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I recently built the "second simplest throttle" A transistorized throttle from Peter Thorne's book Model Railroad Electronics. I built it as a tethered walkaround which I love. Even though I like the "relatively" smooth starts and the feel of the throttle, I am bothered by 2 things. First, the potentiometer is nearly to the halfway point before the locomotive begins to move. Second, then I have to back off a little to get the slow speed operation I want for yardwork/switching. My layout is an industial switching layout with hidden staging. From what I understood from Mr. Thornes book, this throttle is not supposed to be like that. I came across a website recently called the Armadillo and Western which has several throttle projects you can build. One design that I am interested in is a simple LM317 transistor based design. Has anyone built one of these and does it operate better than the 2ST? I have also seen Ken Stapletons site and the beautiful throttles he builds but I would really like to build my own and I can't really afford one of his just yet. Thanks for any feedback!
I'll bet that's the book with the Pacematic throttle in it too. The other two are on my computer desk here. I'll have to hve another look for it unless you have a scanner or can make a rough drawing for me. Sid you substitute any of the components? Kind of sounds like you used a non linear potentiometer instead of a linear. But then again it might be the circuit itself. If you can't post a drawing I'll have another look for the book, I have all three.
Willis
I've found all the books by Peter Thorne that I have [Practical Electronic Projects 12023] [34 New Electronic Projects 12057] [Easy to Build Electronic Projects #12081] and that throttle 2ST isn't in any of them. It must be a book I don't have.
So next question what brand of loco do you have? Some brands have that require more current to get them turning but once turning they require a lot less. The cureor help for that is a pulse throttle {unfiltered DC is not the best but it's simple and sort of works.
Willis
I was going to suggest the locomotive as well. I have pulse throttles (MRC Tech II Railmaster 2400) and have much better slow speed start up with Pulse enabled than with it disabled. Like, slow speed start up exists with it enabled but does not exist without it.
Ok, the full name of the Peter Thorne book is Model Railroad Electronics: Basic Concepts to Advanced Projects. I did not realize there were so many books by him The cover is a picture of an EMD F unit in the Canadian Pacific burgandy and gray color scheme. I used a 5k ohm 0.5 watt linear taper potentiometer for speed control. I actually followed the instructions closely using the Radio Shack part numbers from the parts list. The design, according to Mr. Thorne's description, produces a smooth pulsation at 120hz. This throttle reacts the same with all my locomotives,
Athearn Genesis SD45-2 (dc only)
Athearn RTR SD40-2
Athearn Blue Box GP40 upgraded to newer Athearn motor
Front Range GP9 with newer Athearn motor and trucks
Proto 1000 GP15-1
Bachmann SD40-2
and all the other Athearn locos I used to have but had to sell
I will try to post the schematic soon, dont have internet access at home currently. Thanks so much for the replies!
the "simple transistor throttle" circuit is pretty simple. it uses rectified but unfiltered DC, which should help with slow speed performance, but may result in buzzing at 120 Hz. This type of transistor circuit was suggested by paul mallory in his book back in the 70s. But I have to wonder if the switch connected to the tracks shouldn't be on the collector side of the transistors instead of the emitter (this way the base voltage is references to ground and not the output voltage). An SCR circuit may be just as simple
The LM317 is a variable voltage regulator not a transistor. But i thought it's minimum output voltage is at least a volt, so it can never be fully off.
i thought pulse width modulated (PWM) is common practice today. Sort of an improved version of the stt. somewhat fancier electronics is needed and it switches has a higher frequency, so buzzing isn't an issue.
Question. Did you install the optional indicator lamp?
If so, while the engine is slow moving, is the light bright or dim?
Do you have a volt ohm meter even a cheap one?
Before getting too deep into it, check all your soldered connections, ensure they are smooth and shiny bright. If any are a dull silver color, or look crystaline, reheat them to melting and let cool. Check all connections ensuring mechanicaly sound (not movable)
TR-1 The TIP 120 is just a Darlington transistor (2 transistors in one case) It controls the emitter base current of the 2N3055 TR-2 which is a power transistor, it's a very common circuit.
What are you using for the transformer "T" and what is it rated for? (Volts and current) if it's a wall wart type it may not be able to supply enough current and the locos build up speed through momentum.
I must change part of my previous post. The Bachmann loco requires way more throttle than my other locos before it begins to move.
Greg I guess you answered my question about the lm317 based throttle. And another look at the schematic made me realize it is filtered DC so it would not produce the pulse I am looking for. Pulse Width Modulated is the way to go...
