[volt-nuts] Fluke 731B battery & charge circuit

Orin Eman orin.eman at gmail.com
Wed Jun 19 00:00:36 EDT 2013

On Tue, Jun 18, 2013 at 12:30 AM, Christopher Brown <cbrown at woods.net>wrote:

> On 6/17/13 6:50 PM, Orin Eman wrote:
> > Since it doesn't seem to much mind 11V of 'ripple', I'm tempted to stick
> an
> > LM317L in there instead of the fussy zener/jfet/2n3904 circuit.  I just
> > have to go work out how much current it's drawing so I don't overheat the
> > LM317L.  I figure any slight drift from the LM317's voltage setting
> > resistors isn't going to matter at all.  I might just do this to add to
> the
> > knowledge base here.
> >
> > Orin.
> If the jfet is good (sounds like it is).
> Check the resisters on the PS board, IIRC it is the 510ohm one that is
> the current limiter for the charging circuit.

Just did that - 530 ohms and the other 180 ohm series resistor was 183 ohms
so I think I'm OK there.

> Replace the zener...pennies

Zeners are on order...

> Make sure the batteries are NiCd of about the right capacity (400 -
> 1000mah).

The Batteries Plus NiCd cells are 750 mAH so they are right in there.

>   The charge circuit is dead simple and should float the pack at 40 - 60ma.
> From you description it just sounds like the zener voltage is low, just
> like both of mine.

Sure does.  Seems OK at the moment with the two 1N4148s in series with the
'original' zener.


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