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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 . 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.
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.
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
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.
. 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!)
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.
