I decide t obuild this throttle to go on my DC layout because it sounded like a fairly easy project, i followed the direction pretty much word for word but right now its not working.
i got all the part, the only exception was to use a plastic box but use an heatsink on the transistor. i started by drilling all the hole then hooking up the + and minus to the opposite pole of the 1k pot. then i ran the + and - to the pilot light, so far so good, a quick check and the light light up.
the + terminal then is connected to the C of the transistor, the negative is connected to a 100K 1/4 watt resistor. the resistor then connect to the B of the transistor. The B of the transistor then hook up to one end contact of the DPDT . the - terminal from the pot to the opposite side. finally a diode hooks up to the positive side ( band side to +) and negative of the DPDT.
Now i hook it up, ran power and smoke started to come out. the diode almost melted and the transistor got super hot. i figured: not good at all. so i let it be overnight. This morning , i figured, isnt a LED , nothing more than a fancy light on a diode? so i thought, lets use it to check. so i hook up the LED same way as the diode was uppose to be ( i also use a resistor to make sure i wouldnt damage the LED) now i plugged it up... No smoke, no melting anything... so i thought: cool...
next step was to check and see if it worked, so i used jumper leads to connect to a nearby athearn engine. turned power on, flick the switch and the engine took off... i mean, TOOK OFF. its as if the engine is getting full 12V power and is running a full speed. i tried to play with the pot, tried to use the variable DC... nothing work. its almost like the pot doesnt control anything... the DPDT works fine, the pilot light is alright, the transistor is ok too, doesnt run hot ( just barely warm after 5-10 minute)
now heres what i can deduce:
maybe the pot doesnt work: it would explain why i have to control over the output
maybe the "real" diode will make it work: i doubt it but im no expert
maybe the pot should be increased to 2K: although i dunno if this would change the control issue
any help would be greatly appreciated, i planned originally to build a few of these to use on the layout, hopefully, ill get all the gremlins worked out of this one with your help
I'd have to go dig up that issue to see the circuit to give the best help - I'm at work right now. But a couple things come to mind. First, do you have the correct transistor? You cannot subsitute an NPN for a PNP or vice-versa without completely changing the circuit. Second, i see no mention of conencting the Emitter lead of the transistor to anything - a typo or is there really no wire conencted to that terminal? Something needs to connect there. Third - are you mixing up the transistor terminals? Are you sure what you are using ase the Base is the Base, and Collector is the Collector? Fourth, the position of the diode sounds wrong. The purpose of the diode is so that if you have multiple cabs and you accdently connect two to the same block at the same time, power will not flow into this throttle and damage the transistor. As such the diode should ben in the lead coming from the transistor going to the reversing switch - before the switch, not after it, or your traisn will only run one way. The way you described it, the diode was wired as a dead short across the output of the throttle.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Check the January and February 87 issues to see if they printed a correction. Sometimes they print a circuit that is screwed up and then print the revision a few months later when they realize what has happened.
1- yes i have the transistor described in the article 2n3055
2-E connects to + of DPDT switch ( i know theres no such thing as a + side but one of them has to be the + and the other the - otherwise nothing is going anywhere_
3- the clerk checked it with me, the transistor is offset so u can position it only one way and get the correct reading, beisde i used a simple set of test lead to check this afternoon and the transistor does work
4-I dunno, the article says it can be wired anywhere but the most logic place is across the + and - on the dpdt
thanks, hopefully ill get this running
You did not wire the circuit correctly. Look very closely. The 100 ohm resistor DOES NOT go to minus.
The 100 ohm resistor is between the center pot connection and B of the transistor.
A LED with a 1k resistor makes a good indicator. Do not use an LED as a diode.
One side of the pot to input plus and C.
One side of the pot to minus.
The Cathode, white band, to the E and Plus output lead to switch.
The other side of the diode to minus and output to switch.
If you use the TO3 case, the metal case is C. Looking at the bottom of the device, the left terminal is the B and the right terminal is the E with the device so the leads are closer to one hole.
Also, get your self a digital multimeter at Radio Shack and learn how to use it. The last I knew, they had one for about $20.00. I have bought a couple cheap ones of off ebay for about $10.00 to $12.00.
[url]http://www.google.com/search?hl=en&ned=us&q=using+multimeter&btnmeta%3Dsearch%3Dsearch=Search+the+Web[/url]
Again, take your time and trace everything out. I have the schematic in front of me.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
OK, have the issue in front of me. There's your problem. R2 is 100 ohms, not 100K ohms.
Banded end of the didoe needs to go to the E terminal of the transistor, however you actually place it. And be sure you feed the DC from the pwoerpack in the correct way. A simpel way to make sure would be to put another diode (oh, an LED will NOT work for this - you need a diode of the type specified) in line with the input so that the power pack + wire conencts to the NON banded and the banded end connects to the potentiometer where the pwoer pack + wire used to connect. This will block anythign from goign wrong if you hook up the power pack backwards - the pilot light won't even go on if you wired everything like the picture shows.
If you got the 1K potentiometer from Radio Shack the control isn't going to be that great because RS pots are Really S*****. The circuit will work but there will be a large dead band where nothig happens so only part of the pot's rotation will actually control anything. Best to get a good quality one from a supplier like Mouser - Bournes is a respect and quality name.
My $5 multimeter from Harbor Freight works quite well
I suspect he has one because he mentioned testing the transistor.
As cacole suggested, check the following months. There was a correction to the schematic printed in a later month.
When I built the throttle I still had some problems that required a little more "tweaking" even with the correction. Once I return home I'll see if I can find the MR corrections and my changes. I'll update this thread with the info in the next day or two.
I did get the throttle to work and it worked well. I would suggest a metal box to help dissipate the heat, and it will get warm. I went Digitrax and no longer use the throttle. If someone is interested I would offer it for sale.
Docgartner
The follow up is May 1987, page 93. Look below at the link.
http://index.mrmag.com/tm.exe?opt=S&cmdtext=THROTTLE&sort=A&output=3&view=150
There is no correction. The update refers to buying a 1k pot from Jameco which the article says Radio Shack does not stock.. The other update is the 1k pot was replaced by a rotary switch which selects eleven different resistors for step speed control.
If the circuit is wired exactly according to the schematic, it will work. I have built this throttle. The aluminum chassis helps for heat dissipation.
For one throttle I used a logarithmic pot which compresses the low end so I do not have to move the pot very much before the loco starts to move. I do not know if those pots are available anymore as I did that around 1984.
One throttle I built, I put a small trim pot, 500 ohms I think, between the bottom of the 1k pot and minus. I adjust the trim pot with the 1k pot at zero until the loco just begins to crawl. I then back down the trim pot a little. This can vary with different locos. Turn the 1k pot and the loco starts sooner. I like to experiment.
Not sure you are aware of this but if you connect the 1k pot top and bottom the incorrect way, with the knob fully CCW or zero, you will have full throttle. Reverse the wires. I did that years ago. This is where it is good to have a multimeter. Use it to see if your throttle goes from zero volts up to maximum of 12 volts or so without having to sacrifice your loco.
Let everyone know your results. Good luck.
Ranchero,
Sorry, but it would seem I have confused the electronic throttle you were building from the Dec '86 issue with the walkaround transistor throttle from Jan '86 that I built. That throttle is pretty neat with its ability to unplug and walk to the next plug and the train continues with its memory.
Good luck with your search for solutions.