Deep fried controller components


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psychobeagle12

Member
Ok, as most of you know by now I am making a DC controller for my layout. I purchased potentiometers today, two of them. I think I must have miscalculated the value for the wattage. Here is what I have:

Track B has a supply voltage of 15 volts and the three locomotives I tested ran about .3 to .5 amps each. I used a craftsman multimeter set to detect 10 amps and got readings of 0.31 and 0.53 I think. So what I calculated was 7.5 watts through the potentiometers? If this is correct I need to get some higher wattage potentiometers since the ones I bought handle 0.5 watts. I think they are for stereos. I only ask because when I wired them in I got a nice red glow and a bunch of smoke which I don't think is correct :rolleyes:. So does anyone have any advice as to where I could get the potentiometers I need? RadioShack doesn't have ones above 0.5 watts (suggestions on how to make these ones work would be welcome as well!)
 
It's very primitive to run trains directly off a potentiometer. You need a large expensive pot to handle the power, it burns electricity and stays hot all the time, and you get lousy control. What's not to hate?

Nowadays you'd want a transistorized (microprocessorized, maybe) throttle. There are plans to build one yourself, or you can still buy them, at least until DCC stamps out the last few holdouts.
 
Ah :( Well thats fine I guess I will try to build a transistorized version then. Would I be able to apply the pots that I bought to do so? I will look up the plans and hopefully find a good one.

Ok so I found a plan that is relatively simple that provides braking and minimum and maximum speeds. It can be adapted for a walk-around variety but since my layout is small I'm not going to go that route. However, this throttle uses a BFY50 NPN Transistor and the only place I can find them is on ebay from the UK! I would rather not have to order them from so far away but I can't seem to find a compatible transistor anywhere. Does anyone know what transistor would work w/ this? I'm sorry I'm still not great w/ transistor applications and I would rather not hazard a guess as to compatibility.
 
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Is this the design?

http://www.xdford.digitalzones.com/modelrr8.htm

There the 15K value of R2 makes it clear that the first transistor (TR1) is working in a low-current mode, as the first stage of a Darlington pair along with TR2. So I'd say that any small signal transistor would do the job, like a 2N3904 or 2N2222 ,which cost next to nothing.

However, thinking of the title of this thread, I don't see any provision for overload protection in that design, except maybe the gain of the transistor pair, and that's not at all predictable.

Rich Weyand's Cooler Crawler is really good:
http://users.rcn.com/weyand/tractronics/articles/ccartcl/ccartcl.htm
 
If all you want is a straight forward DC handheld, and are prepared to DIY it, I have a circuit for an "idiot-pruf" throttle from MR away back - It only has a few components. It will need a 12vdc input from a transformer and is the same as the one shown here http://carendt.us/sc...e75a/index.html with the battery replaced by a 12v 1 amp walwart transformer. Make sure that the LM317T is fitted to a heat-sink as it may get warm
 
For overload protection I was going to wire a fuse into the controller that was 1 amp lower than the rating of the power pack that I am going to get. Maybe I will have to look through some of the other throttles and pick one but I really like the design of the first one I said because I understand it and it seems relatively simple.

Edit: In addition, I plan on building three of these controllers. One for my outside main, one for my inside main, and one for my switching yard. I plan on using a laptop power supply rated for 15 volts and hopefully about 3 amps. With that first circuit design will this be enough? Like I said, I'm not a novice circuit builder I have been around the block a few times but am by no means an expert and don't want to make even an educated guess at anything. Thanks guys I prefer to rely on asking so that I don't go up in smoke :)
 
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I built a transitorized throttle about 20 or 30 years ago and it still works fine. I have perfect control with it: brakes; momentumn ect ect. get in touch through my Email and I will be able to help you better.
 
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