Local Noise Problem
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There is a very serious problem with the local noise source from low
voltage lighting systems. These are sold as pendants, single lights, or multiple lights on a support, such as a bar. The retailer supplies them with a choice of two types of transformers, either a regular magnetic type (non interfering), or an "electronic" supply, which is a very noisy switching supply. The latter is most popular because it's small enough to be contained within the smallest fixture. I have two neighbors _a block away_ who have incorporated these into a remodel project. These are kitchen overhead lights that create paralyzing noise, particularly on 40m. I sent the manufacturer/model number (Kovacs) to W1RFI, who plans testing to measure radiation intensity. Retrofit for such lighting is very expensive, mostly because of the mechanical changes involved. One of those neighbors was also causing me a problem with his cheap Chinese laptop supply, which I replaced. On the ARRL website there is a list of letters sent to consumers by FCC indicating a need to correct the noise generated by certain devices; several are listed for lighting systems, which undoubtedly are about the switching power supplies in low voltage systems. FCC Part 15, Sections 15.5 and 18.111 prohibit such interference to a licensed radio station. If you know a neighbor who plans a remodel or someone who is building a house nearby, suggest they select the magnetic transformer. These lights are almost always a part of every remodel project. This is a noise source that could seriously affect our hobby when new construction begins en masse again. 73, Jim W6YA ______________________________________________________________ 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 4/2/2011 6:21 AM, Jim McCook wrote:
> There is a very serious problem with the local noise source from low > voltage lighting systems. These are sold as pendants, single lights, or > multiple lights on a support, such as a bar. The retailer supplies them > with a choice of two types of transformers, either a regular magnetic > type (non interfering), or an "electronic" supply, which is a very noisy > switching supply. The latter is most popular because it's small enough > to be contained within the smallest fixture. SNIP > This is a > noise source that could seriously affect our hobby when new construction > begins en masse again. > Absolutely on target, Jim. I inherited a half dozen of these little monsters in the home I bought in California five years ago. There are two major components of the probem -- first, that these types of devices are exempt from Part 15, thanks to ARRL being asleep at the switch when the exemption was made (perhaps so focused on BPL that they saw nothing else), and to lobbying effort for "small government" that has essentially gutted the FCC. Second, a real 12V transformer big enough to handle the load of these lights is at least 2-4X larger than the the limited space available in the electrical back-box for the fixture. So from a practical point of view, these switching power supplies are the only option. Those sold by the electrical supply houses here in Santa Cruz county, CA, are unbranded and carry no FCC labels. One piece of good news -- most, if not all, of the noise is radiated as a common mode signal on the AC power wiring, so a good AC line filter can make a big dent in the RFI. I was able to fit a filter in the backbox with one of these power supplies. It's also possible to suppress the noise with a multi-turn toroid choke plus a line-voltage rated capacitor across the line. There are two pieces on my website about this -- one on RFI and Ham radio, and the other specificcally about these filters -- how to use them and where to buy them. http://audiosystemsgroup.com/publish.htm 73, Jim Brown 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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In reply to this post by Jim McCook W6YA
Jim,
Thanks for those suggestions! It never occurred to me to decouple the transformers from the AC line. In other words, disconnect the antenna from the monster. I'm told that many of these little switchers have toroids or little transformers in them that are pretty effective with noise supression, and therefore able to get Type Acceptance. However, when they are manufactured in China or Indonesia, etc., they get creative in order to save cost. They can still claim Type Acceptance. Elimination of the toroid winding or small transformer and replacement with plain wire is the answer, so now we have a noise generator. AD6ZJ deals directly with some of these devices and explained this to some of us this morning. He also mentioned that the frequency of many of these switchers has become progressively higher than before, some being up in the 3 MHz region! I'll check out your site for suggestions. My preference would be to purchase something that the electrician can install, since putting some sort of homemade device would probably not be acceptable to the electrician or the consumer. It also is a matter of my own responsibility. I'm open to any suggestions. You may have the answer to the problem! 73, Jim W6YA ______________________________________________________________ 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 4/2/2011 1:07 PM, Jim McCook wrote:
