Arlen,
I just measured the terminal voltage of several SLA and AGM batteries.
After not being charged for over a week, they all measured in excess of
13 volts. So my conclusion is that your wall-wart charger is not fully
charging your battery.
A normal float charge for an SLA battery should be at 13.8 volts - and
even that is not perfect because the best charging voltage varies with
temperature. A good 3 stage charger designed for charging SLA batteries
is the best to use, and those are a bit more expensive than the
"wall-wart" chargers, but worthwhile if you consider the life of your
SLA batteries important.
73,
Don W3FPR
On 8/15/2014 6:03 PM, Arlen Fletcher wrote:
Hi Mark,
Thanks for the response!
I’m guessing that perhaps you’re considering that the voltage of the SLA is
sagging when it’s running the KX3. I wondered that too - so I measured across
the terminals of the SLA while it was powering the KX3. It still measured
12.2V, so it wasn’t sagging. The battery (and it’s little charger) report it as
being fully charged - though I’m dubious about the accuracy of the little
wall-wart charger. :-)
Arlen
AA7F
On Aug 15, 2014, at 11:42 AM, rv6am...@yahoo.com wrote:
Re: …reads 12.2V on my Fluke DMM - the KX3 reports 10.2V while idling.
Arlen,
My first thoughts are that you need to fully charge the battery. I don’t have
a lot of experience with lead acid batteries, though.
The input diode (CMS04 if my memory is correct) should only account for about
0.2v at KX3 receive current levels. I haven't looked at the schematic for a
long time, so I can’t remember what else is in the path from the connector to
where the internal voltage reading is measured, but I seem to recall at least
one FET (on/off switch) and a current sensor.
The 12.2v is getting pretty close to the no-load fully discharged 1.95v per
cell, and the 10.2v is pretty close to the 1.75v per cell of a fully discharged
SLA battery. At these voltages, the discharge curves are getting pretty steep,
so the addition of the KX3 receive current could cause the extra drop you are
seeing.
Of course the problem could also lie in the power cable, connectors, or even
inside the SLA battery itself. A check with a fresh, fully charged SLA battery
will help isolate the problem. You will see voltage drop along the cable, even
with a freshly charged battery, but 2 volts total sounds a bit high. I just
pulled out an SLA that I haven’t used for a while, but it has been charged
recently, and the voltage difference between the battery voltage (no load read
by a cheap DMM) and the KX3 display (while in receive) was less than 1 volt.
Hope this helps.
Mark
KE6BB
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