K3 Voltage drop
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Okay, confession time. My VFO B display area rarely displays anything but frequency. Doing the NAQP RTTY today, I had a brief attack of curiosity. Wanted to see how the PA temperature was doing. On the way I passed the voltage display and stopped for some reason. Noted that the voltage on RX was 13.6. Dropped to 12.6 with 75 watts RTTY TX. Supplied power cord to an Astron RS-35M. I am concerned that the drop may be excessive. I'd like to make sure that there is a problem before I start tearing into things. Cause for concern?
Ron W3ZV ______________________________________________________________ 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 |
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This is not unusual, Ron. The power cable, several connectors, PCB
traces, current-sense resistor, and even the power supply itself all contribute some small drop, and a total of 1 V or so sounds about right. 73, Wayne N6KR On Feb 25, 2012, at 3:55 PM, Ron W3ZV wrote: > Okay, confession time. My VFO B display area rarely displays > anything but frequency. Doing the NAQP RTTY today, I had a brief > attack of curiosity. Wanted to see how the PA temperature was doing. > On the way I passed the voltage display and stopped for some reason. > Noted that the voltage on RX was 13.6. Dropped to 12.6 with 75 watts > RTTY TX. Supplied power cord to an Astron RS-35M. I am concerned > that the drop may be excessive. I'd like to make sure that there is > a problem before I start tearing into things. Cause for concern? > > Ron W3ZV > ______________________________________________________________ > 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 ______________________________________________________________ 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 |
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In reply to this post by Ron W3ZV
This recently came up on the Yahoo K3 list where N4PJ reported a 1.0V drop using a RS-35M (13.6 to 12.6 key down). I also use the RS.35M and my drop is 0.4V (14.6 to 14.2 with 110W key down). I'd check that your connections at the RS-35M are solid. Many of these hum slightly which can cause the nuts to loosen slightly over time. I run my voltage higher to improve TX IMD performance on SSB. Elecraft's maximum spec is 15V. There's a wheeled pot on the underside of the RS-35M control board (or any Astron for that matter) which adjusts the output voltage but be careful when adjusting it! 73, Bill W4ZV |
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In reply to this post by Ron W3ZV
Ron,
I didn't think to look at that last night, but I am testing it now into a dummy load at 50W. I am using an MFJ-4125 with about 18" of #10 "zip cord." This goes to a PowerPole DC distribution panel and there is another run of about 30" of #10 to the K3. On receive, I have 13.4 - 13.5VDC (1.15 - 1.16A). On transmit, it drops to 12.4 - 12.5VDC (~14.5A). The wires are not even remotely warm. I do not have time to test with my Astron RS-35A at the moment, but I will when I get home this afternoon. I also have an Astron RS-20A I can experiment with. Joel - W4JBB On 2/25/2012 5:55 PM, Ron W3ZV wrote: > Okay, confession time. My VFO B display area rarely displays anything but frequency. Doing the NAQP RTTY today, I had a brief attack of curiosity. Wanted to see how the PA temperature was doing. On the way I passed the voltage display and stopped for some reason. Noted that the voltage on RX was 13.6. Dropped to 12.6 with 75 watts RTTY TX. Supplied power cord to an Astron RS-35M. I am concerned that the drop may be excessive. I'd like to make sure that there is a problem before I start tearing into things. Cause for concern? > > Ron W3ZV > ______________________________________________________________ > 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 > 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 |
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Joel,
Measure the voltage drop right at the power supply terminals - that will tell you how much of that total voltage drop is due to the power supply. The rest is in the wire and connectors - there are 12 connectors if your PowerPole distribution box has fuses, and 8 connectors if no fuses. The connectors can account for about 0.2 volts drop at 14.5 amps, and another 0.015 volts drop in the 8 feet of #10 wire (you have to count the length of the return path too. So 0.22 volts of the total drop can be attributed to wire and the connectors. A 1 volt drop at a 15 amp current draw is not unusual. 73, Don W3FPR On 2/26/2012 8:36 AM, Joel Black wrote: > Ron, > > I didn't think to look at that last night, but I am testing it now into > a dummy load at 50W. I am using an MFJ-4125 with about 18" of #10 "zip > cord." This goes to a PowerPole DC distribution panel and there is > another run of about 30" of #10 to the K3. On receive, I have 13.4 - > 13.5VDC (1.15 - 1.16A). On transmit, it drops to 12.4 - 12.5VDC > (~14.5A). The wires are not even remotely warm. > > I do not have time to test with my Astron RS-35A at the moment, but I > will when I get home this afternoon. I also have an Astron RS-20A I can > experiment with. > > Joel - W4JBB > > 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 |
