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OT low esr capacitor source in canada

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  • OT low esr capacitor source in canada

    Looking for a canadian supplier for switching power supply caps. Not much luck so far. I have not done phone calling yet to my usual suppliers, but their online catalogs don't show parts like these, just regular electrolytics. Anyone know of a source in Canada?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    www.digikey.com (or www.digikey.ca ) are great sites for electronics parts, and have VERY cheap shiping to canada, with insane fast delivery times.
    Free shiping on orders over $200 too iirc.
    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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    • #3
      What do you need and how many?
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      • #4
        Evan, I'm going to hack a few computer power supplies to bring the -12 v output up to the same current capability as the + 12 v output. This will give me + - 12 v, or 24 v at 15 or so amps. I don't need any high current 5 volt outputs, and if I need two polarities at 5 volts for a breadboard to experiment with, I'll use a pair of 5 v regulators.

        It looks like the +12v output has a single 1000 uf cap on it, which my brain says is kind of low for any real current output over a length of time. I'm thinking to boost that to 2000 uf, then I need to add 2000 uf to the - 12v circuit. Times two for two power supplies, it looks like I'll need at least 6 1000 uf caps at 16v. Size won't matter since I'll make my own pc board to mount the parts.

        As you know, there's no room in there to do much modifying, so my plan is to pull most of the output-related parts off from the secondary side of the power supply. The feedback trace to the TL494 will be re-fed through a voltage divider from the +12 v output, which will keep the regulation happening, and probably better on the 12 v outputs. With all of the unneeded parts removed, I might get room inside for a larger rectifier heat sink, which should be the major heat-producing part in there. It won't bother me if it's larger and runs cooler because of that. The capacitors will mount on the secondary pc board which will also carry an output terminal block of some kind.

        I'm thinking to re-wind the inductor that's in the 12v output circuit with heavier wire, but still the same number of turns. I can mount it on the output pc board with the capacitors and output terminals. I'll be getting rid of the rat nest of individual wires-

        Essentially I'll be using the primary, drive, and feedback circuitry as-is, but re-building the secondary circuitry to suit my requirements.

        I'm sure enough that this mod will work, so I want to also modify a higher output power supply later on. In total I'll need about a dozen or so caps.

        I looked at pulling some off an old mb I have, but they are only 6.3 v rated, and anyway I'm not into being the guinea pig to see if the caps are going to live or not.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          I will have a look at my stock later. I have a lot of caps from all sorts of power supplies.
          Free software for calculating bolt circles and similar: Click Here

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          • #6
            Darryl,

            If you just need a powerful 24V or powerful +/-12V it is possible to wire two computer power supplies in series.
            In general the GND and the earth are tied together, but if you remove this connection the output is floating and can be used in series.
            On some power supplies this GND link is just one connection, on others it's more elaborate.
            If you google around you can find some examples of people putting them in series.

            This would seem simpler than rewinding the transformer on one.

            Igor

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            • #7
              You don't need to rewind the output transformer since its allready centertaped.

              You will need to add more rectifyers and rewind the output inductor, it does the voltage matching beween outputs, And the -12v is just a parsistic winding off that inductor, so a new heavy duty winding, and new half bridge will be required to make a high current -12v.
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              • #8
                From the power supply schematic, the output transformer secondary is center-tapped, and the two remaining leads are fed to a dual rectifier, a common cathode. The output from that goes through a funny-looking inductor and on to the capacitors. This gives the + 12 v output. The - 12 v output is taken via a common anode dual rectifier, fed from the same two points on the transformer. The only difference is the rectifier for the negative output is smaller in capacity, and there's another rectifier in series before the voltage makes it to the capacitor. If that dual rectifier was as capable current-wise as the other one, the -12 v output could be rated at the same current level as the + 12 v output. Oh, and I'd have to remove the single rectifier that is in series- I think all it does is reduce the voltage on the - output, since very little current is normally drawn from there in computer use.

                The primary circuit drives the transformer in push-pull, and current is delivered from both alternations. The primary won't know if the negative 12 v output has been upgraded, current wise. What it will know is how much power is being drawn in total. Basically my planned mods will be invisible to the circuitry, and of course it will be up to me to keep the total power draw within the capability stated on the case.

