"Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message news:ll0q90$hh9$1@news.albasani.net...> On 5/13/2014 1:52 PM, Ian Field wrote: >> >> >> <mroberds@att.net> wrote in message news:lks75r$rk9$1@dont-email.me... >>> Jurd <guitardorkspamspameggsandham74@gmail.com> wrote: >>>> I'm not above dumpster diving and salvaging parts, but I'll suspect >>>> most transformers in consumer electronics are going to be for 9V-12V >>>> output. A ~36V or whatever might be rare. >>> >>> Look for (solid-state) stereo amplifiers, or tuners with built-in >>> amplifiers. These usually have a big transformer with a center-tapped >>> winding that originally was used to generate +/- 30 to 60 V DC for the >>> main audio output >> >> You beat me to it! >> >> Salvage transformers are pretty much drying up - some end user disposals >> houses still get the occasional antique computer with linear PSU, you >> can get some really chunky transformers - but it could be a long wait. >> > > > My city has a pretty comprehensive electronics recycling system in place. > It's good for the big picture and all because it keeps recyclable > resources out of landfills, but for guys like me it means that 95% of > 'broken' electronics go to a 24/7 monitored dropoff site instead of to the > curb. > > However, it's the insult to injury that makes it the worst- As I > mentioned previously, I work for an electronics recycler so I get to see > (literally) hundreds of thousands of pounds of this stuff on any given > workday. The caveat: I can't have *any* of it. I can't even *buy* it at > all.That would be too much for me to take - I'd be looking for a job where it was out of sight out of mind.
Benchtop Power Supply Options
Started by ●May 7, 2014
Reply by ●May 15, 20142014-05-15
Reply by ●May 15, 20142014-05-15
On Thu, 15 May 2014, Ian Field wrote:> > > "Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message > news:ll0q90$hh9$1@news.albasani.net... >> On 5/13/2014 1:52 PM, Ian Field wrote: >>> >>> >>> <mroberds@att.net> wrote in message news:lks75r$rk9$1@dont-email.me... >>>> Jurd <guitardorkspamspameggsandham74@gmail.com> wrote: >>>>> I'm not above dumpster diving and salvaging parts, but I'll suspect >>>>> most transformers in consumer electronics are going to be for 9V-12V >>>>> output. A ~36V or whatever might be rare. >>>> >>>> Look for (solid-state) stereo amplifiers, or tuners with built-in >>>> amplifiers. These usually have a big transformer with a center-tapped >>>> winding that originally was used to generate +/- 30 to 60 V DC for the >>>> main audio output >>> >>> You beat me to it! >>> >>> Salvage transformers are pretty much drying up - some end user disposals >>> houses still get the occasional antique computer with linear PSU, you >>> can get some really chunky transformers - but it could be a long wait. >>> >> >> >> My city has a pretty comprehensive electronics recycling system in place. >> It's good for the big picture and all because it keeps recyclable resources >> out of landfills, but for guys like me it means that 95% of 'broken' >> electronics go to a 24/7 monitored dropoff site instead of to the curb. >> >> However, it's the insult to injury that makes it the worst- As I mentioned >> previously, I work for an electronics recycler so I get to see (literally) >> hundreds of thousands of pounds of this stuff on any given workday. The >> caveat: I can't have *any* of it. I can't even *buy* it at all. > > That would be too much for me to take - I'd be looking for a job where it was > out of sight out of mind. >I certainly wouldn't volunteer at used book sales for the same reason. As a customer to such sales, I'd be annoyed if I found the "good books" were being skimmed off before the sale, but it would be horrible to see books jump out at me and have to wait till the sale started. It's kind of a shame, since I'd be good at sorting the books. A friend had a good angle on this. Help put things away, the books are likely up for grabs then. Michael
Reply by ●May 15, 20142014-05-15
"Michael Black" <et472@ncf.ca> wrote in message news:alpine.LNX.2.02.1405151335400.27791@darkstar.example.org...> On Thu, 15 May 2014, Ian Field wrote: > >> >> >> "Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message >> news:ll0q90$hh9$1@news.albasani.net... >>> On 5/13/2014 1:52 PM, Ian Field wrote: >>>> >>>> >>>> <mroberds@att.net> wrote in message news:lks75r$rk9$1@dont-email.me... >>>>> Jurd <guitardorkspamspameggsandham74@gmail.com> wrote: >>>>>> I'm not above dumpster diving and salvaging parts, but I'll suspect >>>>>> most transformers in consumer electronics are going to be for 9V-12V >>>>>> output. A ~36V or whatever might be rare. >>>>> >>>>> Look for (solid-state) stereo amplifiers, or tuners with built-in >>>>> amplifiers. These usually have a big transformer with a center-tapped >>>>> winding that originally was used to generate +/- 30 to 60 V DC for the >>>>> main audio output >>>> >>>> You beat me to it! >>>> >>>> Salvage transformers are pretty much drying up - some end user >>>> disposals >>>> houses still get the occasional antique computer with linear PSU, you >>>> can get some really chunky transformers - but it could be a long wait. >>>> >>> >>> >>> My city has a pretty comprehensive electronics recycling system in >>> place. It's good for the big picture and all because it keeps recyclable >>> resources out of landfills, but for guys like me it means that 95% of >>> 'broken' electronics go to a 24/7 monitored dropoff site instead of to >>> the curb. >>> >>> However, it's the insult to injury that makes it the worst- As I >>> mentioned previously, I work for an electronics recycler so I get to see >>> (literally) hundreds of thousands of pounds of this stuff on any given >>> workday. The caveat: I can't have *any* of it. I can't even *buy* it >>> at all. >> >> That would be too much for me to take - I'd be looking for a job where it >> was out of sight out of mind. > I certainly wouldn't volunteer at used book sales for the same reason. As > a customer to such sales, I'd be annoyed if I found the "good books" were > being skimmed off before the sale, but it would be horrible to see books > jump out at me and have to wait till the sale started. It's kind of a > shame, since I'd be good at sorting the books. > > A friend had a good angle on this. Help put things away, the books are > likely up for grabs then.Someone mentioned on one of the groups - ask the charity shop their policy on disposing of unsold books before donating. There may have been a suggestion how to recycle books so they never get pulped as a result.
