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DCC Impulses - Using Ohm's law Magazine feedback
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MRH Media 2,999 posts MRH MRH Media 2,999 posts
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2013-p31.jpg  Click to read this in landscape orientation …Click to read this in portrait orientation …

Read this issue!


Please post any comments or questions you have here.
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santafe49 Active Member 36 posts
santafe49

DCC tester

Both subjects in this column were great. Easily understood and well documented. While i won't use as a camera supply, they will be great for car lighting. And the DCC tester is also a good idea. For a quick check on newly install feeders, muchh easier than dragging out the meter. Thanks for the info.
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nvngrr New member 10 posts
nvngrr

Great article Bruce. I

Great article Bruce. I actually understood it.  

KevinM

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Kevin

Winlock, WA
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JoeKnapp New member 16 posts
JoeKnapp

Another Nice Article

This was a very informative article. I really like your presentation style. Keep them coming!

Joe
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Joe Valentine Active Member 88 posts
Joe Valentine

Always learning something new

Bruce, you always explain things in such a way that it always becomes much clearer...while not building a camera car etc. you unveil they mysteries of electronics to a novice like me....thanks for the great columns, I look forward to them every month....Joe
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splitrock323 Prolific poster 1,364 posts
splitrock323

Good subject, great tip

Thanks again Bruce. DCC is not my strong suit in this hobby, so I appreciate you and many others who help guys like me understand all of this fun stuff. I also like the idea of the LED tester. Faster than dragging out the meter every time, as noted above. Thomas G. PS- Yes, I will take an extra LED tester off your hands.

Thomas W. Gasior MMR

Modeling northern Minnesota iron ore line in HO.

YouTube: Splitrock323      Facebook: The Splitrock Mining Company layout

Read my Blog

 
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DKRickman Prolific poster 3,069 posts
DKRickman

Battery charge current

Is 0.1 C a standard trickle charge current for Ni-mH batteries of all types, or just the ones mentioned in the article?  I'm considering using something like that in place of a keep-alive capacitor for a DCC decoder, or possibly even for something like the Tam Valley wireless system in the future.  It would also be useful in a number of other situations, if I want lights in a car, for example.

While on the subject, what about other battery chemistries, such as NiCad or Li-Po?

Ken Rickman

Danville & Western HO modeler and web historian

http://southern-railway.railfan.net/dw/
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Bruce Petrarca Frequent poster 920 posts
Bruce Petrarca

0.1 C . . .

is a good number for NiCd or NiMh. If you exceed that for extended periods of time, you overheat and, possibly, damage the battery. Not a BIG deal. Lithium are their own universe. Improper charging can result in explosions and fires. That IS A BIG DEAL! I don't know enough about Lithium chemistry cells to comfortable rolling my own charger. Nor will I design a fast charger for Nickle chemistry!

Bruce Petrarca, Mr. DCC; MMR #574
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DKRickman Prolific poster 3,069 posts
DKRickman

Ideas are brewing

Thanks, Bruce.  Using track power to recharge onboard batteries for radio control has intrigued me for quite some time, so when I saw your column that's immediately where my mind went.  I have a feeling I'll be referring back to this issue a few times!

Ken Rickman

Danville & Western HO modeler and web historian

http://southern-railway.railfan.net/dw/
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mrfecteau New member 17 posts
mrfecteau

Thanks

I really enjoy the electrical and electronics topics in your column. Not being very experienced with electronics your articles/columns have encouraged me to both get into DCC and experiment with electronics.

Thanks again for your clear, easy to understand discussions.

Mark Fecteau
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lester perry New member 21 posts
lester perry

Using track power

I was wondering if this DC power could be used to power lights in a signal or even a relay?
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Benny MRH Author 7,125 posts
Benny

...

It's best if you have a dedicated power source - in otherwords, you take that old Bachmann brick and use the DC track leads.  They're good for up to 12-14 volts and a couple amps...at a safe level.

--------------------------------------------------------

Benny's Index or Somewhere Chasing Rabbits
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Bruce Petrarca Frequent poster 920 posts
Bruce Petrarca

As Benny suggested, Lester,

Best to use some other source for your lighting and other fixed needs. For one, it doesn't take power away from your rolling stock, that are best served with DCC. So, yes, it could, but I recommend against it. On our club's layout, I wanted lighting power for a bunch of buildings in South Bend (http://www.pcmrc.org/south_bend.html). I wanted it to go down if track power was lost (off or circuit breaker tripped). I mounted a surplus power supply in a box with a relay driven from track power through a circuit like the power supply section of this article. The relay draws less than 0.1 amp, but turns on and off up to 17 amps of lighting power!

Bruce Petrarca, Mr. DCC; MMR #574
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SD40-Tom New member 23 posts
SD40-Tom

Power flow during track power loss

Hi Bruce    Thank you for all the great articles.  Trying to understand the power flow when track power is interupted?  refering to diagram #8.   Is the on/off switch an electronic switch?  If so, how is it activated?  I thought diodes could only allow power flow in one direction?    Thank you   Tom
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SD40-Tom New member 23 posts
SD40-Tom

Bruce. I reread one of your

Bruce. I reread one of your previous articles and found the answer.  Thank you again for the great articles
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Bruce Petrarca Frequent poster 920 posts
Bruce Petrarca

As you figured out, Tom,

the switch is a physical switch to power the camera from the battery. Turn it on, run the camera, turn it off. With the switch off, the camera is running on track power only, no battery back-up.

