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Power supply transformer advice
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Hi I am building a (240volt in) 13.8 volt (out) PSU along the lines of this plan..
http://www.warc.org.uk/proj_psu.php it is very similar to the old Marchwood practical wireless unit from the early 1980's using 2n3055 transistors. My question. The spec says the transformer must have a secondary of 16.5 volt. Now when I last built a PSU using a similar plan the transformer output could be much higher, in the region of 15 to 20 volts. I have a Talema branded toroid I want to use, its spec is as follows (from maker) +++++ Toroidal transformer type 5028-P3S03: Prim: 0-110V-230V-240V orange-yellow-violet-blue Sec1: 20V/6A green-red Sec2: 20V/6A black-white Sec3: 55V/2,5A braun-braun If you use only the 2x20V you can get out 9A of each winding (no load on the 55V) +++++ as you can see the secondary output is 20 volt, now folks do you think this transformer will suffice at 20 volts, or should I removed a little winding to bring it down? 73 Andy PS the variac is just there for scale. |
Power supply transformer advice
In article ,
Andy GD1MIP wrote: Hi I am building a (240volt in) 13.8 volt (out) PSU along the lines of this plan.. http://www.warc.org.uk/proj_psu.php it is very similar to the old Marchwood practical wireless unit from the early 1980's using 2n3055 transistors. My question. The spec says the transformer must have a secondary of 16.5 volt. Now when I last built a PSU using a similar plan the transformer output could be much higher, in the region of 15 to 20 volts. I have a Talema branded toroid I want to use, its spec is as follows (from maker) +++++ Toroidal transformer type 5028-P3S03: Prim: 0-110V-230V-240V orange-yellow-violet-blue Sec1: 20V/6A green-red Sec2: 20V/6A black-white Sec3: 55V/2,5A braun-braun If you use only the 2x20V you can get out 9A of each winding (no load on the 55V) +++++ as you can see the secondary output is 20 volt, now folks do you think this transformer will suffice at 20 volts, or should I removed a little winding to bring it down? 73 Andy PS the variac is just there for scale. By using it the way it is your only design worry is that you will be dumping more power across the 2N3055 Regulator Transistors, and will need more of them, for the same current output, due to Dissipation Limits of the heatsinks and transistor cases, because of the higher Voltage Drop across the regulators. Also recognise that you will have a much higher DC Voltage going into the regulators, after some Capacitor Filtering. Likely up near 25 Vdc, which means you will be dumping roughly 50% of the provided transformer power in the Regulation System. |
Power supply transformer advice
On Tue, 15 Sep 2009 17:12:41 +0100, Andy GD1MIP wrote:
Hi I am building a (240volt in) 13.8 volt (out) PSU along the lines of this plan.. http://www.warc.org.uk/proj_psu.php it is very similar to the old Marchwood practical wireless unit from the early 1980's using 2n3055 transistors. My question. The spec says the transformer must have a secondary of 16.5 volt. Now when I last built a PSU using a similar plan the transformer output could be much higher, in the region of 15 to 20 volts. I have a Talema branded toroid I want to use, its spec is as follows (from maker) +++++ Toroidal transformer type 5028-P3S03: Prim: 0-110V-230V-240V orange-yellow-violet-blue Sec1: 20V/6A green-red Sec2: 20V/6A black-white Sec3: 55V/2,5A braun-braun If you use only the 2x20V you can get out 9A of each winding (no load on the 55V) +++++ as you can see the secondary output is 20 volt, now folks do you think this transformer will suffice at 20 volts, or should I removed a little winding to bring it down? 73 Andy PS the variac is just there for scale. If you _really_ want to do some work you could remove all the secondary windings and replace them with a single 16V winding; that'll give you 25% more current just from the drop to 16V from 20V, plus whatever extra power you can take because you used the space formerly taken up by the 55V winding to put in bigger wire. Lots -o- work, though. -- www.wescottdesign.com |
Power supply transformer advice
"Andy GD1MIP" wrote in message
