[Elecraft] KX3 internal battery problems

[Peter Lambert]

I can offer a little info :

New charged cells in my KX-3 show about 10.4V when I turn the unit on (after
it's been laying around for weeks).

A new fully charged pack shows about 0.7 ohm internal resistance (by the
voltage drop and current when transmitting).  Ie that's over the 8 cells.

Don't fully discharge NiMH batteries.  Cycling them as you'd do with the old
nickel cadmium cells rapidly raises the internal impedance of the NiMH
batteries.  You'll find them useless long before they get anywhere near the
published number of cycles because of that rise in internal impedance.  Just
top them up after use and that's it.

I've gone through a couple of battery changes in the KX-3.  That internal
impedance is going to be way more important to you than the capacity of the
pack.  On a typical SOTA outing I'd be lucky to use more than about 20% of
the capacity (I use the LSD kind at about 2.5Ahr).  The packs still have
close to their full capacity long after the internal impedance rules them
out for use in the KX-3.

Last pack probably only got cycled about 10 times before the impedance was
too high to get the 5W out.  I concluded from good old google the cause was
deep discharge.  After just 10 cycles I considered them relatively "new" but
they'd not hold up under transmit load (guestimate of around 1.5 ohms for
the pack).  They worked fine for lower current use and still operated the
KX-3 in receive for the same duration (ie capacity had not diminished).  The
"new" pack in the unit will never get cycled just topped up.

73's Peter VK4JD

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of LA7NO
Sent: Friday, 6 May 2016 8:07 PM
To: elecraft at mailman.qth.net
Subject: [Elecraft] KX3 internal battery problems

KX3 (ser. no. 08146) works OK on external power, but recently I am
experiencing problem using it on internal rechargeable cells.

The AA cells are relatively new Varta Professional No. 5706, 2700 mAh NiMH.
They have been charged with a techno-line BC-1000. Measured capacity via an
automatic discharge/recharge cycle is according to spec.

I have attached a 50 Ohm dummy-load to the KX3. When turned on, it indicates
BT 9,7V.  BAT MIN is set to 8,2V.
When I press ATU TUNE, it turn itself off immediately.
With TUN PWR set to 0,1W it works OK when pressing TUNE, but BT drops to
7,6V.
If TUN PWR is set to 1W, it switches off when TUNE is pressed.

Strange that the voltage drops so much, even if the charger indicated normal
cell capacity when automatically discharging them.

Any ideas?

Per-Tore / LA7NO




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