If a power supply sags when lots of power is being drawn, it will affect whatever is trying to draw the power. For a transmitter / amplifier, that means the output power is most likely going to sag as well. The extent of the sag is directly related to how much the power supply sags, which, of course, depends on how well it is regulated.
For the K3, we recommend well regulated power supplies with short supply leads. If the supply is rock solid and well regulated, you should see little voltage drop. Likewise, if you are using short, large wires from the supply to the K3, you will lose little power in that link. Remember that there is power loss in cable, and long skinny conductors will heat up and lose more power due to IIR losses than short fat wires. The K3 will try to correct power output variations, but if the supply / cabling problems won’t allow that, then it cannot. At the same time, it is quite possible the original poster needs to rework his power calibration (again). He had a major change in the components in his transceiver, and over time and use they will age and cause changes. For him, I suggest talking to customer support. The second area is the KPA500. The HV supply is not heavily regulated, by design. It has a pair of very large capacitors on the supply, but when high power is being drawn, the output voltage will sag. This is quite normal. Thus at the start of a transmission the voltage will be high, as will transmitted output power, then will quickly sag to the nominal output value. This can also be affected by power cabling. Some operators may see more sag than they should due to long power cables. We usually see this with amplifiers plugged into 120V outlets. Make sure your 120V cable is large and as short as possible, AND make sure the 120V wall cabling is likewise large. I believe the NEC specifies 12 gauge wire for outlets, my experience with that size is very good. If you can use a 240V supply for the KPA, then it is much better. As pointed out above, power losses in wire is I*I*R. Since current will be dropped in half when using 240V over 120, the cable power losses will be one-quarter with 240 when compared to 120V. Perhaps it might be time for some of us to perform their annual system check and maintenance, starting with the shack power supply? I’ll start this round with my own station today! - Jack Brindle, W6FB > On Mar 1, 2016, at 7:17 AM, Jim Sheldon <w...@cox.net> wrote: > > Thanks David for posting this. I noticed this from time to time with my old > K3 and now also with the new K3S. I keep the KPA500 output set to around > 400-450 watts most of the time and notice spikes to 550 or so on the first or > second dit when sending CW at times. I just built the kit and have done the > TX calibrations properly and they all passed via the Utility program. > > I'm using the factory supplied #12 gauge power cable and the power supply is > a pretty well regulated MFJ 4245MV switcher (RFI quiet here). This supply is > adjustable and evidently the meter isn't totally accurate or there is a > larger voltage drop in the cable than I thought there should be. I checked > the K3S' meter display after receiving this email and it read 13.2 volts. > Keyed to 13.8 volts on the meter, but at 20 watts out, driving the amplifier, > it dropped to 12.6 volts while keyed. > > In line with your findings, I set the MFJ supply to read 13.8 volts on the > K3S display and it now only drops to 13.3 volts under the 20 watt load. The > occasional power spikes seem to have disappeared, so it's something everyone > should take a look at if they do experience the power spike problem. > > Again, thanks for posting this David. > > Jim - W0EB > Park City, KS > > ------ Original Message ------ > From: "David via Elecraft" <elecraft@mailman.qth.net> > To: elecraft@mailman.qth.net > Sent: 3/1/2016 5:40:46 AM > Subject: Re: [Elecraft] K3 output power spikes > >> My K3 s/n 4487 has exhibited similar behaviour since I built it in 2010. >> Despite calls to Elecraft Support no solution was found despite Gary talking >> me through various items until a month or so ago when the spike was causing >> problems with my amp on 24 Mhz. It was mentioned that the K3 must see 13 >> volts whenever it is transmitting and to check this on the front panel by >> tapping the Display button. Mine showed 13.6 volts on receive and 12.6 volts >> on Tx. Turned out my old power supply regulation was faulty. Anyway after a >> power supply rebuild and further check it now shows 13.6 volts on receive >> and 13.3 volts on Tx at 100 watts output. A further TX calibration completed >> the process and so far no power spikes! So check your power supply is >> supplying sufficient voltage on key down. >> >> Dave G0AIX >> >> > > > --- > This email has been checked for viruses by Avast antivirus software. > https://www.avast.com/antivirus > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to jackbrin...@me.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