                The torroidal inductor in there is used in a way I'm not familiar with. Directly after the rectifiers is a winding through this torroid core, then it's on to another inductor and the cap. Each rectifier, four in this case, feeds its own winding through the same torroid. In other words, there's four separate coils wound on one core. I'm not sure what purpose this serves, but possibly it's more than just giving some inductance in series from the rectifiers. At any rate, it's these windings that I would consider replacing with a heavier gauge, just to keep some of the losses down. I will in no way be opening up the power transformer to mess with windings. These things are pretty well glued up tight- all that would happen if you tried to get into it is it would break.
                Last edited by darryl; 07-22-2011, 08:43 PM.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                • #9
                  Originally posted by darryl
                  The torroidal inductor in there is used in a way I'm not familiar with. Directly after the rectifiers is a winding through this torroid core, then it's on to another inductor and the cap. Each rectifier, four in this case, feeds its own winding through the same torroid. In other words, there's four separate coils wound on one core. I'm not sure what purpose this serves, but possibly it's more than just giving some inductance in series from the rectifiers. At any rate, it's these windings that I would consider replacing with a heavier gauge, just to keep some of the losses down. I will in no way be opening up the power transformer to mess with windings. These things are pretty well glued up tight- all that would happen if you tried to get into it is it would break.
                  That inductor is wound with a proportional winding from each output to improve "cross-regulation", meaning that a load on one is reflected more equally in others.

                  Otherwise, a load on one that has the feedback from it may cause others to go drastically upwards in voltage, as the PWM duty cycle varies upwards to hold the load.

                  It is usually the main inductor, and the others are more like "hash chokes".

                  If you mess with it, and want the other outputs, keep the windings at same proportional turns ratio. (otherwise delete the other rectifiers). However, more current may end up saturating it, which will not be what you want. PC power supplies CAN be hacked, but they usually are pretty optimized designs, so any changes need to be compensated for. Removing the other unused windings gives more winding window, and also more ampere-turns left for the one(s) you want. But the issue of inductance is still there, the inductance needs to be "designed" for the supply to work well.

                  Some PC supplies are more advanced types, not simple "forward converters", but high efficiency quasi-resonant types, etc, which are only hackable with expert knowledge.
                  Last edited by J Tiers; 07-22-2011, 09:44 PM.
                  1601

                  Keep eye on ball.
                  Hashim Khan

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                  • #10
                    A couple of points- first, I don't want to wire two power supplies together for 24 volts when one will produce it, though I know it could work. Secondly, if I re-wire the output inductor I wouldn't be altering the number of turns on it, just increasing the size of the wire (or winding it bi or tri-filar). I think in this case I will be eliminating the 5 v output and the -5 v output, so I would only need two windings through the inductor. In addition to making the gauge larger, I would wind the same number of turns through it for the -12 v output that already exist for the +12 v output.

                    Referring to my schematics, some have the feedback coming from the +5 output, others have it coming from the +12 output. I will have to physically follow the feedback trace in the power supplies I'm using to make sure I don't leave it open circuit when I pull the parts out that won't be needed.

                    Here's something I didn't notice before- one of the schematics shows some very low capacitance values on the outputs, like 1 uf. They must be relying on the motherboard to provide sufficient filtering. The ATX 200 is like this.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                    • #11
                      Eliminating the 5V will save lots of ampere-turns on the inductor, since the 5V or a lower voltage is usually the highest current output.

                      But the 5V MAY be a primary regulating output, as you say...... "somebody has to be the boss". It will be hard to move that to a different winding unless you know some things, and do some "design". Or you may get lucky.

                      And, some supplies COMBINE two feedbacks, making it difficult to separate them
                      1601

                      Keep eye on ball.
                      Hashim Khan

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                      • #12
                        Iv never seen a supply with low output capacitance on anything but the -12v and -5v lines, it just would'nt work without localized capacitance on the +5v/3.3v and 12v lines, the wires have too much resistance to the motherboard to use the motherboard. (Not to mention hard drives and such have next to no onboard filtering, and motherboards only have enough filtering for there own needs and would likey pop if they had to filter psu ripple too)

                        That said, Iv never seen -12v generated from the transformer itself, its allways a parasitic winding on the common inductor (ie, ground->inductor coil->diode->cap, it uses voltage induced from the buck cycle of the other supplys to actualy produce -12v) And then -5v is generated from a 7905 off -12v (making -5v by far the best regulated, lowest noise supply of a ATX psu!)

