CSX RobertAt speed step 1 it showed ~0.9 volts and the light was on but very dim.
have you tried using Schottky diodes? lower voltage drop
greg - Philadelphia & Reading / Reading
gregc CSX Robert At speed step 1 it showed ~0.9 volts and the light was on but very dim. have you tried using Schottky diodes? lower voltage drop
CSX Robert At speed step 1 it showed ~0.9 volts and the light was on but very dim.
There was no diode in the circuit. I had just the bulb wired straight to the decoder output and then added a capacitor.
Poor OP.All he wanted was a circuit of 4 diodes, which is "close enough" to full brightness before motion.Just like I used for 25 years before switching to DCC. 4 1 amp 50 PIV diodes.Boom. Done.
Disclaimer: This post may contain humor, sarcasm, and/or flatulence.
Michael Mornard
Bringing the North Woods to South Dakota!
Overmod There was a famous quote in one of the Doc Smith Lensman novels about 'women driving automobiles' -- if you know how to turn the key and pull the levers and work the pedals, you don't need to know about spark and combustion and gear surface finish. Until it makes a funny noise and stops... and you have to decide whether to keep going or call AAA...
There was a famous quote in one of the Doc Smith Lensman novels about 'women driving automobiles' -- if you know how to turn the key and pull the levers and work the pedals, you don't need to know about spark and combustion and gear surface finish.
Until it makes a funny noise and stops... and you have to decide whether to keep going or call AAA...
Rich
Alton Junction
richhotrainThe problem with that chauvinistic logic, of course, is that if a woman knew about spark and combustion and gear surface finish, she would know what to do when the automobile made a funny noise and stopped.
And yes, when a woman knows about spark and combustion and gear surface finish, it's not a 'funny noise', it's a symptom for diagnosis.
To answer the OP's question;
rbturner
seems odd that the lamp circuit is in series with the motor. can see how the lamps come on right away but reduces the motor voltage by ~2.1V
Yes, it does. I've never had an engine fail to run easily up to 60 mph or so, however.
gregc rbturner seems odd that the lamp circuit is in series with the motor. can see how the lamps come on right away but reduces the motor voltage by ~2.1V
I had that circuit in all my engines years ago. I also added a metal stop on the throttle knob so fully counter-clockwise wasn't completely off, but still about 1.5 to 2 volts. That way, I could stop the engine with the light still on not looking at the throttle setting.
As for taking away the first 2 volts, didn't pose a problem as they didn't need to run like slot cars anyway.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Been out of town several days....
Wowwww! This thread is long enough to make a high-end, king-size bed sheet! I appreciate all the input and discussion. As I said, I'll probably try the circuit M.L. Rollins published on his website, which appears to be the same one Randy Turner shows in his post.
I'm still wondering, though, how the diode pairs in parallel with the lamps prevent voltage to them from rising above 1.5 as the track voltage is increased; since that's their apparent function, why are two instead of a single, diode necessary to do that?
Also, it appears that the 3rd pair of diodes are the ones that control directionality since one pole of the d.c. supply is connected at the junction of the diodes' anode and cathode. When the polarity of that pole is alternated between positive and negative the direction of the loco changes accordingly. Have I got that right?
As I said earlier, my knowledge of solid-state electronics is limited. My electronics background comes from the era of vacuum tube technology when I got into amateur radio way back when (!).
staybolt Been out of town several days.... Wowwww! This thread is long enough to make a high-end, king-size bed sheet! I appreciate all the input and discussion. As I said, I'll probably try the circuit M.L. Rollins published on his website, which appears to be the same one Randy Turner shows in his post. I'm still wondering, though, how the diode pairs in parallel with the lamps prevent voltage to them from rising above 1.5 as the track voltage is increased; since that's their apparent function, why are two instead of a single, diode necessary to do that? Also, it appears that the 3rd pair of diodes are the ones that control directionality since one pole of the d.c. supply is connected at the junction of the diodes' anode and cathode. When the polarity of that pole is alternated between positive and negative the direction of the loco changes accordingly. Have I got that right? As I said earlier, my knowledge of solid-state electronics is limited. My electronics background comes from the era of vacuum tube technology when I got into amateur radio way back when (!).
Yes, when the right hand rail is positive, the loco moves forward and the front light is on.
