Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11
Another thing that states this is current ratings on switches (ever look at the specs?). Typical toggle switch may be rated 20A at 125vac and 10A at 250vac. Why? If the load resistance is the same then twice the voltage will double the current. Heat dissipation of the switch is the same for either voltage thus the current rating is halved at higher voltage. For my station my Astron 50A PS outputs 14.2 vdc thru about 18-feet of 6awg welding wire to the main station fuse, a 30A BUSS fuse. Under max load of nearly 30amps the voltage drop is about 0.4v to 13.8v. From my engineering pocket handbook awg6 is rated at 0.3952 ohms/1000-feet. 18/1000*0.3952 = .007 ohms. IR = E: 30*.007 = 0.21 volts Of course there is smaller wiring from the distribution terminal strip to individual equipment, so additional voltage drop will exist depending on the wire size and length (resistance). One reason to keep high power amp power cords short. Ron' point to measure internal voltage and current is that what you have at the terminal of the RF transistor is how much work it will do (making RF). In general having slightly more voltage will run the transistor cooler as less current is needed for a given output power. Transistors all run at below 100% efficiency and the amount of power not making RF makes heat (per I^2*R law). 60% is typical efficiency of a HF transmitting device. So if that equals 100w RF, then 67w is being dissipated as heat. My 8877 running at 660ma at 3700v = 2442w dc input. With 1500w RF output 2442-1500= 942w of heat to dissipate! Luckily the 8877 is rated at 1500w dissipation. The cooling system is really tested when I key down for roughly a minute in JT65. 73, Ed - KL7UW http://www.kl7uw.com dubus...@gmail.com Kits made by KL7UW __ 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] Elecraft Digest, Vol 114, Issue 11
Ed and all, When calculating the voltage drop like this, you need to add the voltage drop in the negative side wire as well as the positive side. The same current flows on both sides, so the voltage drop must be calculated using the length of both wires. This fact is often forgotten. .007 ohms coming and .007 ohms going. The other sneaky fact of this is that the power supply negative terminal and the equipment negative are not at the same potential. That can produce noise pickup and amplify RF-IN-THE-Shack problems. Bond all equipment together with heavy gauge wire to minimize that effect. 73, Don W3FPR On 10/8/2013 7:00 AM, Edward R Cole wrote: For my station my Astron 50A PS outputs 14.2 vdc thru about 18-feet of 6awg welding wire to the main station fuse, a 30A BUSS fuse. Under max load of nearly 30amps the voltage drop is about 0.4v to 13.8v. From my engineering pocket handbook awg6 is rated at 0.3952 ohms/1000-feet. 18/1000*0.3952 = .007 ohms. IR = E: 30*.007 = 0.21 volts __ 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] Elecraft Digest, Vol 114, Issue 11
On 10/7/2013 3:44 PM, Neal Enault wrote: To determine the effects of ambient temperature, one has to do some not so accurate calculations or refer to a document like MIL-W-5088 which also provides guidance for wire ratings in bundles and at various altitudes. In the civilian/industrial world, the (U.S.) National Electrical Code (NPFA 70) has a whole series of Ampacity tables (that's the term for current rating). I've always used that as my guide. 73 de K2ASP - Phil Kane Elecraft K2/100 s/n 5402 From a Clearing in the Silicon Forest Beaverton (Washington County) Oregon __ 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] Elecraft Digest, Vol 114, Issue 11
Are those codes applied to low voltage isolated supplies by law or are there separate codes for this? In the context of the original question, the 13.8V dc supply will not have the same shock hazard, though it may have the same fire hazard, so, perhaps a different code/standard applies. House wiring requires a high degree of safety because its potential (risk) for fire, but the risk of fire in isolated low voltage equipment which is on view (ie not hidden in building cavities etc) is different. David G3UNA - Original Message - From: Phil Kane k2...@kanafi.org To: elecraft@mailman.qth.net Sent: Tuesday, October 08, 2013 5:16 PM Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 On 10/7/2013 3:44 PM, Neal Enault wrote: To determine the effects of ambient temperature, one has to do some not so accurate calculations or refer to a document like MIL-W-5088 which also provides guidance for wire ratings in bundles and at various altitudes. In the civilian/industrial world, the (U.S.) National Electrical Code (NPFA 70) has a whole series of Ampacity tables (that's the term for current rating). I've always used that as my guide. 73 de K2ASP - Phil Kane Elecraft K2/100 s/n 5402 From a Clearing in the Silicon Forest Beaverton (Washington County) Oregon __ 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] Elecraft Digest, Vol 114, Issue 11
