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KPA500 Temps?

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CX7TT

KPA500 Temps?

For the NAQP cw party this past weekend, I ran low power. Rather than
'stress' the K3s with 100W, I chose to run 6W thru KPA500, giving me 100w.

During a one hour run period, 125+ Qs on 15m, I noticed the KPA500 temp
at 51C which surprised me. Idle temp in the shack is generally around 33
to 35C. I expected much lower temp at 100w output.

Why the higher temp and is it not related to power out?

73
Tom
HP1XT
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Arthur Nienhouse

Re: KPA500 Temps?

/*I have chosen to put a Noctua helper fan on the inlet pushing air
through it has helped, This fan is powered on from the k3 12 volt out it
comes on with the radio runs all the time, my room temp is 67 degrees f
the amp is idling at 24c I can usually get a reasonable cw rag chew over
in before the fan gets to launch speed. This is not a total fix but does
help. This fan sits on the soft rubber feet that you pull into
positioning through holes in the 4 corners.
Here is a link to this fan these are very good at quietly moving a lot
of air I have a pair on the k3 as well.
https://www.google.com/webhp?sourceid=chrome-instant&rlz=1C1CHFX_enUS513US513&ion=1&espv=2&ie=UTF-8#q=Noctua+nf-a9x14pwm
Interesting reading is the development of the design venture, ribs,
blade shape.....
Regards
ka9zap
*/

On 1/16/2017 8:22 AM, [hidden email] wrote:

> For the NAQP cw party this past weekend, I ran low power. Rather than
> 'stress' the K3s with 100W, I chose to run 6W thru KPA500, giving me 100w.
>
> During a one hour run period, 125+ Qs on 15m, I noticed the KPA500 temp
> at 51C which surprised me. Idle temp in the shack is generally around 33
> to 35C. I expected much lower temp at 100w output.
>
> Why the higher temp and is it not related to power out?
>
> 73
> Tom
> HP1XT
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Wes Stewart-2

Re: KPA500 Temps?

In reply to this post by CX7TT

When you put the KPA500 into transmit there is some fixed (FET) drain current
regardless of whether you are driving the PA or not. Likewise, the power supply
is supplying this current. So the efficiency is zero and all of this DC power
is converted to heat, not RF. Efficiency increases with drive.

So what you are doing is poor practice. Furthermore, IMD performance of the
driver (K3) is likely better at higher power. It's for sure better at 20W than 10W.

Wes N7WS

On 1/16/2017 7:22 AM, [hidden email] wrote:

Elecraft mailing list

Re: KPA500 Temps?

In reply to this post by Arthur Nienhouse

I use the KPA500 utility and just set the Fan to constantly run at a lower speed, the fan will speed up if needed.

From: Arthur Nienhouse <[hidden email]>
To: [hidden email]; [hidden email]
Sent: Monday, January 16, 2017 10:13 AM
Subject: Re: [Elecraft] KPA500 Temps?

/*I have chosen to put a Noctua helper fan on the inlet pushing air
through it has helped, This fan is powered on from the k3 12 volt out it
comes on with the radio runs all the time, my room temp is 67 degrees f
the amp is idling at 24c I can usually get a reasonable cw rag chew over
in before the fan gets to launch speed. This is not a total fix but does
help. This fan sits on the soft rubber feet that you pull into
positioning through holes in the 4 corners.
Here is a link to this fan these are very good at quietly moving a lot
of air I have a pair on the k3 as well.
https://www.google.com/webhp?sourceid=chrome-instant&rlz=1C1CHFX_enUS513US513&ion=1&espv=2&ie=UTF-8#q=Noctua+nf-a9x14pwm
Interesting reading is the development of the design venture, ribs,
blade shape.....
Regards
ka9zap
*/

On 1/16/2017 8:22 AM, [hidden email] wrote:

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______________________________________________________________
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Jim Brown-10

Re: KPA500 Temps?

In reply to this post by Wes Stewart-2

On Mon,1/16/2017 8:02 AM, Wes Stewart wrote:
> Furthermore, IMD performance of the driver (K3) is likely better at
> higher power. It's for sure better at 20W than 10W.

Actually, the reason IMD performance is worse at 10W than at 20W is that
at 10W you're still in the 10W section of the radio, while at 20W you're
using the 100W amp. Once you're into the 100W amp, IMD performance
degrades with increasing power. The K3 is capable of 120W, but since IMD
increases rapidly above 100W, output is limited to 110W in firmware.

As I see it, IMD is most important when a radio is driving a power amp,
and most modern amps will get to rated power with about 50W. The KPA500
needs 25-30W drive. As indicated by measured CW keying bandwidth, the K3
is a VERY clean radio below 60W.

IMD performance also degrades with reduced DC supply voltage. As I
understand it, 13.8V is the nominal design voltage, and 15V is max rated.

As to the original query about temperature -- Wes is exactly right about
low power and efficiency. I do little or no ragchewing and mostly
operate CW and SSB, but I do run RTTY for contesting and some digital
modes that run keydown for about 50 sec and repeat every minute. When I
do that on 6M, where the amp has the lowest efficiency, the fan will get
pretty loud before the end of each TX cycle. That can be reduced a bit
by setting the idle fan speed higher. It's a menu setting.

73, Jim K9YC

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