Re: Z-RAM ultra 2... replacing the battery?

[mjmahon@aol.com (Michael J. Mahon)]

John Van Winkle wrote:

>I would suggest changing the batteries first.  The batteries I used were the
>1.2V AA rechargables from radio shack.  I would suggest using the 1.7V AA
>that radio shack has and a battery holder that you can wire to the board.
>Email me and  I will send you a pic of what I did.

I appreciate that your repair with two NiCd cells worked, but I caution
you and others that this is not guaranteed to work universally.

The clock chip that Gary's board uses will work down to 2.0v, which,
with 1 series diode drop, means that he needs at least 2.6v to keep
time with power off, and preferably a few tenths of a volt margin.

I have never heard of a rechargeable battery chemistry that delivers
1.7v per cell.  I'll check into this...  But in any event, the board is
designed to recharge a 3.6v NiCd battery of three cells of 100mAh
capacity.  Such batteries are still readily available.  I would advise
replacing the battery with a new NiCd battery of very similar capacity
but different form factor.  It will be smaller than the original, so there
should be little mechanical difficulty.

As a practical matter, a battery capacity in the range of 60mAh to
150mAh would be satisfactory.  Going much smaller would reduce
the period of time that the clock would keep time with power off, and
going much higher would increase the self-discharge current so that
the trickle charging current might be marginal, and this current would
be the timekeeping limiter in any case.

-michael

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