David, I believe the same codes do apply since they are based on current, not voltage. Codes aside, do not take low voltage, high current sources lightly (particularly batteries) because they are a very large source of energy. If shorted, molten metal spewing all over is not an exaggeration, it is real. That is why the power cables should be fused for the Ampacity rating of the wire with the fuse placed near the power source. You are protecting the wire against fault conditions, not necessarily the equipment connected. Shock hazards are a different thing - fuses will not help with shock hazards. True, low voltage supplies may not be a shock hazard, but they are a hazard just the same because of the high energy available should there be a fault. 73, Don W3FPR On 10/8/2013 1:45 PM, David Cutter wrote: Are those codes applied to low voltage isolated supplies by law or are there separate codes for this? In the context of the original question, the 13.8V dc supply will not have the same shock hazard, though it may have the same fire hazard, so, perhaps a different code/standard applies. House wiring requires a high degree of safety because its potential (risk) for fire, but the risk of fire in isolated low voltage equipment which is on view (ie not hidden in building cavities etc) is different. __ 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] Elecraft Digest, Vol 114, Issue 11
Thanks, Don, that was the reason for my question. I've had dealings with large MW motors and getting the right cables for them and in contrast low voltage, high current applications. Over here, once you get below the Safety Extra Low Voltage (SELV) limit (meaning isolated and from memory 42V) regime the rules change, but my memory fails me as to specifics. I have a feeling that the automotive industry have different insulation requirements for instance. David G3UNA - Original Message - From: Don Wilhelm w3...@embarqmail.com To: David Cutter d.cut...@ntlworld.com Cc: elecraft@mailman.qth.net Sent: Tuesday, October 08, 2013 7:17 PM Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 David, I believe the same codes do apply since they are based on current, not voltage. Codes aside, do not take low voltage, high current sources lightly (particularly batteries) because they are a very large source of energy. If shorted, molten metal spewing all over is not an exaggeration, it is real. That is why the power cables should be fused for the Ampacity rating of the wire with the fuse placed near the power source. You are protecting the wire against fault conditions, not necessarily the equipment connected. Shock hazards are a different thing - fuses will not help with shock hazards. True, low voltage supplies may not be a shock hazard, but they are a hazard just the same because of the high energy available should there be a fault. 73, Don W3FPR On 10/8/2013 1:45 PM, David Cutter wrote: Are those codes applied to low voltage isolated supplies by law or are there separate codes for this? In the context of the original question, the 13.8V dc supply will not have the same shock hazard, though it may have the same fire hazard, so, perhaps a different code/standard applies. House wiring requires a high degree of safety because its potential (risk) for fire, but the risk of fire in isolated low voltage equipment which is on view (ie not hidden in building cavities etc) is different. __ 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] Elecraft Digest, Vol 114, Issue 11
Many a fire has been caused by overloaded or defective exposed extension cords. And, melting insulation on an overburdened 13volt power cord smells terrible and lucky it wasn't directly across the battery. ...bill nr4c Sent from my Verizon Wireless 4G LTE DROID David Cutter d.cut...@ntlworld.com wrote: Are those codes applied to low voltage isolated supplies by law or are there separate codes for this? In the context of the original question, the 13.8V dc supply will not have the same shock hazard, though it may have the same fire hazard, so, perhaps a different code/standard applies. House wiring requires a high degree of safety because its potential (risk) for fire, but the risk of fire in isolated low voltage equipment which is on view (ie not hidden in building cavities etc) is different. David G3UNA - Original Message - From: Phil Kane k2...@kanafi.org To: elecraft@mailman.qth.net Sent: Tuesday, October 08, 2013 5:16 PM Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 On 10/7/2013 3:44 PM, Neal Enault wrote: To determine the effects of ambient temperature, one has to do some not so accurate calculations or refer to a document like MIL-W-5088 which also provides guidance for wire ratings in bundles and at various altitudes. In the civilian/industrial world, the (U.S.) National Electrical Code (NPFA 70) has a whole series of Ampacity tables (that's the term for current rating). I've always used that as my guide. 73 de K2ASP - Phil Kane Elecraft K2/100 s/n 5402 From a Clearing in the Silicon Forest Beaverton (Washington County) Oregon __ 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 __ 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] Elecraft Digest, Vol 114, Issue 11
