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Building a replacement 386/486 CMOS battery

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Re: Building a replacement 386/486 CMOS battery

#31

Post by devilbunny »

roytam87 wrote: post #30
johnklos wrote: post #27

It's good to see this getting some attention. People should know that removing batteries and replacing them with something modern, particularly non-leaking modern, is a good thing. Most motherboards work with 3 to 4.5 volts. If a circuit doesn't charge, then it's a simple matter of using two or three AA or AAA batteries. If it does, we can use rechargeable batteries (I've a box of Ikea ones), or we can put a diode in…

AA or AAA batteries will leak.

If you have enough case space, that's not really a big issue. I work in a surgery suite; we have single-use (for sterility) items that use 8 AA's that will be discarded after five minutes' use. I effectively have all the free AA batteries I could ever use. Seriously, I could get easily get 40-50 a week if I needed them.

Re: Building a replacement 386/486 CMOS battery

#32

Post by rasz »

smitelli wrote: post #2

The 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

>no way

you drill/dremel in two spots, solder tow wires and you are done.

https://www.classic-computers.org.nz/blog/2009-10-10-renovat...

Re: Building a replacement 386/486 CMOS battery

#33

Post by geon »

rasz wrote: post #32
smitelli wrote: post #2

The 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

>no way you drill/dremel in two spots, solder tow wires and you are done. https://www.classic-computers.org.nz/blog/2009-10-10-renovat...

You can also heat them up, making the resin brittle so you can chip it away and replace the battery.

Re: Building a replacement 386/486 CMOS battery

#35

Post by hyhconito »

buildsjets wrote: post #26
hyhconito wrote: post #24

Earlier quoted context omitted.

Just a note with those holders. They shouldn't be used in anything that will be shipped as the battery can get knocked out. The original shipped batteries were soldered in so they could be shipped safely. In fact a lot of the time the cells were taped or cable tied as well as soldered in on some bits of hardware! The newer CR2032's have much lower mass and can withstand many more G's before it's an issue so they are…

That is why I added the second Mouser link for the retaining clip, which is frequently missing from old stock. It takes a screwdriver to unclip it, plenty secure for transportation.

Got it thanks. That link crashed Mouser the first time so I assumed it was a dead one :)

Re: Building a replacement 386/486 CMOS battery

#36

Post by johnklos »

roytam87 wrote: post #30
johnklos wrote: post #27

It's good to see this getting some attention. People should know that removing batteries and replacing them with something modern, particularly non-leaking modern, is a good thing. Most motherboards work with 3 to 4.5 volts. If a circuit doesn't charge, then it's a simple matter of using two or three AA or AAA batteries. If it does, we can use rechargeable batteries (I've a box of Ikea ones), or we can put a diode in…

AA or AAA batteries will leak.

Lithium AA or AAA batteries won't, nor will good rechargeable.

I just took some lithium AA batteries out of a system that were 25 years old. Not even a hint of leaking.

Re: Building a replacement 386/486 CMOS battery

#37

Post by ruslan »

londons_explore wrote: post #22
ruslan wrote: post #15

Why not use a 5F/5V supercapacitor, DGH505Q5R5 or anything alike ? You may need to solder a 10R current reducing resistor in series.

What advantage does a supercap have over batteries?

Supercaps don't not leak and do not require to be changed regularily. Yes, offline time on supercap would be small, a couple of months, but for a machine which is used often that is not a problem.

Re: Building a replacement 386/486 CMOS battery

#38

Post by ruslan »

Denvercoder9 wrote: post #19
ruslan wrote: post #15

Why 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.

You don't need that much of energy to keep CMOS memory and RTC clock running. The battery will self-discharge way before it's exhausted by the load. IMHO.
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