tapping more than once from a transformer?

pjb999January 19, 2009

Not sure if this is a wiring or electronics question. I think I know the answer but want confirmation.

Until recently, thanks to the building downturn, I was working as an apprentice/junior alarm installer/technician, and I've inherited enough secondhand equipment to build my own system. There are several devices that require DC power, and the panel dc supply is limited. In these cases at work we would use a separate, commercially produced dc supply, and we would connect it to a separate transformer (the doorbell style that connects to a mud ring) - my question is this - provided I stay within the capacity of the power supply - in dc land we usually said no greater draw than 80% of the rated output of the supply, is there any reason why I can't tap off the transformer twice (note this is not a multitap) ie run one set of wires to power the panel, and another set to my own dc/rectifier setup for the additional devices (I've built many dc supplies myself and have enough parts to build many more)

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no reason not to do it as long as you stay within teh rating of the transformer.

    Bookmark   January 19, 2009 at 1:44PM
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Thanks - I suppose it's no different from houses being fed from a substation, I just wanted to run it past someone :)

    Bookmark   January 19, 2009 at 2:02PM
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It is different from houses being fed from a substation.

For one it is different equipment, that may or may not be manufactured to perform with multiple loads.

Unless the equipment is intended for multiple taps(will have multiple lugs for connection) adding an additional load may void the warranty and create liabilities.

    Bookmark   January 21, 2009 at 5:22PM
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I think you misread my question. The substation analogy was a crude one.

Sure, there are some multitap transformers that are probably ok to supply more than one voltage (the transformers in hi-fi amps for one) and some that are probably not. Some multitap transformers can supply a larger current on one tap, and less on another, again I guess an amplifier is a good example, as you will need a small amount of current, which will be rectified and probably regulated, to drive the preamp, whereas you will need a second supply, again rectified but almost definitely not regulated (unless it's a honking big one or used in conjunction with a power transistor or two) which will drive the power amp. I am talking about a simple transformer, basically a higher capacity alarm transformer (they're usually secondary 16.5vac) that would normally feed 16.5vac to just one panel, my query was, could you drive a second device from the same transformer provided you didn't exceed the load rating.

    Bookmark   January 24, 2009 at 8:21PM
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