Re: Temperatures vs. Time


Were you expecting something different?

Your ambient temperature was around 24 C. Your starting temperatures were quite a bit higher than that. Either the temperature sensors should be recalibrated, or the radio was not truly at ambient temperature when you started. The manual description of the temperature calibration process suggests waiting 15 minutes with the radio off before recalibrating, but I would suggest that that is a serious underestimate of the time required. In my experience, it can take a few hours for the temperature to get all the way back to ambient. In fact, if I were doing the temperature calibration and wanted it to be accurate to within the precision of the display (1 C degree), I would leave the radio off overnight and do the calibration immediately after turning the radio on in the morning.

With the radio in receive, it is still consuming energy. According to the display, mine uses about 1.15 A at 13.7 V, which amounts to nearly 16 watts of energy to be dissipated. It's not being transmitted, and it's not coming out appreciably as audio, so virtually all of that 16 watts is being turned into heat. The majority of the dissipation in receive is taking place in or near the front panel (microprocessor and DSP), which is why the FP temperature rises faster than the PA temperature.

For comparison, when I turned my rig on, the FP temp read 17 C and the PA temp read 19 C. The difference between the two is calibration error (it's been 12 years since I did the calibration). The actual values seem reasonable; we keep our thermostat at 20 C, the shack is in the basement, and although the shack is next to the furnace room, which keeps it warm in cold weather, the furnace was not running at the time. It's unseasonably warm here, plus 2 C outside,. 18 C is not an unreasonable estimate for the ambient temperature in my shack today. After 15 minutes in receive, the FP temp had risen to 24C and the PA temp had risen to 20C. After another 15 minutes the FP was at 27C and the PA at 22 C. These temperature increases over 30 minutes are not all that different from yours.

Transmitting of course uses a lot more energy, not only as transmitted RF, but also as dissipated heat. Based on the displayed voltage and current, when I transmit a steady carrier at 49 watts, the radio consumes about 150 watts, of which about 50 watts appears at RF and 100 watts is dissipated as heat. (Incidentally, I don't set the transmitted power to exactly 50 watts - that's the power setting that results in an automatic TX gain recalibration, which should be done into a 50 ohm load, not into an antenna.) Transmitting at 100 watts, the power consumption is close to 200 watts, i.e. 100 watts RF and 100 watts of heat dissipation (the finals are more efficient at full power). At either power level, that 100 watts of extra heat is mostly dissipated in the PA, so naturally the PA temp rises quite quickly (the FP temp also rises somewhat, as everything in the radio gets hotter). The fans are set to come on at various speeds as temperature set points are reached; I'm not going to try to quote exact threshold values here, you can find them by experimentation.

One oddity in my radio is that the PA temperature sensor reads higher in receive than in transmit, i.e. when I first start to transmit and before the temperature starts to rise, the indicated temperature drops by a degree or two, perhaps due to the drop in voltage when the PA draws more current from the power supply. Anyway, that means that there can be a period during operating when the fans come on during receive and turn off again during transmit, at least until I have transmitted enough so that the fans stay on full-time. If you let the transmitter stay on for longer, the fans speed up as the temperature rises, and they can get quite loud. I treat that as an audible warning signal.

Rich VE3KI

On Tue, Feb 23, 2021 at 12:06 PM, Robert wrote:
Purchased a used K3 (excellent condition), studied the "Owner's Manual" (Revision D10),
installed "K3 Utilities" and updated the firrmware to 05.67 (the latest).
Bellow the Temperatur vs. Time I logged with no transmit intervals and CONFIG: KPA3 = nor(mal):

Time T(amb) T(PA) T(FP) FAN
0 (start) 74.3°F 32°C 27°C no
15 min 74.4°F 33°C 31°C no
30 min 74.6°F 35°C 35°C no
45 min 74.8°F 36°C 36°C no
60 min 75.2°F 35°C 37°C no
75 min 75.2°F 36°C 38°C no
90 min 75.5°F 36°C 38°C no

After this, transmitting a carrier for about 10 seconds with 50 Watts output, the FANs start to run for a short while.
Any comments are appreciated.
73, Robert (W4BCZ)

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