Electronics > Projects, Designs, and Technical Stuff
lowering a.c. voltage output for power supply
mgvguy:
I have a device that requires 9v a.c. and rated for 2.1 amps. I thought I could modify the output of either of the following:
1.) a power transformer that outputs 24 v, 50 va
2.) a power supply walwart - output 15v a.c., 1.5 amps
Is there a simple way to do this - any schematics/component values possible?
Thanks!
Ian.M:
--- Quote from: mgvguy on February 11, 2020, 07:00:12 pm ---Is there a simple way to do this ...?
--- End quote ---
No!
If it *NEEDS* AC, then there is no easy way to change the voltage. Even if the transformers have a dual voltage primary, going from the 120V connections to the 240V connections while keeping the supply at 120V would halve the output voltage, and as neither of them is 18V to start with, you cant get 9V from them so it wouldn't help.
KaneTW:
Yeah, there's a simple way. Go on Amazon and buy a 9V AC wallwart.
If you have a transformer with an appropriate winding ratio lying around, sure, you could do that. If you don't, just get the wallwart.
Prehistoricman:
Modifying transformers isn't particularly easy, especially at wall-wart sizes. Even if you did decrease the voltage of option 2, you wouldn't have enough current capability.
For option 1 you would probably have to find a way to convert the unit to accept DC. That could be easy or it could be hard - completely depends on the circuit within. Or you could get a DC power amplifier to output 9VAC lol
mariush:
I would recommend actually buying a transformer, it's not expensive.
9v 2.1A is around 20VA, so anything higher than that would work.
Ex.
27VA 9v/18v https://www.digikey.com/product-detail/en/hammond-manufacturing/266K18/HM2140-ND/2358044
25VA 9v/18v https://www.digikey.com/product-detail/en/triad-magnetics/VPT18-1390/237-1323-ND/2090061
Get the toroidal transformer, put it in a plastic project box, install a IEC C7 connector on the box and the cable with barrel jack connector or whatever your device needs on the other side and you're done.
If you want to modify one of the transformers, probably the easiest would be to get the 15v AC 1.5A one and unwind the secondary winding, measure the length and then cut a bit of the wire to match the 9v ... you'd get 9v 1.5A ... hope that your device doesn't actually need 2.1A and is happy with 1.5a
To increase current, you'd have to mess with the diameter of the primary and secondary wires, calculating magnetic flux and other crap.
With the 24v transformer, maybe you could unspool the 24v secondary winding and make 3 x 8 secondary windings and parallel them and hope that your device will be happy with 8v AC
Or maybe make 2 x 9v secondary windings and parallel them.
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