FW: K1 Battery Question

[Dan Barker]

Actually, the 40% Tx duty is only 50% key down (there's spaces betewwn the
elements). So, you use .2 for the Tx factor.
.8 Ir + .2 It = .24 or 16 hours.

Now, after you work the 9 hours, you might fall over and hit your head on
the key, and then the CW duty cycle goes to 100%. But the Tx duty cycle
would go to 100% also, and you'd be off the air sooner. Not that it matters
much as you are napping on the key<g>.

Dan / WG4S / K2 #2456

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]]On Behalf Of John R. Lonigro
Sent: Friday, June 11, 2004 10:39 PM
To: Elecraft Reflector
Subject: Re: [Elecraft] K1 Battery Question


John:

Here's my guess:
1) Measure the receive current in Amps (Ir).
2) Measure the transmit current at the power level you plan to operate,
in Amps (It).
3) Estimate your transmit duty cycle, which will usually be quite a bit
less than 50%.
4) Compute average current drain (I).
    Assuming a 40% duty cycle, your average current drain (I) would be
0.6 x Ir +  0.4 x It
5) Divide 4  Amp Hrs by your average current drain and that will give
you an estimate of your time with the battery.

I don't have a K1, but the spec says as little as 55 ma on receive, so
assume 60 ma (0.06 Amps).  If your transmit current is 1.0 Amp, then
with a 40% transmit duty cycle (probably high), your average current
drain would be 0.6 x .06 + .4 x 1.0 or 0.44 Amps.  With those
assumptions, your fully charged 4.0 Amp Hr battery should last about
4.0/.44 or 9 hours.  A 40% duty cycle might be equivalent to continuous
heavy operating during a contest.

John AA0VE

John J. Bahun wrote:

>I have a 4 Amp Hour Gel Cell pack that I just acquired.  I was wondering if
anyone has any input as to how long I should expect the K1 to operate off
this battery with typical transmit behavior (Not sure exactly what that
is...)
>
>Thanks
>
>JB - WB8UFA / 7
>
>
>

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[John Lonigro]

Hi Dan:

As I wrote the reply, I was thinking that 40% duty cycle was way too
high, because, as you say, there's lots of dead time even while
transmitting, but I figured the example would show John how to go about
estimating the life of his battery using his own guesses.

There are lots of unknowns involved.  I have no idea what power setting
he uses, how efficient the K1 transmitter is, his SWR, etc.  My K2 draws
anywhere from 1.5-2.4 Amps at  5 Watts into a dummy load, depending on
the band.  Another thing not factored in is the 4.0 Amp Hr battery
rating assumes a 20 hour discharge.  A 1 Amp load would finish off the
battery in less than 4 hours.  Battery temperature is also a factor, but
not so much in the Summer.

In my case, I'm sure I'd be asleep well before the battery died.

Thanks for the clarification.  I should think twice before I hit the
send key.  This group's too smart!

73's

John AA0VE

Dan Barker wrote:

>Actually, the 40% Tx duty is only 50% key down (there's spaces betewwn the
>elements). So, you use .2 for the Tx factor.
>.8 Ir + .2 It = .24 or 16 hours.
>
>Now, after you work the 9 hours, you might fall over and hit your head on
>the key, and then the CW duty cycle goes to 100%. But the Tx duty cycle
>would go to 100% also, and you'd be off the air sooner. Not that it matters
>much as you are napping on the key<g>.
>
>Dan / WG4S / K2 #2456
>
>  
>

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[G3VVT]

John,

One factor that is being missed out on the calculations is how good is the
battery in question. Most assume that say a 7Ah capacity battery will give that,
but in practice this can often fall short. I've witnessed experienced
installation contractors with skills of loading in the last mAh into large
communication battery plant, sweating to get over the 90% mark to the defined pass
figure for acceptance. They use techniques probably not used by most hams in order
to achieve this and get the acceptance certificates signed off.

So how good is the battery being used today? It may have only 75% of original
capacity left, so better to be on the generous side what the duty cycle may
be and be pleasantly surprised when the estimated battery life is exceeded.

Not too sure if this applies in the USA, but there is a source of 12V 7Ah
sealed batteries available from commercial alarm systems in the UK at least. The
batteries in these systems are trashed at about 3 years after new battery
installation. I guess it must be a lot more cost effective for the maintenance
companies to do this rather than experience costly failures. We have a few
recycled batteries here providing power backup for local repeaters. It pays
dividends to get to know who your local alarm technicians are to tap this source of
batteries for field operations. Should get at least two or three years more life
out of these batteries depending on temperatures experienced during their
usage as high temperatures dramatically shorten their useful life.

Bob, G3VVT
K2 #4168
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