... Hi I am building a (240volt in) 13.8 volt (out) PSU along the lines of this plan.. http://www.warc.org.uk/proj_psu.php it is very similar to the old Marchwood practical wireless unit from the early 1980's using 2n3055 transistors. My question. The spec says the transformer must have a secondary of 16.5 volt. Now when I last built a PSU using a similar plan the transformer output could be much higher, in the region of 15 to 20 volts. I have a Talema branded toroid I want to use, its spec is as follows (from maker) +++++ Toroidal transformer type 5028-P3S03: Prim: 0-110V-230V-240V orange-yellow-violet-blue Sec1: 20V/6A green-red Sec2: 20V/6A black-white Sec3: 55V/2,5A braun-braun If you use only the 2x20V you can get out 9A of each winding (no load on the 55V) +++++ as you can see the secondary output is 20 volt, now folks do you think this transformer will suffice at 20 volts, or should I removed a little winding to bring it down? 73 Andy PS the variac is just there for scale. -- Andy GD1MIP The transformer will work in the project that you are looking at, however, the pass transistors will run significantly hotter than if you used the transformer voltage specified. Your transformer will produce about 28VDC after the rectifier/filter. The pass transistors must drop the difference between 28 VDC and the output voltage (13.8VDC), which is roughly 14 VDC. Multiply that by the output current to get the power that the pass transistors must dissipate. Watts = Voltage * Current. Watts create heat, which must be dissipated by the heatsink. Since you're wanting some respectable current from this project, you could do as you suggested; remove a few windings from the 20VAC secondaries to reduce the power that the pass transistors dissipate. But, depending on the construction of the transformer, it might be difficult to do. Another way to reduce the voltage from the transformer is to put a "bucking" transformer in the primary of your transformer to reduce the primary voltage to it. -- Dave M masondg44 at comcast dot net |
Power supply transformer advice
On Sep 15, 12:12*pm, Andy GD1MIP
wrote: Hi *I am building a (240volt in) 13.8 volt (out) PSU *along the lines of this plan..http://www.warc.org.uk/proj_psu.php*it is very similar to the old Marchwood practical wireless unit from the early 1980's using 2n3055 transistors. My question. The spec says the transformer must have a secondary of 16.5 volt. *Now when I last built a PSU using a similar plan the transformer output could be much higher, in the region of 15 to 20 volts. I have a Talema branded toroid I want to use, its spec is as follows (from maker) +++++ Toroidal transformer type 5028-P3S03: Prim: 0-110V-230V-240V orange-yellow-violet-blue Sec1: 20V/6A green-red Sec2: 20V/6A black-white Sec3: 55V/2,5A braun-braun If you use only the 2x20V you can get out 9A of each winding (no load on the 55V) +++++ as you can see the secondary output is 20 volt, *now folks do you think this transformer will suffice at 20 volts, *or should I removed a little winding to bring it down? 73 Andy PS the variac is just there for scale. -- Andy GD1MIP As others have indicated the increased voltage will cause the transistors to have to dissipate more power but the result will be better regulation. I recommend that you don't use the 3055 transistors, there are better choices. I blew many of them before replacing them with ECG 181, there is a 2N number this is equivalent to but I cant remember it right now. Jimmie |
Power supply transformer advice
Andy GD1MIP wrote:
Hi I am building a (240volt in) 13.8 volt (out) PSU along the lines of this plan.. http://www.warc.org.uk/proj_psu.php it is very similar to the old Marchwood practical wireless unit from the early 1980's using 2n3055 transistors. My question. The spec says the transformer must have a secondary of 16.5 volt. Now when I last built a PSU using a similar plan the transformer output could be much higher, in the region of 15 to 20 volts. I have a Talema branded toroid I want to use, its spec is as follows (from maker) +++++ Toroidal transformer type 5028-P3S03: Prim: 0-110V-230V-240V orange-yellow-violet-blue Sec1: 20V/6A green-red Sec2: 20V/6A black-white Sec3: 55V/2,5A braun-braun If you use only the 2x20V you can get out 9A of each winding (no load on the 55V) +++++ as you can see the secondary output is 20 volt, now folks do you think this transformer will suffice at 20 volts, or should I removed a little winding to bring it down? 73 Andy PS the variac is just there for scale. Find a 240/50 volt transformer , and wire the 50 volt output in antiphase with the mains input to the target transformer, and don't fool with windings at all.... Brian W |
