Electrical / Electronic Project! Need Help.

Classic Toy Trains Forum
1

I have been toying arround with this project for a few months now.

Here is my situation.
As some of you may know I am supplying power to my layout using a single industrial transformer. It is rated at 1kva and has an output of 24vac.
It is controled by 2 TPC’s and 1 PM.

I have been using this setup for track power for over 5yrs.

The so called ‘Project’ is to further utilize the 24vac output of the trans. for various lights and accessories in the most cost effective way.

ACC. in use include, but are not limited to, Building lts., Street lts., Crossing gates, Hobby shop, Water tower, Saw mill, Switch tower, Draw bridge, etc…

I determined that I would need voltages of 10, 12, 14, 16, & 18.

Control;
Some will be on at all times, i.e. Lights
Some will be manual and some trough SC-2.

Solutions obtained so far!
Feel free to add to or comment on the following;

1)Add cheap, smaller transfomers. (This does not utilize the 24v output)

2)Use an AVC (Not cost effective. Need 1 for each output)

3)Bridge rectifiers in series (This is a possibility)
(see http://home.cogeco.ca/~rpaisley4/xACdropper.html)

4)Rheostats (Maybe, but how much current can they handle)

5)Mini commander from Electric RR (Not cost effective)

Any suggestion are wellcome!

Thank You and Have a Good Day!

2

Don’t forget the single rectifier diode in series, for simple loads like lights and heaters. You should get about 16 volts rms.

And you may be able to wire similar loads in series, for example, two 12-volt lights of the same type.

3

Hi!

I’ve got similar issues. I found what I thought was a relevant and interesting article at:

http://home.att.net/~basicelectronics/faq.htm#volt_drop

See what you think! This talks about resistors (“voltage ladder”), and a voltage regulator, and also using diodes. Using a diode will convert your AC to DC, but this may or may not affect the accessory that you are powering.

Good luck, and I’d like to know what you decide on!

4

Rheostats are a good idea. They can handle whatever load that they are rated for. Also, later you can alter the output if necessary.

underworld

[:D][:D][:D][:D][:D]

5

Pat, if you decide to take the power from the large supply, make sure that you have some kind of fuse or circuit breaker to limit the total current that can reach any device.

There is a really neat gizmo called a poly fuse, available from Digi-Key. They are really inexpensive, and work great. They come in a variety of current ratings. They sense too much current, and shut down the flow, and heat up. They reset themselves automaticly when they cool down. This is what I am using to create power districts on my layout for TMCC.

As for the voltage, does that huge supply have any taps?

6

Pat, by any chance, does your transformer have more than one secondary winding? If so, you could put one secondary winding in series with the primary, reducing the voltage from 24 to 20 volts, which may still be enough for the trains while making it easier to get the accessory voltages. This would also probably make the transformer run a bit cooler, since power transformers are usually designed to saturate a little at their rated voltages.

I also see from a previous posting that you have two of these transformers. Putting the two primaries in parallel would be a another way to get the second secondary winding, if the transformer doesn’t already have one.

7

Bob,
What is a “single rectifier diode” ?
“You should get about 16 volts rms” Is that true? That would be an 8v drop.
Do you have a schematic?

underworld,
Rheostats maybe the way to go.

Elliot,
I have taken safety into account, But I never heard of a ‘poly fuse’.
I’ll have to look into that.

8

Just a diode big enough to carry the current that you need. Here is a big 6-ampere one from Radio Shack: http://www.radioshack.com/product.asp?catalog_name=CTLG&category_name=CTLG_011_002_006_000&product_id=276-1661

Yes, it’s true. The rms (root-mean-square) measurement of an ac voltage is the dc voltage that would develop the same power in a resistor. It is the ordinary way of describing ac voltage. So, for example, the 24 volts from your transformer is actually rising to a peak of about 34 volts, then down through zero to a negative peak of -34 volts each cycle. But, if you use it to power an incandescent lamp, which looks like a constant-value resistor over that time, it delivers as much average power as a steady 24 volts dc. The peaks near 34 volts average out with the valleys near zero.

When you put a diode in series with the circuit, you shut off the voltage completely half the time, so the power delivered to the lamp is cut in half. This has the same effect as turning down the equivalent 24 volts dc to about 71 percent, or about 17 volts. (Notice that .71 squared is .5.) Therefore the rms voltage is 17 volts, or actually more like 16 volts when we consider the drop across the diode.

One thing to look out for is that the load current through the rectifier circuit has a dc component, which tends to saturate the transformer. However, if the current is small compared to the rating of the transformer (which is certainly the case with yours!) there is not much of a problem. Nevertheless, if you have more than one load, it is a good idea to balance the dc current as much as possible by putting some diodes in one way and some the other way.

A nice thing about losing 8 ugly volts this way is that there is almost no energy lost (there would be none with a perfect diode), unlike the rheostat and modified-bridge schemes, which get hot.

9

Pat, here’s the link to the Digi-Key catalog page. I had a little trouble finding it since they updated the catalog and added a lot of pages. They actually call it a “Polyswitch”. None of the ones we would want to use are over $1 per unit. I used the RUE600-ND for track power, limiting the current to 6 Amps per block.

http://dkc3.digikey.com/PDF/T051/1106.pdf

By the way, I have to say that I have no love lost for Radio Shack. Their prices constitute highway robbery , and the qulaity of anything with moving parts is highly suspect. They are OK in a pinch for small stuff, but there so many better sources for electronic components.

The other day I checked them out for a white LED, I want to do that bulb replacement project that was in OGR run 202. I need about 20 LED’s, the store I visited had ONE in stock. They wanted $5.29 per LED. A little online shopping, and I found them for $2 each at All Electronics. White ones are always more, but that is ridiculous. Maybe Radio Shack buys them from All and repackages them.[swg]

10

Here’s a great link for electronic parts…Check it out: http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=31
BillFromWayne
www.modeltrainjournal.com

11

For an update and further clarification on this subject see the thread entitled

Electronic problem / In Summary!