I am using Peco low voltage switch machines on Peco turnouts. I have them running of an old DC/AC power pack using the 16v AC. The Peco instructions state that you may us a capacitor discharge unit with these machines. However, they will work with out a CD. I have been using the old Atlas slide switches to power the machines. What are the ups and downs of not using a cd unit and if I do use one where do I connect it?
Ed
I've got several Peco HO gauge turnouts on my layout. They bench-tested fine with a plain old power pack, but once I got them installed on the layout with the full-length wire runs, they were intermittent. For reliability, a CD circuit is what you need for Pecos.
The circuit also protects your switch machines. If your SPDT momentary toggle sticks, the CD circuit will limit the current that can flow through it and protect the switch machine from burnout. Without the CD circuit, a minute or so of stuck toggle is enough to send your switch machine to that big roundhouse in the sky. And, since you mentioned them, the Atlas slide switches have a bad reputation for sticking in exactly this manner. Even with a CD circuit, I'd advise replacing them with toggle switches.
If you buy a commercial CD circuit, it plugs into the wall and has two outputs. These connect up the same as the outputs of your old power pack. If you want to save some money, you can make a circuit yourself for about $5 in Radio $hack parts. From an AC power pack, you need a diode bridge, 2 resistors and 2 capacitors. The power pack feeds the diode bridge inputs, they feed the circuit, and the output of the circuit goes to your system.
It takes an iron man to play with a toy iron horse.
Here is a link to a DIY suggestion. Just watch out for capacitor polarity if you go this route.
http://www.2guyzandsumtrains.com/Content/pa=showpage/pid=27.html
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.
The only downside I can think of is the additional cost of a CD unit, which if you can assemble your own, is negligible.
- A CD unit is good if you have turnouts that do not operate reliably when controlled with a simple power pack. This is often the case if you have a number of turnouts thrown by one switch all at the same time. Often there is just a bit too much power demand to operate them all reliably. The CD unit will help with that.
- A CD unit will ensure that the coils in the switch machines do not burn out from being energized for too long.
-CD units protect the control switches from back emf from the switch machine coils. Often if a control fails it is the result of back emf fusing or burning the switch contacts. Again the CD unit will prevent back emf from damaging control switches and often saves the switch machine coils from damage as a result of a control switch being fused by back emf arcing at the switch contacts. Back emf is generated by the switch machine coils upon disconnecting the power from the coil. If not protected with diodes or a CD unit the control switch can be damaged.
Some modelers use a CD unit to fire the twin coil machines in a ladder yard. I use a CD unit in a club layout to fire two twin coil machines for a three way.
Some people have had the switch contacts stick on the old way of firing these twin coil machines which causes the twin coil machine to burn up. The old way causes a lot of current to flow though the switch contacts. The switch is released, the voltage in the coil collapses causing an arc at the switch contacts. Eventually the contacts stick.
First things first -- throw away those Atlas slide switches and get something better. The Atlas switches have a bad habit of sticking and burning out switch motors. A momentary (ON)-OFF-(ON) toggle switch is much more reliable and trouble-free.
A good source of momentary toggle switches is Jameco Electronics at http://www.jameco.com
They have several types available, including their catalog number(s) 75889, 317252, and 317316.
A CD power supply would normally connect between your existing power supply and the switch controller(s).