Poul-Henning Kamp wrote:
In message<7c37.12cdef25.39a12...@aol.com>, ewkeh...@aol.com writes:
I am not seeing it, what should I use to measure it 3561 and 70000 spec
analyzer do not show it?
It is probably the 3561 not the 70k that has the best chance.
I am not aware of the precise characteristics of the noise, but it
sounds somewhat like a boiling pot.
I became aware of it first time when I ran a small class-A audio
amplifier from a couple of, probably too, small VRLA's some years
ago, just for the fun of it.
With no input signal, the speakers would gurgle faintly and it took
me some time to locate the source of the noise to the batteries.
I would guess its amplitude correlates with the ratio of discharge
current to plate area, since it is chemical/mechanical in nature.
These days, I would build a super-cap battery instead if I needed
a low-power PSU with low noise.
Poul-Henning
PS: also be aware that almost all VRLA's have a very nasty resonance
frequency somewhere in the low MHz band. If you are after low noise,
you should always decouple the battery good poly/plastic caps right
at the terminals.
NIST found that NiCd cells are very quiet at least for low load currents:
http://tf.nist.gov/general/pdf/1133.pdf
Thus batteries are useful as low noise voltage references or for
providing the relatively low base current of a BJT in a low phase noise
RF amplifier.
Perhaps its the gelled electrolyte that is the source of the noise
problem with VLRA batteries??
Bruce
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