> You may have the answer to the problem! Your electricians should be happy with one of the small 1A line filters, Corcom, Delta, or equiv. 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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In reply to this post by Jim Brown-10
I'm looking forward to a time when all domestic lighting can be run from a
12V supply at the main switchboard. With led lights progressing as they are, I can see no reason for continuing to build houses with high voltage ac for lighting. The wiring will be cheaper and safer and hopefully that will be a driving force for change. Indeed a lot of domestic equipment outside the kitchen can also be run from 12V (I'm thinking of laptops, lcd tv, audio, gaming, side lamps). If governments can ban incandescent light bulbs to save energy, then why not change the building regs to encompass new lighting systems when they come into mass use. One might beget the other. This will concentrate noise producing power sources and make them easier to treat, especially being adjacent the main earth/ground point into the house. David G3UNA > On 4/2/2011 6:21 AM, Jim McCook wrote: >> There is a very serious problem with the local noise source from low >> voltage lighting systems. These are sold as pendants, single lights, or >> multiple lights on a support, such as a bar. The retailer supplies them >> with a choice of two types of transformers, either a regular magnetic >> type (non interfering), or an "electronic" supply, which is a very noisy >> switching supply. The latter is most popular because it's small enough >> to be contained within the smallest fixture. > > SNIP > >> This is a >> noise source that could seriously affect our hobby when new construction >> begins en masse again. >> > > Absolutely on target, Jim. I inherited a half dozen of these little > monsters in the home I bought in California five years ago. There are > two major components of the probem -- first, that these types of devices > are exempt from Part 15, thanks to ARRL being asleep at the switch when > the exemption was made (perhaps so focused on BPL that they saw nothing > else), and to lobbying effort for "small government" that has > essentially gutted the FCC. Second, a real 12V transformer big enough > to handle the load of these lights is at least 2-4X larger than the the > limited space available in the electrical back-box for the fixture. So > from a practical point of view, these switching power supplies are the > only option. Those sold by the electrical supply houses here in Santa > Cruz county, CA, are unbranded and carry no FCC labels. > > One piece of good news -- most, if not all, of the noise is radiated as > a common mode signal on the AC power wiring, so a good AC line filter > can make a big dent in the RFI. I was able to fit a filter in the > backbox with one of these power supplies. It's also possible to suppress > the noise with a multi-turn toroid choke plus a line-voltage rated > capacitor across the line. There are two pieces on my website about this > -- one on RFI and Ham radio, and the other specificcally about these > filters -- how to use them and where to buy them. > > http://audiosystemsgroup.com/publish.htm > > 73, Jim Brown 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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> If governments can ban incandescent light bulbs to save energy, then > why not change the building regs to encompass new lighting systems > when they come into mass use. One might beget the other. Quite simply because their IBEW (electricians union) clients will not allow it. Low voltage wiring can be done by anyone - or does not need the extensive safety training required for high voltage systems - and the unions are not about to allow "their jobs" to be taken over by low voltage (cable, telephone and IT) technicians. 73, ... Joe, W4TV On 4/3/2011 6:24 AM, David Cutter wrote: > I'm looking forward to a time when all domestic lighting can be run from a > 12V supply at the main switchboard. With led lights progressing as they > are, I can see no reason for continuing to build houses with high voltage ac > for lighting. The wiring will be cheaper and safer and hopefully that will > be a driving force for change. Indeed a lot of domestic equipment outside > the kitchen can also be run from 12V (I'm thinking of laptops, lcd tv, > audio, gaming, side lamps). If governments can ban incandescent light bulbs > to save energy, then why not change the building regs to encompass new > lighting systems when they come into mass use. One might beget the other. > > This will concentrate noise producing power sources and make them easier to > treat, especially