Where do I connect a 22v AC power supply ? - Page 1
Forum section: electronics / projects

author: Hextejas
author_rank: Frequent Contributor
timestamp: January 04, 2019, 06:31:06 pm
content: I am trying to test my recently constructed power supply with a scaled down wall wart transformer rather than the hooking up the full voltage which is 120v AC.If it works ok, I will connect it to the full 120v AC main.Unfortunately, my toroid transformer will not turn on with the 22v as input, so I have to wire the wall wart directly to the power supply. Hence my confusion.I have 2 wires coming out of the wall wart and I have 4 input connectors on the power supply.Power supply input connectors are AC1, 0V, AC2, 0VAnd of course I have 2 AC wires from the wall wart. (WW)So, which mains wire to which power supply connector ?My 1st guess was that WW1 to AC1, WW2 to AC2. But i am afraid to do it as i have destroyed a lot of componenfs so far.

author: ebastler
author_rank: Super Contributor
timestamp: January 04, 2019, 06:46:12 pm
content: Your power supply has two independent parts. One with inputs U1 and U2 (AC1 and 0V), and output on U9 and U10. The other with inputs U3 and U4 (AC2 and 0V), and outputs U7 and U8.The toroidal transformer which will eventually power it has two separate secondary windings, which you will connect to the respective pairs of inputs. If you want to test it with another transformer (your wall wart), which has only one secondary output and hence only one pair of output connections, you will have to test the two parts of your circuit separately, one after the other.But before you do that: You have not told uns what voltages your power supply is meant to produce, and your schematic does not state any voltage ratings for the capacitors. Can your circuit tolerate the 22V supply?Also -- your power supply schematic does not show any fuses, on the primary as well as the secondary side of the transformer.You need fuses!Certainly for safe operation going forward; and they are also most helpful to protect the more expensive components in case you wired something wrong, and to protect yourself. Was this supply built from a kit, or from a building plan? What did that source have to say about fuses? What about other protective measures -- enclosure, safety ground?As a general question: Are you sure that you are ready to build a mains-powered device from scratch? You could put not only yourself in danger while you are experimenting, but can also create shock and fire hazards for future users!

author: In Vacuo Veritas
author_rank: Frequent Contributor
timestamp: January 04, 2019, 07:27:46 pm
content: Very odd all around. What is C10 doing there?? And what do you mean "turn on"? It's a toroid, it might have remanence.https://www.bicronusa.com/resources/tech-guide-toroidal-power-transformers

author: soldar
author_rank: Super Contributor
timestamp: January 04, 2019, 08:19:34 pm
content: Quote from: Hextejas on January 04, 2019, 06:31:06 pmAre you sure the wall wart is putting out AC? Most will put out DC.As others are telling you, it may be that you really are not prepared enough to be playing with mains power. If you are not absolutely certain that you know what you are doing then better not do it.You might want to put a fuse in there and learn the old trick of putting an incandescent lamp in series.

author: Hextejas
author_rank: Frequent Contributor
timestamp: January 04, 2019, 10:28:43 pm
content: Let's see.Yes I am sure that the wall wart is putting out AC.The circuit is fused, 4A, between the mains and the toroid. There is also a thermistor there.I do have an incadescent light in series. It drops the AC down to about 53V AC. For some reason, the toroid does not do anything with this lower voltage. It works just fine with the full 120V.I don't know what else to call it when the toroid hums and begins to put out a lower voltage. It puts out 38v AC but not with the light bulb.So, I wanted a smaller AC voltage so I can test my amplifier. Hence the wall wart.As to what is the purpose of C10, this is not my design.http://www.circuitbasics.com/design-hi-fi-audio-amplifier-lm3886/#Wiring-it-All-TogetherEbastler, thank you. That is the explanation that I was looking for.

author: soldar
author_rank: Super Contributor
timestamp: January 04, 2019, 11:02:02 pm
content: If you connect the primary of the transformer in series with the lightbulb and leave the secondary open then the primary should be seeing almost the full voltage and the secondary should be showing their correct voltages. If this is not the case then it may be that the transformer is defective.

author: ocset
author_rank: Super Contributor
timestamp: January 05, 2019, 12:06:23 am
content: yes with mains work like that, very low value fuses are recomended and protective safety glasses.Get yourself a 20mm fuse holder and start with fuses right on the border of what will break on normal running current....you can always change up.Also, never trust any second hand , reclaimed mains transformers, as the insulation may have broken down.Even if its new, you can still get a capacitive mains electric shock via the interwinding capacitance.