Simple DC Power Supply Schematic Needed

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haklesup
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Post by haklesup » Wed Jun 18, 2008 3:36 pm

if the train is reversable, its likly DC. If it is not, that's inconclusive. I expect he is correct about it being DC but the specs out of context are strange. They more resemble what you might find on a tiny variac.

Clearly they are Train Engineers not Electrical Engineers

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CeaSaR
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Post by CeaSaR » Wed Jun 18, 2008 3:47 pm

Well,

Seeing as "dad" bought the trains, transformer and controllers, he
must be pretty sure of compatibility. Also, seeing as the controllers
need 16V DC, Craig should be on his way to making his dad's garden
train a reality. It still wouldn't hurt to know the train specs, though.

CeaSaR
Hey, what do I know?

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dacflyer
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Post by dacflyer » Thu Jun 19, 2008 3:06 am

the motors on trains draw very little power, the powerpacks mainly consist of a small transformer, almost 1 amp, a dridge rectifier, and a small rheo-stat, and a switch DPDT slide switch for reverse for the train.
and there is also a pair of contacts for acessories and them contacts are just plain a/c off the transformer, back in my wounger days i used one of them packs as my 1st power supply for the longest time.
i am pretty sure that the train is a typical HO scale set. :D

so i know that your transformer you wanna use is overkill.
you would be better off using a 24 volt transformer from radio shack rated at about 2 amps, also you should be able to get that bridge rectifier there also, if you haven't gotten it yet.
also i agree what the other poster said, about running it in a 12 volt mode, because the rectifier will boost the voltage up a bit.

and don't forget your speed control, variac or heavy duty rheostat rated for at least a few amps.

good luck.

Yerry
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Post by Yerry » Thu Jun 19, 2008 12:42 pm

I happen to help friends down in Fla with their Garden Railroad. Here's what's up, plus a few questions that actually matter:

The DC trains run typically 2V-12V/14V. Most transformers output higher, like 16V or even 18V, on the understanding that the extra voltage is "headway" for the track sections that are the furthest from the power connections, as track is normally a less-conductive brass alloy. My friends use 12g copper wire connected to the track every four feet, and there are STILL slow spots.

Here's something everyone missed: Running two trains, three methods.

BAD: plopping two locos down with one controller. They cannot run or change direction independently, and will quickly smack into each other, as varying load (uphill, downhill, number of cars hauled) varies speed.

JUST AS BAD: Cutting the track into blocks and having a throttle for each block. Unnecessarily expensive, and highly erratic behavior when crossing between blocks when each supply only has to source half the current..

BETTER: Cutting the track into electrically isolated blocks, and assigning individual blocks to each train using a bank of DPDT toggle switches. This has been the best traditional way for over 40 years. However, you cannot use one transformer to power both throttles-- as wheels cross blocks, you can easily have a short! A hot short across an irreplaceable, heat-sensitive, tiny spring inside Pop's $400 Consolidation won't please him. You need two transformers. One center-tap transformer is NOT "two transformers".

BEST: Digital command control, which came about about 1980, is now quite reasonable, price and equipment-wise. One huge block, one huge supply, and as many small, low-current digital throttles as you need that feed into the power source.

Craig
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Post by Craig » Mon Jun 23, 2008 10:21 am

Hi guys. I tried the train out on the weekend using my 0-30 volt, 3 amp test bench power supply hooked to the ArtisoCraft controller that I mentioned earlier.

I ran it at 12 volts, and the train was very slow. I then bumped it up to 16 volts, and it was still somewhat slow. It brought it up to 20 volts, and it seemed to run well like that. I watched the digitial readout to see what current was being drawn, going from a dead stop to full speed drew less then 1 amp. So yes, I guess that transformer is overkill, but now I know for sure that it will easily power both trains as well as some future accessories.

There were some slow spots, which seemed to be caused by the track being dirty. I scuffed it up a bit with some steel wool and it seemed to improve the speed. The way the track is setup, there are two completely independant tracks that do not come into any contact with each other at all.

I have almost finished the power supply. I have it all working, but I just haven't fastened it into it's case yet.

I had configured the transformer to output 24 volts rather than 12, since 12 seemed too low for the train to work at proper speed. However, after I did that, then measured to DC volts, I found that the voltage is at 36 volts DC. Since that goes well over the specs of the train controller, I will rewire the transformer to output 12 volts AC, which I guess should turn into about 16 volts DC, as sghioto had said.

Just as a side note, I decided to put an LED on the power supply to light up when it's turned on, however, I did not hook that up right away. I first just hooked up the basics to make sure that it all worked. Once I hooked up the wires to the LED I was surprised to find that it lit up. The first thing I thought was "oh crap, I left this thing turned on!", but it turned out to just be the extra juice left in the two 4700uf capacitors. :???:

Craig
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Post by Craig » Mon Jun 23, 2008 2:40 pm

Here are some pictures of the power supply. As stated earlier, the power supply isn't quite finished, I still need to fasten down the transformer and clean up and heat shrink some of the wires.


