[time-nuts] Lead acid battery noise levels

Chuck Harris cfharris at erols.com
Fri Jul 12 13:40:40 UTC 2013


The thing is, when a SLA is being charged at the float charge voltage
range... 13.8V for a 12V SLA, it isn't all that low impedance.  Remove the
charger, and it will almost instantly drop to 13.2V.  At best, the SLA
is behaving as a very ugly high ESR electrolytic capacitor.

If you want low noise, and drift, you are better off building a good linear
supply.

-Chuck Harris

Gary wrote:
> The instruments I have used that employed an internal battery supply were meant to
> run off the batteries only intermittently. But that isn't the case for the OCXO. So
> the comparison has to be made with trickled charged batteries versus a power supply.
> But once we get to trickle charging, NiCads are not suitable. That might be why lead
> acid was used. [I'm thinking of the old Quantum noise measuring gear.] Technically
> SLA since we are using the batteries indoors around electronic equipment.
>
> Incidentally, I favor shunt regulators if noise is the primary concern. They are
> easier to design with ginormous cap filtering, while LDOs can have issues if the cap
> ESR is too low. Of course, shunt regulators aren't green.
>
>
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