I converted my '76 Holden ute to a fuel injected engine. Sized the battery cable to small which dropped the ECU supply voltage to 7 volts when cranking he engine. So she would crank over but never start. I would bench test the ECU with a battery drill on the cam angle sensor and my cheap single channel scope looking at the ignition coils and fuel injector outputs. Never had a problem on the bench. Took me ages to work it out.

Guys i think you couldnt understand my question. During normal shutdown or when i intentionally switch off the breaker of the PLC and then restart the system the PLC retains the program but when during unplanned shutdown such as it shutdown in night and we are unable to rerach over there in night , during that time when the compressor is down and the alternator is also down, then the external battery for PLC Panel starts to drain its voltage gradually during that time i have seen that the PLC when restarted doesnt havae the program.

Maybe a low voltage cut-off would help. See links below for an example.

http://atkinsonelectronics.com/manufacturing/product_pdfs/VRDC-40A.pdf

http://www.google.com/#hl=en&tbo=d&...50,d.cGE&fp=ed37b7f9496e4d03&biw=1495&bih=807

If the battery is keeping the plc powered then drains it must be that the internal backup battery in the plc has drained.
Taking the power off a plc will not loose the program if the internal backup battery is in good condition, I suggest you replace the plc backup battey (Note: if my memory serves me right the installed battery is soldered in & non removable, however there is a battery holder built into the casing where a replacement one can be fitted.
PLC backup batteries will last 4-10 years depending on how long the plc power is removed, for example the mitsubishi "Q" series a battery will only last months if no power applied, however when powered with only short outages will last about 5 years.
Some like the FX range will keep it;s charge for about 2 years without being powered this was proved when I had a sapre on the shelf for over 2 years & it still had the program in it.