being adjacent the main earth/ground point into the house. > > David > G3UNA > > > >> On 4/2/2011 6:21 AM, Jim McCook wrote: >>> There is a very serious problem with the local noise source from low >>> voltage lighting systems. These are sold as pendants, single lights, or >>> multiple lights on a support, such as a bar. The retailer supplies them >>> with a choice of two types of transformers, either a regular magnetic >>> type (non interfering), or an "electronic" supply, which is a very noisy >>> switching supply. The latter is most popular because it's small enough >>> to be contained within the smallest fixture. >> >> SNIP >> >>> This is a >>> noise source that could seriously affect our hobby when new construction >>> begins en masse again. >>> >> >> Absolutely on target, Jim. I inherited a half dozen of these little >> monsters in the home I bought in California five years ago. There are >> two major components of the probem -- first, that these types of devices >> are exempt from Part 15, thanks to ARRL being asleep at the switch when >> the exemption was made (perhaps so focused on BPL that they saw nothing >> else), and to lobbying effort for "small government" that has >> essentially gutted the FCC. Second, a real 12V transformer big enough >> to handle the load of these lights is at least 2-4X larger than the the >> limited space available in the electrical back-box for the fixture. So >> from a practical point of view, these switching power supplies are the >> only option. Those sold by the electrical supply houses here in Santa >> Cruz county, CA, are unbranded and carry no FCC labels. >> >> One piece of good news -- most, if not all, of the noise is radiated as >> a common mode signal on the AC power wiring, so a good AC line filter >> can make a big dent in the RFI. I was able to fit a filter in the >> backbox with one of these power supplies. It's also possible to suppress >> the noise with a multi-turn toroid choke plus a line-voltage rated >> capacitor across the line. There are two pieces on my website about this >> -- one on RFI and Ham radio, and the other specificcally about these >> filters -- how to use them and where to buy them. >> >> http://audiosystemsgroup.com/publish.htm >> >> 73, Jim Brown 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 > 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 David Cutter
On 4/3/2011 3:24 AM, David Cutter wrote:
> I'm looking forward to a time when all domestic lighting can be run > from a 12V supply at the main switchboard. Be careful what you wish for. A major advantage of higher voltage distribution is that copper losses are much less, and much smaller copper conductors are required. This makes the 240V system used in much of the world superior to the 100V and 120V systems used in Japan and North America. It gives 240V a 20:1 advantage over 12V. More important, try a quick calculation for the cost of converting every building in the world from the existing 120VAC or 240VAC to your 12VDC. Remember -- none of the old wiring is sufficient, so one must rip out the walls and start over. Please tell me when this is going to happen -- I want to buy stock in the copper industry, because the price is going to multiply by a factor of at least 5X, because copper is going to become VERY scarce. In addition, distribution of power as an AC voltage means that it is easily transformed from one voltage to another by transformers that don't make electrical noise. The electrical noise produced by switching power supplies to do that would wipe out all radio communications! 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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In reply to this post by David Cutter
Forgive me for participating in this OT thread fork, but my next house will have a code-approved sub-panel for overhead and sconce lighting that I'll pull off 120 VAC after inspection and feed with eight series-parallel 6V golf cart batteries for nominal 24 VDC. The overhead boxes will each be fed from two wall switches and support 24 VDC paddle fans with added runs to added LED overhead lights. The sub-panel will also have a 30 amp circuit to my "shack," feeding a 24 VDC to 13.8 VDC converter for full nominal voltage to our 100 watt rig. There are many advantages to 24 VDC over 12 VDC in residential use.
