'Variac' power transformer?

Yes(ish) The rectifiers will lose a near constant amout so the track voltage won't be lineal, but the track voltage (in train control terms) will directly relate to the knob position within something like 0.1 volts.

Reply to
Gregory Procter
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I always assumed it had turned into a generic name, like Hoover, Thermos, Biro etc.

Reply to
Christopher A. Lee

Fine. I hapen to have a variac that will go to 145 volts. I also have a 10:1 stepdown transformer rated at 72VA continuous. Although I use DCC now for the trains, this might be a fun experiment. I have a tabletop layout that is still DC. Maaybe I will hook this up there and see what I see.

..............F>

Reply to
Froggy

I did it, back in the 70's. As I recall I ran the ac out into a train power supply set to max. This would NOT work with a transistor system. What I did, essentialy, is use the step down transformer and diodes as a way of converting the 120 ac to 12 dc. The variac has a great 'feel.'

Right now, I'm using the power pack that came with the bachmann lafayette (2-2-0) set. My wife only wanted the train, but it came with track and poser. The power has a neat zero center control, which I am using on my turntable (easy to slow down and reverse.) However with less that 10 hours (actual on) I can feel the "scratch" of a wire-wound potentiometer.

I'm more than a little dis-enchanted with bachmann.

Reply to
larry l.

They make great power supplies for lighting, tortoise switch motors, turntables and other motorised accessories. Once you have got the right brightness, motor speed etc you can expoxy the control to lock it. You can pick them up for a song at shows from people who are glad to get rid of them.

Reply to
Christopher A. Lee

I was thinking of older Athearn engines. I've seen them pull nearly

3 amps going uphill with a full train. I recall triple-headed Athearn trains drawing around 5 amps upgrade back in the '70s.
Reply to
Rick Jones

It works quite well. I've done it at work many times to get some exact value of small AC, where using the Variac directly would not work as well.

Reply to
Rick Jones

On Wed, 24 Sep 2003 21:55:20 UTC, Christopher A. Lee wrote: 2000

It is misused in just this way. Variac was a trademark of General Radio and defined a particular type of variable transformer (an autotransformer). There were other brands of variable transformer but the ones I know of in the U.S. were all autotransformers.

Reply to
Ernie Fisch

It pretty nearly has. "Variac", a specific brand, is now a near generic name for an autotransformer. There are many other makes of autotransformer, of course, "Powerstat"and "Staco" being a couple.

Dan Mitchell ==========

"Christ>

Reply to
Daniel A. Mitchell

Yes, the old "first generation" Athearn locos could pull over one amp ... but that's just 12 VA plus. Working real hard three might indeed draw five amps ... that's just 60 VA total.

Your stated 250 VA is about 21 amps ... that much current can make a LOT of heat! It would run more than 15 of the 'old' Athearns, and perhaps

100 plus of the newer more efficient locos.

Dan Mitchell ==========

Rick J>

Reply to
Daniel A. Mitchell

I meant for variable transformes. I've seen then with proper secondary windings that were variable, not just autotransformers - I never used the name Variac for a genereric autotransformer.

Reply to
Christopher A. Lee

Many of the European MR transformer controllers are variable transformers - for example, every Marklin transformer is that type.

Reply to
Gregory Procter

Oops! You're right, of course. I was thinking of 3 amps at 120V, not

12 V. Sorry. I repair industrial automation equipment (variable speed drives and programmable logic controls) and am used to thinking in terms of equipment running on from 120 VAC to 480 VAC.
Reply to
Rick Jones

Why are newer locos much more efficient? Is it the engine magnets?

Reply to
railrider

Yes indeed, TRUE variable TRANSFORMERS exist. There are several types, and brands. Some have been used in model train controls. They are all more expensive, bulkier, and heavier than a comparable autotransformer. The simplicity of the autotransformer has made it a popular variable AC voltage source. Unfortunately, it does have some safety issues, used improperly, as we've been discussing here. These mostly have to do with lack of 'isolation' from the power lines ('mains').

I must stress that a Variac is perfectly safe (as much so as any electric device) if used properly.

I know little of common European (or elesewhere) practice, but in the USA autotransformers, like Variacs, probably outnumber real variable transformers by a ratio of hundreds to one. I've only even SEEN a few variable transformers. On the other hand I see or work with perhaps 30 autotransformers on a daily basis. They're VERY common, though less so than they once were.

Today a lot of Variacs have been replaced with simple electronic 'lamp dimmers' or 'motor speed controls'. These devices do much the same thing for many purposes, but in different ways. Depending on use, they may be better (often) or worse. They're certainly far smaller and cheaper.

Dan Mitchell ==========

Gregory Procter wrote:

Reply to
Daniel A. Mitchell

Mostly motor design. Part of it is stronger magnets (less current draw, all else being equal), part due to using more turns of finer wire in the armatures (higher armature resistance, less current draw), and part due to better lower friction drive trains. The new more efficient motors are far better in a variety of ways, but do cost more money. They are also more delicate, and often shorter lived, than the rugged old 'war-horses' like first generation Athearn and Pitman motors.

Dan Mitchell ==========

railrider wrote:

Reply to
Daniel A. Mitchell

On Fri, 26 Sep 2003 15:44:04 UTC, "Daniel A. Mitchell" wrote: 2000

The new motors have much stronger magnets than the old open frame motors and the design gives much stronger fields. As a result the same power can be delivered with a lot less current.

Reply to
Ernie Fisch

Are their any disadvantages to using a light dimmer or motor speed control for model trains? I'm referring to the kind which chops up the AC waveform to change the duty cycle rather than changing the voltage output.

Reply to
railrider

Two problems come to mind:

- you're likely to find that the output curve is not very lineal and slow speed control is missing.

- the waveform will cause smaller motors and motors with wear in the bearings to rattle at around 120Hz.

Reply to
Gregory Procter

That's what I said. However, the permanent magnet does NOT deliver any power whatever ... all that comes from the current. The stronger magnet just allows more efficient use of the available current.

Dan Mitchell ==========

Ernie Fisch wrote:

Reply to
Daniel A. Mitchell

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