Why do some PLC's "die" if you change the coin battery inside?

Thread Starter

StrongPenguin

Joined Jun 9, 2018
233
I spoke with the company electrician the other day, a very skilled man. He was on our ship doing some maintenance on our converters, where he also changed the batteries for the PLC. He said if I removed the power supply and changed the battery, the PLC would not work when we were to start it up again. But som PLC's could handle the power loss.

How come this is so? One guy said the EPROM lost it's data, which I find very unlikely.
 

MaxHeadRoom

Joined Jul 18, 2013
20,405
Depends on the make and how the back-up is done, some the power has to be retained when the battery is changed..
This is why any company that supplies the program, should supply the end-user with a copy.
I recall working on Fanuc CNC machines that have 4 D cells to back up memory, if you don't obey the warning the whole memory software has to be reloaded.
Some don't keep a record of it, they end up with a chunk of iron!
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
20,405
A remember one instance when I was in charge of technical maintenance of a manufacturing facility
We started getting repeated memory loss on a CNC machine in mornings when the day shift came in,
This required reloading memory every time.
After some investigation we discovered that the evening electrician was swapping the batteries for his work flash light every time they died.! o_O
Max.
 

Thread Starter

StrongPenguin

Joined Jun 9, 2018
233
Wow, that's just..I don't know what to say, speechless.

Do you have any thoughts on why they/some loose memory? Is it because of DRAM, or does the EPROM really go belly up? Is it correct to say that the code is still there, but it can't load into the memory banks? Volatile, non-volatile..? I'm curious in hearing the gritty details.
 

ElectricSpidey

Joined Dec 2, 2017
1,056
Well, the obvious answer is something is being stored in volatile memory. I have a phone that the battery must be changed while power is provided.

In an industrial environment I would expect a small super cap to be used so you could change the battery in x seconds, I have a clock like that.

And no, EPROMs don't lose their memory when the power is disconnected. (none that I have ever used anyway)
 

MaxHeadRoom

Joined Jul 18, 2013
20,405
And no, EPROMs don't lose their memory when the power is disconnected. (none that I have ever used anyway)
I have seen a problem where the eprom windows were no covered, and in hot weather, maintenance used to leave the cabinet doors open, The sun streaming through the windows erased some of the Eproms.
Max.
 

GetDeviceInfo

Joined Jun 7, 2009
1,702
Could be as simple as the battery fault routed to a major fault. The SLC /05 was a problem with a Ethernet fault on power up. Would have to DFI on to clear and re enable. I've also seen code that hangs If comms aren’t established in a certain order. I have heard the same you’ve mentioned several times, but in the cases I’ve been involved with, investigation led to correcting the issue. Logging on and checking status bits can often reveal problems.
 
Your PC CMOS battery is a good example. Remove the soldered in battery and passwords mysteriously dissappeer. i think my laptop has a couple of pads after you remove ram to short as well.

CMOS memory doesn't take a lot of power to maintain it. If the laptop is powered it isn't used.

Mom and I have glucose monitors. I change the batteries quickly and I don;t loose the date/time.

The AA battery version; Change them quickly - one at a time

My meter uses two CR2032 with a white and black pull tab one battery runs the meter and the other just the backlight, If the meter dies you can swap batteries, but you have to pull the backlight first. The white tab is the meter an the black tab is the backlight. I wish it was the other way around. They are now labeled.

EEproms have limited write cycles and may loose their data in 10+ years.
FRAM is the probably the best technology.

if you know they have issues, put a capacitor across the battery, but charge it slowly.

DALLAS in their RTC and memory backup works pretty cool except: No warning, Some hold the calibrations to Tektronix scopes. I have to do the exercise.

So, you have to remove and copy the device and hope you don't loose anything. it's not always socketed and heat is a problem.
Would be nice if the manufacture provided a clone routine and socketed the chip.

Worst case, reload any firmware and re-calibrate.

for parts that are unobtanium, there is an elaborate procedure where you carefully mill the IC to access the battery pin and put the battery external.

Another cool thing about the parts is that the batteries are disconnected untill first used. there are two batteries inthe chip. The highest voltage used first,
 
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Thread Starter

StrongPenguin

Joined Jun 9, 2018
233
@MaxHeadRoom It was either ABB or Siemens. I can find out tomorrow. The electrician didn't knew if the PLC would loose it's data, or not, so he just gave me the tip of always having power on, when changing batteries. I assume he means the main 24V power supply, right? So the inside battery is just for keeping the microcontroller alive?

@KeepItSimpleStupid If I have to reload firmware and re-calibrate 5 thrusters, that is not going to be fun. I highly doubt we have firmware disks lying around, though we could probably dig them up.
 

MaxHeadRoom

Joined Jul 18, 2013
20,405
It was either ABB or Siemens. I can find out tomorrow. The electrician didn't knew if the PLC would loose it's data, or not, so he just gave me the tip of always having power on, when changing batteries. I assume he means the main 24V power supply, right?
So the inside battery is just for keeping the microcontroller alive?
I highly doubt we have firmware disks lying around, though we could probably dig them up.
The battery is for the loaded program memory.
.You also need the programming/loading software and interface cable.
Max.
 

Thread Starter

StrongPenguin

Joined Jun 9, 2018
233
The battery is for the loaded program memory.
.You also need the programming/loading software and interface cable.
Max.
Ok, so there is some memory inside some PLCs that can't loose power, or they die. It's not firmware that is lost per se, but memory required for booting back up again, some settings loaded from the factory..?

Sorry for being this thick headed, I am just very curious to hear what is actually lost. I also remember the guy saying they had to start all over again. This incident was on a 850 kw converter.
 

MaxHeadRoom

Joined Jul 18, 2013
20,405
Usually it is the Ladder program that is written specifically to run your system, it is written by the system/machine tool builder at the time of commissioning.
You need to have a copy of this on hand in case of program memory loss.
Some are written for a system that is marketed in number, or it can be a unique system to your factory floor system.
If it is the latter, then especially important to own a copy.
Another scenario is that the PLC itself can go belly up and has to be replaced.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
20,405
Coincidentally I was just contacted this week to inquire if I had the program parameters for a CNC machine due to someone not having back up.
Their only hope is either the original MTB, or someone with the same machine.
What often happens, buyers go to machine auctions, they will check the machine operation, but rarely ask for documentation, which is often sitting in the maintenance dept the equipment was used at.
At some future point, the parameters are lost due to dead battery etc, then panic ensues! :rolleyes:
Max.
.
 

Thread Starter

StrongPenguin

Joined Jun 9, 2018
233
I assume ours is written for the ship, not standard code/parameters. Makes it even more crucial to keep power on, I suppose. Thanks for the info.

Man, I wish them the best of luck.
 

MaxHeadRoom

Joined Jul 18, 2013
20,405
Every program is unique to that application.
It might pay you to get someone with the S/W to download a copy of the program, if you don't have it!
Just in case!
Max.
 

Thread Starter

StrongPenguin

Joined Jun 9, 2018
233
Even if we had the software, I doubt we would be able to get the whole thing up and running again. But yes, to have is better than to have not. I will investigate if we have it. I am on a different ship now, so can't do it until a couple of months.
 

Thread Starter

StrongPenguin

Joined Jun 9, 2018
233
I believe the system is commonly sold, though all ships are individual in their parameters. Guess that will be the tricky part, getting all the parameters back in.
 
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