[volt-nuts] fluke 731b battery pack

[Christopher Brown]

If even with a fully charged pack the batt charge side gets high enough
to feed into the ref you need to check the current value of the current
limiting resistor in the charge circuit.

Don't have the exact details in my head at the moment (was about 3 years
ago) but in both of my 731Bs that resistor had dropped in value by more
than a little and was floating the batteries at a higher voltage.  I
replaced with a correct value over-rated metal film type and no more
issue, max floating voltage for ~ C/20 maint to the pack is below cutoff.

If it is climbing high enough compared to the other feed, then resistors
have drifted and the batt circuit is running to hot or the filter AC ->
ref supply is running too low.

On 8/3/16 13:30, Orin Eman wrote:
> On Wed, Aug 3, 2016 at 2:08 PM, David <davidwhess at gmail.com> wrote:
> 
>>
>> I looked at the schematic and is seems feasible without excessive
>> effort.  Either the existing simple series preregulator can be
>> modified or replaced allowing it to both charge the battery (through a
>> blocking diode) and power the instrument or a completely separate
>> power charging circuit can be added in parallel.
>>
> 
> 
> The existing charging circuit _is_ in parallel with the pre-regulator; they
> are separated by CR5 and CR6 and the pre-regulator/battery outputs are
> combined by CR8 and CR9.  The only problem with the existing circuit is
> with a fresh, strong, fully charged battery pack, charging pulses will leak
> past CR8 with only R1/C1 to filter them.
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