K3 Field Day Note: QRO/Battery

[wayne burdick]

The K3 can be used at QRO power levels (13-120 W) when powered from a
car battery or a large gel cell. Here are a few things to keep in mind:

- A battery that's significantly discharged will have higher internal
resistance, which will cause the voltage to drop when high current is
drawn. (Small-gauge battery cables should also be avoided.)

- You can monitor your battery's vital signs during RX and TX using the
K3's built-in voltmeter and ammeter. Just tap DISP, then rotate VFO B
to see the voltage or current.

- The specified minimum supply voltage for the K3 is 11 V. This is a
conservative rating, intended to ensure spectral purity and stability.
But maximum power output will drop almost linearly with supply voltage.
You'll typically get 120 W at 13 V, 100 W at 12 V, and about 75 W at 11
V. At 10.5 V, you should drop to QRP levels. Below 9.5 V the rig may
turn itself off. Reduce the power setting manually when voltage drops,
just to be safe.

- If you see an unexpected "HI TEMP" warning during QRO transmit, it
could be due to an excessive dip in battery (or generator) voltage at
the PA monitor circuitry. If you see this happen, try configuring the
temperature sensor to sample only during receive mode. To do this,
locate the PA TEMP menu entry (CONFIG menu), then tap the '1' key until
you see "R ONLY" (rather than the default, "T AND R"). This mode of
operation is completely safe as long as you're not "standing on the
key" for several minutes at a time.

73,
Wayne
N6KR


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[Carl Clawson]

Don't underestimate the voltage drop in your battery cables.

My old ICOM 735 shipped with a ten-foot #12 battery cable, which I used on
Field Day without thinking. Later I realized that I was losing more than
half a volt in the cable. That's a lot when you're running from batteries
with a rig that ceases to function a little below 12 V. A lot of "12 V" rigs
are spec'ed at 13.8 V +/- 15% (some are even +/- 10%, which hardly qualifies
as "12 V"). You don't have a lot of volts to lose running them on battery.

Now I use two paralleled #10 cords, four feet long, with just a short length
of #12 to the radio. Yeah, it's overkill but it makes me feel better.

So:

1. Kudos to Elecraft for designing a rig that runs down to 11 V!

2. Look up a copper wire table and do the math on your power cables. You
might be surprised. Don't forget that you have two wires in series with the
battery.

73 and thanks for listening,

Carl WS7L
K3 #486

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[Bill Steffey NY9H]

I was somewhat fearful of taking my K3 to field day without "protection".....
we all know how important that is these days. :)

So I made a "field case" for th K3 ...  and one for a pair of  7ah
batteries....
all fits into pelican 1520....

Aside from a minor concern of not adequately cooling the right side
panel with the
pair of regulators mounted...( wayne??),  I think I covered all the bases....

Still working on 'finishing' the case and integrate a pair of
speakers in the lid...


take a look
bill

K3  field case
http://picasaweb.google.com/Bill.SteffeySr/ElecraftK3FieldCase

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[wayne burdick]

On Jun 26, 2008, at 9:29 AM, Bill NY9H wrote:

> So I made a "field case" for th K3 ...  and one for a pair of  7ah
> batteries....
> all fits into pelican 1520....
>
> Aside from a minor concern of not adequately cooling the right side
> panel with the
> pair of regulators mounted...( wayne??),

The right side panel does need adequate ventilation, Bill. What
temperatures are you measuring on the TO220 tabs on the regulators?

Wayne
N6KR

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[KK7P]

> Aside from a minor concern of not adequately cooling the right side
> panel with the
> pair of regulators mounted...( wayne??),  I think I covered all the
> bases....

Bill,

Looks good!

As long as you are not going to operate the radio while wrapped in the
wooden sheath, it ought to protect it nicely.

The DSP depends on reasonable airflow around the top and bottom of the
case towards the front for cooling.

As you note, the right side panel must have air for cooling the
regulators -- especially if a second receiver is installed.

73,

Lyle KK7P

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