ZeroPower RAM Battery Life

[NY2KW]

I have some NOS ZEROPOWER MK48Z02B-25 RAM custom for a vintage radio.  Is there a  method to assess the remaining battery life?  These were rated for 10+ years but they are probably older at this point

Thanks
Jerry

[legacy]

Probably no. The battery is embedded in the case 

[james_s]

You can cut into the case to expose terminals but that is a rather extreme approach. Anecdotal experience tells me they typically last about 20 years before they start getting flaky, which sounds about right considering they are guaranteed for 20 years.


I have carved into similar Dallas parts to add an external battery when new ones of the type were not available or prohibitively expensive.

[edpalmer42]

Maybe.  Sort of.  I've had success with this trick.  YMMV.

Don't use any kind of power drill for this.  Use a hand drill aka 'pin chuck'.

Use a small magnet (smaller the better - I use a cylindrical magnet that's 2mm dia. x 3mm long) to find the battery inside the case.  At the point on the side or end (not the top) where the magnet is most strongly attracted, drill a small hole through the plastic so you can probe the battery.  You need to be accurate so that the hole hits the edge of the battery.  You might even use the drill as the probe and stop when you get a stable reading.  You certainly don't want to drill into the battery!  This should be the positive pole of the battery.  The negative of the battery is connected to the chip ground.

Now you've got the battery voltage, but that doesn't tell you too much about the remaining life because the discharge curve for a typical lithium battery is so flat.  However, if it's less than 2V9 or certainly 2V8, you need to start thinking about a replacement.

There are also various projects on the net to replace the built-in battery with a replaceable battery.

Ed

[IDEngineer]

Wouldn't the life be infinite? After all, "ZeroPower".... 

[james_s]

They require zero power to be applied externally to maintain the memory contents (because they have an internal battery) vs the more conventional approach of having an external battery to keep the SRAM powered.

[IDEngineer]

Darn, I guess my little devil's head wasn't enough of a hint that my comment was a joke!

BTW, I used the Dallas Semi version of those parts (DS1220 if I recall correctly) in about 1984. In fact I think Dallas may have been the first to do the battery-in-the-package thing.

[NiHaoMike]

Make a backup of the contents if it's something that would be difficult to recreate like calibration constants, then just forget about it. Once it finally starts going flaky, carefully cut out the battery and replace it with a 2032 in a holder.

[IDEngineer]

Or, create your own backup supply (external batteries) and keep the Vcc pin powered. As I recall, the spec sheet included a minimum Vcc above which the RAM was powered externally rather than the internal battery. Of course, you'll also be powering the I/O logic so current consumption may be too high for a convenient external battery solution. As I recall, some packages also brought out a separate "memory only" power pin that allowed external power without the current consumption of the rest of the interface logic... check yours, you might get lucky.

[johnkenyon]

Maybe.  Sort of.  I've had success with this trick.  YMMV.

Don't use any kind of power drill for this.  Use a hand drill aka 'pin chuck'.

Use a small magnet (smaller the better - I use a cylindrical magnet that's 2mm dia. x 3mm long) to find the battery inside the case.  At the point on the side or end (not the top) where the magnet is most strongly attracted, drill a small hole through the plastic so you can probe the battery.  You need to be accurate so that the hole hits the edge of the battery.  You might even use the drill as the probe and stop when you get a stable reading.  You certainly don't want to drill into the battery!  This should be the positive pole of the battery.  The negative of the battery is connected to the chip ground.

Now you've got the battery voltage, but that doesn't tell you too much about the remaining life because the discharge curve for a typical lithium battery is so flat.  However, if it's less than 2V9 or certainly 2V8, you need to start thinking about a replacement.

There are also various projects on the net to replace the built-in battery with a replaceable battery.

Ed

Here's my experience playing with a MK48T02 Timekeeper device - same era as the 48Z02, but with an RTC on the silicon, and a crystal in the top hat.

With a MK48T02 (timekeeper), the battery terminals emerge from the IC package at the "pin 12/pin 13" end of the package, and a 32.768kHz crystal is connected to similar terminals at the "pin 1/pin 24" end. (I would imagine the 48Z02 battery pins would be in the same location to keep the Z02 and T02 assembly processes similar)

The pins emerge from the plastic DIP package on the same plane as the normal pins into cutouts which are occupied by the clip of the plastic case which holds the battery+crystal.
The pins are narrow (i.e. the same width the bit of the normal pin which fits in the PCB or IC socket, and (obviously) point up rather than down.

Cautionary points:
1) The plastic DIP package does not have any pin 1 marking. (May not be a problem with an MK48Z02 which will probably have two pins at one end), but MK48T02 tinkerers may want to mark pin 1 on the underside of their device before hacking it.
2) to repeat - The pins going to the "top hat" are thin/fragile. Use wire to match (e.g. wirewrapping thickness insulated wire, and make sure any leads to battery holders etc have sufficient strain relief.

john

[legacy]

isn't there a way to melt the protective package in order to access pins?

[legacy]

does anyone have an Xray image of the chip showing its inside?

[james_s]

I've xrayed several of the Dallas chips, not one of the ZeroPower ones though. If someone wants to send me a dead one I could do that.

[SiliconWizard]

I don't know how recent they would be, but you can find spare ones on eBay. It's probably possible to also use an equivalent (didn't look at the DS, but those chips usually have a standard JEDEC pinout).

If you need to keep the old content, you could copy it to the new NVRAM with some universal programmer (such as the TL866, it apparently supports writing to SRAMs).