-- Moe - AB8XA ARRL LOTW, eQSL, Fists #13020, SKCC #7460, FPQRP #2617, NAQCC #5352, QRP-ARCI #14326 On Apr 3, 2011, at 6:24 AM, David Cutter wrote: > I'm looking forward to a time when all domestic lighting can be run from a > 12V supply at the main switchboard. With led lights progressing as they > are, I can see no reason for continuing to build houses with high voltage ac > for lighting. The wiring will be cheaper and safer and hopefully that will > be a driving force for change. Indeed a lot of domestic equipment outside > the kitchen can also be run from 12V (I'm thinking of laptops, lcd tv, > audio, gaming, side lamps). If governments can ban incandescent light bulbs > to save energy, then why not change the building regs to encompass new > lighting systems when they come into mass use. One might beget the other. > > This will concentrate noise producing power sources and make them easier to > treat, especially being adjacent the main earth/ground point into the house. > > David > G3UNA > > > >> On 4/2/2011 6:21 AM, Jim McCook wrote: >>> There is a very serious problem with the local noise source from low >>> voltage lighting systems. These are sold as pendants, single lights, or >>> multiple lights on a support, such as a bar. The retailer supplies them >>> with a choice of two types of transformers, either a regular magnetic >>> type (non interfering), or an "electronic" supply, which is a very noisy >>> switching supply. The latter is most popular because it's small enough >>> to be contained within the smallest fixture. >> >> SNIP >> >>> This is a >>> noise source that could seriously affect our hobby when new construction >>> begins en masse again. >>> >> >> Absolutely on target, Jim. I inherited a half dozen of these little >> monsters in the home I bought in California five years ago. There are >> two major components of the probem -- first, that these types of devices >> are exempt from Part 15, thanks to ARRL being asleep at the switch when >> the exemption was made (perhaps so focused on BPL that they saw nothing >> else), and to lobbying effort for "small government" that has >> essentially gutted the FCC. Second, a real 12V transformer big enough >> to handle the load of these lights is at least 2-4X larger than the the >> limited space available in the electrical back-box for the fixture. So >> from a practical point of view, these switching power supplies are the >> only option. Those sold by the electrical supply houses here in Santa >> Cruz county, CA, are unbranded and carry no FCC labels. >> >> One piece of good news -- most, if not all, of the noise is radiated as >> a common mode signal on the AC power wiring, so a good AC line filter >> can make a big dent in the RFI. I was able to fit a filter in the >> backbox with one of these power supplies. It's also possible to suppress >> the noise with a multi-turn toroid choke plus a line-voltage rated >> capacitor across the line. There are two pieces on my website about this >> -- one on RFI and Ham radio, and the other specificcally about these >> filters -- how to use them and where to buy them. >> >> http://audiosystemsgroup.com/publish.htm >> >> 73, Jim Brown 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 ______________________________________________________________ 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 4/3/2011 10:12 AM, AB8XA wrote:
> The sub-panel will also have a 30 amp circuit to my "shack," feeding a 24 VDC to 13.8 VDC converter for full nominal voltage to our 100 watt rig. There are many advantages to 24 VDC over 12 VDC in residential use. Yes, BUT -- that 24VDC to 12VDC converter is almost certainly some sort of switching power supply, and you will need to carefully search to find one that is not a source of RF noise.. AND the conductors are going to need to be pretty large, because they're carrying a 10A load (at 24V) just to run your 100W rig. Multiply that current (and copper) by about 9X if you also want to run a 500W amp. And the only one I know of that runs on 13.8V is the Ten Tec Hercules II, a very nice amp that's been out of production for about 20 years. 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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Hi,
Clearly, a switch to 12 or 24VDC power distribution in homes is not going to happen for all the reasons given by K9YC, Jim. Even in cars there is a move to higher voltage, such as 36VDC. We are stuck with switchers for conversion to the lower voltages required by many devices and they *can* be and *are* made quiet. The trouble is the total lack of accountability by the cheap offshore knock-off manufacturers and FCC's inability to enforce its rules. Even if wall warts are exempt from the part 15 rules, they do have to meet the standards for conducted emissions below 30MHz and the really bad one clearly don't. AB2TC - Knut
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In reply to this post by Jim Brown-10
I'm quite happy with my wish. I've seen led clusters in a MR16 package