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In reply to this post by Joel Black-2
Also check the Power Pole connectors to make sure the tabs are fully seated
into the plastic housing till it clicks. Greg On Sun, Feb 26, 2012 at 5:36 AM, Joel Black <[hidden email]> wrote: > Ron, > > I didn't think to look at that last night, but I am testing it now into > a dummy load at 50W. I am using an MFJ-4125 with about 18" of #10 "zip > cord." This goes to a PowerPole DC distribution panel and there is > another run of about 30" of #10 to the K3. On receive, I have 13.4 - > 13.5VDC (1.15 - 1.16A). On transmit, it drops to 12.4 - 12.5VDC > (~14.5A). The wires are not even remotely warm. > > I do not have time to test with my Astron RS-35A at the moment, but I > will when I get home this afternoon. I also have an Astron RS-20A I can > experiment with. > > Joel - W4JBB > > On 2/25/2012 5:55 PM, Ron W3ZV wrote: > > Okay, confession time. My VFO B display area rarely displays anything > but frequency. Doing the NAQP RTTY today, I had a brief attack of > curiosity. Wanted to see how the PA temperature was doing. On the way I > passed the voltage display and stopped for some reason. Noted that the > voltage on RX was 13.6. Dropped to 12.6 with 75 watts RTTY TX. Supplied > power cord to an Astron RS-35M. I am concerned that the drop may be > excessive. I'd like to make sure that there is a problem before I start > tearing into things. Cause for concern? > > > > Ron W3ZV > > ______________________________________________________________ > > 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 > > > ______________________________________________________________ > 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 > 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 |
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In reply to this post by Ron W3ZV
This really got me curious. I was in the NAQP RTTY Contest.....and decided to look at the voltage on my K3. I checked the meter on the RM-35A, but those meters are not very good. The volt meter says 14.5 volts. NaH! So, I went to the K3 internal meters and got the following 100 watts out 22.5 amps 11 volts 13.8 volts key up..... 11 volts seems low to me. So, I might have to do some checking out as well. Lee k0WA In our day and age it seems that Common Sense is in short supply. If you don't have any Common Sense - get some Common Sense and use it. If you can't find any Common Sense, ask for help from somebody who has some Common Sense. Is Common Sense divine? Common Sense is the image of the Creator expressing revealed truth in my mind. - John W. (Kansas) Never interfere with anything that isn't bothering you. ________________________________ From: Ron W3ZV <[hidden email]> To: Elecraft <[hidden email]> Sent: Sat, February 25, 2012 5:55:59 PM Subject: [Elecraft] K3 Voltage drop Okay, confession time. My VFO B display area rarely displays anything but frequency. Doing the NAQP RTTY today, I had a brief attack of curiosity. Wanted to see how the PA temperature was doing. On the way I passed the voltage display and stopped for some reason. Noted that the voltage on RX was 13.6. Dropped to 12.6 with 75 watts RTTY TX. Supplied power cord to an Astron RS-35M. I am concerned that the drop may be excessive. I'd like to make sure that there is a problem before I start tearing into things. Cause for concern? Ron W3ZV ______________________________________________________________ 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 ______________________________________________________________ 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 |
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On 2/27/2012 6:48 AM, Lee Buller wrote:
> The volt meter says 14.5 volts. NaH! So, I went > to the K3 internal meters and got the following > > 100 watts out > 22.5 amps > 11 volts IR drop in the DC cable will account for much of the difference. 73, Jim K9YC ______________________________________________________________ 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 |
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One of the more common sources of resistance are the various 'DC distribution' devices.
