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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: Dingo_aus on December 26, 2005, 06:10:34 AM

Title: A500 RTC Battery replacements
Post by: Dingo_aus on December 26, 2005, 06:10:34 AM

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?

Title: Re: A500 RTC Battery replacements
Post by: Chain on December 26, 2005, 09:38:21 AM

Go for lithium battery :)


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

Title: Re: A500 RTC Battery replacements
Post by: Dingo_aus on December 26, 2005, 10:02:26 AM

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?

Title: Re: A500 RTC Battery replacements
Post by: zipper on December 26, 2005, 11:08:23 AM

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

Title: Re: A500 RTC Battery replacements
Post by: Dingo_aus on December 29, 2005, 11:48:37 AM

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! :)

Title: Re: A500 RTC Battery replacements
Post by: Chain on December 30, 2005, 03:31:11 AM

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! :) (http://www.amiga.org/gallery/index.php?n=1261=38)

Title: Re: A500 RTC Battery replacements
Post by: Dr_Righteous on December 30, 2005, 03:46:32 AM

Ahh something my A501 needs desperately.

Title: Re: A500 RTC Battery replacements
Post by: Dingo_aus on December 30, 2005, 06:12:27 AM

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.

Title: Re: A500 RTC Battery replacements
Post by: Castellen on December 30, 2005, 10:57:24 AM

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 (http://amiga.serveftp.net/Datasheets/MSM6242-RealTimeClock.pdf)

We've flogged this subject to death in various other threads as well, more info here (http://www.amiga.org/forums/showthread.php?t=17812) for starters.

Title: Re: A500 RTC Battery replacements
Post by: BadBigBen on December 30, 2005, 04:50:19 PM

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...