Re: [NTLK] two Newton UMP2K problems

From: Robert Downs (rkadowns_at_mac.com)
Date: Fri Dec 07 2001 - 20:39:42 EST


On 12/7/01 5:44 PM, "Sushi" <Sushi_at_ragingbull.com> wrote:

>
>>> On Sat, 8 Dec 2001, Sushi wrote:
>>>
>>> Then discharge the battery completely. After your
>>> Newt automatically shuts off, try to turn it back
>>> on again. Do this a couple of times.
>>
>> On 12/8/01 @ 6:04 AM, speedy2 wrote:
>>
>> This is a bad idea!! You should NEVER discharge a
>> battery pack (with NiCDs,NiMH) below about .6V/cell,
>> .8V/cell is perfectly acceptable.
>
> Hey Speedy,
>
> Disagree with your "This is a bad idea!" comment. I have done this on
> numerous devices besides the Newton and have never had a problem with it.
> Not once!
>
> In this case, after the Newton shuts down after giving you the low
> battery warning, let it set for a second or two, then switch it on again.
> Let it shut itself off. Try it once more, if it will do it. Then after
> the Newt shuts itself down the second time, then plug in the adapter and
> recharge the battery until it is completely charged.
>
> Using that pattern, I've recovered/improved 3 battery packs so far.
>
> Remember, the Newton circuitry is determining whether or not it can turn
> on by the amount of juice that is available. If there isn't enough, it
> simply won't turn on. All the devices that I have that come with
> rechargeable batteries basically work the same way.
>
> Note, I don't hold the switch to try to force the Newt/device on. I just
> press the on switch and let the Newt/device deterimine if it can turn on
> based on the current battery status. In the case of the Newt, if it
> turns on, I will then activate the backlight via Adam Tow's Backlight
> package to speed the process.
>
> Regards.
>
> Sushi
>
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>
I agree with speedy. The reason you do not want to discharge a "pack",
"pack" being the key word, is because each cell discharges at a different
rate and at such low levels of voltage you stand a chance at reversing the
polarity of a cell. I have never seen this happen, but know it is possible.
However, since TTL circuitry (which I'm pretty certain the power supply of
the Newton is) requires .7 volts or more to activate, you should never be
able to drain any particular cell in a newton's battery pack below that
level. If you wish to drain a battery outside the newton, determine, using
ohms law, what resistor will provide a current draw from the pack that the
newton usually pulls under a full charge, combine that with a diode (LED)
and connect that combination to the terminals of the pack and let it go
until you can no longer see light from the led. (unfortunately this method
is NOT a constant current method and can take days to discharge. If anyone
knows a simple constant current method, speak up.) The pack should be
discharged to .7 volts. About as far as you should go. If you are
conditioning, charge the pack up again, using the proper method for the
battery type, and discharge again. After a few cycles the pack should be
back to a healthy enough state to be serviceable.

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