                        Often ATX supplys will have a compairitor or two that will act as an overvoltage cutout, and sometimes overcurrent cutout (they usally have some method of overcurrent cutout, however its more for protecting from shorts/sudden huge loads then overheating from overcurrent), Not sure if any of them have undervoltage cutouts, However a GOOD psu should'nt put powergood high untill all voltages are up to spec (Many bad psus tie power good to +5v)

                        And yes, psus do vary a little from power supply to power supply, however most fall into a few catagorys of design for the 150~400 watt range. Bigger psus often start using a diffrent design that iv not really looked into because I quit PC repair and stoped taking psus apart before over 400W psus became commonish.

                        And yes, +5v will be the master regulated output, With 3.3v regulated by its own TO-92 transistor+another inductor+Black Magic (Honest! 30A at 3.3v is regulated by a TO-92!) and some extra circuity. the +12v is regulated just by the inductor since nothing that uses 12v is gonna care much if its 11v or 13v. (the inductor acts as a transformer, Except sideways... Basicly, Every coil to ground will produce the same 'ratio' voltage as its turn ratio during the 'buck' stage (Input transistors off, Current flowing from ground (through off transformer) through diodes (not important) to inductor to output.)

                        Note very little current flows to +12v during the 'on' stage of the input transistors, Because the transformer is actualy 20:10:0:10:20 and the 20v taps feed the 12v, so the ratio doesnt work out to allow much current flow during the on stage. Also results in a typical +10v to the 12v output when there is no 5v load to cause higher duty cycle and proper matching via the inductor.
                        Last edited by Black_Moons; 07-23-2011, 10:53 AM.
                        Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                        • #13
                          Well now from all you guys have said and from what I've read, I feel confident that this mod will work out fine. The TL494 ic has been common in car amplifiers for years, and I did spend some time studying it both in aid of servicing equipment and for use on my own. I have an application guide on it, and I don't think I'm going to have a problem maintaining the output voltage properly through the use of the feedback terminal.

                          I did find some old vcr power supplies that have switching rated capacitors in them. Have not checked the values, but there may be some usable caps I can rob. They sure are small physically- it's hard to imagine them handling much ripple current, but then depending on the waveform feeding the output circuitry, they may only need to deliver short spikes of current between pulses from the rectifiers. The average power dissipation in the caps is likely to be quite low- maybe I don't need to worry about having enough capacitance.

                          It's hot here today, much nicer to be in the shop. Maybe I'll start to strip parts and get this phase of the project in gear.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                          • #14
                            You all have tolerated this OT thread very well. Some of you are into electronics in some ways and probably don't object- others, well, it doesn't hurt to learn some things about electronics- some of it is useful in the metalworking field.

                            Just wanted to pose a question to a few in the biz- I've got one of my power supplys unpopulated of parts that won't be needed in the finished version. One of those parts is a dual 30amp, 45 volt rectifier. It was in the 5 volt circuit- I want to use it in the 12 volt circuit. Am I going to get in trouble with the voltage rating? I'm thinking no, because the reverse voltage it will see is double the output voltage plus perhaps 20% for spikes, so about 30 volts. Because the transformer is never unloaded for either polarity of voltage swing, there shouldn't be a major spike being generated. I'm concerned though that the addition of the output inductor would allow higher spikes to occur on the rectifier side. Does this make sense?

                            I can always 'scope the secondary side of things to see what the waveforms look like, using an unmodified power supply.
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                            • #15
                              Switching supplies are unlike others, the voltage requirements may be lots higher than you think.

                              The power supply transformer turns ratio is almost certainly a lot different than it seems like it should be... because the effective ratio is an average, and the thing regulates over a wide range by varying the pulse width.

                              Translated, that means that the supply applies higher voltage pulses to the inductor, which (with the capacitor) averages them. The 12V winding may get 20V or more applied to the inductor depending on the design, and mains voltage, etc.. But the pulses are short, and the average is 12V.

                              Reverse voltage pulses of similar voltage will probably occur, and it is wise to allow at least 30% of the total extra for spikes.

                              When switch is "off", with significant current flow (continuous conduction mode), the input side of the inductor will be just below ground. but at low current it may not be, it may have "run dry" and be "ringing" at some intermediate voltage.

                              So you need to figure that you may need 20V, plus 20V, plus 30%. Or more. Depends on the design.

                              So..... 45V might work, but it looks too close for me.
                              1601

                              Keep eye on ball.
                              Hashim Khan

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