Reply by ●May 24, 20142014-05-24
On 5/8/2014 7:15 AM, George Herold wrote:> If you've got more time than money, then I like the idea of building your own power supply. Either from a kit... or better yet (more learning potential) building it yourself from pieces/parts. There are lots of places that will show you how to make a linear supply. ("Art of Electronics", for one.) > > And hey you can draw up a schematic and post it here for comments. > > If not, I also like the mastech linear supplies that John L. linked to. > > George H. >>Well... Other than a nearly complete Athlon X2 PC, dumpster diving has been pretty unfruitful. I haven't found a single transformer. On places like Mouser they don't seem that expensive, but what secondary rating would I need to hit ~30V? Here's a basic LM317T setup from my old Mims book, which seems fairly ubiquitous: http://i1276.photobucket.com/albums/y479/guitardork74/mims_psu_zps20e14f3a.jpg The text to the lower left says the design will deliver 1.2V to 37V at up to 1.5A, but also mentions a "25V (or higher) secondary and at least 2A rating" on the transformer. Is there some voltage amplification that happens between the bridge rectifier and the filter caps? (C1, C2) Or for 30V do I need a transformer that'll go higher, (i.e. 32V) to cover losses? Thanks. -J
Reply by ●May 24, 20142014-05-24
On Sat, 24 May 2014 20:06:45 -0500, Jurd <guitardorkspamspameggsandham74@gmail.com> wrote:>On 5/8/2014 7:15 AM, George Herold wrote: > >> If you've got more time than money, then I like the idea of building your own power supply. Either from a kit... or better yet (more learning potential) building it yourself from pieces/parts. There are lots of places that will show you how to make a linear supply. ("Art of Electronics", for one.) >> >> And hey you can draw up a schematic and post it here for comments. >> >> If not, I also like the mastech linear supplies that John L. linked to. >> >> George H. >>> > >Well... > >Other than a nearly complete Athlon X2 PC, dumpster diving has been >pretty unfruitful. I haven't found a single transformer. On places >like Mouser they don't seem that expensive, but what secondary rating >would I need to hit ~30V? Here's a basic LM317T setup from my old Mims >book, which seems fairly ubiquitous: > >http://i1276.photobucket.com/albums/y479/guitardork74/mims_psu_zps20e14f3a.jpg > >The text to the lower left says the design will deliver 1.2V to 37V at >up to 1.5A, but also mentions a "25V (or higher) secondary and at least >2A rating" on the transformer. Is there some voltage amplification that >happens between the bridge rectifier and the filter caps? (C1, C2) > >Or for 30V do I need a transformer that'll go higher, (i.e. 32V) to >cover losses? > >Thanks. > >-JThat bridge configuration will in theory charge the caps to 1.41 times the RMS voltage of the transformer secondary, because a sine wave has a peak voltage 1.41x its RMS. In real life you'd typically get more DC than that at light loads and less at heavy loads. And the "DC" will have ripple, which makes the voltage dip at 120 Hz (100 Hz in the hinterlands).
