[Elecraft] What battery to use?

[Mike Morrow]

Mark wrote:

>I am gearing up for a portable station for emergency
>communications and have decided to use my K2/100 and
>KAT100 combo.  I want to be able to power it with
>batteries, if the need arises...I've been thinking about using
>something on the order of a 50-60 Ahr size.


I've been playing around with portable HF gear at campsites for 25 years.
My only QRO rig for such use is a TS-50S running about the same power as the
K2/100.

I won't speculate on other battery technologies, but I'll just say I've
found deep-discharge batteries to work fine as long as they are periodically
well discharged and re-charged (about every 90 days or so).  At the very
least, they need to be put on charge once or more during the same interval
even if they've been sitting unconnected.

Even for short camping trips less than a week long with casual HF
operations, I've found it best to choose the highest amp-hour capacity
battery that you can find and easily move around (something about 100
amp-hours or better).  I think you'll find the 50 to 60 amp-hour capacity
you mention to be too low, even for short trips portable, but especially for
stationary emergency use.

I don't know how the K2 is, but for many solid state QRO rigs the various
bandswitch and control relay switching circuits are the first things to
falter as the battery voltage drops from the 12.6 vdc max that you'll have
when the battery is at full charge.   Low source voltage combined with
voltage drop in the solid-state relay coil switching circuits (at least 0.7
vdc) can result in coil voltage that is too low  to reliably operate the
relays.   I had one rig that wouldn't function much below about 11.0 volts
due to that effect.  Under transmit loads on the battery and with the
voltage drop in the power cables, 11 vdc at the rig happens a lot sooner
than you'd think for a QRO rig.  Since you'll be starting with a relatively
low 12.6 vdc, you'll want to use the shortest and heaviest wire that's
practical for the power cables.

I think you've got a great idea about preparing your station to operate at a
power output level that is conducive to reliable communications.  Any HF
station truely intended to function for emergency communications should be
capable of 100 watts output at least.  QRP is a great hobby mode that tests
the proficiency and equipment of the operator at the other end, but it has
no place in serious emergency communications planning except as a very last
resort.

BTW, I've been able to operate for a week a 100 watt HF rig (SSB and CW) a
few hours a day, and as a shortwave receiver for several times that, while
camping in the boonies.  I still had plenty of energy left in the
deep-discharge battery I took, which was rated for 105 amp-hours.  I also
was using that battery to feed a 50 watt 2m FM rig and a scanner radio, and
to feed a small electric light.  It's really surprising how much service can
be gotten from one charge from a decent-sized battery.  I've had a 400 watt
12vdc/120vac portable gas-powered generator for 20 years but I've never
needed to run it to re-charge the battery on any trip.

The nice thing about these high capacity deep discharge batteries is that,
compared to the price of typical handy-talkie battery packs, they are dirt
cheap.  I keep a couple charged at all times.

73,
Mike / KK5F