[time-nuts] Battery backup of frequency standards

Chuck Harris cfharris at erols.com
Thu Jun 9 13:33:00 EDT 2005

Hi David,

 > Mine are not retained by the plastic sheet, as that sits about 1mm above
 > the caps.

One way you can tell if a battery has been abused, is you will
find the rubber caps stuck to the plastic lid.  Under normal
conditions, there is no gas generation, and the rubber caps stay
down where they were installed.  But the way they (the usual style I
have seen) vent is the sides of the cap move outwards, and the
cap raises up to protective plastic cover.

> One option might be to mill the plastic until is is thin and hence weak, 
> but perhaps not very practical.

Then you would have to do testing to see if it failed in the way you
had planned, and suddenly this becomes a big research project.

>> -Chuck (who has spent too much time designing rapid chargers)
> I have no desire to rapidly charge them.

I didn't think that you did, but in the process of, uhmmm.. Agressively
charging batteries, I have had the opportunity of witnessing the protective
safety measures in operation.  (A fancy way of saying I have blown a few
batteries up.)

> I guess a separate box for batteries, (that several suggested) is the 
> least hassle. I was just keen to
> keep the unit a reasonable size, and self-contained, but it certainly 
> does not look easy to do.

It would make your instrument more managable, weight wise, and would
keep all the yucky stuff in one place.  Plus, it would allow you to use
a variety of means to keep your system operational during power loss.

If you keep the charging and load lines separate, you can even explore
using a large primary battery, as Brooke suggested.


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