Lithium battery hack: 2 x AAA instead of coin battery?

[dnelsonfl]

I have a battery that's starting to become fuzzy, so it's time to be replaced. I was looking at the lithium battery hack, but I'm having difficulty finding a coin battery clip. The CR2025 and CR2032 batteries the instructions suggest using look to actually be 3V not 3.6V. I remember reading that the minimum voltage necessary was actually 2.2, so the 3V battery less the diode would give about 2.3.

So the question is, would it be feasible to use 2 x AAA 1.5v lithium batteries instead of the coin battery? Parts for AAA clips are easily obtained. This would give 3V as well.

Thoughts?

-David

[Skyrunner]

You can desolder ANY coin battery clip from a PC motherboard. It's more than easy and it fits the mobo perfectly! I did it on my A3000 a few days ago! Do it and don't bother with AAA batteries. Look for lithbatt.lha on Aminet for instructions.

[dnelsonfl]

It looks like Jameco has the CR2032 battery clips in stock here,
and it's only 63 cents, but shipping is $4.95. I don't have any old PC motherboards to hack for the part. There is no PC recycling center near me, and the goodwill/consignment shops want more than a couple bucks for old PCs. I checked those out when I was looking for old Commodore gear. The AAA holder from Radio Shack (here)    is only $1.59 plus tax.  The "N" style batteries are small, but they're 6V. Too much, right?

I certainly agree the coin style takes up less space and looks better. But I'm trying to do a good job at the lowest price, given what's available in my locale.


-David

[melott]

Hi David ....

I tried the coin battery hack on an A2000 rev 4.5 MoBo.
It didn't work ... I tried with 2 different NEW batteries.
What I found on the A2k is it needs the extra point 6 volts
to hold the time/date. I posted this results on A.Org here
awhile back. There was a few comments from others that have
done the hack with varying degrees of success from "Didn't
work" to "holds time for awhile".
I'd say try it, if it works 'Great', if not, add another
battery. (I din't think you would hert anything by having
4.5 volts. I'm sure someone will correct me if I'm wrong)

[dnelsonfl]

melott wrote:
I'd say try it, if it works 'Great', if not, add another
battery. (I din't think you would hert anything by having
4.5 volts. I'm sure someone will correct me if I'm wrong)

I do remember seeing that post, but didn't think much of it at the time. Probably because it was regarding a 2000, and I'm looking at a 3000 and a 4000. I was wrong about the "N" by the way; it's still just 1.5v, and only in alkaline. I'd have to stay with AAA for small lithium (energizer). Those should last quite a long while. Thanks for the tip.
-David

[platon42]

I'm using two standard AAA batteries replacement in my A4000T -- without a diode though, because the cell battery was a lithium cell before, so I supposed there is no reloading mechanism deployed. Worked nicely for a year now.

[melott]

Ummm... Lithium batteries ARE NOT supposed to be
rechargable, they can explode. No need to say what would
happen to your Amiga then :-x

If you use the Lithium battery you REALLY should add
the diode.

[melott]

Hi David ...

You have PMail

[dnelsonfl]

A real quick technical question and it applies for any kind of battery being connected to the Amiga... what is the acceptable voltage range? The barrel battery is a 3.6v, but the coin lithium is a 3v. Using two AAA's will give 3v, and four will give 4.5v. Some of that is going to be lost from the diode and the wires. Or is it more a matter of how many amps (or in this case milliamps) rather than the volts?

-David

[Castellen]

The RP5C01A real time clock has two modes of operation:
Operating and backup.

With a supply voltage of 5.5-4.7V it's in operating mode, draws significantly more current (250µA) and can be communicated with via the address/data bus.

If the supply voltage falls below 4.7V, it switches to low current (15µA) backup mode, where only the crystal oscillator and an internal counter runs in order to keep the time/date.

So to answer your question, the battery voltage at the RTC input (pin 18) must be between 4.7V and 2.2V for it to run in backup mode and without loosing data.


An easy solution for you would be to use 3 x Ni-Cd or Ni-MH cells in series.  Either AAA, AA or whatever.  That will give you a nominal terminal voltage of 1.2 x 3 = 3.6V.
This is exactly what's in most cordless phones.  The batteries are rechargable, so no modifications to the board are necessary.

I've written a guide for replacing batteries as well as using alternativcordless phone battery types:

http://amiga.serveftp.net/battery.html

[Zac67]

Castellen wrote:
So to answer your question, the battery voltage at the RTC input (pin 18) must be between 4.7V and 2.2V for it to run in backup mode and without loosing data.

That's the explanation for the coin battery/diode mod not working reliably. A brandnew CR2032 has a voltage of 3.1 to 3.2V. Minus .7V for the diode leaves us with 2.4V. When the battery has dropped below 2.9V (might be at 80% of its capacity) there's not enough voltage to feed the clock/RAM.
Many coin batteries sold have quite some shelf life behind them, so don't expect them to last very long.

[dnelsonfl]

@Castellen,

Thanks for the link and the tech info.

-David

[dnelsonfl]

Hi,

An update because in the end it might have been all for nothing. But I did get some interesting experiment results. I tried the coin battery hack first. The battery tested 2.94v new out of the package. After it was hooked up, it showed about 2.84v. Measuring across the RTC chip (U178), it showed about 2.7v.

Not satisfied with the voltage, I switched to using 3 x AAA rechargable batteries. The batteries tested 3.96v when hooked up. This gave 3.85v across the RTC chip. Much better.

The coin battery hack can be done to look very clean and very professional. Using another form of rechargable battery might not look very pretty, but it does give a more desirable voltage.

BUT ... in the end ... I have a problem. I *thought* the battery had been caught in time. It was just barely fuzzy. I cleaned the area around the battery very good and removed the little bit of green I saw. Using the guide on that posted web site earlier, I carefully checked all the traces with my multimeter. Everything looked good to the naked eye, including my average-skilled soldering job. But the RTC clock is still not seen by the system. I took a picture and blew it up on the computer. OMG. The traces on side of U177 closest to the upper + of the battery did not look as clean as other traces. Some of the legs of U177 also still looked a little greenish and duller than others. The soldering job looked a lot worse, too ... well, I had trouble removing the solder from the hole to stick the wire through, so I soldered it on top. It's secure and the voltage checks out okay. Speaking of which, with the system on, 4.99v is across U178 and 4.88v is across U177. As I stated earlier, I checked all the connections with the multimeter and everything is good. What gives? Did U177 itself suffer corrosion internally perhaps and is the problem? I'd appreciate any thoughts on the matter. I know U177 can be repaired with good skills, and obviously I am not that skilled (yet).  :-D   In the meantime I can use one of those scripts to set the time via an internet atomic clock on boot.

Thanks,
David


EDIT: Here are the pictures to see what I'm trying to describe. This is the whole board and this one is the damaged area. The underside shows some damage, too, in this photo near the C177 label. The pictures were originally 1600x1200 to see the detail, but it looks like Yahoo might have dumbed it down. Sorry.

[BadBigBen]

Hola, and sorry if I intrude on the post here...

but if someone is interested, I still got two Barrel Batteries, New from Varta rated at 60mAh 3.6V...

is someone wants them let me know...

Cost only the shipping charge... no more no less...

Ben

[orange]

What about that little potentiometer for precise adjusting of clock speed; does it help for making clock more precise and how can one use it? (it would be hard to just rotate it a bit, measure time, rotate it more.. and so on)