NiMH in a mouse ?

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Posted by Osiris on August 3, 2006, 4:43 am

from wikipedia:

"Care must also be taken during discharge to ensure that one or more
cells in a series-connected battery pack, like the common arrangement
of four AA cells in series in a digital camera, do not become
completely discharged and go into polarity reversal. Cells are never
absolutely identical, and inevitably, one will be completely
discharged before the others. When this happens, the "good" cells will
start to "drive" the discharged cell in reverse, which can cause
permanent damage to that cell."

NiMH cells deliver energy at a very constant rate. They do not "slow
down" very much.
But they drop down in capacity very fast towards the end of a charge.

Hypothesis:
For modern mice, that use very little power, NiMH would not be a good
choice, because before you know it, you're at the end of a charge and
reversing occurs.

Plausible ?

Posted by Rod Speed on August 3, 2006, 5:37 am

Osiris wrote:

> from wikipedia:
> "Care must also be taken during discharge to ensure that one or more
> cells in a series-connected battery pack, like the common arrangement
> of four AA cells in series in a digital camera, do not become
> completely discharged and go into polarity reversal. Cells are never
> absolutely identical, and inevitably, one will be completely
> discharged before the others. When this happens, the "good" cells will
> start to "drive" the discharged cell in reverse, which can cause
> permanent damage to that cell."
> NiMH cells deliver energy at a very constant rate. They do not "slow
> down" very much.
> But they drop down in capacity very fast towards the end of a charge.
> Hypothesis:
> For modern mice, that use very little power, NiMH would not be a good
> choice, because before you know it, you're at the end of a charge and
> reversing occurs.
> Plausible ?

Nope, because reversing can only happen with a significant
drop in the total voltage and so thats completely trivial for
the mouse electronics to detect and to shut down the laser
before any reverse voltage happens.

Posted by Osiris on August 3, 2006, 6:06 am

On Thu, 3 Aug 2006 19:37:03 +1000, "Rod Speed"

>Osiris wrote:

>> from wikipedia:
>> "Care must also be taken during discharge to ensure that one or more
>> cells in a series-connected battery pack, like the common arrangement
>> of four AA cells in series in a digital camera, do not become
>> completely discharged and go into polarity reversal. Cells are never
>> absolutely identical, and inevitably, one will be completely
>> discharged before the others. When this happens, the "good" cells will
>> start to "drive" the discharged cell in reverse, which can cause
>> permanent damage to that cell."
>> NiMH cells deliver energy at a very constant rate. They do not "slow
>> down" very much.
>> But they drop down in capacity very fast towards the end of a charge.
>> Hypothesis:
>> For modern mice, that use very little power, NiMH would not be a good
>> choice, because before you know it, you're at the end of a charge and
>> reversing occurs.
>> Plausible ?

>Nope, because reversing can only happen with a significant
>drop in the total voltage and so thats completely trivial for
>the mouse electronics to detect and to shut down the laser
>before any reverse voltage happens.

So you say todays' mice shut down in time ?

(I e-mailed this same question to Varta... see what they say.)

Posted by Rod Speed on August 3, 2006, 1:56 pm

Osiris wrote:

> On Thu, 3 Aug 2006 19:37:03 +1000, "Rod Speed"

>> Osiris wrote:

>>> from wikipedia:
>>> "Care must also be taken during discharge to ensure that one or more
>>> cells in a series-connected battery pack, like the common
>>> arrangement of four AA cells in series in a digital camera, do not
>>> become completely discharged and go into polarity reversal. Cells
>>> are never absolutely identical, and inevitably, one will be
>>> completely discharged before the others. When this happens, the
>>> "good" cells will start to "drive" the discharged cell in reverse,
>>> which can cause permanent damage to that cell."
>>> NiMH cells deliver energy at a very constant rate. They do not "slow
>>> down" very much.
>>> But they drop down in capacity very fast towards the end of a
>>> charge.
>>> Hypothesis:
>>> For modern mice, that use very little power, NiMH would not be a
>>> good choice, because before you know it, you're at the end of a
>>> charge and reversing occurs.
>>> Plausible ?

>> Nope, because reversing can only happen with a significant
>> drop in the total voltage and so thats completely trivial for
>> the mouse electronics to detect and to shut down the laser
>> before any reverse voltage happens.

> So you say todays' mice shut down in time ?

The decent ones do, anyway. Obviously all bets are off with the cheapest crap.

> (I e-mailed this same question to Varta... see what they say.)

Posted by Osiris on August 3, 2006, 9:18 am

e-mail from Varta: NiMH cannot be damaged when used in a mouse.

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