Glen said...
>Battery. The backup battery is dead or missing. You need to replace
>the backup battery immediately or you will lose the information in
>your Newton.
>Well, the little backup battery was just changed this summer and I
>just measured the new battery and it's giving a reading of 3.29 volts.
Winston answered...
>Even 'dead' batterys show almost full voltage. One must apply a resistive
>load to a battery to determine if it has usable energy left. Can you
>measure the voltage in place (in the Newt)?
Leland chimed in...
>Actually, every DVM/DMM that I've ever used had the load built-in. All you
>need to do is apply the leads to the contacts on the battery.
And if that wasn't enough, here's another of my well-known unworthy
comments...
It is correct that "dead" batteries show almost full voltage. The reason is
that usually they are measured when they don't have to supply any power.
If they have, the voltage drops. The more current is sucked out of them, the
more the voltage drops.
However, this is theory. The backup battery of the MessagePad has to supply
next to no current, that is why it lasts so long. In this case the
difference
between being in or out of the Newton is pretty much negligible. I'd expect
a lithium battery showing 3.29 volts outside the Newton would show at least
3.0 volts (which is the specified voltage for a "full" cell of that kind)
inside the Newton.
However, it certainly *does* make sense to measure the voltage inside the
Newton. An excellent freeware capable of doing that is Nick's BattMon,
available for both PC and Mac download at
http://www.logictools.de/newton/index.html
That way, you'd be able to determine the voltage the Newton really "sees"
which can be even zero if for example a lead was broken or so.
As to DVM/DMM's having the lead built in, I'm afraid you are wrong here.
DVM's usually have an input resistance of about 10 MegaOhms or more. This
is because when measuring voltage you usually don't want your measuring
tool suck any current out of the circuit you're trying to measure.
10 Megaohms, applied to a voltage of about 6 volts for the Newton's main
battery, would result in a current of 0.0000006 Amperes or 600 nanoAmperes
(at that current, you'd be able to continuously run your Newton for about
407 years with a 1500 mAH NiMH rechargeables pack).
So obviously this can't be any real-life condition for measuring a battery.
Another thing are the battery testers. These are basically voltmeters with
a built-in lead with a low enough resistance to suck current out of the
batteries under real-life conditions.
Frank
******************************************
This month's NewtonTalk brought to you by:
EVOTE.COM, the ultimate Political Junkie site on the 'Net.
The Clinton Administration, the George Bush
2000 Campaign, and almost every other major
U.S. politician has said something nasty
about us at some time. Find out why at:
http://www.evote.com
******************************************
Need Subscribe/Unsubscribe info?
Visit http://www.planetnewton.com
This archive was generated by hypermail 2b29 : Tue Feb 01 2000 - 00:00:43 EST