deliver the equivalent light to a 43W incandescent for a consumption of 3.6W: that's 300mA at 12V. Our rooms over here are probably smaller than yours, Jim, but I might have 4 ceiling-mounted units to give me a nice light in most of my rooms (<150sq ft). Our lighting wiring is mostly rated 5A, so, the 1.2A ac/dc I would need is well within spec if I just put a 12V transformer on the lighting circuit. So, in my house (fairly typical in the UK) my wiring would not change, but in a new build it could be not only smaller, but not have an earth/ground wire with it and no outer sheath, ie just twin. That's a lot less copper and a lot less pvc. It's easy to incorporate thermal trips (ptc devices) which are cheap and last my lifetime. All this adds up to taking a lot less current out of the mains and therefore a lot easier to suppress if switching supplies are used. Sorry for the thread drift, but it's an interesting subject. David G3UNA > On 4/3/2011 3:24 AM, David Cutter wrote: >> I'm looking forward to a time when all domestic lighting can be run >> from a 12V supply at the main switchboard. > > Be careful what you wish for. A major advantage of higher voltage > distribution is that copper losses are much less, and much smaller > copper conductors are required. This makes the 240V system used in much > of the world superior to the 100V and 120V systems used in Japan and > North America. It gives 240V a 20:1 advantage over 12V. > > More important, try a quick calculation for the cost of converting every > building in the world from the existing 120VAC or 240VAC to your 12VDC. > Remember -- none of the old wiring is sufficient, so one must rip out > the walls and start over. Please tell me when this is going to happen -- > I want to buy stock in the copper industry, because the price is going > to multiply by a factor of at least 5X, because copper is going to > become VERY scarce. > > In addition, distribution of power as an AC voltage means that it is > easily transformed from one voltage to another by transformers that > don't make electrical noise. The electrical noise produced by switching > power supplies to do that would wipe out all radio communications! > > 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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In reply to this post by Joe Subich, W4TV-4
Hi Joe
Over here I've noticed that whenever "wiring" of any kind is to be installed, businesses and domestics that I've heard about always employ qualified electricians. The wiring itself may not need a qualified electrician but how it is routed and juxtaposed with mains, particularly when 3-phase is about, still needs that expertise. On a new build site, why bother with different grades of wireman when one can do the lot? 73 David G3UNA > >> If governments can ban incandescent light bulbs to save energy, then >> why not change the building regs to encompass new lighting systems >> when they come into mass use. One might beget the other. > > Quite simply because their IBEW (electricians union) clients will not > allow it. Low voltage wiring can be done by anyone - or does not need > the extensive safety training required for high voltage systems - and > the unions are not about to allow "their jobs" to be taken over by > low voltage (cable, telephone and IT) technicians. > > 73, > > ... Joe, W4TV > > 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 Jim McCook W6YA
It would seem 120/240 to 12v converters will be the logical solution
for low-voltage lighting. Regarding high-current dc distribution: I ran into that issue lots of years ago when I wanted to run some ham gear outside my travel trailer and use the 12v system as power source. I quickly found that 30-feet of #14 or #12 wire would not do. I finally used a 12v battery and floated it from the trailer power. And I was only running 150w on 2m. At one time I was considering solar power for a two-story log-cabin in the bush, but the wiring gets expensive (so do the panels). The cabin now has 120vac utility service so its a moot issue (and I sold it in 2003). My present shack has 13.8v provided by 50A Astron which is connected via a 12-foot run of #6 welding wire to the main 30A buss fuse. This connected to a heavy barrier terminal strip to provide power to all the amplifiers and high-current equipment. I see about 13.5v at the main fuse when running loads; unloaded it shows 13.75v. Two power leads run from there to two more barrier strips: one is #12 solid house wire and the other #8. Both about 3-foot long. My new 144-28 50w transverter runs off the strip fed by #8 wire and voltage runs at 13.2 under load. My K3/10 is fed from the #12 wired strip. There are only two other items connected there: panel lights for my manual antenna tuner and the main station controller (fused at 5A). Many of my new amps require 28vdc. I have a 8A and two 50A supplies for 28vdc. One 50A PS runs the 16-foot dish rotator-motors and will run 432-100w and 1296-300w PA's at the dish. I run #12 romex out there for 120vac power (remotely switched). The other 50A PS may go to the base of one tower where I may install some big amps for 900 and 1296 MHz. To place the amps at 50-feet will require #6 wiring up the tower. Installing a switching PS at tower-top becomes attractive (not the 90-lb. 50A PS). Ohms law rules dc-wiring! Ed ------------------------------ Message: 5 Date: Sun, 03 Apr 2011 11:05:02 -0700 From: Jim Brown <[hidden email]> Subject: Re: [Elecraft] Local Noise Problem To: [hidden email] Message-ID: <[hidden email]> Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 4/3/2011 10:12 AM, AB8XA wrote: > The sub-panel will also have a 30 amp circuit to my "shack," feeding a 24 VDC to 13.8 VDC converter for full nominal voltage to our 100 watt rig. There are many advantages to 24 VDC over 12 VDC in residential use. Yes, BUT -- that 24VDC to 12VDC converter is almost certainly some sort of switching power supply, and you will need to carefully search to find one that is not a source of RF noise.. AND the conductors are going to need to be pretty large, because they're carrying a 10A load (at 24V) just to run your 100W rig. Multiply that current (and copper) by about 9X if you also want to run a 500W amp. And the only one I know of that runs on 13.8V is the Ten Tec Hercules II, a very nice amp that's been out of production for about 20 years. 