Question about real time clock - M48T12-150PC1

[EasyGoing1]

I hope this is the right place for this question. If not, please let me know where the correct place would be.

I have a circuit board that controls lighting for fish tanks - rather a complex system actually.

The board has an M48T12-150PC1 real-time clock with the ability to store programming where the clock is maintained through power cycles with an INTERNAL lithium-ion battery. However, the battery is only rated for 10 years and this board is at least 18 years old. Needless to say, it does not retain the settings through power cycles.

I was hoping that I could solder on an external battery and use it in place of the internal battery, but after looking at the datasheet, I do not think this is possible.

I am asking for confirmation from someone who is more practiced than I am with datasheets to confirm my conclusion.

The datasheet is attached and the info I am looking at specifically is on pages 2 and 3. VSS it says is ground (for whatever reason - not sure why they would label a ground as a voltage source, but I'm not an EE) ... and from what I am seeing, Vso is the positive side of the internal battery, but it has no pin accessible for an override battery ... at least that's the conclusion I came to.

So ultimately, it looks like my only option here it to replace this component because there does not seem to be a way to use an external battery with it and if someone can confirm that for me, I would be most grateful.

Thank you,

Mike

[PGPG]

I am asking for confirmation

Your conclusion about datasheet is correct.

So ultimately, it looks like my only option here it to replace this component

It is probably the best option but not the only one.
The other option is more complicated - you can add external circuit providing continuously power to this IC. As it is probably powered from the same source as other elements at PCB then to power only this one (to not use battery too fast) you will have to disconnect it from the rest (probably cutting some tracks at PCB) and then ensure that:
- when power is on it is powered from that power (not consuming battery),
- when power is off it (and only it) is powered from your battery.
If your battery will have little smaller voltage than VCC at your PCB than it can be probably done with two Schotky diodes. But if your battery will have higher voltage ensuring that it is not used when standard power is on can be little more complicated.

[EasyGoing1]

I am asking for confirmation

Your conclusion about datasheet is correct.

Thank you.

So ultimately, it looks like my only option here it to replace this component

It is probably the best option but not the only one.
The other option is more complicated - you can add external circuit providing continuously power to this IC. As it is probably powered from the same source as other elements at PCB then to power only this one (to not use battery too fast) you will have to disconnect it from the rest (probably cutting some tracks at PCB) and then ensure that:
- when power is on it is powered from that power (not consuming battery),
- when power is off it (and only it) is powered from your battery.
If your battery will have little smaller voltage than VCC at your PCB than it can be probably done with two Schotky diodes. But if your battery will have higher voltage ensuring that it is not used when standard power is on can be little more complicated.

That is far more involved than I would prefer to go with this board. I would rather keep it in its original design, so I will replace the component.

It would be nice, if there were a compatible replacement for it that could leverage an external battery such as a button cell (CR2032 type) so that the component is not rendered useless after 10 years. But I have no idea how to find out if such a drop in replacement exists or not ... not to mention that it might be impossible for such a replacement to exist given the pinouts listed where it seems none of them could be suitable to use to kick out the positive side of the internal battery...

It does seem odd to me that such a component would be considered useful given its limited 10-year life though I suppose there might be applications where 10 years is far longer than a circuit would ever be expected to be in use... but this circuit is a main board controller for a fish tank lighting array and so I would assume that it should be expected to be in use for more than 10 years ... making this component a poor design choice in my opinion.

Thank you for your reply.

Mike

[squadchannel]

DS12887 can be easily made by getting an DS12885 and installing xtal and battery.
But what about M48T12? The datasheet says it is compatible with DS1642.
There is a replacement part on ebay that has a battery socket for the DS1642. How about a try with it?
eBay auction: #304227612700

PS:
The ebay one is probably based on the DS1558.

[Peabody]

Can you clarify what you mean by "power cycle"?  Is this a power failure, or is power deliberately switched off every day?  If the former, perhaps you could just get a small UPS that would keep everything running when the power goes out.

Is the MT48T12 in a socket?  Could you possibly post pictures of the top and bottom of the circuit board?

Would you be replacing the whole board, or just the MT48T12?  Digikey carries the MT48T12 for $25.

[EasyGoing1]

DS12887 can be easily made by getting an DS12885 and installing xtal and battery.
But what about M48T12? The datasheet says it is compatible with DS1642.
There is a replacement part on ebay that has a battery socket for the DS1642. How about a try with it?
eBay auction: #304227612700

PS:
The ebay one is probably based on the DS1558.

