I'm trying to repair a Model Railroad transformer. I need a circuit that will use a 18 VAC input and have an output
from 0 to 18 vac using a 10 K pot. The input voltage and 10K pot CANNOT be changed. Only circuits I can find all have higher input voltage. Approx. 10 amps on output.
Thanks Ed

 

180W is a lot of power for a model train.

 

Welcome to AAC!

AAC is for all electronics enthusiasts, hobbyists and professionals. No need to advertise your level of competence.
What I mean is, a title such as "Need to control 0-18VAC power output for model railroad" is a much better title.

 

Welcome to AAC!

A voltage divider won't work well for any circuit that requires more than minimal power.

How much power/current do you need? Do you need a continuously variable voltage (vs a few set voltages)?

 

I thought model trains run on rectified DC voltage from the transformer.

 

I'm trying to repair a Model Railroad transformer. I need a circuit that will use a 18 VAC input and have an output

How does that help you repair a transformer?

 

180W is a lot of power for a model train.

Not really. This one is a Lionel ZW with external power supply rated at 10A 180VA. 4 outputs.
Can control 4 trains. One I use is 275W. This is "O" guage .

 

How does that help you repair a transformer?

Transformer has a PCB that is burnt out and cannot be repaired/replaced. Also has 40 pin chip that can't be programmed. I want to build a circuit that will work. Like using a Triac.. The transformer will put a set voltage,user selected, and on board electronics ,in the engines, will do the rest. Start, stop , etc..

 

I thought model trains run on rectified DC voltage from the transformer.

Lionel "O" guage and 027 guage have always been AC . These are 3 rail trains. Check out CTTA.
The smaller guages, HO .N ,Z , are DC.

Welcome to AAC!

A voltage divider won't work well for any circuit that requires more than minimal power.

How much power/current do you need? Do you need a continuously variable voltage (vs a few set voltages)?

Depends on trains being run. Conventional engines have no electronics and speed is controlled by the transformer. DCC type use a set track voltage and are controlled remotely by hand held devices.
10 amps is normal.

 

Do you need smooth DC or just variable rectified AC?

 

This is all rather vague and scattered.

It's unlikely that the Transformer is damaged.
The measured Output of the disconnected Transformer Secondary is required.

If You must use an existing Pot,
it should be tested to make sure that it's not damaged in any way.

I assume that this Transformer is contained in a Box of some sort,
how much space is available ?,
Pictures are needed.

The desired Output needs to be specified, not a "nominal" colloquial-term.

A Block diagram is needed for multiple-Outputs.
Are there multiple Pots ?, one for each Output ?
.
.
.

 

I think the TS is using 'transformer' to denote the whole supply, not just a core with bobbins and windings.

 

I'm trying to repair a Model Railroad transformer. I need a circuit that will use a 18 VAC input and have an output
from 0 to 18 vac using a 10 K pot. The input voltage and 10K pot CANNOT be changed. Only circuits I can find all have higher input voltage. Approx. 10 amps on output.
Thanks Ed

Welcome to AAC.

Your thread has been moved to the Power Electronics forum to match the content.

Glad to have you join us, good luck with your project.

 

Just a note about terminology…

The word “transformer” means different things to different groups. Among electrical engineers and enthusiasts, a transformer is a component, that is, part of some other system.

A clearer way to communicate the meaning you have in mind, and reduce the amount of mutual confusion and its concomitant back and forth is power supply. A power supply may or may not have a transformer as a part, but the key is that it provides power to something in a form that is usable by that thing.

In your case, you have a power supply (not at all clear if it does have a transformer) that is damaged and you need to make it work again. I would strongly suggest you take clear, well lit and sharply focused photos of the disassembled supply, its damaged PCB, and any labels on it. This will be an enormous help to those trying to help you.

Information is key, and the more that we get at the outset the more likely a successful outcome.

 

OK, folks—this is what we are dealing with…

​

It is a complicated controller that uses up to four supples (like the ones in front). Exactly which part the TS is trying to repair is not clear yet but I think it must be the ZW (the fancy phenolic controller bit).

A DESCRIPTION:

There’s only one ZW. No single product has come to symbolize the legend of Lionel more than the Lionel ZW. Molded to original dimensions in classic phenolic resin, the ZW can run up to four trains at the same time on different layouts, plus accessories. The two engineer-type handles provide independent control of two variable voltage circuits, each with built-in whistle, direction, and bell controls. Two additional accessory circuits can be set by means of dial-type controls to any desired voltage. Or, if you prefer, you can control all four outputs with a single handle! The ZW controller can be powered by any combination of one to four 135-Watt or 180-Watt Lionel PowerHouse Power Supplies. And if you use the TrainMaster Command or LEGACY Control system, you can adjust each output using your walk-around remote control up to the level pre-set by its corresponding ZW handle. It’s a great way to help less-experienced railroaders keep their trains under control while enjoying the thrill of independent remote-controlled operation. Offered with two 180-Watt PowerHouse Power Supplies, this ZW package provides the power and control you dream of for your vintage or state-of-the-art Lionel locomotives and accessories.

Unfortunately, all the information about it has been purged from Lionel’s website except that. I didn’t go spelunking to see if I could find more, but without more information from the TS I‘m afraid we are stumbling around in a huge problem space with the lights off and one leg tied behind our backs.

 

Do you need smooth DC or just variable rectified AC?

NO DC at all. Trains run on AC only. Need to control the 18 VAC output.

 

Thanks to everyone. The external power supply works fine.. The controller [transformer] is broken, There is a PCB ,with all the components, that is burnt out. There are no replacements available. The handles [4] only control a 10K pot.. I need a circuit that will vary the output voltage using the 10K pots. Circuits I find on line all use 110/220 vac.. I need one that uses 18VAC.

 

Is the AC waveform that powers the rails a square-wave, a pure sine-wave, or simply pulsating voltage of a single polarity?

Edit:
Just checked. From the Lionel site it seems pure sine-wave, with superimposed control signals for bell/whistle, is used.

 

So would the trains work on DC, or just AC only?
as it's easier to make a variable DC power supply.

 

So would the trains work on DC, or just AC only?
as it's easier to make a variable DC power supply.

The motors might run, but the function of the model locomotives would be compromised.