This is cool, but I'm pretty sure you get these off the shelf. I've scavenged them from old computers and I doubt people were building them themselves.
Building a replacement 386/486 CMOS battery
11–20 of 38 posts
Re: Building a replacement 386/486 CMOS battery
#12Love this, but iirc this was very common back in the day. Many of the XT, AT, 286, 386, 486 clones came with these types of triple AA battery packs, some with shrink wrap around them. It was easy to cut the shrink wrap and replace the cells with generic AA.
Re: Building a replacement 386/486 CMOS battery
#13The only thing worse than these soldered-in batteries are those motherboards with the Dallas DS1287 RTC “brick” ICs. They had a coin cell buried inside the chip[1] with no way to provide external power should it drain. [1]: http://www.mcamafia.de/mcapage0/dsrework.htm
Yeah, those are a thing on old Sun workstations. They have a clock and they also store a small amount of data.
https://www.sun3arc.org/FAQ/sun-nvram-hostid.faq.phtml
I remember replacing one in the mid 1990s. The machine's ethernet address is stored on this chip, and I believe it's battery-backed RAM (not flash, EEPROM, etc.), so when the battery dies, the data on the chip is lost.
When you install a new chip, you need to program in the ethernet address so the machine can get on the network. The proper thing to do is use the factory-assigned ethernet address to ensure that it is unique. But you can't get the address from the old chip. So, like many people, I just picked some random numbers. It worked.
Re: Building a replacement 386/486 CMOS battery
#14The only thing worse than these soldered-in batteries are those motherboards with the Dallas DS1287 RTC “brick” ICs. They had a coin cell buried inside the chip[1] with no way to provide external power should it drain. [1]: http://www.mcamafia.de/mcapage0/dsrework.htm
Necroware has a replacement design for Dallas RTCs: https://github.com/necroware/nwX287
Re: Building a replacement 386/486 CMOS battery
#15Why not use a 5F/5V supercapacitor, DGH505Q5R5 or anything alike ? You may need to solder a 10R current reducing resistor in series.
Re: Building a replacement 386/486 CMOS battery
#16The only thing worse than these soldered-in batteries are those motherboards with the Dallas DS1287 RTC “brick” ICs. They had a coin cell buried inside the chip[1] with no way to provide external power should it drain. [1]: http://www.mcamafia.de/mcapage0/dsrework.htm
Is this some attempt to get around "contains batteries" shipping restrictions, since if anyone looks inside it'll just be like any other chip and there's no way to tell unless you start googling part serials lmao.
"No batteries here, officer! Move along."
Re: Building a replacement 386/486 CMOS battery
#17The only thing worse than these soldered-in batteries are those motherboards with the Dallas DS1287 RTC “brick” ICs. They had a coin cell buried inside the chip[1] with no way to provide external power should it drain. [1]: http://www.mcamafia.de/mcapage0/dsrework.htm
I'm not sure if it's worse, since AFAIK these don't leak. I have a IBM PS/2 system that I inherited that I plan to restore some day. Sure it's a pain but glad there was no damage to the board.
Re: Building a replacement 386/486 CMOS battery
#18Love this, but iirc this was very common back in the day. Many of the XT, AT, 286, 386, 486 clones came with these types of triple AA battery packs, some with shrink wrap around them. It was easy to cut the shrink wrap and replace the cells with generic AA.
That's my recollection as well. RTC batteries from this era often came in four possible flavors:
* Varta barrel battery, subject to leaking and corroding traces
* AA/AAA style brick + leads to motherboard, easy to replace
* Dallas DS1287 epoxied battery + chip - can be replaced, cut into to tap directly into the chip, or replaced with Necroware's nwX287 RTC module [0]
* Lastly, the standard CR2023 style. I started seeing these appear in later 486 Socket 3 boards, very rarely on anything earlier
Re: Building a replacement 386/486 CMOS battery
#19Why not use a 5F/5V supercapacitor, DGH505Q5R5 or anything alike ? You may need to solder a 10R current reducing resistor in series.
Not OP, but with supercapacitors you're talking about a wildly different amount of energy. A 5F/5V cap stores about 62 J, while a 2500mAh 1.2V AA battery stores 10 kJ. With three of them you can store almost 500x as much energy.
Re: Building a replacement 386/486 CMOS battery
#20The only thing worse than these soldered-in batteries are those motherboards with the Dallas DS1287 RTC “brick” ICs. They had a coin cell buried inside the chip[1] with no way to provide external power should it drain. [1]: http://www.mcamafia.de/mcapage0/dsrework.htm
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