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K3 Transmit current drain

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k6mgo

K3 Transmit current drain

I was playing around with my K3 and MFJ 4225 switching power supply, when I noticed a strange thing. As you increase the power output, the input current rises very quickly. Example: in Receive mode, the K3 was drawing 2 amps. In Transmit mode, CW, SK key down, at 1 watt out, it was drawing 4 amps 5 watts out, it was drawing 5 amps 8 watts out, it was drawing >6 amps 15 watts out, it jumped to 15 amps 30 watts out, it jumped to 20 amps Didn't want to increase the power anymore, but, this seems excessive to me, anyone else ever notice this? Would appreciate any comments on this matter, 73, Bill, k6mgo

Phil Hystad-3

Re: K3 Transmit current drain

On my K3, Serial No. 3799, I have the following (two measurements only)...

--- 30 watts output: 13 amps

--- 100 watts output: 21 amps

Note that these are measured on my Astron power supply ammeter and I have at least 1.5 to 2 amps of other loads so my actual K3 load is probably closer to 11 amps on 30 watts and 19 amps on 100 watts.

73, phil, K7PEH

On Feb 6, 2012, at 6:14 PM, k6mgo wrote:

> I was playing around with my K3 and MFJ 4225 switching power supply, when I
> noticed a strange thing. As you increase the power output, the input current
> rises very quickly. Example:
> in Receive mode, the K3 was drawing 2 amps.
> In Transmit mode, CW, SK key down, at 1 watt out, it was drawing 4 amps
> 5 watts out, it was drawing 5 amps
> 8 watts out, it was drawing >6 amps
> 15 watts out, it jumped to 15 amps
> 30 watts out, it jumped to 20 amps
>
> Didn't want to increase the power anymore, but, this seems excessive to me,
> anyone else ever notice this?
>
> Would appreciate any comments on this matter,
>
> 73, Bill, k6mgo
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K3-Transmit-current-drain-tp7260744p7260744.html
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Brian Hunt

Re: K3 Transmit current drain

In reply to this post by k6mgo

Remember that at 12 watts and below the KPA3 is in bypass so the current
will be lower relative to the output power. Also the K3 configuration
has something to do with it. My K3/100 (SN 4113) is bare bones with no
additional current drawing options. Using the internal metering in the
K3 and running into a 50 ohm dummy load, my comparable readings (plus
supply voltage) are:

Receive = 0.77 A, 13.7 v
Transmit @ 1 w = 2 A, 13.6 v
Transmit @ 5 w = 2.8 A, 13.4 v
Transmit @ 8 w = 3.2 A, 13.3 v
Transmit @ 15 w = 7.8 A, 13.3 v (KPA3 enabled)
Transmit @ 30 w = 10.3 A, 13.3 v
Transmit @ 100 w = 17 A, 12.9v

I'm using a linear Astron RS-35A power supply which doesn't seem very
well regulated above 15 amps but the voltage as measured by the K3
internal metering has all the cable and connector voltage drop in it.

Also you might want to make an independent check of the accuracy of the
ammeter in the MFJ 4225 (if that is what you are using to measure the
current).

HTH

73, Brian, K0DTJ

On 2/6/2012 6:14 PM, k6mgo wrote:

> I was playing around with my K3 and MFJ 4225 switching power supply, when I
> noticed a strange thing. As you increase the power output, the input current
> rises very quickly. Example:
> in Receive mode, the K3 was drawing 2 amps.
> In Transmit mode, CW, SK key down, at 1 watt out, it was drawing 4 amps
> 5 watts out, it was drawing 5 amps
> 8 watts out, it was drawing>6 amps
> 15 watts out, it jumped to 15 amps
> 30 watts out, it jumped to 20 amps
>
> Didn't want to increase the power anymore, but, this seems excessive to me,
> anyone else ever notice this?
>
> Would appreciate any comments on this matter,
>
> 73, Bill, k6mgo
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K3-Transmit-current-drain-tp7260744p7260744.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> 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
>
>

Les Gasser W9XC

Re: K3 Transmit current drain

In reply to this post by k6mgo

Yes, it's the PA kicking in; here's a small study I did earlier this year:

http://w9xc.net/articles/k3-measured-power-consumption.html

Other than the bump at the PA transition, the power increase per output watt
seems pretty linear.

The interesting implications come when running from an energy-limited
source like batteries: how much power cost (operating time penalty)
do you want to pay per dB increase in signal?

- Les, W9XC
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