Re: [Boatanchors] 12 volt supply question
I have used a 650 watt computer P.S. for many purposes with no real problems other than having to: 1) Filter & Shield for the RFI that it generates 2) Put a resistor load on one of the outputs so that the thing would be stable (as mentioned in an earlier email). But I think the best solution is the old-fashioned linear supply: Take a big, (say 450 watt) and free UPS transformer and apply 120 VAC to its 120v side. Rectify the output using a sturdy bridge rectifier and filter it well. The output will be about 12v x 1.414 = ~16 volts which will feed a low-dropout regulator chip. Run this ~16v output into a 12 volt regulator chip (or a variable voltage one) that is placed above ground to deliver 12 - 15 volts (adjustable, using a pot). Use pass transistors in the negative rather than the positive lead - these can be bolted right to a heavy chassis used as a heat sink. Here's a good reference for doing this: http://www.qsl.net/wb4kdi/PowerSupply/UpsideDown.html Derate the 450 (or larger) watt UPS transformer by about 1/3 as they are not intended for long periods of use. Mine powers a 100 watt Yaesu without getting hot. Add a $5 Chinese digital voltmeter from eBay - makes a very nice output indicator. Bend your own aluminum case or put it in a metal UPS case. Or a wood case with Masonite panel. Or breadboard it and keep the cat away from it. Others can make a good case for the switching supply but I find them hard to repair if a unique component fails. My linear supply is built of junk I found in recycle yards - total cost is about $15, mostly for a good can of spray paint and the voltmeter. On the other hand, computer P.S. can often be had free, are small and don't need much modification other than changing a resistor (sometimes a variable one) to raise the voltage. Lots of articles on the internet about using computer p.s. Frank W4NPN On Wed, Nov 30, 2016 at 11:03 PM, Alex [Temple Boatanchors] < temple.boatancho...@miwww.com> wrote: > ATX PC power supplies are very inexpensive ($20-$30), highly efficient and > very lightweight, and basically use the same concept as those modern > lightweight "wall-wart" wall transformers. But due to their switch-mode > nature they generate a great deal of RFI in the HF regions, specially the > lower frequencies bellow 10-15MHz or so, but should be fine for use with > gear on 6M, VHF, UHF and up. The level of RFI perceived in the receiver > much depends on how well the radio itself and coax to the antenna is > shielded and grounded, and the distance between the gear and power supply > is a factor as well. Also, the output is 12V, not the required/desired > 13.8V that most mobile DC operation gear needs to attain full output power. > But with small modifications by changing one or more resistors (varies from > model to model), in most cases one can "fool" the regulator to raise the > voltage as needed without tripping the protection circuit. Another issue is > that the power supply usually requires a minimum load on one or more of its > outputs for stable operation of the regulator circuit, as one or more of > these outputs are used as a reference voltage. A resistor or appropriate > incandescent light bulb might do the trick as a load. > > I use a 700W ATX power supply that I modified for 14.4V output to manually > charge a 150Ah lead-acid backup battery bank. It easily will charge it at > 20-25Amps and generates minimum heat as long as its internal fan is > running. Basically these power supplies can be used as very inexpensive > power sources or charger. But while charging it basically wipes out my > reception on 80 and 40 meters. Then again the internal power supply of my > nearby Apple TV does pretty much the same, only at a lesser degree than the > charger. > > Just search for "ATX power supply modification", there is quite a bit of > info out there. > > > > At 07:17 PM 11/30/2016, you wrote: > >> OK gang .. Can someone provide a definitive answer to this question? >> I see all kinds of conflicting opinions and would like to know what the >> thinking is here. Or, if someone here is using them for that purpose. >> >> >> Computer power supplies. Can they or can they not be used to power ham >> rigs such as two meter rigs, or even >> >> low power HF rigs? >> > > > ___ > Boatanchors mailing list > Boatanchors@puck.nether.net > https://puck.nether.net/mailman/listinfo/boatanchors > > -- Frank Barnes W4NPN Chapel Hill, NC Grid Square FM05 Cell 919.260.7955 ___ Boatanchors mailing list Boatanchors@puck.nether.net https://puck.nether.net/mailman/listinfo/boatanchors
Re: [Boatanchors] 12 volt supply question
ATX PC power supplies are very inexpensive ($20-$30), highly efficient and very lightweight, and basically use the same concept as those modern lightweight "wall-wart" wall transformers. But due to their switch-mode nature they generate a great deal of RFI in the HF regions, specially the lower frequencies bellow 10-15MHz or so, but should be fine for use with gear on 6M, VHF, UHF and up. The level of RFI perceived in the receiver much depends on how well the radio itself and coax to the antenna is shielded and grounded, and the distance between the gear and power supply is a factor as well. Also, the output is 12V, not the required/desired 13.8V that most mobile DC operation gear needs to attain full output power. But with small modifications by changing one or more resistors (varies from model to model), in most cases one can "fool" the regulator to raise the voltage as needed without tripping the protection circuit. Another issue is that the power supply usually requires a minimum load on one or more of its outputs for stable operation of the regulator circuit, as one or more of these outputs are used as a reference voltage. A resistor or appropriate incandescent light bulb might do the trick as a load. I use a 700W ATX power supply that I modified for 14.4V output to manually charge a 150Ah lead-acid backup battery bank. It easily will charge it at 20-25Amps and generates minimum heat as long as its internal fan is running. Basically these power supplies can be used as very inexpensive power sources or charger. But while charging it basically wipes out my reception on 80 and 40 meters. Then again the internal power supply of my nearby Apple TV does pretty much the same, only at a lesser degree than the charger. Just search for "ATX power supply modification", there is quite a bit of info out there. At 07:17 PM 11/30/2016, you wrote: OK gang .. Can someone provide a definitive answer to this question? I see all kinds of conflicting opinions and would like to know what the thinking is here. Or, if someone here is using them for that purpose. Computer power supplies. Can they or can they not be used to power ham rigs such as two meter rigs, or even low power HF rigs? ___ Boatanchors mailing list Boatanchors@puck.nether.net https://puck.nether.net/mailman/listinfo/boatanchors
