[time-nuts] Low noise power supplies?
gary
lists at lazygranch.com
Thu Jan 31 07:11:44 UTC 2013
I've measured AA nicad impedance at a few kHz, but it was years ago. My
recollection is it was in tens of milliohms.
ESR does have a frequency dependency. In the same time frame, I was
trying to find a simple non-instrusive way to detect alkaline cells
versus nicads. The key was in impedance versus frequency curve. It
looked more than a bit hair brained, and given that there are no
consumer devices that do automatic detection today, I gather no one else
found an elegant solution.
But low ESR may not translate to low noise. Yeah, I know everyone is
thinking thermal noise, but a battery is a chemical device. You can
detect gas bubbles from electrical artifacts in some types of batteries.
At least under high discharge. Also the impedance of nicads increases
when they get old. I spent a ridiculous amount of time dealing with a
customer that found some old batteries that were not being detected by
the safety scheme built into a particular chip.
Lastly, the chemistry in these batteries isn't constant. Once you have
one battery technology nailed down, they increase the capacity and it is
a new ballgame. That lead to "chemistry independent" charging schemes
where the chargers had uP interface so that the charging could be
tweaked by the customer.
Personally, if the device you are using needs a power supply from god,
it wasn't designed well. The manufacturer should incorporate the
required regulation in the product so that it meets spec with run of the
mill supplies. Nobody likes to spend time debugging some customer
complaint due to a component outside your product.
On 1/30/2013 9:44 PM, Arthur Dent wrote:
>> But the only NiCd I know about are the AA sized ones.
>
> I have some of the wet NiCd batteries that are capable of
> putting out 200A continuously. I'm assuming the internal
> resistance is pretty low. ;-)
>
> Arthur
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