[time-nuts] Low noise power supplies?

[Fabio Eboli]

Hello, interesting discussion about noise.
It's all way over my knowledge, so my contribution
to discussion maybe is only noise :)

Re batteries I agree with Mark, see below:

Il 2013-01-31 06:42 Mark Sims ha scritto:
> A123 20Ah LiFePO4 cells have an internal resistance in the milliohm
> range.  Their M1 26650 format cells are around 8 milliohms.  Most 
> high
> capacity (>3000 mAh) 18650 style lithium cells are around 10-15
> milliohms.

I made some tests of high rate RC batteries,
and their internal resistance seem to be below 10mOhm
These are Li-ion pouch cells, their selfdischarge
seem very low, but I dont have figures for this.
Their cost is very low, and are used for RC airplanes
or cars, only thing I'm expecting is that they
will age and their internal resistance (and capacity)
probably will worsen after some time.
This is a graph of a 3-cell battery of 1.8Ah capacity,
charged and discharged at 3.6A and 7.2A (red and blue
curves):
<http://www.eevblog.com/forum/reviews/high-rate-li-ion-batteries/?action=dlattach;attach=31097>
Here tested up to maximum declared rate:
<http://www.eevblog.com/forum/reviews/high-rate-li-ion-batteries/?action=dlattach;attach=31185>

I report this here about noise, because I
remember that while I was charging and discharging
them, I was watching with awe the voltmeter
stable readings. The power supply/load
was an HP6632B and the meter a keithley 2015,
the meter reading was stable up to last digit
(10uV over 10-11V)and counting digit by digit up
while charging or down while discharging, "no missing
codes" sort of thing :)
It was like watching a counter instead of a voltmeter.
So I was wondering what could be the real noise
of a chemical battery. Reading this discussion
I'm learning that the batteries can be low noise
voltage sources.

Thanks,
Fabio.