In article ,
Barrett wrote:

This is unbelievable.

Alas, MFJ equipment's reputation for sterling quality control would
cause some to disagree with you.

I was sent another new unit, my second MFJ-259Z from
WSPLC and its another bad unit. The batteries won't charge. It does have
39mA on the jumper switch this time. But still will not charge the
batteries. I will phone them again tomorrow after the unit has been on
charge for over 24 hours.

39 mA is probably *not* enough to effectively charge 2000 mAh NiMH
cells. It only a C/50 rate.

NiMH cells have a low "charge acceptance" efficiency at such low
current rates... relatively little of the energy going into them
actually goes into the electrochemistry. The manufacturer's
literature I've read, recommends against using this sort of "trickle
charge" with NiMH cells... it just doesn't work very well. It might
be adequate to maintain fully-charged NiMH cells against
self-discharge, but it's apparently less than idea even for that.

40 mA of charge current might make sense if you loaded the analyzer up
with typical 1000 mAh NiCd cells - it'd be a C/25 rate, and since
this battery chemistry responds reasonably well to low charge rates
you'd probably find the batteries topped up in 36 hours or so.

As it is, you might need to wait a week or more for the NiMH batteries
to charge up, *if* they do so at all.

Seems to me you have three workable alternatives:

- Return this charger and insist that they provide you one with a
more sophisticated/effective NiMH charging circuit. Seems unlikely
to me that they have one at this time - it would require
significantly fancier circuitry.

- Figure out how the charging circuit works, and modify it yourself
to provide a significantly higher charging current. NiMH cells
seem to react well to a C/10 charge rate - around 14-16 hours from
a fully-discharged state seems to bring them up to full power and
break them in properly. This change might require no more than
replacing a single resistor in the charging circuit, depending on
how MFJ designed it.

- Use NiCd cells rather than NiMH (which is what I do with my MFJ
259/269 analyzers). 36 hours of charging should bring 'em up to
the Plimsoll line.

- Use a real NiMH AA charger to break in and charge your NiMH cells
outside the analyzer, then install them and plug it into the brick
for a few hours a day to keep the batteries from self-discharging.
Remove the batteries and recharge externally whenever they've been
run down significantly.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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