I’ve built a capacitor discharge unit for firing Peco turnout motors. It’s the classic circuit using a transistor, couple of diodes, resistor and 2200mfd capacitor and takes 16vAC power. It works well and has enough “juice” to fire two motors at a time - but not quite enough juice to fire three. Would there be a simple component change I can make to increase the punch?
yeah - a bigger capacitor - try a 3300mfd, 50v unit. You might also try feeding it 18v DC, instead of 16vAC… Just make sure your cap has a working voltage at least twice the input voltage. That voltage reading is a mean, not an absolute. Keep in mind that it might take a bit longer to charge the cap…
Thanks Gary. I thought that might be the solution. I’ll give it a go.
Just keep increasing the capacitance value until you find one that will throw as many turnouts at once that you will need. My unit I built is essentially the same as yours - I have two 10,000 capacitors wired in parallel and will easily fire the maximum I require of twelve machines … takes three seconds to recharge.
Mark.
Mark with two 10 000 MFD caps I’m surprised your twin coil switch machines don’t jump out of the bench work and run away. My go***hat’s a lot of kick. I run a 4700 MFD, works fine for two PECO twin coils.
Wakaiti, if you can find a second 2200 mfd cap you can pigging back em with no problems.
If the recharge time is too long with a monster caps, you can fiddle a bit with the resistor that connects to the transistor - the purpose there is to limit the max recharge current to somethign the transistor can handle. So long as you don’t exceed the transistor’s rating (or use a different transistor with a higher current capability) you can reduce that and speed up recharge. Even my little one i built fo rN scale had the transistor in a heat sink. I beleive it had a 2200mfd cap, that could throw 3 Atlas N scale turnouts with no problem - the Peco coils need more power than the tiny Atlas N scale ones - and it would recharge fast than I could press the buttons. Peco also has a second version of their coils that don’t draw as much power - they are often advertised as “for DCC” since the lower current draw makes them more suitable to use with DCC stationary decoders.
–Randy
MORE turnouts = larger Capacitor. (I use 8,000 mfd.).
Charging time is regulated by the Resistor. More R.= more charging time, and vice versa. Shoot for 1 sec. (I use W.W.)
The key is the ability of your power supply - and it’s cicuit breaker. The resistor slows the recharging down for the power supply to handle. The capacitor doesn’t care how long it takes.
Um, the resistor is to save the turnout coils guys, it limits the current so the coils don’t get hot!!! Using less than a ~700ohm can cause heat problems if a switch sticks (that’s why you use it, remember?LOL ). Now if you are using it to ONLY power 3 at a time it’s OK to use a smaller resistor or bigger cap, but if you use it to also fire 1 coil it’s kind of defeting the purpose to “power up”. I reccomend just building more units.
Another way to up the power a bit is use a full wave bridge and no filter cap. With a 16VAC transformer and a fullwave you can get around 20 volts at the cap. Fred
MAY I respectfully disagree?
The coil sees the Capacitor, and is fully dicharged when the momentary button is pressed. Isn’t the RESISTOR’s primary role in preventing charging circuit overload, as any resitance to the switch coil side would act to defeat the primary function of the capacitor.
I have never heard of anyone using Twin Coils with anything but momentary contacts.
2. WHY would anyone rather use resistance instead of a positive momentary switch?
3. To prevent arcing? (Wouldn’t a small capacitor do this better?).
Actually, you’re both right. There’s TWO resistors in most of the circuits. One in the collector of the transistor and one that bypasses the transistor (and connects to the base). The bypass resistor limits current if a pushbutton gets stuck so the coils won’t burn out. It’s not really there to allow you to use a non-momentary switch - unless the circuit is opened the transistor will never turn on and charge the capacitor. The other resistor, which is usually a low value, keeps the capacitor from being a dead short across the power supply via the transistor - without it the repeated momentary short circuits while the capacitor charges would wreck the transistor.
I happen to be looking at the circuit about halfway down this page on Rob Paisley’s site. http://home.cogeco.ca/~rpaisley4/CDPSU.html. It’s called the CUrrent Blocking Type, and is pretty much identical to the circuit I built from Practical Electronic Projects for Model Railroaders. Also appears to be similar to the commercial Circuitron Snapper.
–Randy