Posted by
Don Wilhelm-3 on
Jul 30, 2005; 6:33pm
URL: http://elecraft.85.s1.nabble.com/K2-and-internal-battery-tp380861p380862.html
Charlie,
Hopefully to simplify the battery thing:
First, for an SLA battery to charge properly from a supply, there are
seveeral ways to accomplish that 1) put a constant 'float' voltage on the
battery terminals along with a current limiting resistor in series.
Normally the 'float' voltage is to be 13.8 volts for a 12 volt SLA battery.
Then consider that the K2 uses a protective diode at its power input. The
drop across this diode is about 0.3 volts. As a result, if you are to
charge the internal battery from the normal K2 power port, you must have a
power supply capable of producing the 13.8 volts (battery float voltage)
PLUS the drop across the protective diode (0.3 volts) - that means your
power supply must deliver 14.1 (or 14.2) volts IF you are going to properly
charge the internal battery. You may be able to adjust the voltage of your
present supply, you may want to open the case and see if you can spot a
voltage adjust pot inside.
I personally use a Smartcharger on my internal battery, and any smartcharger
must connect directly to the battery terminals, not as a bypass, but because
the charger must detect the battery terminal voltage to work properly. I
run my K2 from the battery at all times and when at the home station (most
of the time) the Smartcharger is plugged in and ready to charge the battery
on an 'as-needed' basis. You can see my implementation at my website
http://w3fpr.qrpradio.com or a mirror at www.qsl.net/w3fpr.
Your power supply voltage may be a bit lower than its nominal nameplate
indicates, but in any case, you will never fully charge your internal
battery with a 13.8 volt K2 power supply because of the protective diode -
sorry, but that is just the facts of life.
You COULD remove the K2 protective diode (or short across it), but that is
NOT (I repeat NOT!!!) recommended, and IMHO is not a good way to solve the
problem.
73,
Don W3FPR
> -----Original Message-----
>
> I have read what I could find on the Elecraft web site and in this group's
> archives and am still confused about proper use and care of the
> K2's internal
> battery. I know that some owners install a new jack on their K2s
> to bypass the
> K2's built-in battery protection (a resistor and a diode?).
> However, I can't
> imagine that Elecraft would design a radio or one of its accessories that
> required modification in order to work properly.
>
> I have two batteries for my K2 (both the Elecraft-supplied
> Power-Sonic models).
> One was receoved from Elecraft less than a week ago. I have not
> been able to
> charge either one to a voltage higher than 12.8 VDC yet. The
> original battery
> eventually got to 12.8 volts. The new one stays at 12.7 volts
> even after the K2
> has been charging for a couple days on my SEC-1223 power supply (rated for
> 13.8VDC @ 23 amps).
>
> It seems that the battery must be charged at a voltage of 14.2
> volts in order to
> avoid lead sulfate deposits from accumulating on its plates. On
> the other hand,
> I don't see any recommendations for chargers or power supplies
> that will provide
> that voltage at the proper amperage without risk of overcharging
> the battery.
> Also, I'd like to avoid buying a separate charger and power
> supply if possible.
> My question is whether or not there is a charger or power supply
> available that
> will power the K2 during home base use and also charge the
> battery properly when
> it is not being used. I apologize for my ignorance of battery
> technology and I'd
> appreciate any suggestions. Thanks!
>
>
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