On 09/09/2014 09:28 AM, Ali wrote:
I have a battery backed ISA RAM card by SemiDisk. It
currently has a number
of Panasonic P-25AA 1.2V 250MAh rechargeable Nickel Cadmium batteries. Given
the card date backs from 1990 I am guessing the batteries are a bit dead and
I'd like to replace them. However, my Googlefu did not turn up anything.
Does anyone know if Panasonic still makes these batteries and if so where I
can purchase some in the USA? I did find some Chinese generic batteries:
http://www.amazon.com/Size-Rechargeable-Battery-250mAh-NiCd/dp/B005NRSQS8#
but I am not sure as to the quality of said battery. Any help is appreciated
in sourcing some batteries. Thank you.
If it's SRAM and a rechargeable battery, I might be tempted to
substitute a "keeper" supercap. Here's a paper from Cooper-Bussman:
http://www.digikey.com/Web%20Export/Supplier%20Content/CooperBussmann_283/P…
Some of the pinball folks are using Panasonic supercaps for SRAM backup
supplies and report retention times on the order of 45 days between
power cycles.
If that's enough for you, then you may want to consider using a
component that doesn't have the liability of leaking.
Another alternative is to simply use a primary battery, such as a couple
of AA alkaline cells and a Shottky diode or MOSFET to block the reverse
(charge) current. An AA in this application should last its shelf life.
I've got a couple of old systems set up with AAs that are still going
strong after 10 years. The added advantage is that you can separate the
battery from the device to avoid damage should the battery leak.
I've wondered about the use of a solar cell operating off of normal room
lighting and a supercap for memory/RTC retention. If you stash your
equipment in a dark closet, that's maybe not a good idea, however.
--Chuck