If I wanted to add the most basic "momentum" feature after my power pack, is an RC network useful (to smooth out the voltage, I think), and where might I find a schematic and component values for such a thing?
Large capacitors are polarized, so they won't work after the power pack. Rather than try to add momentum to a cheap power pack, get or build one that has momentum in it. The momentum circuitry comes before the output transistor and keeps the power on after the throttle is shut off. There are some good designs in th old book Practical Electronic Projects for Model Railroaders, which I'm pretty sure is long out of print. There are some throttle circuits here: http://home.cogeco.ca/~rpaisley4/Throttles.html
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinker...Rather than try to add momentum to a cheap power pack, get or build one that has momentum in it. The momentum circuitry comes before the output transistor...
I agree with Randy. If you were to add it to the output,you would need a rather large cap to get a decent momentum effect. Since the momentum ciruitry on a power pack with built-in momentum comes before the power transistor, the cap can be much smaller. Also, with a cap on the output, the momentum effect becomes very dependent on the current draw of the locomotive, but not with a good built in momentum circuit.
OK, I lied. I'm trying to use 3 batteries, each probably 1.5v, and each with an on/off switch. Their outputs will be wired in series (to add voltage, I think). These will be mounted in an F45 dummy chassis or something like that. I want an RC network to smooth out the voltage transitions as I switch between levels depending whch batteries I have selected to be in the circuit.
The output is then connected to a powered unit, naturally.
Look at the below circuit for a momentum circuit. A cap and a zener for momentum.
http://www.talkingelectronics.com/projects/ThrottleMkI/Throttle.html
I saw, "I Think" a couple times. Post a circuit of what you would like to do with your throttle.
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.
3 batteries will net you 1.5V, 3V, and 4.5V steps. Depending on the loco, a single battery may not even move it. Most locos from the recent past will start and run at 3V. 4.5V will be noticeably faster but not that much faster. What you describe to reduce the rate of change should theoretically be possible, though a simple transistor throttle circuit running off the batteries would be much simpler and not have step issues - you could even make it stepped with a rotary switch, givening say 8 'notches' between whatever you experimentally determine to be the slowest minimum speed and getting the full 4.5 volts, which would make each step quite small and not a big noticeable jump. Rotary switch and fixed resistors instead of the potentiometer as the speed control in the throttle circuit.
I built a momentum throttle many years ago using two N.O. push button switches, a 10k resistor and 2.2k resistor along with a 220 ufd electrolytic. Simple and worked very well. Using the 10k, normal service and the 2.2k, quick service for momentum. Did not have to use the main pot very much. Worked well for switching. I would set the main pot for max speed of the particular loco and use the buttons.
I liked experimenting with throttle circuits.
My idea is a dummy unit housing 3 batteries. LiPo looks like the newest/best technology. These (may) come in 3.7 volt iterations, so when combined, using 3 on/off pushbutton switches hidden somewhat in the fan housings, this would give 3.7, 7.4, and 11.1 volts. I think there will also be a kill switch as a safety feature, hidden in the dynamic brake fan housing.
Whatever combined output is selected is then supplied to a powered locomotive. To smooth the transition between the 3 voltage levels (4 if you count 0 v.), I want to use some circuitry; whether it is an RC network or something else does not matter to me. That's what I'm after.
damn this phone