The math looks correct, but the analysis is wrong. The first statement rated for 20 amps at 120 volts is wrong. A more correct statement would be that a given wire size (12 gauge for example) is rated for 20 amps. Voltage has nothing to do with it. The amp rating of wire is based on gauge only and how much heat it is generating per unit length. Heat is watts, or I^2*R. An example: 100' of 12 gauge wire has a resistance of about 0.159 ohms. At 20 amps, this 100' of wire is generating 20*20*0.159 watts of heat (63.7 watts). This is what is considered safe for that wire gauge. Having said it has nothing to do with voltage, there is one thing to be considered. Over that 100' of wire with 20 amp going through it, there is a voltage drop of E=IR or E=20*0.159 or 3.18 volts. Now, in a 120 volt circuit, a drop of 3.18 volts may not be very significant. But in a 13.8 volt circuit, you're down to 10.6 volts which is quite significant. So, you may want to up the wire size to cut down on voltage drop. -Brad NN0R Date: Mon, 7 Oct 2013 09:51:56 -0500 From: Richard Fjeld rpfj...@embarqmail.com To: j...@audiosystemsgroup.com,elecraft@mailman.qth.net Subject: Re: [Elecraft] K3 Suddenly died Message-ID: 40B6D4509C21413B80B1A7B30D30E99F@HPCompaq Content-Type: text/plain; format=flowed; charset=iso-8859-1; reply-type=response To those who replied on, and off line, I don't mind factual disagreement, but aren't we above insults? It doesn't get much simpler than this. R is the resistance of the conductor (wire). I is the current flow. E is the Electromotive Force, or voltage. Ohms law is E=IR, and with simple algebra is I=E/R If a conductor (wire) is rated for 20 amps at 120 volts for a given length (due to it's R), and we want to use that same wire for 20 amps at 13.8 volts, we must reduce R by either increasing the wire size, decreasing the length, or a combination of both. Dick, n0ce __ 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] Elecraft Digest, Vol 114, Issue 11
I didn't check your figures, but I agree with your understanding except at 240 volts, that same wire gauge would have twice the capacity. Dick, n0ce -Original Message- From: Brad Blasing Sent: Monday, October 07, 2013 1:22 PM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 The math looks correct, but the analysis is wrong. The first statement rated for 20 amps at 120 volts is wrong. A more correct statement would be that a given wire size (12 gauge for example) is rated for 20 amps. Voltage has nothing to do with it. The amp rating of wire is based on gauge only and how much heat it is generating per unit length. Heat is watts, or I^2*R. An example: 100' of 12 gauge wire has a resistance of about 0.159 ohms. At 20 amps, this 100' of wire is generating 20*20*0.159 watts of heat (63.7 watts). This is what is considered safe for that wire gauge. Having said it has nothing to do with voltage, there is one thing to be considered. Over that 100' of wire with 20 amp going through it, there is a voltage drop of E=IR or E=20*0.159 or 3.18 volts. Now, in a 120 volt circuit, a drop of 3.18 volts may not be very significant. But in a 13.8 volt circuit, you're down to 10.6 volts which is quite significant. So, you may want to up the wire size to cut down on voltage drop. -Brad NN0R __ 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] Elecraft Digest, Vol 114, Issue 11
I didn't check your figures, but I agree with your understanding except at 240 volts, that same wire gauge would have twice the capacity. twice the capacity What does that mean? Earlier you were talking about current. At 240 volts the current carrying capacity of your wire would be the same as it was at 120 volts. This is engineering not politics ... please be a little more precise. Mark AD5SS __ 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] Elecraft Digest, Vol 114, Issue 11
I better say 'twice the current carrying capacity'. -Original Message- From: Richard Fjeld Sent: Monday, October 07, 2013 1:44 PM To: Brad Blasing ; elecraft@mailman.qth.net Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 I didn't check your figures, but I agree with your understanding except at 240 volts, that same wire gauge would have twice the capacity. Dick, n0ce -Original Message- From: Brad Blasing Sent: Monday, October 07, 2013 1:22 PM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 The math looks correct, but the analysis is wrong. The first statement rated for 20 amps at 120 volts is wrong. A more correct statement would be that a given wire size (12 gauge for example) is rated for 20 amps. Voltage has nothing to do with it. The amp rating of wire is based on gauge only and how much heat it is generating per unit length. Heat is watts, or I^2*R. An example: 100' of 12 gauge wire has a resistance of about 0.159 ohms. At 20 amps, this 100' of wire is generating 20*20*0.159 watts of heat (63.7 watts). This is what is considered safe for that wire gauge. Having said it has nothing to do with voltage, there is one thing to be considered. Over that 100' of wire with 20 amp going through it, there is a voltage drop of E=IR or E=20*0.159 or 3.18 volts. Now, in a 120 volt circuit, a drop of 3.18 volts may not be very significant. But in a 13.8 volt circuit, you're down to 10.6 volts which is quite significant. So, you may want to up the wire size to cut down on voltage drop. -Brad NN0R __ 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] Elecraft Digest, Vol 114, Issue 11
