Using transformer secondary windings

Can I use both secondary windings to power separate loads?

I have a need for two 4.5VAC power supplies.

I have a transformer that is 9VAC with a center tap. I would like to connect one load to one 4.5VAC O/P and the other load to the other 4.5VAC. I'm assuming I can do this, provided I don't exceed the max current rating. It has been a long time since I have dabbled this low in analogue. I was looking for some reassurance or refresher.

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Jan Cumps over 3 years ago

Yes if they power two separate circuits that don't share any DC nodes.
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colporteur over 3 years ago in reply to Jan Cumps

Thanks JC for the reply. The AC loads are two small model railroad buildings that require 4.5VAC. It looks like they have some internal electronics to generate power for the few LEDS scatter around.

It is hard enough to find an AC output adaptor but to find one with that small a voltage was difficult. My electronics training from 40 years ago suggested, why not take apart a DC wall wart and just use the transformer. Some na-sayers on the floor said, "you can't do that!" so I began to have second doubts.

It too me a few tries to find a suitable DC adaptor at the thrift store. After getting at the guts of the adapater and measuring the windings, I still had my doubts. I do more digital electronics than analogue with my legacy knowledge so it tends to be a bit rusty. I got lazy and didn't want to dig out my text books to find the answers. I figured one of the smart peoples that hang out here would respond.
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gdstew over 3 years ago

As far as I can remember you can use a half wave rectifier on both output taps and the share the center tap as ground there is no
problem with the circuits connecting to each other. Using half wave rectification will require that the cap on the diode output to be
much larger to hold the voltage during the unused half wave to keep the ripple voltage to acceptable levels.
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colporteur over 3 years ago in reply to gdstew

Only need the AC. I have no need for the rectifier stuff.
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gdstew over 3 years ago in reply to colporteur

You can still use the center tap as the common ground to both circuits. This is how the AC power in a US house works. There is a 240VAC CT step down transformer
that supplies two 120VAC circuits to the breaker box, and both circuits are used to supply 240V where needed. The center tap from the transformer is connected to
earth ground at the breaker box. It is also connected to the common (white) wire in the 120V AC outlets in the house.
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colporteur over 3 years ago in reply to gdstew

Never thought of the 220VAC scenario. Fits perfect for what I am trying to do. Thanks for the insight. I will use it to explain it to the model railroaders.
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colporteur over 3 years ago

Worked like a charm the very first time. Thanks for for your input.
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