Power supply transformer advice
On Sep 16, 9:41*am, brian whatcott wrote:
Andy GD1MIP wrote: Hi *I am building a (240volt in) 13.8 volt (out) PSU *along the lines of this plan.. http://www.warc.org.uk/proj_psu.php*it is very similar to the old Marchwood practical wireless unit from the early 1980's using 2n3055 transistors. My question. The spec says the transformer must have a secondary of 16.5 volt. *Now when I last built a PSU using a similar plan the transformer output could be much higher, in the region of 15 to 20 volts. I have a Talema branded toroid I want to use, its spec is as follows (from maker) +++++ Toroidal transformer type 5028-P3S03: Prim: 0-110V-230V-240V orange-yellow-violet-blue Sec1: 20V/6A green-red Sec2: 20V/6A black-white Sec3: 55V/2,5A braun-braun If you use only the 2x20V you can get out 9A of each winding (no load on the 55V) +++++ as you can see the secondary output is 20 volt, *now folks do you think this transformer will suffice at 20 volts, *or should I removed a little winding to bring it down? 73 Andy PS the variac is just there for scale. Find a 240/50 volt transformer , and wire the 50 volt output in antiphase with the mains input to the target transformer, and don't fool with windings at all.... Brian W- Hide quoted text - - Show quoted text - 240 volt input with 55 volts (antiphase) i.e. 'bucking' the 240 input is 240 minus 55 = 185 volts. The input voltage being educed from 240 to 185 volts. And 185/240 = 0.77 With that the two remaining secondaries would be 20 x 0.77 = 15.4 volts. Maybe that's a little bit too low for what is needed? But worth a try? But also if the 55 and 240 windings are connected in series (aiding or in-phase) and 240 is applied to that; we could have a 240 + 55 = 295 winding. Then with 240 connected to what is now, in effect, a 295 volt winding? So 240/295 = 0.81 And 20 x 0.81 = 16.27 Very close to 16.5? Also' and if NOT with two 6 amp rated secondaries I would certainly 'try' getting 9 amps from each of them. BTW the insulation of any secondary connected in series with the mains voltage primary must have adequate insulation to withstand peak mains voltages (about 340 v AC). I haven't done this at 140 volts but have done it at 120 volts; by connecting 12 volt secondaries in series with the input to simulate voltage increase/decrease of plus/minus 10% etc. It worked fine when I didn't have a variac! |
Power supply transformer advice
Andy GD1MIP wrote: Hi I am building a (240volt in) 13.8 volt (out) PSU ... the transformer must have a secondary of 16.5 volt. ... I have a Talema branded toroid ... Toroidal transformer type 5028-P3S03: Prim: 0-110V-230V-240V orange-yellow-violet-blue Sec1: 20V/6A green-red Sec2: 20V/6A black-white Sec3: 55V/2,5A braun-braun If you use only the 2x20V you can get out 9A of each winding (no load on the 55V) +++++ ...do you think this transformer will suffice at 20 volts?... 73 Andy [brian] Find a 240/50 volt transformer , and wire the 50 volt output in antiphase with the mains input to the target transformer, and don't fool with windings at all.... [Stan] 240 volt input with 55 volts (antiphase) i.e. 'bucking' the 240 input is 240 minus 55 = 185 volts. The input voltage being reduced from 240 to 185 volts. And 185/240 = 0.77 Make that 240 V AC less 50 V AC = 190 V AC input to the toroid. That would provide 190/240 X 20 volts = 15.83V Close enough. [Stan] With that the two remaining secondaries would be 20 x 0.77 = 15.4 volts. Maybe that's a little bit too low for what is needed? But worth a try? But also if the 55 and 240 windings are connected in series (aiding or in-phase) and 240 is applied to that; we could have a 240 + 55 = 295 winding. Then with 240 connected to what is now, in effect, a 295 volt winding? So 240/295 = 0.81 And 20 x 0.81 = 16.27 Very close to 16.5? Well, let's see now. If you choose that rather intriguing approach of applying its own secondary to buck the input, what might the 20 volts outputs really become? 240 volts input into a 240 + 55 volt winding pair means that the 240 volt input winding gets 240 / 295 volts, so the outputs would be (50 V nominal) = 40.7 volts and (20 volt nominal) = 16.3 volts But WAIT: that 50 volt winding does NOT develop 50 volts, but rather 40.7 volts so the 240 V input winding gets 240V - 40.7 volts = 199.3 V So the 20 Volt output is 199.3/240 volt X 20 V = 16.6 Volts....