[Elecraft] K3 Transmit current drain
Bill, Yes, good lesson in ohm's law, that too often is overlooked. So the current draw dropped for 20A to 11.7A. That means you were heating your lamp cord with 8.3A at 12.7v (= 105w). Not necessarily bad on a cold winter's night (humour)! But actually a waste of electrical power and perhaps a safety issue. I recently wired a 150w amp to a 28v PS (assume 250w dc load), the wiring has to carry 9A. I ran some #12awg zip cord (red/black). Seeing about 0.5v drop in the cable, which is about 4-foot long, under load. This is temp as the PS and amp will be installed in a 19-inch wide standard cabinet where the dc cabling will be about 12-inch. MY 300w HF amp will also run from this PS and needs about 4-feet dc wiring. I guess a swap is indicated. the 300w amp draws 20A which might even suggest 10awg wiring? The real ohms law test is the 50v 50A draw (2500w) that will be made by the 1100w 6m sspa. I got some #8 for that (doubled up). 73, Ed - KL7UW Thanks to the many who pointed out that the K3 draws a high current even at low power once you get above the 12 watt level, due to the bias for the power amp. I never considered this, and so when I made up a power cable to operate indoors with my MFJ 4225 switching power supply, I used a single light weight lamp cord at six feet long and a cigar lighter plug for the power cord. My reasoning being I would only operate low power, not more than 30-35 watts indoors with my antenna right over my head. So, either the lamp cord was too light, or the cigar lighter plug had too much drop for the current being drawn, and so the current meter in the K3 was indicating 20 amps being drawn at only 30 watts output. Once I fixed the power cord by using two #18 ga. lamp cords in parallel to spade lugs rather than the cigar lighter plug, the K3 now draws 11.73 amps @ 12.7 volts, with 35 watts output, from the MFJ 4225 power supply, which seems more normal than the previous 20 amps at the same power out setting. I hope my experience saves someone else some grief. 73, Bill, k6mgo 73, Ed - KL7UW, WD2XSH/45 == BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-? DUBUS Magazine USA Rep dubus...@gmail.com Kits made by KL7UW http://www.kl7uw.com/kits.htm == __ 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
Re: [Elecraft] K3 Transmit current drain
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 __ 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
[Elecraft] K3 Transmit current drain
This is a follow-up to my post of yesterday, about the excessive current drain on my K3 in Transmit. Here is my original post: 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 Thanks to the many who pointed out that the K3 draws a high current even at low power once you get above the 12 watt level, due to the bias for the power amp. I never considered this, and so when I made up a power cable to operate indoors with my MFJ 4225 switching power supply, I used a single light weight lamp cord at six feet long and a cigar lighter plug for the power cord. My reasoning being I would only operate low power, not more than 30-35 watts indoors with my antenna right over my head. So, either the lamp cord was too light, or the cigar lighter plug had too much drop for the current being drawn, and so the current meter in the K3 was indicating 20 amps being drawn at only 30 watts output. Once I fixed the power cord by using two #18 ga. lamp cords in parallel to spade lugs rather than the cigar lighter plug, the K3 now draws 11.73 amps @ 12.7 volts, with 35 watts output, from the MFJ 4225 power supply, which seems more normal than the previous 20 amps at the same power out setting. I hope my experience saves someone else some grief. 73, Bill, k6mgo __ 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
[Elecraft] 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 -- 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] 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 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ 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
Re: [Elecraft] K3 Transmit current drain
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 drawing6 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ 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
