# DC power question



## lincoln pin (Feb 24, 2009)

Hello All,
I am an electronics neophyte, but can solder and have wired many indoor small scale layouts. I have a MRC AG990 Power G 10 Amp power pack, I would like to run two independant loops of track with independant control. Could I use the transformer as a DC power supply and make some sort hand held control. Something to to control direction and speed. What would I need to do this? 
Thanks, Mike Anderson


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## Stan Cedarleaf (Jan 2, 2008)

Mike, you sure can. You use one of the 27 mhz Aristo Craft train engineeers but you must maintain the proper positive/negative input polarity at all times. Plus to red, minus to black. Lock the direction switch so it can't be reversed........ OR... If you have 20-24 volts DC coming out of the power supply, hook the TE up there.

The new REVOLUTION will handle up to 24 volts and you don't need to worry about polarity.


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## lincoln pin (Feb 24, 2009)

Stan,
Thanks for the quick response, I forgot to mention that I am a cheap a$$ (on a tight budget) and would like to cobble something together. Unless the Aristo TE is the the cheapest way to go, I have more time than money !


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## altterrain (Jan 2, 2008)

These are pretty cheap for speed control - http://www.bakatronics.com/shop/item.aspx?itemid=444 
You'll have to use a DPDT with it for direction control. 

-Brian


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## Greg Elmassian (Jan 3, 2008)

The Aristo 55401 is a controller that is wired, and of course a lot cheaper than a wireless system. Take a look at that and see if it fits your bill. 

Regards, Greg


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## Dan Pierce (Jan 2, 2008)

A controller of sorts can be built. What will be run? 

LGB with sound units will not like the PWC type of controllers, the sound units get confused. 

You can build a circuit with a LM 338 or LM350 and use a DPDT center off switch for direction control. This type of unit will run most any engine if the power source is DC. 

DC supplies are available from MPJA.com at good prices, under $20 and for over 5 amps at 24 volts!!! 

http://1stclass.mylargescale.com/danpierce/LM350T.bmp 

LM350 for 3 amps, LM338 for 5 amps. 
Output will not go to 0 volts, hence the center off switch. 
LM device needs a good size heat sink as it can get hot with a large current drawing engine/train.


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## lincoln pin (Feb 24, 2009)

Dan, Can you check out:
http://1stclass.mylargescale.com/lincolnpin/Dan.bmp
I have some questions concerning your schematic
Thank you,
Mike Anderson


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## Greg Elmassian (Jan 3, 2008)

I'll try to help, but I hope I do not screw it up for dan!










The capacitor on the input should not have had a plus and minus, it probably should have been a 0.1 mfd disc capacitor, since Dan talks about noise.
The capacitor to the right of the regulator ic likewise...

The last capacitor is an electrolytic, the plus and minus are correct, and he meant the "working voltage" of the capacitor can be double the output voltage... you always want to have some "margin" in electrolytic capacitors, they do not tolerate overvoltage well.. electrolytic capacitors are rated in microfarads (mfd) and the working voltage. The more of either, the larger and more expensive they get... so get an electrolytic that is AT LEAST twice the output voltage of your circuit.


Of the funny "uf" really should have been the greek letter/symbol... I use mfd becacuse I cannot find the "micro" character... same difference...

Yes ohms is a resistor, Dan should specify the wattage here...

you can get everything at Radio shack, and using the terminology I used, people in the store should understand you.

Regards, Greg


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## lincoln pin (Feb 24, 2009)

Wow! Thank you Greg. So if my input voltage is 22v dc then what would be the output voltage, so that I can figure what I would need for the electrolytic capacitor? This might be the first of many questions. Thanks,
Mike


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## Greg Elmassian (Jan 3, 2008)

Output can be no higher than input... 35v would be fine... especially if it's relatively clean input power.. 

Bring on the questions... 

Greg


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## krs (Feb 29, 2008)

I made two changes to the circuit shown if it's used as a throttle - I assume that's the application. 

For one, if the wiper of the 5K pot ever looses contact, the output will jump up to the maximum voltage as determined by the 330 ohm and 5K resistors. 
The other problem is that the voltage never goes completely to zero so my LGB engines never stopped. 

First problem can be fixed by arranging the pot and resistors differently, the second by adding a diode at the output of the regulator to give an additional voltage drop. 

Knut


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## lincoln pin (Feb 24, 2009)

Thank you Knut, Yes this is going to be used as a throttle. Can you elaborate on the "by arranging the pot and resistors differently" and what (size) type of diode you would use. Do you have a schematic?
Thanks,
Mike


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## krs (Feb 29, 2008)

Mike -

I used this resistor arrangement shown in the lower diagram but I don't remember which actual values I used.
The "standard" arrangement is at the top, the alternate arrangement at the bottom. I just didn't want to take a change of my engines suddenly taking off at full speed.










I also used a relay to switch polarity instead of the DPDT switch and the relay was set up so that one could only change polarity (ie direction) if the throttle was at zero.
That was mostly for kids using the throttle - I didn't want them to change direction while the engine was moving at any speed.


As to the diode at the output to drop the voltage - if you don't have any LGB ebgines, you may not need the diode.
I just mentioned it if you have the problem where the loco won't stop even when the throttle is at zero. 
The diode is just any silicon diode with a current rating equal or higher than the rating to the adjustable regulator.

Regulators I had senn at the time - this was years ago - were available with 3, 5 and 10 amp outputs. 


In general I found that this throttle works very well because it keeps the output voltage constant (whatever you set it to) under different loads liked going up and down hill.
On many commercial model train throttles the output voltage drops as the current draw increases. going up a hill say, that slows the train down more than you would like and one usually has to compensate by adjusting the throttle.

Knut


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