K3 on Order

[Guy, K2AV]

If one is going to float this across a battery, need to take notice of
the normal float voltage for the cell.  This is a nominal 13.8 which
is just a characteristic of an automotive six cell lead acid battery.
There are other kinds, and this 13.8 may change to something else.

If you can actually provide a stiff 13.8 that does not droop with 25
amp draw you will be able to keep a fully charged battery in line for
power blips and drop-outs.  But the stiff 13.8 will not return certain
kinds of batteries to full charge after significant discharge,
requiring current limited 14.4 for charging to full specific gravity
readings. The Trojan T105 aux cells in my RV are like this, NOT the
same as the battery that starts the engine.

A charging system must be tailored for the kind of cells you are
using.  The telephone company uses low specific gravity cells that are
different.  These cells are sometimes available when some cells in a
24 or 48 string fail and the string is near normal replacement.  They
are outstanding backup batteries as that is exactly what they are
designed for.  You cannot treat these like car batteries.

So a battery is not just a battery.  Definitely need RTFM on mfr's web
page for this subject.  A battery manufacturer will tell you exactly
how they want a particular kind of cell maintained and charged.
Follow the manufacturer's instructions for your best results.

 My two T105's in series charge at 45 amps or 14.4 volts for four
hours.  The intelligent charger for this is specially made for this RV
application for this particular kind of battery, and to provide DC
from park power or gen around the RV for the raft of stuff that runs
off "12" volts or uses it for controls.

Should note that a power pole run from my RV DC distribution panel is
a perfect supply for a K3 or K2.  Even when the system is up on a 14.4
touchup, or a four hour full charge cycle, the K3 and K2 are perfectly
happy.

These chargers are available in 45 and 65 amp max load versions, and
if you want to invest in T105's or equivalent, you can go see your
local golf cart dealer and be able to bridge several hours of outage
and have it brought back up with a commercial charger made exactly for
that.

73, Guy


On Wed, Jul 21, 2010 at 2:25 PM, Tom W8JI <[hidden email]> wrote:

>> Interesting.  I run a K3 off a couple of pseudo deep cycle 12 volt
>> batteries with an Iota smart charger hooked up.  I run mostly digital
>> so IMD is important to me.  The Iota runs between 13.1 and 13.6 volts
>> by my K3's meter.  Would the difference between that and 14 volts make
>> a meaningful difference in the IMD ?
>
> It makes a difference when I test amplifiers at a constant power. I have not
> tested a K3, but I would be really amazed if it was not noticeably affected
> by reduced voltage.
>
> The problem is worse than an impedance mismatch. The problem is the loadline
> of the transistor. You can't get as much swing in the output device without
> getting into a non-linear part of the curve.
>
> It would take some compelling proof for me to believe reducing voltage does
> not hurt IM performance. In general the notion that all we need to do is let
> the rig draw more current to make up for low voltage is misplaced.
>
> It would also be very important to be sure the booster to stay at the
> voltage under full load.
>
> 73 Tom
>
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