73, Jim K9YC 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 144-1.4kw, 432-100w, 1296-testing*, 3400-winter? DUBUS Magazine USA Rep [hidden email] ====================================== ______________________________________________________________ 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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There were rules when I worked in the big 24 volt power supply cave
underneath the AT&T building at 13th & G in Washington DC. No rings, no watches, nothing hanging on your neck, no tools that were not wrapped, etc. Long sleeve shirts out in the locker. I always brought tee shirt to work in there. Hot place to work. One of the 10k ampere 24 volt supplies used four 1 by 6 inch copper slabs in parallel as a "lead". The positive and negative were side by side with about four inches in between. A Western Electric guy was working above with an unwrapped 8 inch crescent wrench and dropped it down on the bus bars. The story I heard was that the middle of the wrench dropped through the space between the bus bars without even slowing down as both ends exploded into a room full of tiny copper-steel bb's. It took us two days to clean up the place. Western guy wasn't hurt, but I never saw him in our building again. Might have been fired, but I don't know that. There was a kind of "dent" on the top of the bar, but they never replaced it. It did NOT blow the master fusible link, so it was not "working hard" to evaporate the wrench. Shorts on large conductors will definitely eat things even at 24 volts. 73, Guy. On Mon, Apr 4, 2011 at 6:25 PM, Ron D'Eau Claire <[hidden email]> wrote: > In the 24 volt aircraft systems I worked with power was typically routed > into the cockpit via 1/2" diameter copper rods that ran along behind the > breaker panels. Breakers for each circuit were tapped into the rod with > threaded holes and screw. > > That's what it takes to avoid excessive I^2R losses for a system that draws > significant current. > > And never lose sight of the danger of a low-voltage high-current system. > First, if you have an inductive load, the pulse that occurs when it's > disconnected can run into many hundreds of volts - enough to do real damage > if you're holding the two ends of the circuit as you disconnect it. > > But more commonly is the danger of a short circuit. Things turn red-hot > instantly and even thick bus-bars can melt. I saw a guy drop a screwdriver > into an aircraft 24-volt bus once. I was glad I was 50 feet away in the next > plane. It looked like a bomb went off as the shaft of the screwdriver melted > so fast it literally exploded with a huge bang, showering the poor guy with > molten steel and setting the plane on fire. > > I also knew techs missing fingers after getting a ring across a low-voltage > source. The rings heated so fast it welded to the terminals before he could > pull away and the hapless fellow had to suffer the melting metal burning his > finger off until he was able to jerk his hand away without the finger. I > heard of one fellow who wore a metal watch band and, yes, he reportedly lost > his whole hand. > > To this day, I remove any jewelry when I'm working around a high-current > low-voltage source like an automobile battery. > > Ron AC7AC > > > > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of Edward R. Cole > > > Regarding high-current dc distribution: I ran into that issue lots > of years ago when I wanted to run some ham gear outside my travel > trailer and use the 12v system as power source. I quickly found that > 30-feet of #14 or #12 wire would not do. I finally used a 12v > battery and floated it from the trailer power. And I was only > running 150w on 2m. > > At one time I was considering solar power for a two-story log-cabin > in the bush, but the wiring gets expensive (so do the panels). The > cabin now has 120vac utility service so its a moot issue (and I sold > it in 2003). > > My present shack has 13.8v provided by 50A Astron which is connected > via a 12-foot run of #6 welding wire to the main 30A buss fuse. This > connected to a heavy barrier terminal strip to provide power to all > the amplifiers and high-current equipment. I see about 13.5v at the > main fuse when running loads; unloaded it shows 13.75v. > > Two power leads run from there to two more barrier strips: one is > #12 solid house wire and the other #8. Both about 3-foot long. My > new 144-28 50w transverter