Re: [Boatanchors] 12 volt supply question
Sounds like maybe I should just scrounge my well stocked junk boxes and build a supply from scratch. I am sure I have all the components diodes, transformer, filter choke and caps.Just like we did in the "old days" HI HI From: Brian Clarke Sent: Wednesday, November 30, 2016 8:24 PM To: 'Jim Wiley'; 'RAY FRIESS'; 'boatanchors'; 'Old Tube Radios'; boatanchors@puck.nether.net Subject: RE: [Boatanchors] 12 volt supply question Sorry Jim, You need to take your exceptions to world reality, thus: The only thing almost correct about your assertions is your first sentence and only for the USA. Everywhere else in the world, safety is taken seriously, and the SMPSU case is connected directly to the mains Ground pin in the mains plug, usually an IEC chassis connector. The computer SMPSUs that adorn our various computers, printers and other digital devices all take the mains directly into the SMPSU box or printed wiring board. Inside that box or on that printed wiring board are: *EMC filters, unless of the SMPSU is of Asian origin *Mains fuse *Rectifier *Filter capacitor *Series inductor, usually the transformer primary *SCR And all these are operating at your mains Voltage multiplied by sq rt 2. So, in Japan, 141 Vdc, in USA, 163Vdc, and in almost all other parts of the world, where 93% of the world's population lives, 325 Vdc. In some of the earlier SMPSUs, there was a switch to shift from direct rectification to Voltage doubling, almost entirely for the US market. In slightly later SMPSUs, this switching was automatic, based on sensing the mains input Voltage. In modern SMPSUs, the duration of pulses fed to the SCR takes care of any input mains Voltage variations; hence, the universal SMPSU running on between 90 and 264 Vac. These items are separated along the transformer core by an isolating strip of circuit board. On the secondary of the transformer are various low Voltage windings followed by cheap-as-chips half-wave rectifiers and their associated filter capacitors. All provision of low Voltages comes directly from the SMPSU box or printed wiring board. Some mother boards have Point of Application regulators or switchers to provide a local Voltage. Only one of the output Voltages is regulated in the SMPSU. A sensing circuit comprising two resistors in series is across this regulated output, the junction of the resistors if fed to the control IC, eg, a 494 or later chip. The output of this chip is fed via an opto-isolator to drive the SCR on the primary side. All the other output Voltages are then related to this regulated output via the turns ratio in the transformer. In some SMPSUs, the 12 V line may be regulated via a 7812 or similar chip - but this is by no means universal. 73 de Brian, VK2GCE On Thursday, 1 December 2016 1:35 PM, Ray said: I have to take exception to some of this. The mains power is not directly connected to case ground. In all the desktop computer power supplies I have ever fiddled with, the rectified raw AC goes directly to the switching converter, and nowhere else, which then delivers several different high-frequency AC voltages to the rest of the circuitry. Those voltages are rectified and filtered (and regulated) before they connect to the computer. The "raw" AC from the line never reaches the computer "innards". Let me try this another way: The rectified and brute-force filtered DC runs the switching inverter (for lack of a better word). The high frequency AC from the SECONDARY of that transformer is what is used for the various voltages inside the computer cabinet. If you check with a VOM, you will find that neither side of the AC line is directly connected to the cabinet or motherboard ground. The high frequency inverter transformer performs the "isolation transformer" function. A person still has to deal with all of the other issues that were raised, including dealing with voltages approaching 200 volts (or more) DC inside the power supply, but getting electrocuted by a direct path to the incoming AC line is almost certainly not one of them. This does not mean that a person cannot be injured by voltages found inside a desktop power supply. This can definitely happen, so caution is important. If you are not familiar with working on power supplies, of any kind, the best advice is to leave that sort of thing to someone who knows what they are doing. The author of the article had mentioned using the 12-volt portion directly for smaller loads and modifying the 5-volt section (with appropriate component changes) for larger loads. As I said, look up the QST article for more info. Also, and again as I pointed out, this applies to the "standard" configuration AC operated DESKTOP system. Laptops and other portable equipment may have other configurations where the above comments do not apply. - Jim, KL7CC _
Re: [Boatanchors] 12 volt supply question
Yes, but ... You will need to adapt the connectors, perhaps add metering, and test for RFI. They generally work OK. The big ones designed for huge server arrays can power full legal SS amps. 73, David KD4E OK gang .. Can someone provide a definitive answer to this question? I see all kinds of conflicting opinions and would like to know what the thinking is here. Or, if someone here is using them for that purpose. Computer power supplies. Can they or can they not be used to power ham rigs such as two meter rigs, or even low power HF rigs? ___ ___ Boatanchors mailing list Boatanchors@puck.nether.net https://puck.nether.net/mailman/listinfo/boatanchors