They put at least two additional connectors and sometimes switches and fuses into the circuit. Also cables with inline fuses often add excessive resistance if the fuseholder isn't high quality. Incidentally, in a fixed (not mobile) application, only the positive line should be fused. On 2/27/2012 9:00 AM, Jim Brown wrote: > On 2/27/2012 6:48 AM, Lee Buller wrote: >> The volt meter says 14.5 volts. NaH! So, I went >> to the K3 internal meters and got the following >> >> 100 watts out >> 22.5 amps >> 11 volts > > IR drop in the DC cable will account for much of the difference. > > 73, Jim K9YC > ______________________________________________________________ > 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 -- Vic, K2VCO Fresno CA http://www.qsl.net/k2vco/ ______________________________________________________________ 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 |
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In reply to this post by k0wa@swbell.net
A couple of questions:
I use 4 wire voltage sensing as Ron suggests below. I have calibrated my K3 voltage readings and power supply set point voltage using a 4 1/2 place DVM. I always see a lower voltage on the K3. Somewhere around 200 mv on receive (depends on accessary load). I also see on the schematic that there is a polyfuse and 'low current sense' circuit between the 12V connector and the +12V feed point in the K3. My question is where is the K3 sensing 12V? If it is downstream of the polyfuse, then the indicated voltage drop is of little significance because the KPA3 is picking off power ahead of the polyfuse and will not see the same voltage drop. Also if the voltage sense is downstream then where is the current sense? It must be upstream before the current divides between the KPA3 breaker and the +12V feed point. 73, Fred, AE6QL -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Ron D'Eau Claire Sent: Monday, February 27, 2012 8:58 AM To: 'Elecraft Reflector' Subject: Re: [Elecraft] K3 Voltage drop 2.8V at 22.5 amps is 0.12 ohms total resistance in the cable, connectors, etc. That's rather normal. That's why those cables between your 12V car battery and starter motor are so big. One approach used to maintaining voltage in spite of the unavoidable ohmic losses is to run a third wire for the voltage regulator sense circuit to the load. That way, the regulator is adjusting the voltage to maintain the set value at the load, not at the output of the power supply. Be aware that if anything interrupted that connection, the power supply would go to maximum voltage with serious consequences to the rig and any other equipment connected at the far end. Also, a voltage sense circuit can be rather sensitive to RF pickup which may cause the circuit to increase or decrease the voltage. 73, Ron AC7AC ______________________________________________________________ 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 |
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In reply to this post by k0wa@swbell.net
I think 0.12 ohms is a lot and is not normal. 10 feet of #12 wire has a
resistance of only 0.016 ohms. A good, tight-fitting connector should add about 1 milliohm each - don't forget there are two connections for each "connector", you have to count the one in the return path too. There is more than 0.1 ohms to locate, and at 22 amps, that is a lot. I suspect bad connections that have a lot more resistance than that 1 milliohm - note that the PowerPole specs show a contact resistance from 0.0001 to 0.000578 ohms which is less than 1 milliohm for a properly assembled APP connector. Don't forget to look at the connections inside the power supply too. Sometimes the terminals become loose and it does not show on the outside. 73, Don W3FPR On 2/27/2012 11:58 AM, Ron D'Eau Claire wrote: > 2.8V at 22.5 amps is 0.12 ohms total resistance in the cable, connectors, > etc. That's rather normal. > > That's why those cables between your 12V car battery and starter motor are > so big. > > One approach used to maintaining voltage in spite of the unavoidable ohmic > losses is to run a third wire for the voltage regulator sense circuit to the > load. That way, the regulator is adjusting the voltage to maintain the set > value at the load, not at the output of the power supply. > > Be aware that if anything interrupted that connection, the power supply > would go to maximum voltage with serious consequences to the rig and any > other equipment connected at the far end. Also, a voltage sense circuit can > be rather sensitive to RF pickup which may cause the circuit to increase or > decrease the voltage. > > 73, Ron AC7AC > > -----Original Message----- > > > > This really got me curious. I was in the NAQP RTTY Contest.....and decided > to > look at the voltage on my K3. I checked the meter on the RM-35A, but those > meters are not very good. The volt meter says 14.5 volts. NaH! So, I > went > to the K3 internal meters and got the following > > 100 watts out > 22.5 amps > 11 volts > > 13.8 volts key up..... > > 11 volts seems low to me. So, I might have to do some checking out as well. > > Lee > k0WA > > ______________________________________________________________ > 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 > 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 |
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In reply to this post by k0wa@swbell.net
Hi,
Your current also seems high. Here is what I get on the 3 bands I use the most: RX voltage reads 14.1V current 0.85A TX RTTY power set to 100W: 10m 100W 13.7V 14.5A 15m 102W 13.6V 15.5A 20m 105W 13,6V 17.5A Power is measured by LP-100A (factory calibrated) into precision dummy load, voltage and current from the K3 display. The power supply is a 25/30A switcher branded Kenwood KPS-15 although I suspect they did not make it. I have modified it with 4 APP connectors (it's ugly but on the back so I can't see it). The cable to the K3 is a #12 cable, much shorter than the one supplied with the K3 and no fuses or other stuff inline. The APP connectors are soldered. I guess I am fine, no reason to get out that deoxit yet and I never mess with anything that works FB. I suspect the K3 voltmeter reads about 200-300mV high as I read 14.83V out of the supply with a DVM in receive. But the deltas should be accurate. AB2TC - Knut
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That should read 13.83V with the DVM of course.
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