Nice component for sure ... but at $65 ... Odd thing is, I just got the unit put back together today and for the first time got to work with the settings and they seem to be retaining in between power cycles, so I'm thinking that even though this battery is rated for 10 years, it might still be a good battery. I guess I'm not going to sweat it for now until it becomes a problem.

Mike

[EasyGoing1]

Can you clarify what you mean by "power cycle"?  Is this a power failure, or is power deliberately switched off every day?  If the former, perhaps you could just get a small UPS that would keep everything running when the power goes out.

The unit is a lighting system for fish tanks so it can be switched off, though I'm not sure how often that will happen since it's not mine and I don't own any fish.

Is the MT48T12 in a socket?  Could you possibly post pictures of the top and bottom of the circuit board?

No, it is not in a socket, it is directly soldered to the board. But that's not a big deal, I have a very nice hot air re-working station if I have to remove it. And, here are a couple of images showing the component:

Would you be replacing the whole board, or just the MT48T12?  Digikey carries the MT48T12 for $25.

The board is not replaceable since I would have to design a new one from scratch and I have no clue how they programmed this MC ... it's a rather complex lighting system that is able to adjust the lighting color and intensity based on several factors such as the position of the sun, the moon and it's phases and even which hemisphere the unit is in... having read some fish forum posts from the mid 2000's apparently this unit was quite the "catch" (punn intended) for fish owners LOL.

You can read more detail on the unit in this post (scroll down to my last post in that topic): https://www.eevblog.com/forum/projects/how-to-calculate-pcb-trace-sizes-based-on-amperage/

[squadchannel]

If the NVRAM is just used to manage the time, then it only needs to be replaced.
But, if you hear about the complexity of the control, it may contain not only the clock but also some important data.
Even if the watch is still usable, it may die suddenly. It may not be possible to repair it after it dies, so it is better to remove the NVRAM and read it with the TL866 while it is still living.
Also, since NVRAM seems to be available for sale, it would be safer to replace it.

[Peabody]

It seems replacing the part is the best option if you don't want to mess with the circuit.  But that might be the time to install a socket while you're at it.  But don't throw away the old part.  There are Youtube videos on disconnnecting and replacing the batteries of NVRAMs like this.  You would need a Dremel tool.  If successful, you would end up with a CR2032 holder hot-glued to the top of the part.  Actually, if you aren't using this thing now, you might desolder the part and try the dremel thing before ordering the replacement, which you wouldn't need if the modification is successful.  It would be nice to know where under the cap the connections to the existing battery are.  ST has a forum which might provide that info.  You just have to be careful because the crystal is also in there somewhere.

[floobydust]

These parts were offered in several speed versions, the -70 is faster than -150 and would work and is more popular, lower price. Still available at Digi-Key:
497-2831-5-ND M48T12-150PC1 $25 USD
497-2833-5-ND M48T12-70PC1 - $20 USD
I think the 48T02 is also compatible, just a bit higher low voltage cutout (4.2-4.5V vs 4.5-4.75V).

Otherwise, how to add a battery:
He rips off the top slab (rip 4 pins up, battery and crystal) https://users.glitchwrks.com/~glitch/2017/08/01/gw-48t02-1
On Tindie he sells a battery replacer PC board kit https://www.tindie.com/products/glitchwrks/gw-48t08-1-repair-board-module/
Open-source for the project M48Txx battery fix

This guy cuts off just the battery: https://sonnenblen.de/index.php/topic,6866.0.html

[Testtech]

Why not just replace it with a new one? Mouser has stock.

[EasyGoing1]

But that might be the time to install a socket while you're at it.

This is a good idea. There is plenty of room In this unit to go vertical with this component and I do like having sockets on PCBs.

But don't throw away the old part.  There are Youtube videos on disconnnecting and replacing the batteries of NVRAMs like this.  You would need a Dremel tool.  If successful, you would end up with a CR2032 holder hot-glued to the top of the part.  Actually, if you aren't using this thing now, you might desolder the part and try the dremel thing before ordering the replacement, which you wouldn't need if the modification is successful.  It would be nice to know where under the cap the connections to the existing battery are.  ST has a forum which might provide that info.  You just have to be careful because the crystal is also in there somewhere.

This is the most interesting thing I've heard yet concerning this thing. I already purchased some external CR2032 battery holders ... but being able to Dremel into the existing RTC and use the external battery would be ideal.

When I think of small components like this, I think in terms of microscopic sizes but this one does have an internal battery which means there is definitely a connection in there that attaches to the internal battery and should be accessible with a fine tip iron for a quick tap to connect an external.

I'll look for some videos or write-ups on doing the mod ... nothing to lose really so may as well give that a go.