( or a smidgeon higher?) This sounds good! [Stan] Also' and if NOT with two 6 amp rated secondaries I would certainly 'try' getting 9 amps from each of them. BTW the insulation of any secondary connected in series with the mains voltage primary must have adequate insulation to withstand peak mains voltages (about 340 v AC). I haven't done this at 140 volts but have done it at 120 volts; by connecting 12 volt secondaries in series with the input to simulate voltage increase/decrease of plus/minus 10% etc. It worked fine when I didn't have a variac! Actually, with careful wiring, this concern for increased PDs on the secondaries is unneeded. If the secondary bucking windings are placed on the neutral end of the supply, then the increase in the peak primary PD is percentage wise quite small.... In summary, using secondary windings of the SAME transformer to buck the mains input is a neat idea if you can find the ratios you need, and doesn't seem to add much risk to the enterprise Brian W |
Power supply transformer advice
Andy GD1MIP wrote:
Hi I am building a (240volt in) 13.8 volt (out) PSU ... the transformer must have a secondary of 16.5 volt. I have a Talema branded toroid I want to use, its spec is as follows (from maker)... 73 Andy Now that the ideas are cooking.... consider this. 1100 watt defunct microwaves can be had for the asking. They have a particular transformer core design that makes it easy to saw off the 1 KV secondary, and with the generous core window, you could wind 18 to 20 turns of wire good for 10 amps. The turns per volt is not much over 1 tpv.... And you have a decent rectifier diode for the spares box too.... Admitted - a bandsaw in the workshop makes a 15 minute job out of this transformer hack.(if you don't nick the primary) Brian W KA5WOG |
Power supply transformer advice
On Sep 16, 8:46*pm, brian whatcott wrote:
Andy GD1MIP wrote: Hi *I am building a (240volt in) 13.8 volt (out) PSU ... * the transformer must have a secondary of 16.5 volt. I have a Talema branded toroid I want to use, its spec is as follows (from maker)... 73 Andy Now that the ideas are cooking.... consider this. 1100 watt defunct microwaves can be had for the asking. * * They have a particular transformer core design that makes it easy to saw off the 1 KV secondary, and with the generous core window, you could wind 18 to 20 turns of wire good for 10 amps. The turns per volt is not much over 1 tpv.... * And you have a decent rectifier diode for the spares box too.... Admitted - a bandsaw in the workshop makes a 15 minute job out of this transformer hack.(if you don't nick the primary) Brian W KA5WOG Brian, I have done this with old uwave transformers, the ones I could knock out the magnetic shunt with a hammer and punch, but on the newer ovens the shunt is a weld. Will these still work? Jimmie |
Power supply transformer advice
JIMMIE wrote:
On Sep 16, 8:46 pm, brian whatcott wrote: Andy GD1MIP wrote: Hi I am building a (240volt in) 13.8 volt (out) PSU ... the transformer must have a secondary of 16.5 volt. I have a Talema branded toroid I want to use, its spec is as follows (from maker)... 73 Andy Now that the ideas are cooking.... consider this. 1100 watt defunct microwaves can be had for the asking. They have a particular transformer core design that makes it easy to saw off the 1 KV secondary, and with the generous core window, you could wind 18 to 20 turns of wire good for 10 amps. The turns per volt is not much over 1 tpv.... And you have a decent rectifier diode for the spares box too.... Admitted - a bandsaw in the workshop makes a 15 minute job out of this transformer hack.(if you don't nick the primary) Brian W KA5WOG Brian, I have done this with old uwave transformers, the ones I could knock out the magnetic shunt with a hammer and punch, but on the newer ovens the shunt is a weld. Will these still work? Jimmie I left the magnetic bypass leg in the core on the one I used for a spot weld source. Its a security blanket against core saturation due to the magnetron,I reckon. Brian W |
thanks for all the comments folks. I considered all and decided to take the learning curve. I was lucky the transformer was only held togethert by a non sticky clear plastic wrap.