Reply by ●May 24, 20142014-05-24
On 5/24/2014 8:48 PM, John Larkin wrote:> On Sat, 24 May 2014 20:06:45 -0500, Jurd> > That bridge configuration will in theory charge the caps to 1.41 times > the RMS voltage of the transformer secondary, because a sine wave has > a peak voltage 1.41x its RMS. > > In real life you'd typically get more DC than that at light loads and > less at heavy loads. And the "DC" will have ripple, which makes the > voltage dip at 120 Hz (100 Hz in the hinterlands). > >Ah thanks. Good to know about the ripple, as that's certainly something I'd like to avoid. Back to the Googling board! -J
Reply by ●May 25, 20142014-05-25
"Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message news:llrkq5$hr4$1@news.albasani.net...> On 5/24/2014 8:48 PM, John Larkin wrote: >> On Sat, 24 May 2014 20:06:45 -0500, Jurd > >> >> That bridge configuration will in theory charge the caps to 1.41 times >> the RMS voltage of the transformer secondary, because a sine wave has >> a peak voltage 1.41x its RMS. >> >> In real life you'd typically get more DC than that at light loads and >> less at heavy loads. And the "DC" will have ripple, which makes the >> voltage dip at 120 Hz (100 Hz in the hinterlands). >> >> > > Ah thanks. Good to know about the ripple, as that's certainly something > I'd like to avoid. Back to the Googling board!Search under "active ripple cancelling" - pretty much just an emitter follower with some bias and a not quite as huge electrolytic as you'd need on its own. There is an "insertion loss" but for modest loads it can get you out of a jam if you need a really smooth rail.
Reply by ●May 25, 20142014-05-25
On Sun, 25 May 2014 17:53:03 +0100, "Ian Field" <gangprobing.alien@ntlworld.com> wrote:> > >"Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message >news:llrkq5$hr4$1@news.albasani.net... >> On 5/24/2014 8:48 PM, John Larkin wrote: >>> On Sat, 24 May 2014 20:06:45 -0500, Jurd >> >>> >>> That bridge configuration will in theory charge the caps to 1.41 times >>> the RMS voltage of the transformer secondary, because a sine wave has >>> a peak voltage 1.41x its RMS. >>> >>> In real life you'd typically get more DC than that at light loads and >>> less at heavy loads. And the "DC" will have ripple, which makes the >>> voltage dip at 120 Hz (100 Hz in the hinterlands). >>> >>> >> >> Ah thanks. Good to know about the ripple, as that's certainly something >> I'd like to avoid. Back to the Googling board! > >Search under "active ripple cancelling" - pretty much just an emitter >follower with some bias and a not quite as huge electrolytic as you'd need >on its own.That doesn't help when you're building a power supply. You may as well just connect the rectifier caps to the main linear regulator. That's better, actually; a ripple canceler ahead of the regulator makes things worse. The issue is energy storage. 120 times a second, the transformer output goes to zero volts. If you want to keep powering the load then, the energy has to come from somewhere, and in this case it's the filter caps.
Reply by ●May 25, 20142014-05-25
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message news:e794o9tj2im9tflvlbisagg29g1crl7468@4ax.com...> On Sun, 25 May 2014 17:53:03 +0100, "Ian Field" > <gangprobing.alien@ntlworld.com> wrote: > >> >> >>"Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message >>news:llrkq5$hr4$1@news.albasani.net... >>> On 5/24/2014 8:48 PM, John Larkin wrote: >>>> On Sat, 24 May 2014 20:06:45 -0500, Jurd >>> >>>> >>>> That bridge configuration will in theory charge the caps to 1.41 times >>>> the RMS voltage of the transformer secondary, because a sine wave has >>>> a peak voltage 1.41x its RMS. >>>> >>>> In real life you'd typically get more DC than that at light loads and >>>> less at heavy loads. And the "DC" will have ripple, which makes the >>>> voltage dip at 120 Hz (100 Hz in the hinterlands). >>>> >>>> >>> >>> Ah thanks. Good to know about the ripple, as that's certainly something >>> I'd like to avoid. Back to the Googling board! >> >>Search under "active ripple cancelling" - pretty much just an emitter >>follower with some bias and a not quite as huge electrolytic as you'd need >>on its own. > > That doesn't help when you're building a power supply. You may as well > just connect the rectifier caps to the main linear regulator. That's > better, actually; a ripple canceler ahead of the regulator makes > things worse. > > The issue is energy storage. 120 times a second, the transformer > output goes to zero volts. If you want to keep powering the load then, > the energy has to come from somewhere, and in this case it's the > filter caps.I never said don't use reservoir caps - an unregulated emitter follower with a heavily decoupled base does its best to follow the insignificant ripple on its base.
Reply by ●May 25, 20142014-05-25
On 5/25/2014 12:18 PM, John Larkin wrote:> > That doesn't help when you're building a power supply. You may as well > just connect the rectifier caps to the main linear regulator. That's > better, actually; a ripple canceler ahead of the regulator makes > things worse. > > The issue is energy storage. 120 times a second, the transformer > output goes to zero volts. If you want to keep powering the load then, > the energy has to come from somewhere, and in this case it's the > filter caps. > >So I guess my questions (that I was afraid to ask previously) are: 1) Is the ripple due to C1 and C2 being unable to keep up with the 120hz swing, and 2) Would increasing the value of the output cap (C3) help at all with this? If not, what kinds of design features of a linear regulated power supply am I looking for? Thanks. -J