You are correct. I answered too quickly. I stand corrected. Dick, n0ce -Original Message- From: Mark Bayern Sent: Monday, October 07, 2013 1:50 PM To: Richard Fjeld Cc: Brad Blasing ; Elecraft Reflector Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 I didn't check your figures, but I agree with your understanding except at 240 volts, that same wire gauge would have twice the capacity. twice the capacity What does that mean? Earlier you were talking about current. At 240 volts the current carrying capacity of your wire would be the same as it was at 120 volts. This is engineering not politics ... please be a little more precise. Mark AD5SS __ 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] Elecraft Digest, Vol 114, Issue 11
I retract this. I have no excuse. -Original Message- From: Richard Fjeld Sent: Monday, October 07, 2013 1:51 PM To: Brad Blasing ; elecraft@mailman.qth.net Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 I better say 'twice the current carrying capacity'. -Original Message- From: Richard Fjeld Sent: Monday, October 07, 2013 1:44 PM To: Brad Blasing ; elecraft@mailman.qth.net Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 I didn't check your figures, but I agree with your understanding except at 240 volts, that same wire gauge would have twice the capacity. Dick, n0ce -Original Message- From: Brad Blasing Sent: Monday, October 07, 2013 1:22 PM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 The math looks correct, but the analysis is wrong. The first statement rated for 20 amps at 120 volts is wrong. A more correct statement would be that a given wire size (12 gauge for example) is rated for 20 amps. Voltage has nothing to do with it. The amp rating of wire is based on gauge only and how much heat it is generating per unit length. Heat is watts, or I^2*R. An example: 100' of 12 gauge wire has a resistance of about 0.159 ohms. At 20 amps, this 100' of wire is generating 20*20*0.159 watts of heat (63.7 watts). This is what is considered safe for that wire gauge. Having said it has nothing to do with voltage, there is one thing to be considered. Over that 100' of wire with 20 amp going through it, there is a voltage drop of E=IR or E=20*0.159 or 3.18 volts. Now, in a 120 volt circuit, a drop of 3.18 volts may not be very significant. But in a 13.8 volt circuit, you're down to 10.6 volts which is quite significant. So, you may want to up the wire size to cut down on voltage drop. -Brad NN0R __ 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 __ 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] Elecraft Digest, Vol 114, Issue 11
Geesh, how is that possible - twice the current equals twice as much heat and will exceed the capacity of the wire. The current rating for a wire is the *same* no matter what the voltage. Also note that the safe rated current is different for wires in a bundle and for a single wire - the heat is not dissipated as easily in a bundle. Now if we are talking about Power delivered to the load, that is an 'horse of a different color' twice the power can be delivered over a wire (of any gauge) at 240 volts as opposed to 120 volts. A bit of study on basic Ohm's Law (both for EIR and for EIP should make all that clear. 73, Don W3FPR On 10/7/2013 2:51 PM, Richard Fjeld wrote: I better say 'twice the current carrying capacity'. -Original Message- From: Richard Fjeld Sent: Monday, October 07, 2013 1:44 PM To: Brad Blasing ; elecraft@mailman.qth.net Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 I didn't check your figures, but I agree with your understanding except at 240 volts, that same wire gauge would have twice the capacity. __ 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] Elecraft Digest, Vol 114, Issue 11
On 10/7/2013 5:31 PM, Don Wilhelm wrote: Geesh, how is that possible - twice the current equals twice as much heat and will exceed the capacity of the wire. Sorry, Don ... twice the current = *four times* the heat. Heat (energy in Joules) = Watts * seconds. One Joule (one Watt-second) is 2.78e-7 kW*h 73, ... Joe, W4TV On 10/7/2013 5:31 PM, Don Wilhelm wrote: Geesh, how is that possible - twice the current equals twice as much heat and will exceed the capacity of the wire. The current rating for a wire is the *same* no matter what the voltage. Also note that the safe rated current is different for wires in a bundle and for a single wire - the heat is not dissipated as easily in a bundle. Now if we are talking about Power delivered to the load, that is an 'horse of a different color' twice the power can be delivered over a wire (of any gauge) at 240 volts as opposed to 120 volts. A bit of study on basic Ohm's Law (both for EIR and for EIP should make all that clear. 73, Don W3FPR On 10/7/2013 2:51 PM, Richard Fjeld wrote: I better say 'twice the current carrying capacity'. -Original Message- From: Richard Fjeld Sent: Monday, October 07, 2013 1:44 PM To: Brad Blasing ; elecraft@mailman.qth.net Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 I didn't check your figures, but I agree with your understanding except at 240 volts, that same wire gauge would have twice the capacity. __ 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] Elecraft Digest, Vol 114, Issue 11