When the right hand rail is negative, the loco goes backwards and the back light is on.
Depending on the power pack/throttle you have, and the current draw of the motor in the loco, as per the long discussion, you may get light well before the loco moves, a little before, or right as the loco moves.
A full voltage pulse width modulated throttle will give the best most controlable effect in this regard.
I will leave it to someone else to explain how the diodes do this, or I will explain it when it is not so late in the evening.......
Sheldon
stayboltI'm still wondering, though, how the diode pairs in parallel with the lamps prevent voltage to them from rising above 1.5 as the track voltage is increased; since that's their apparent function, why are two instead of a single, diode necessary to do that?
as you know, a diode only passes current in one direction once the voltage is greater than ~0.7 V. and when passing current, the voltage across the diode remains ~0.7 as the current increases.
as the voltage between the rails increases, it only begins to flow once it excedes ~0.7 due to the 3rd diode. that small current passes thru that diode, the lamp and motor.
as the voltage increases above ~2.1V (3 diode drops), current begins to flow thru the pair of diodes across the lamp in addition to the lamp and the lamp is fully on
as the current increases, the voltage across the lamp increases because it is resistive (V=IR). but current thru the diode pair increases if the voltage across the diodes and lamp is above ~1.4V
so the voltage across the diode pair and lamp remains ~constant at ~1.4V. the current remains ~constant thru the lamp as current increases thru the diodes
Greg,
So, at a particular current draw level the two diodes in parallel with each lamp will stop conducting above ~1.4 volts thereby preventing the 1.5 volt lamps from burning out? My 1.5 volt lamps draw ~90 mA each. If that is the level at which the diodes stop conducting, how does the motor draw the current it needs to operate at full capacity? The motors I'm using draw a maximum of 60 mA (no load) and 850 mA at the stall point (full load), according to the seller (NWSL).
stayboltwill stop conducting above ~1.4 volts
the 2 diodes in parallel with the lamp will start conducting at ~1.4 V.
Staybolt, don't over think this.
Think of the diode as a one way door for current and voltage that needs the .7 volts to open.
The first diode, before the lamps, only lets that one lamp be powered in that direction.
Next, it will take 1.4 volts to open the next two diodes, the 1.4 volts would rather go thru the lamp, the lamp lights and the diodes are opened as the voltage starts to exceed 2.1 volts.
All the rest of the current and voltage goes thru the diodes and on to the motor, because once the diodes are open, that is the path of least resistance.
The lamps see 1.4 volts, the motor see the rest.
The other side of the circuit flows no current, until the polarity is reversed.
Then the other light lights, and the motor spins the other way.
So the circuit responds even better to the rapid 12 volt pulses of PWM control, the lights and diodes are fully loaded right away, but the motor sees the "average voltage" of the pulses and runs at the desired speed, or not at all at first.
It works with regular DC power, it just works better with PWM.
The difference in voltage between one end of a diode and another is .7 volts.The difference in voltage between one end of two diodes and the other is 1.4 volts.The bulb connected across the two diodes sees only that 1.4 volts.
Here is bonus fun for you:This circuit gives you 1 light bright, the other dim, and reverses when you reverse the engine. I used this one in switchers. Works great.I can never remember which is which, so I always wired it in and then ran the chassis a bit to see which bulb was forward and which reverse
Back in the 1970s and 1980 I built a lot of these diode arrangements for Hobbytown drives and other unis and they worked great.
I did Hobbytown drives and Train Miniature shells for an ABA set of New Haven engines . I often ran those togetherthen one day I noticed that the FB1 unit seemed to sometimes be spinning its wheels. I finally figured out that the FB did not have this constant light unit so the motor was getting the full track voltage and the 2 FA units were getting the track voltage minus the voltage drop because of the constant lighting units. The solution was to build a unit for the FB with the4 diodes and wire it in serieswith the motor so that the voltage was the same in all three engines.
If I recall the was a bulb called Protolight that had a bit of a lense cast into the front of the bulb to enhance the appearance. I think these bulbs were rated at 3 volts so you could get a good light effect with the drop accross the diode arrangement. The other plus was a longer life on the bulb since you running them at half voltage.
These days I use warm white LEDs for headlights.
Ron High