Having unwrapped the windings I took the 55v secondary off completely. Re the 20v secs, I worked out the value in volts of each turn, then removed 8 turns from each of the 4 secs. I now have 16.48 volt (near enough to 16.5 volt for me) I had to re-space the secondary windings (i did it to look neat - there may be a sound physics reason too). Lets hope it works. Before the 'surgery' the 20 volt secondaries were good for 18amp in parallel (according to manufacturer). Tim stated that lowering the volts to 16 will give 25% more current. so I should be good for at least 20 amps. I only wanted 15 so the margin is ok. thanks again folks Andy |
Power supply transformer advice
On Thu, 17 Sep 2009 11:55:59 -0500, brian whatcott wrote:
JIMMIE wrote: On Sep 16, 8:46 pm, brian whatcott wrote: Andy GD1MIP wrote: Hi I am building a (240volt in) 13.8 volt (out) PSU ... the transformer must have a secondary of 16.5 volt. I have a Talema branded toroid I want to use, its spec is as follows (from maker)... 73 Andy Now that the ideas are cooking.... consider this. 1100 watt defunct microwaves can be had for the asking. They have a particular transformer core design that makes it easy to saw off the 1 KV secondary, and with the generous core window, you could wind 18 to 20 turns of wire good for 10 amps. The turns per volt is not much over 1 tpv.... And you have a decent rectifier diode for the spares box too.... Admitted - a bandsaw in the workshop makes a 15 minute job out of this transformer hack.(if you don't nick the primary) Brian W KA5WOG Brian, I have done this with old uwave transformers, the ones I could knock out the magnetic shunt with a hammer and punch, but on the newer ovens the shunt is a weld. Will these still work? Jimmie I left the magnetic bypass leg in the core on the one I used for a spot weld source. Its a security blanket against core saturation due to the magnetron,I reckon. Brian W I _think_ that shunt serves to limit the secondary current and therefore protect the magnetron. I should go through the math on that... -- www.wescottdesign.com |
Power supply transformer advice
On Thu, 17 Sep 2009 23:08:23 +0100, Andy GD1MIP wrote:
thanks for all the comments folks. I considered all and decided to take the learning curve. I was lucky the transformer was only held togethert by a non sticky clear plastic wrap. Having unwrapped the windings I took the 55v secondary off completely. Re the 20v secs, I worked out the value in volts of each turn, then removed 8 turns from each of the 4 secs. I now have 16.48 volt (near enough to 16.5 volt for me) I had to re-space the secondary windings (i did it to look neat - there may be a sound physics reason too). Lets hope it works. Before the 'surgery' the 20 volt secondaries were good for 18amp in parallel (according to manufacturer). Tim stated that lowering the volts to 16 will give 25% more current. so I should be good for at least 20 amps. I only wanted 15 so the margin is ok. No no. Tim stated that _after_ you _completely_ rewind the secondaries with wire that's got 25% more cross-sectional area you can run 25% more current. if you increased the secondary current to 20A the per-inch dissipation in the secondary would go up by about 56%; you can probably run more than 16A in the secondaries now because they're more spread out and because the primary will be cooler, but I very much doubt that you can go as high as 20A and maintain the same temperature. -- www.wescottdesign.com |
Power supply transformer advice
Tim Wescott wrote:
