Novice Question- Transformer Voltage

[donhalshanks]

I have a couple old train transformers, and I thought I would use one of them at around 5 or 6 DC volts to power a turntable motor.  With the transformer plugged in, and a multimeter hooked to the track terminals on the back of the transformer.......  should the DC voltmeter scale show increases in voltage as the transformer throttle goes from 0 to max?  It reads 12v no matter what the throttle setting is at, and is the same for both transformers.  Is the conclusion that rheostats for these transformers are no good, or is it because I have no load across the terminals?  Thanks for helping the electrical challenged!

Hal 

 

[jeffrey-wimberly]

Being that they are old transformers I would think it's because there's no load.

[richg1998]

Those old transformer power supplies will show 12 volts with nothing connected to them, as Jeffrey said, "no load".  The older ones were v ery basic as in cheap, toy quality. Connect a motor/locomotive and you will about zero volts with the control at zero. The voltage will increase as you turn up the control.

Rich 

[Mark R.]

I found the same thing to happen with older "wall warts" ! I must have thrown a dozen of them in the garbage before I discovered they needed a load on them to operate at their specified voltages ! 

Mark.

[richg1998]

[/url]You can usually assume a wall wart is unregulated. Some do specify. Many line voltage type wall warts are regulated. Those types are lighter in weight than a conventional wall wart of the same size.

Links

http://www.repairfaq.org/sam/aapsfaq.htm#adpscaa

http://wolfstone.halloweenhost.com/Power/powwal_WallWarts.html

Rich

[donhalshanks]

Thanks for your responses.  I kinda of figured my old transformers were still OK.  Appreciated the wll mart discussion, because I also have some of those and was experiencing what you described when measuring the voltage. 

Thanks much, Hal