A500 RTC Battery replacements

[Dingo_aus]

I presume that most (all) memory boards that can with a RTC battery backup actually charge up the battery?

I need to replace my RTC battery and was wondering if I can just replace the original NiCad with 3 AAA NiMH? via wires to  a battery holder.

Are there any problems doing this?  I presume the charging circuit is a trickle charge? and that this method of charging wouldn't be to harmful to the NiMH, and they might actually charge up?

Or is it better to replace them with 3 AAA NiCad batteries?

[Chain]

Go for lithium battery


http://www.amiga.org/gallery/index.php?n=1124

[Dingo_aus]

That is cool.

So the 3v is enough? and the Lion doesn't need charging I take it.

So you don't connect the "charging" terminal, you just wire the coin battery into the + and - and it works happily?

[zipper]

There are also rechargeable lithium batteries. For non-rechargeable you need to put a diode to stop the charging current.

[Dingo_aus]

Thanks for your help everyone.

I finally got to the shop today and got a coin battery holder.

Whacked it on with a diode and finally my Miggy can remember 2005 and not keep having flash backs to 1978, before it was even born!

[Chain]

even with diode+lith. nonrechargeable battery you will get around 2.5V, and it still keeps teh rtc running, no problem


/me preparing (a little bit late, i know) something from replaced baterries for ya! (got 16 pieces this year, so 16 miggys saved from leakage ... vill be funny surprise i think
here is it!

[Dr_Righteous]

Ahh something my A501 needs desperately.

[Dingo_aus]

Oops, spoke too soon.

IT seems to hold the time for up to an hour with the power off, after that it loses it.

Any ideas?

With a fresh cr2032 and a diode I am getting 3.00V flat on no load.

This is my board (before I got rid of the NiMH.
http://www.users.on.net/~symes/other/a500/Mem%20Expansion%20and%20RTC%20backup.JPG

Maybe this particular board needs more voltage or something. I have a few other mem expansion boards, I'll whack the setup on one of them and see if it can hold the time.

[Castellen]

From memory, the A501 uses the Oki/Epson MSM6242 real time clock, which has a minimum data retention voltage of 2.0V.

You need to measure the supply voltage at the RTC itself as due to the series diode, it will be less than the battery voltage.
Datasheet for the MSM6242 here

We've flogged this subject to death in various other threads as well, more info here for starters.

[BadBigBen]

I would have send you one, but the shipping charge is around 8 Euro from Germany to Australia...

I still got two barrel (Varta 3.6v) battaries laying around...