[time-nuts] Oscilloquartz BVA has been sold. Thank you all who expressed an interest.

[Poul-Henning Kamp]

--------
Mark Spencer writes:

> I like the idea of using a diode arrangement to facilitate changing the power
> source for the BVA.   I expect I will also add some form of over voltage
> protection as well.

If you are after the low noise, be weary of "integrated" lithium batteries of 12V and higher, many of them have a built in buck-converter to take the real battery voltage down to 12V and provide over-current protection.

If you go lead-acid, don't forget rule #1:

  Your fuses can never be too numerous or too close to the battery.

Lead-Acid batteries float-charge at 13.8V[1] so two 12V in series you gets you 27.6V.

Subtract the drop over a series diode and add a linear voltage regulator and you have nice and quiet 24V.

(A lot of professional fire and burgler-alarms run on such configs, and the hardware is actually pretty nice, being a nieche and high-margin business, look out for it in scrap-heaps.)

When the charger looses power, you will drop below 24V after some time (1-60 minutes depending on battery capacity), but if the rest of your lab is dark anyway, that can still keep the BVA warm until power comes again.

If on the other hand you want to disconnect the charger to make low-noise measurements running from battery, you will need more voltage headroom.

I would not go with five 6V batteries.  6V batteries are almost universally lower quality than 12V, probably because nobody "serious" uses them, so manufacturers do not get yelled about on quality.

Three 12V blocks will put you at 41.4V when float-charging, which is a lot to swallow for a linear regulator, both in terms of voltage and power.

Poul-Henning

[1] Tons of footnotes on this but find and trust the manufacturer is a very good starting point, unless you want yet another hobby.

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