Bruce Petrarca, Mr. DCC; MMR #574
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Michael Tondee MRH Author 5,522 posts
Michael Tondee

BTW.....

If you write OHM's law like this  _  E _                                                                                                                                                                                       I X R        

You can always figure out which equation you need by covering the value you want to solve for. Same with the power equation. The line is supposed to be solid for division but it's the best I could do. Just a little trick I learned years ago when preparing to take my ham radio license exam. Before long you just remember the various ones but when I was a nervous 15 year old taking my test, writing that "crutch" on my scratch paper saved me!

Michael                                                                                                

Michael, A.R.S. W4HIJ

 Model Rail, electronics experimenter and "mad scientist" for over 50 years.

Member of  "The Amigos" and staunch disciple of the "Wizard of Monterey"

My Pike: The Blackwater Island Logging&Mining Co.
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Ken Biles Greyhart Frequent poster 551 posts
Ken Biles Greyhart

Ohm's Law

Yes, I learned Ohm's Law the same way in High School Electronics.

           __E__

             I x R

You just have to remember which is Amps and which is volts. As long as you have any two of the three, you can figure out the third.

  • E = I x R (Voltage = Amps times Resistance)
  • I = E / R (Amps = Volts divided by Resistance)
  • R = E / I (Resistance = Volts divided by Amps)

It's one of the most useful formulas you'll ever learn, and if you put it into an Excel Spreadsheet, you can create a table that will give you the answers automatically.

 

 Ken Biles

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Bruce Petrarca Frequent poster 920 posts
Bruce Petrarca

One more analogy

Again, from high school electronics: E = Eagle I = Indian R = Rabbit The eagle sees the Indian and the Rabbit on the same level, therefore E = I x R. The Indian sees the Eagle flying over the Rabbit, therefore I = E / R. The Rabbit sees the Eagle flying over the Indian, therefore, R = E / I. Before somebody pokes me for political correctness, I'll relate a story. I was at a concert by R. Carlos Nakai, a multi Grammy award winning Navajo-Ute flute player. Between songs he asked the audience to raise their hands if they were born in America. He raised his, too. Then he said, "See, we are all native Americans. I'm an Indian, too!" For you hams out there, 73 de KX0E!

Bruce Petrarca, Mr. DCC; MMR #574
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GeorgeV New member 18 posts
GeorgeV

I know Olm's law but....

I have known Olm's law and what a capacitor does but I never thought about actually trying to design something.  Great article, easy to follow.  I may actually create a circuit one day!

George V.
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Bruce Petrarca Frequent poster 920 posts
Bruce Petrarca

Great, George!

That was my hope. Start simple, like an LED and battery and a resistior.

Bruce Petrarca, Mr. DCC; MMR #574
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Bruce Petrarca Frequent poster 920 posts
Bruce Petrarca

Ron Smith's DC question

Ron started another thread about a dc use of this circuit. I'm moving his question over here.

Quote:

Tue, 2013-06-11 23:10 — smithron455 Track and electrical/DCC

The article was just what I was looking for.  I have inserted a mini-camera into a dummy diesel loco and have powered it with a 9-volt battery with a mini on-off switch.  I am not using track power at all because I reasoned that its ups and downs of voltage would cause the transmission of the camera picture to be an on again-off again condition.  Your circuit seems to solve the problem of not only constant power to the camera, but re-charging it from the tracks so that it doesn't run down.  My layout isn't DCC sophisticated, but even a straight DC setup can be considered with your circuit in place.

I wish, however, that you had actually built the circuit on a small board to show the components in place and properly soldered, et.al.  I understand electricity and electronics a little bit, but would be much helped if I knew which ends of the diodes to solder to which ends to make the bridge rectifier--or to know which of the four legs of the module to connect to the wiring shown.  Seeing the whole circuit in reality would clear up any questions of getting from the schematic to the actual circuit.

Ron Smith

I never built the circuit in a format that would go in a model. The waveform came from a circuit "breadboard" of the power supply section only. I'm not too sure how much good a look at it would be, but here it is.

5435-001.jpg 

As you can see, the DCC signal goes to the two pins on the rectifier labeled with ~ and the DC side is labeled + and -!

Not having constant, known voltage on the track at all times, makes the DC version pretty complex. It will take about 11 volts on the track to charge the battery. Most trains run so fast on that voltage that the results wouldn't be a pleasant sight.

My suggestion is to build the circuit as shown, less the one resistor for the camera, and buy (or scrounge) a wall-wart power supply in the range of 15 to 18 volts. OFF THE LAYOUT, connect this power supply to a short length of track. Store the car there when it is not in use, with the power supply connected to the wall. That will keep the battery topped up. It will run the camera for about 2 to 3 hours on a full charge. If you fully discharge the battery, it will take a full 24 (or more) hours to get back to a full charge. The charge current is only a few milliamps, so most any current rating will work (50 mA or larger).

Bruce Petrarca, Mr. DCC; MMR #574
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