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| My newly built power supply is blowing fuses. |
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| Hextejas:
It also blew out a 24V AC wall wart. As I first plugged the power supply into a toroidal transformer, it blew the 3.15 slow blow fuse. So I thought that I would reduce the voltage by using the transformer and maybe get it to slightly work so that I could see what was wrong. Nope, it blew out the wall wart. So, here is the schematic and a picture. Before all this, I put a thermistor in the input to the transformer and it stopped the fuse blowing for the toroid but apparently the power supply itself also has issues. I dont know where to start. I had a 2nd thought. The xformer is a 35-0-35 whereas the design called for 18-0-18. The output of the xformer is 38v. Is that too much for the design of the power supply ? Should some of the components be beefed up ? |
| Zero999:
You have 16.5mF on the output of each bridge rectifier, so this is exactly what you should expect to happen. Presumably by thermistor, you're taking about a resistor with a negative temperature coefficient? If so, that's exactly what you should use. |
| Kleinstein:
If the supply (rectifier and filter) is build for 18 V, the capacitors and maybe the diodes may not like twice the voltage. For 36 V AC the capacitors should be good for 63 V at least, 50 V types would be too low. The diodes, worst case see the peak to peak voltage, so something like nearly 3 times the RMS value. So 100 V diodes would be already too close. The TO220 like case could be schottky diodes, and these tend to be low voltage only. For a first test one would use a large (e.g. 1 K ) series resistors, just to check for a dead short and maybe give the capacitors time to reform. |
| cbc02009:
--- Quote from: Hextejas on December 30, 2018, 07:50:36 pm ---It also blew out a 24V AC wall wart. As I first plugged the power supply into a toroidal transformer, it blew the 3.15 slow blow fuse. So I thought that I would reduce the voltage by using the transformer and maybe get it to slightly work so that I could see what was wrong. Nope, it blew out the wall wart. So, here is the schematic and a picture. Before all this, I put a thermistor in the input to the transformer and it stopped the fuse blowing for the toroid but apparently the power supply itself also has issues. I dont know where to start. I had a 2nd thought. The xformer is a 35-0-35 whereas the design called for 18-0-18. The output of the xformer is 38v. Is that too much for the design of the power supply ? Should some of the components be beefed up ? --- End quote --- If you're blowing fuses and power supplies, it's probably the current inrush to charge those capacitors. You have no resistance in series with those capacitors, so they're essentially charging at the input voltage divided by the ESR of the caps. Actually, scratch that. It would only be the resistance of the wire since caps are essentially shorts initially at DC conditions. |
| Hextejas:
Referring to the schematic, there are 4 wires coming from the toroid. AC1, AC2, 0V1, and 0V2. Would I put the 1K resistor on each of the AC lines only ? Thanks |
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