6 Feb
2016
6 Feb
'16
6:35 p.m.
On Feb 6, 2016, at 16:59, Chris Pye <pye at
mactec.com.au> wrote:
This is what I normally do, preferably mounted away from the board. Generally you can get
away with simply using a diode to prevent the circuit trying to charge the battery.
I think that a blocking diode added in the positive lead of a non-rechargeable replacement
battery should work in this application. After further thought, lifting one end of the
diode in the existing charging circuit would not be ideal because that would mean the RTC
would always draw power from the battery, rather than drawing power from the main power
supply when the computer is turned on.
On Feb 6, 2016, at 15:37, Brent Hilpert <hilpert at
cs.ubc.ca> wrote:
My favorite solution, for the right circumstances, is to mount a 2, 3 or 4 cell AA or AAA
battery holder on the outside/rear and use common alkaline cells.
That's not a bad idea!
Right circumstances comes down mostly to current draw.
If the function is purely CMOS memory retention the current draw is equivalent to
static/idle leakage and you can expect shelf life from alkaline batteries. An RTC is going
to draw some current due to the active circuitry. I'm not sure what the current draw
for an RTC of that era is, the tech should be CMOS and the draw small but not as small as
simple memory retention.
Let's see, the RTC in this case is a Ricoh RP5C01. It has 26 x 4 bits of RAM, but
I'm not aware of any parameters stored in it (neither have I investigated thoroughly;
I just don't recall ever seeing the sorts of parameter settings on Amigas that PC
family machines usually have). Its rated maximum operating supply current at Vcc = 5.0V is
250?A. It's probably quite a bit lower at typical conditions while operating from a
backup battery at Vcc = 3.0-3.6V, but still a lot higher than the 500nA ratings I recall
seeing on much newer RTC chips.
On Feb 6, 2016, at 17:03, Chuck Guzis <cclist at
sydex.com> wrote:
I see all the talk about NiCd cells--does no one use NiMH nowadays? Why go with the
toxics?
--Chuck
NiMH is worth considering; I would just need to study the charging circuit carefully
before changing secondary battery chemistry.
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/