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Craig
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Post by Craig » Mon Jun 23, 2008 2:49 pm

Here's the train layout.


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MrAl
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Post by MrAl » Tue Jun 24, 2008 6:58 am

Hi there,

Nice power supply there. Are you going to build a speed control
too for it?

Watch out with electical stuff outside though, as shocks are common to
earth ground. Maybe use a GFI.

I have to wonder too, because the tracks are outdoors i wonder how
much they will oxidize over time. When the tracks oxidize the train
doesnt get power and stops until the tracks are cleaned with something
abrasive. Ever have this problem with the tracks outside like this?

Nice setup btw. Next you need a drawbridge where the train goes
over the 'lake' that goes up and down automatically as the train
comes near the bridge. A boat going back and forth underneath also.
Would be too cool ha ha.
LEDs vs Bulbs, LEDs are winning.

Craig
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Post by Craig » Wed Jun 25, 2008 12:08 pm

No, I am not going to build a controller, my dad already has two of them that work just fine.

The power supply will only be taken outside when the train is going to be used, it won't stay outside (as far as I know anyways).

Yes, the tracks get dirty and need to be cleaned. They actually have special train cars that go along the tracks to scrub them clean.

The train doesn't actually go over the water. The original design called for this (hence the bridge you see), however, when they went to install the bridge they found that the walls for the water are an inch or so higher than the gravel, and the incline is too much for the train. So for now, no bridge over the water.

One thing I would like to build is a railway crossing for the road, complete with flashing lights and a gate that goes up and down. I haven't really sat down to think about how it will be done, but it sure sounds like a fun project.

Craig
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Using a voltage diveder circuit

Post by Craig » Mon Jun 30, 2008 5:00 am

Hi,

The transformer I have puts out either 24 or 12 volts AC, which translates into 16 or 36 volts DC. Since the train requires (or can handle) up to 24 volts, I figure I need to wire up the transformer to output 36 volts, then use a voltage divider curcuit to get the voltage down lower.

What I decided to do was use a 1k ohm and a 500 ohm resistor in series to divide the power output to 24v and 12v. I figured we could use the 24 volts to power the train, and use the 12v for any other accessories.

What do you guys think about this, does it sound like a viable solution?

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MrAl
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Post by MrAl » Mon Jun 30, 2008 5:29 am

Hi again,


Well, voltage divider solutions dont work too well for power applications
like this one, instead you should look into a linear regulator or better
yet a switching regulator. If you need help with this just yell.

BTW, with a 1k and 500 ohm resistor your current output would be
limited to 36ma, not enough for the train(s) motor(s). To use a
resistive voltage divider for a 1 amp motor you would have to
use a 6 ohm resistor in series with a 12 ohm resistor, and the
power rating for these resistors would have to be around
35 to 70 watts, just for an example. This would not even regulate
the voltage very well as when the train goes up and down hill.
As an extreme simple possibility, you might use around 17 diodes
in series (with enough current rating for 1 or 2 amps) with the
train motor, but regulation wont be that good either.

The best choice is a switching regulator, built from a Simple Switcher
IC chip available from National Semiconductor, or another type
of switcher chip.
LEDs vs Bulbs, LEDs are winning.

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Lenp
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Post by Lenp » Mon Jun 30, 2008 5:40 am

Craig,

If you want a cheap and nearly lossless speed control, use a common light dimmer on the input. Yes, there may be some that will wrinkle their nose at this idea, but it does work. It's available, inexpensive, small and virtually no heat. Since the dimmer output is not a sine wave the transformer may buzz if the laminations are a little loose and any transformer heating is usually minimal. If you want to set min/max values just change resistors around the dimmer's pot to set the values. That's what a fan speed control has. It sets a value so the fan will run slow but not stall when the control is turned down.

Len

Craig
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Post by Craig » Tue Jul 01, 2008 8:21 am

The best choice is a switching regulator, built from a Simple Switcher
IC chip available from National Semiconductor, or another type
of switcher chip.
This sound like a good idea, however, I have looked and looked for a 20-24 volt, 3 amp+ voltage regulator but have been unable to find one. Do you know the part number for one, or point me in the right direction?

sghioto
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Post by sghioto » Tue Jul 01, 2008 8:45 am

You can use a LM350 and adjust the output voltage as needed. It's rated at 3 amps.

http://www.electronics-microcontroller. ... M350-D.pdf
Steve G

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philba
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Post by philba » Tue Jul 01, 2008 11:02 am

Craig wrote:
The best choice is a switching regulator, built from a Simple Switcher
IC chip available from National Semiconductor, or another type
of switcher chip.
This sound like a good idea, however, I have looked and looked for a 20-24 volt, 3 amp+ voltage regulator but have been unable to find one. Do you know the part number for one, or point me in the right direction?
I would look at the LM25116. It requires a couple of external mosfets but looks like it would meet your needs.
http://www.national.com/pf//LM/LM25116.html

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