[time-nuts] Battery backup of frequency standards

Chuck Harris cfharris at erols.com
Thu Jun 9 12:03:46 EDT 2005

Hi David,

I think I misunderstood your solution.

The plastic sheet that covers the caps is there to protect
the caps, and to keep them from popping off of the cells.  The
caps usually aren't retained in any other way.

You are absolutely correct, any gas or liquid that gets past
the rubber caps is lost.

If your solution provides the same level of support for the rubber
caps as they had before, and doesn't block or impede the passing
liberated gas, the SLA should be chemically safe.

The plastic sheet is also a secondary safety release.  It is welded
only superficially so that rather than blowing out the sides of
the battery, it will pop free in cases of extreme (rapid) outgassing.

I am not especially comfortable with modifications to the SLA's
safety mechanisms.  If I make such a modification, then I take
responsibility for any failures that may occur.  (including those
created by the battery manufacturer) SLA's can fail in dramatic
ways if the charging circuit gets too aggressive, and the safety
features don't work as advertised.

I might do it for myself (probably not), but certainly not for
a device that could be used by someone else.

-Chuck (who has spent too much time designing rapid chargers)

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