.... 1100 watt defunct microwaves can be had for the asking. They have a particular transformer core design that makes it easy to saw off the 1 KV secondary, and with the generous core window, you could wind 18 to 20 turns of wire good for 10 amps. The turns per volt is not much over 1 tpv.... And you have a decent rectifier diode for the spares box too.... Admitted - a bandsaw in the workshop makes a 15 minute job out of this transformer hack.(if you don't nick the primary) Brian W KA5WOG Brian, I have done this with old uwave transformers, the ones I could knock out the magnetic shunt with a hammer and punch, but on the newer ovens the shunt is a weld. Will these still work? Jimmie I left the magnetic bypass leg in the core on the one I used for a spot weld source. Its a security blanket against core saturation due to the magnetron,I reckon. Brian W I _think_ that shunt serves to limit the secondary current and therefore protect the magnetron. I agree.... Brian W |
Power supply transformer advice
Andy GD1MIP wrote:
Hi I am building a (240volt in) 13.8 volt (out) PSU along the lines of this plan.. http://www.warc.org.uk/proj_psu.php it is very similar to the old Marchwood practical wireless unit from the early 1980's using 2n3055 transistors. My question. The spec says the transformer must have a secondary of 16.5 volt. Now when I last built a PSU using a similar plan the transformer output could be much higher, in the region of 15 to 20 volts. I have a Talema branded toroid I want to use, its spec is as follows (from maker) +++++ Toroidal transformer type 5028-P3S03: Prim: 0-110V-230V-240V orange-yellow-violet-blue Sec1: 20V/6A green-red Sec2: 20V/6A black-white Sec3: 55V/2,5A braun-braun If you use only the 2x20V you can get out 9A of each winding (no load on the 55V) +++++ as you can see the secondary output is 20 volt, now folks do you think this transformer will suffice at 20 volts, or should I removed a little winding to bring it down? 73 Andy PS the variac is just there for scale. Is this transformer potted in the middle? If it isn't you could add some turns and connect them in series with the primary to reduce the secondary voltages. This would be a lot easier than removing turns from the secondaries, especially if the secondaries are NOT wound on top! |
Power supply transformer advice
On Sep 20, 7:43 am, Kenneth Scharf wrote:
Andy GD1MIP wrote: Hi I am building a (240volt in) 13.8 volt (out) PSU along the lines of this plan.. OK, we are all being technical here - can I ask if the crowbar IC is still available? Is the specified relay still available? At an overvoltage condition,there will be over 200 watts being dissipated in the 2r2 resistor in series with the SCR - hopefully it wont instantaneously go open circuit....if the overvoltage protection works, wont the thing go into cyclic oscillation as it attempts to restart?....(not sure here, perhaps the gate never goes low enough for this) LM723 regulators tend to be a bit unstable - VHF ground plane type construction is recommended. The transformer ratings - the manufacturer rates them at a specified current for a reason. For low duty cycle use, eg SSB, you can get away with pulling more current. But a solid state Class C FM amplifier? - also, as mentioned, there is very little headroom at 16v - 18v would be better.....and thats assuming the mains input voltage is reference quality - here in OZ, its a design variable, up to 20% fluctuations are not uncommon, especially at the end of a long run. Motorola 2N3055 transistors are fine - BUT- when the original Motorola patents expired, and Motorola stopped making them, a lot of substandard crappy ones (typically Eastern European) came onto the market. Be warned, they can be unpredictable. TO3 is a pretty well obsolete case style anyway. Good luck. And the Motorola symbol was widely forged as well. The above, of course, are my Neanderthal rantings on a newsgroup and will no doubt start an impassioned debate on points of theory , or maths, or how it was done in 1935. Remember, free advice is worth what you pay for it. But I would advise putting a 5w 15V zener across the output terminals, and before that put a 30amp fuse. Minimal cost for added insurance. Go for it - build it, experiment. Blowing something up is always a fantastic spur to learn the correct theory for the application..if it works first up, then its just a mechanical exercise. Andrew VK3BFA. |
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