runs off the strip fed by #8 wire and > voltage runs at 13.2 under load. My K3/10 is fed from the #12 wired > strip. There are only two other items connected there: panel lights > for my manual antenna tuner and the main station controller (fused at 5A). > > Many of my new amps require 28vdc. I have a 8A and two 50A supplies > for 28vdc. One 50A PS runs the 16-foot dish rotator-motors and will > run 432-100w and 1296-300w PA's at the dish. I run #12 romex out > there for 120vac power (remotely switched). The other 50A PS may go > to the base of one tower where I may install some big amps for 900 > and 1296 MHz. To place the amps at 50-feet will require #6 wiring up > the tower. Installing a switching PS at tower-top becomes attractive > (not the 90-lb. 50A PS). > > Ohms law rules dc-wiring! > Ed > > ------------------------------ > > ______________________________________________________________ > 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 AC7AC
There are many deisel mechanics who are missing fingers because they didn't take rings off while working on 12 volt electrical systems on trucks with paralleled bateries. Tom N5GE On Mon, 4 Apr 2011 15:25:25 -0700, "Ron D'Eau Claire" <[hidden email]> wrote: >In the 24 volt aircraft systems I worked with power was typically routed >into the cockpit via 1/2" diameter copper rods that ran along behind the >breaker panels. Breakers for each circuit were tapped into the rod with >threaded holes and screw. > >That's what it takes to avoid excessive I^2R losses for a system that draws >significant current. > >And never lose sight of the danger of a low-voltage high-current system. >First, if you have an inductive load, the pulse that occurs when it's >disconnected can run into many hundreds of volts - enough to do real damage >if you're holding the two ends of the circuit as you disconnect it. > >But more commonly is the danger of a short circuit. Things turn red-hot >instantly and even thick bus-bars can melt. I saw a guy drop a screwdriver >into an aircraft 24-volt bus once. I was glad I was 50 feet away in the next >plane. It looked like a bomb went off as the shaft of the screwdriver melted >so fast it literally exploded with a huge bang, showering the poor guy with >molten steel and setting the plane on fire. > >I also knew techs missing fingers after getting a ring across a low-voltage >source. The rings heated so fast it welded to the terminals before he could >pull away and the hapless fellow had to suffer the melting metal burning his >finger off until he was able to jerk his hand away without the finger. I >heard of one fellow who wore a metal watch band and, yes, he reportedly lost >his whole hand. > >To this day, I remove any jewelry when I'm working around a high-current >low-voltage source like an automobile battery. > >Ron AC7AC > > > >-----Original Message----- >From: [hidden email] >[mailto:[hidden email]] On Behalf Of Edward R. Cole > > >Regarding high-current dc distribution: I ran into that issue lots >of years ago when I wanted to run some ham gear outside my travel >trailer and use the 12v system as power source. I quickly found that >30-feet of #14 or #12 wire would not do. I finally used a 12v >battery and floated it from the trailer power. And I was only >running 150w on 2m. > >At one time I was considering solar power for a two-story log-cabin >in the bush, but the wiring gets expensive (so do the panels). The >cabin now has 120vac utility service so its a moot issue (and I sold >it in 2003). > >My present shack has 13.8v provided by 50A Astron which is connected >via a 12-foot run of #6 welding wire to the main 30A buss fuse. This >connected to a heavy barrier terminal strip to provide power to all >the amplifiers and high-current equipment. I see about 13.5v at the >main fuse when running loads; unloaded it shows 13.75v. > >Two power leads run from there to two more barrier strips: one is >#12 solid house wire and the other #8. Both about 3-foot long. My >new 144-28 50w transverter runs off the strip fed by #8 wire and >voltage runs at 13.2 under load. My K3/10 is fed from the #12 wired >strip. There are only two other items connected there: panel lights >for my manual antenna tuner and the main station controller (fused at 5A). > >Many of my new amps require 28vdc. I have a 8A and two 50A supplies >for 28vdc. One 50A PS runs the 16-foot dish rotator-motors and will >run 432-100w and 1296-300w PA's at the dish. I run #12 romex out >there for 120vac power (remotely switched). The other 50A PS may go >to the base of one tower where I may install some big amps for 900 >and 1296 MHz. To place the amps at 50-feet will require #6 wiring up >the tower. Installing a switching PS at tower-top becomes attractive >(not the 90-lb. 50A PS). > >Ohms law rules dc-wiring! >Ed > >------------------------------ > >______________________________________________________________ >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
Amateur Radio Operator N5GE
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