Willis, I was using the track outputs set at maximum of an old power pack I had laying around as my power source to the throttle. Then I aquired a rectifier and switched to the fixed AC outputs of that power pack. The slow speed operation improved, but the locos still did not begin to move until nearly half throttle. Except the Bachmann which required nearly 2/3 throttle I then tried a 12.5 volt transformer I salvaged from a Triplight power supply. I know its a beefy one because my Fluke meter measured nearly 10 amps when I used it to test some power window motors I installed in a customers car! That transformer made no difference in the throttle gain. I did not install the optional indicator lamp, all my solder joints are good. I need to remember to bring my meter home from work when I know I will be playing with the layout and measure voltage at the track.
The power pack I'm using is 7VA max at 20 volts on the AC outputs. The Triplite T is 12.5 volts at around 10 amps. Maybe my issue is wattage.
I experienced the same problem with the first transistor throttle I ever made. Since these are NPN transistors I would try a 500ohm or K resistor on the negative side of the 5K pot. That should move the sensitivity to the one end of the throttle in two ways. It reduces the reverse-bias on the first stage transistor and makes the low end of the throttle be closer to the cross over of reverse-forward bias.
As they say this is a very simple throttle. Many that I have seen have pots on either side of the main throttle POT just to control the sensitivity and max speed.
Another thing I don't see in that circuit is any reverse-bias resistors to prevent leakage of less than perfect transistors.
If you can get hold of a copy, MR away back had an article about an ultra simple "Goof Proof" throttle using an LM317 - it only has a half dozen or so parts and works fine - make sure you use a heatsink - they can get awfully warm very quickly! Also on the AWRR site - the "Not-a-throttle" is a good bit of kit for switching - acts like an electronic gearbox
7 VA is close to 3 amp output so it's unlikely the problem is there unless there is an actual fault with transformer. Two things to know now (1) Resultant track voltage as throttle is increased, and (2) Voltage at the rectifier bridge as throttle is increased
I believe it's more of a voltage drop across a component thats causing your problem, the above 2 tests will determine if it's the bridge rectifier or the transistor cct.
I experienced the same problem with the first transistor throttle I ever made. Since these are NPN transistors I would try a 500ohm or K resistor on the negative side of the 5K pot. That should move the sensitivity to the one end of the throttle in two ways. It reduces the reverse-bias on the first stage transistor and makes the low end of the throttle be closer to the cross over of reverse-forward bias.
As they say this is a very simple throttle. Many that I have seen have pots on either side of the main throttle POT just to control the sensitivity and max speed.
Another thing I don't see in that circuit is any reverse-bias resistors to prevent leakage of less than perfect transistors.
7 VA is close to 3 amp output so it's unlikely the problem is there unless there is an actual fault with transformer. Two things to know now (1) Resultant track voltage as throttle is increased, and (2) Voltage at the rectifier bridge as throttle is increased
I believe it's more of a voltage drop across a component thats causing your problem, the above 2 tests will determine if it's the bridge rectifier or the transistor cct.
Hey Willis, I thought VA (or wattage) was calculated by voltage x amperage = wattage If I have voltage (20) and wattage (7) than to find amps I would divide 7 by 20 which would equal .35 amps. Unless I have it all wrong?
Anyway, using my DVOM I measured DC voltage at the rails with my Proto 1000 GP15 on the track. As I turned up the POT voltage began to register at around 1/8 gain. The motor began to hum at around I volt and sporadic movement at about 1.5 volts. By about 2 volts I had somewhat smooth running. It was a little fast for coupling but acceptable. I then increased the throttle to maximum while watching the meter. Voltage increased smoothly and maxed out around 16.5 volts. Now when I double head my 2 Athearn locos voltage results are cut in half. Slow speed movement is terrible and max speed at about 8 volts is quite slow for mainline running. Now when I measure the AC voltage at the power pack before the rectifier idle voltage is 20.4 volts. As throttle is increased AC voltage drops to 18 volts. There is only about a half volt difference between the loco starting to move and running. I will say that slow speed operation has improved now that I am using the AC outputs with a rectifier
The cover is a picture of an EMD F unit in the Canadian Pacific burgandy and gray color scheme. I used a 5k ohm 0.5 watt linear taper potentiometer for speed control. I actually followed the instructions closely using the Radio Shack part numbers from the parts list. The design, according to Mr. Thorne's description, produces a smooth pulsation at 120hz. This throttle reacts the same with all my locomotives,
