Hi The first thing I see as a problem is the toroid transformer. At 60 Hz none of the common cores are going to work. You really need some steel in the core. I have seen some transformers made for 60 Hz wound on a spring steel toroid core. This is not something that is easy to build. I would use a small transformer from radio shack or even better a door bell transformer as they are very well shielded to meet class 2 UL requirements. On the input to the transformer use 2 .01 uf 600 volt caps from each input wire to earth ground. I would then come out to a bridge diode rectifier bypassed by .01uf caps across each diode. Then into a large filter cap about 2000-4000 uf also bypassed with a .01 uf disk across the filter cap for the RF bypass. If you are using a 10 volt doorbell transformer you should have about 14 volts DC at this point. From there I would use a three terminal regulator like a LM117 or LM337 followed by a 10 uf filter and finally pass both the plus and minus wires through a 1 inch ferrite toroid core several turns. If you would like me to draw up a schematic for you I could email it to in PDF format. There are many other ways to do this this is just one off the top of my head. Someone may come up with a better idea but these simple power supplies are fun and easy to build
Don Brown KD5NDB ----- Original Message ----- From: "Daniel Reynolds" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, January 10, 2006 8:54 AM Subject: [Elecraft] OT: Help designing power supply and toroid transformer > This is slightly off topic - but since there is such a generous group of > guys > that are very knowledgable in electronics (and since my brain is a little > soft > in this area), I think I'll toss this request out and hope for the best. > > First off - please reply off the list since this does not pertain directly > to > Elecraft equipment (except that it might be fun to eventually take the > same > design and build a larger p/s for the K2/QRP). > > My goal is to build a non-switching, voltage regulated 9V/1.5A power > supply > with enough isolation and filtering to keep RFI out of a Grundig Satellite > 800. > My father has one of these radios, and so do I (unfortunately, he lives > out of > state - so I couldn't compare the two radios and p/s side by side). When I > visited him over the holidays, I discovered that the OEM power supply my > father > has is either producing RFI or is conducting RFI, because he can tune in > daytime AM/MW signals from over 100 miles away when running the thing on > batteries, but he has a hard time with signals beyond 50 miles away as > soon as > he plugs the power supply into the outlet (this was AFTER we already > turned off > the worst RFI generating offenders in the house). > > The Grundig Sat 800 power requirements are spec'd at 7-10V DC up to 1 Amp > (530mA with 1/4W output and lamp off, and 830mA with 1/4W output and lamp > on), > and it says in the manual that the supplied adapter is 9V/1.5A. > > I've got an old 1987 copy of the handbook which I've got up in the attic > for > reference, and I realize some of the basic things (from my license/testing > days) that go into a power supply (transformer, diodes, capacitors, > inductors, > regulators). I want to actually build my own power supply from scratch - > starting with the transformer. If I'm not mistaken, I should be able to > use a > medium-large toroid core and some heavy wire to do this. > > [I could go down to Radio Shack and buy a wall wart, but I want to > actually > make something that is going to work 'really well' in terms of reducing > RFI > passing through the AC power supply - something that a cheap power adapter > probably won't be designed for.] > > So - here's where I'm hoping you can help me with... > > What core (size and material composition) should I use for transforming an > AC > signal? > > How many windings of what kind of wire would be the 'best' for the power > requirements of this supply? > > Should I build a 120/12V transformer and voltage regulate it down to 9V, > or > would it be better to simply build a 120/9V transformer and rectify the AC > and > smooth it out with passive components? > > How can I best filter out RFI being carried on the AC line? > > Are there any other considerations I should be aware of? > > Do you know of any helpful websites I should visit (I haven't googled this > topic yet)? > > I'm sorry to waste the bandwidth of others here. > > Any help supplied is greatly appreciated! > > - Daniel AA0NI > Oklahoma City > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