OK Joe, You are correct. It has been a very long time since I have been involved with heat related science issues. More current equals more heat (for a given resistance) has been sufficient for me most of the time without getting into the exact math. It is good to know that some folks here still have those formulas on the top of their heads. 73, Don W3FPR On 10/7/2013 5:57 PM, Joe Subich, W4TV wrote: On 10/7/2013 5:31 PM, Don Wilhelm wrote: Geesh, how is that possible - twice the current equals twice as much heat and will exceed the capacity of the wire. Sorry, Don ... twice the current = *four times* the heat. Heat (energy in Joules) = Watts * seconds. One Joule (one Watt-second) is 2.78e-7 kW*h 73, ... Joe, W4TV __ 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] Elecraft Digest, Vol 114, Issue 11
So far nobody has mentioned insulation material. The rating of a cable has little to do with melting the wire and mostly to do with melting or softening the insulation which would create a shock and/ or fire hazard. The same size wire insulated with PVC is allowed to rise to a much lower temperature compared to insulation of PTFE or numerous other materials. And what is good or bad for mains circuits will not be the same in a vehicle or aircraft circuit. David G3UNA - Original Message - From: Don Wilhelm w3...@embarqmail.com To: elecraft@mailman.qth.net Sent: Monday, October 07, 2013 11:14 PM Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 OK Joe, You are correct. It has been a very long time since I have been involved with heat related science issues. More current equals more heat (for a given resistance) has been sufficient for me most of the time without getting into the exact math. It is good to know that some folks here still have those formulas on the top of their heads. 73, Don W3FPR On 10/7/2013 5:57 PM, Joe Subich, W4TV wrote: On 10/7/2013 5:31 PM, Don Wilhelm wrote: Geesh, how is that possible - twice the current equals twice as much heat and will exceed the capacity of the wire. Sorry, Don ... twice the current = *four times* the heat. Heat (energy in Joules) = Watts * seconds. One Joule (one Watt-second) is 2.78e-7 kW*h 73, ... Joe, W4TV __ 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] Elecraft Digest, Vol 114, Issue 11
If you look at most wire specifications (military in particular), you will note that the temperature rating of the wire is based on the conductor temperature which is the combination of current heating and ambient temperature. To determine the effects of ambient temperature, one has to do some not so accurate calculations or refer to a document like MIL-W-5088 which also provides guidance for wire ratings in bundles and at various altitudes. Neal WA6OCP From: David Cutter d.cut...@ntlworld.com To: d...@w3fpr.com; elecraft@mailman.qth.net Sent: Monday, October 7, 2013 3:33 PM Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 So far nobody has mentioned insulation material. The rating of a cable has little to do with melting the wire and mostly to do with melting or softening the insulation which would create a shock and/ or fire hazard. The same size wire insulated with PVC is allowed to rise to a much lower temperature compared to insulation of PTFE or numerous other materials. And what is good or bad for mains circuits will not be the same in a vehicle or aircraft circuit. David G3UNA - Original Message - From: Don Wilhelm w3...@embarqmail.com To: elecraft@mailman.qth.net Sent: Monday, October 07, 2013 11:14 PM Subject: Re: [Elecraft] Elecraft Digest, Vol 114, Issue 11 OK Joe, You are correct. It has been a very long time since I have been involved with heat related science issues. More current equals more heat (for a given resistance) has been sufficient for me most of the time without getting into the exact math. It is good to know that some folks here still have those formulas on the top of their heads. 73, Don W3FPR On 10/7/2013 5:57 PM, Joe Subich, W4TV wrote: On 10/7/2013 5:31 PM, Don Wilhelm wrote: Geesh, how is that possible - twice the current equals twice as much heat and will exceed the capacity of the wire. Sorry, Don ... twice the current = *four times* the heat. Heat (energy in Joules) = Watts * seconds. One Joule (one Watt-second) is 2.78e-7 kW*h 73, ... Joe, W4TV __ 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 __ 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
