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| I have a short ( i think) and don't know where to start |
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| Gregg:
I think nick_d is on the right track; capacitors seem to have been left out of the discussion but certainly could be the problem. You could try connecting your 35V DC power supply at full voltage but a couple amps current limit to each half of your power supply output and see if it will charge the caps or not. This would be quicker than unsoldering all of them. If the caps are good, the power supply should go into current limit at a low voltage and slowly increase voltage until it reaches full voltage as the caps charge. You may find only one half of your supply is at fault (pun intended). If you have to take the caps off the board, you can test each one with the variable bench power supply in a similar manner, they should accept a charge and hold a slowly dropping charge with a high impedance multimeter when the power is removed. Follow the traces on the actual board to make sure none of the electrolytics are installed reverse polarity. |
| Hextejas:
--- Quote from: ebastler on December 19, 2018, 10:05:05 pm --- --- Quote from: Hextejas on December 19, 2018, 05:30:52 pm ---Picture attached. --- End quote --- But you did not actually install the resistor as shown in your schematic (in parallel with the wire), right? It needs to be in series, i.e. you must disconnect the original wire or trace. Apologies if this was already clear. --- End quote --- It was installed in series. |
| Hextejas:
Before I start at this again, I think I will post some of the specs. Capacitors: C1 ~ C4 = 8200uf 50v C5, C6, C11, C12 = 100nf 850vdc C10 = 1.5uf 450vdc C13, C14 = 100uf 50v ------------- And some readings that I took before it burned up. Transformer out = 39vac V+ = 53 V- = 53 Why I chose such an oversized toroid, i cannot recall, but if i continue to struggle with this i think that i will exchange it. Ok, that's it and I replaced 2 of the diodes so let me get back to testing. Thanks again |
| GeoffreyF:
--- Quote from: Hextejas on December 20, 2018, 12:42:09 am --- --- Quote from: ebastler on December 19, 2018, 10:05:05 pm --- --- Quote from: Hextejas on December 19, 2018, 05:30:52 pm ---Picture attached. --- End quote --- But you did not actually install the resistor as shown in your schematic (in parallel with the wire), right? It needs to be in series, i.e. you must disconnect the original wire or trace. Apologies if this was already clear. --- End quote --- It was installed in series. --- End quote --- You expect help with a schematic where it is in parallel? If you installed it in series, please provide an actual schematic which goes with your project! The schematic you provided, as I stated awhile back, is rather strange. I would suggest you get a book such as "the Art of Electronics", "Practical Electronics for inventors", learn about capacitance, inductance, resistance. Look at other designs for power supplies. I don't think you will solve the problems you are having without more learning of the fundamentals. |
| nick_d:
If the transformer output is 39VAC then the peak is 39 * 1.414 = 55.146 VDC. In the bridge rectifier 2 diodes are conducting at a time and these are in series with the 55.146 VDC, each giving a drop of about 1 VDC under load. Thus the 39 VAC measurement at the secondary is consistent with the stated 53 VDC output measurement. You didn't notice that this is over-voltage for your 8200uF 50 VDC reservoir capacitors? As I mentioned they don't give any real margin, you are allowed to operate them at 50 VDC and no more. Otherwise, bad things happen. Problems can be immediate or take time to manifest. Capacitor over voltage may be damaged over time reducing their voltage limit even further. cheers, Nick |
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