Stupid 24v Transformer Question!


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Old 03-04-10, 06:18 AM
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Stupid 24v Transformer Question!

Hey guys,
I have installed an Aprilaire humidifier to my furnace and am ready to power it up but i have a stupid question. I had to install (2) 24v power supplies 1 - for constant 24v to power the control, and 1 - to down the 120v that is sent from my furnace.

My Question is how do i hook up to the 24v power supply to get the 24v. I cannot tell what side is hot or common? I actually cannot find any information on the web about this at all which makes me believe it does not matter.

I checked it with my probes and like AC I expected to see a -24v if I had the positive probe on the common so I could tell which was the hot screw on the transformer.

any thoughts?
 
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Old 03-04-10, 07:50 AM
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By "Power Supply" ,are you referring to 24 volt control-power transformers ?
 
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Old 03-04-10, 07:59 AM
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I am refering to a 24v AC 10VA Transformer that has 2 leads that com out of the bottom (1 bladk and 1 white) that hooks up to a metal outlet box that transforms the voltage from 120V AC to 24 V AC.
 
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Old 03-04-10, 08:03 AM
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On the input side, black is hot (sometimes marked with brass), white is neutral (sometimes marked with silver). On the output side, if the terminals are unmarked, power up the transformer and test AC voltage from the input neutral to each output terminal. One should read about zero -- this is the output neutral; one should read about 24VAC this is the output hot.
 
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Old 03-04-10, 08:13 AM
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I checked it with my probes and like AC I expected to see a -24v if I had the positive probe on the common so I could tell which was the hot screw on the transformer
When measuring AC with the meter correctly set to AC voltage measurement the probes are not positive and negative. You get the same reading to neutral either probe.
 

Last edited by ray2047; 03-04-10 at 10:15 AM. Reason: Clarity
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Old 03-04-10, 08:37 AM
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so i should put one of my probs on let say the duct work that should be grounded and then couth the output of the transformer and one sould read aprox 24v and other should read 0... did i get that right?
 
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Old 03-04-10, 08:56 AM
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Depends on the design of the transformer, but usually one of the terminals will be grounded.
 
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Old 03-04-10, 09:09 AM
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here is a link to the actual transformer just so you know what i am talking about...

IAQ Living.com: Furnace Filters | Humidifiers | IAQ Filtration
 
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Old 03-04-10, 02:31 PM
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The coil of say , a 110 volt generator , is an "isolated" power-source, i.e., "independent" from other power-sources, and without any connections to any other circuits ,or to "Ground" , until such connections are made.

The secondary-coil of your transformer is also an isolated power-source ; simply 24 volts of "seperate' power without any connections to any other circuits or to "Ground" , until you connect wires to the terminals.

Much depends on what type of equiptment the transformer is powering; if you "Ground" one of the terminals, you will also be Grounding the circuits that are being powered; these may be internal solid-state circuits that may be effected by a Ground-connection.

The "Load" side of a GFI device is Ground-Isolated; if you Ground a wire, the device will open the circuit.
 
 

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