ECN Forum Forums General Topics of the Trade General Discussion Area Transformers: what determines the amp rating?

Hey Joe & Rodalco,

Thanks for your input. There's just a transformer, no diodes, caps or regulator, and I believe it's an AC transformer because my Fluke meter gives me readings in the AC range but not DC. This transformer is probably 3 or 4 amps, I guess.

I figure it can handle a steady load since it's from a Malibu light system, but I do have another transformer that looks like it's from some kind of musical equipment, and it has diodes, resistors, caps, heat sinks etc. I just want the transformer out of it. A couple of friends had 2 transformers each and dropped them on me, so I'm sitting here with 4 of them.

Well Spark, since you're playin' & learnin', and your peeps stopped by with a couple extra transformers....
Try placing the primary of one of them in series with the coil of a 120VAC cube relay. Leave the secondary of the transformer open and connect the series primary, relay coil to the AC line through the smallest fuse you have that exceeds the coil requirement. Take voltage and current readings and note if the relay is picked. De-energize, short the seconday, and re-energize. Check your voltages and currents and relay status again and contemplate your results.

Have fun,
Joe

You could contact Coils Inc. at - http://coilsinc.com/contactus.asp

Or look at Malibu's website with the model number from the timer case. - http://www.intermatic.com/

steve

Hey Joe,

Thanks for your always-professional responses.

Are you saying to short the secondary because there's some capacitance in the secondary, or remaining magnetic field in the core (capacitance?) from the primary? Does shorting the secondary eliminate the remaining magnetic field in the core, eliminate the capacitance, current and voltage? I assume all of these things work hand in hand, and that you can't have one without the other.

Thanks again

SMF

Ahhhhh Grasshopper, not so fast.. I don't want to diminish your learning experience by making it too easy on you. But of the various "ances" out there, "capacit" wasn't the one I had in mind. And perhaps, instead of contemplating your results, I should have asked you to "reflect" upon them. So if you do the experiment, and get the results I think you will, you might pick up on another transformer application.

OK, I'll give you two hints since it is Christmas. Think of the concepts of, "isolated switching", and "intrinsically safe"
Have fun,
Joe

Hello SMF,

A normal mains transformer usually has a laminated core, while a switched TX or inductor which may look like a TX has a "solid" type core of compressed ferro granules type material.

An AC choke or ballast has a laminated core but has a welded track across the laminations visible from outside.

This is my perspective. I could be totally wrong.

Basically, a transformer with a particular rating has a given mass, each in the windings (which will have a relatively equal mass), and the core.

The primary will have a guage of wire suitable to adequately magnetize the core, and the secondary will have the required size the get saturated by the magnetic field, in a shorter, but heavier size, but a similar mass of material to the to the primary (I will have to dismantle a blown transformer and verify that theory).

Somebody said that the secondary side has thicker wire because it's subject to a higher amp load than the primary side on a step-down transformer.

I guess if it was a step-up transformer the wire would be thinner on the secondary side because of the reduced amps because of more volts because of more secondary wraps around the core.

SMF

[This message has been edited by Spark Master Flash (edited 12-24-2005).]

True.
Think of it more that the higher voltage side would have the smaller wire. "Primary" and "secondary" can be misleading....maybe the "H" and "X" designations would be better.

While it's true that most transformers are designed for a specific purpose, any transformer can be used in either direction.
We have 14.4/7.2 Kv transformers at work that we use to step up or step down the voltage as needed.

Thanks, WFO, that helps!