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

[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

[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

[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

[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.

[dnelsonfl]

@Castellen,

From the limited detail in the pictures, the damage doesn't look too bad.  Or you've made a really good job of cleaning it :-)

The damage actually wasn't too bad, and I did work at it to clean up what little there was. It's an important lesson that only a little bit of leakage was enough to kill the RTC. Too bad this 4000 and me didn't meet earlier. I could have prevented it altogether.

Your guide was very useful. I did run through checking all the connections it specified, and everything looks good. I found this company ChipQuick that gives out free samples of its SMD removal kit. I requested one. If the kit does indeed make it easy to remove SMD chips safely and easily, then all I have to consider is practicing on replacing it. Maybe they have a kit to do that easily, too. In a few months I might just attempt it.

-David

[dnelsonfl]

The SMD removal kit arrived yesterday. Your instructions make it look fairly simple, so as soon as I find a suitable replacement chip for the U177 I'll be on my way.

All I've found so far is a Texas Instruments SN74HC174D in the States. It looks the same as the Farnell part on your guide, except it uses the term "clear" instead of "reset". Clear is a reset, right?

-David