Part of a series on turnouts (track switches) and Digital Command Control
Digital Command Control: Turnouts - PECO Electrofrog
- 1 Differences between PECO's Electrofrog and Insulfrog Turnouts
- 2 Shorting In the Electrofrog
- 3 Making the Electrofrog DCC Friendly
- 4 Peco Electrofrog - Modifications for DCC
- 5 External Links
Differences between PECO's Electrofrog and Insulfrog Turnouts
The electrical power routing of the Peco Electrofrog is different than that of the PECO Insulfrog.
The Electrofrog is a well designed turnout. With the exception of the guard rails, there is no plastic for wheels to run on. The positive locking action of the switch points makes it the ideal turnout for anyone's layout. The main feature is an all metal frog. The Insulfrog may have an all plastic (non-conducting) frog, or a metal one with gaps.
- Be aware of the images used to illustrate PECO switches. In many ads the pictures are of Electrofrog types, despite the ad copy saying differently.
With DCC operation, there are a couple of problems. The solutions, however, are simple.
How to Spot the Differences between Electro and Insulfrog Turnouts
- Frog may be cast entirely in plastic;
- Closure and wing rails are solid;
- Plastic filled gap where closure rails meet the frog;
- Beginning of frog itself is plastic;
- Switch rails are electrically connected;
- Power Routing: Closure rails are electrically connected to the appropriate point rails.
- Closure rails are gapped before the frog.
- Jumper wires underneath bridge those gaps
- Frog, closure rails and switch assembly are electrically a unit.
- Closure rails are not electrically connected as a pair.
Power-Routing In An Unmodified Peco Electrofrog
The Peco Electrofrog switch was designed in the days of analog operation with the ability to power sidings depending on which way the points were aligned. Drive a locomotive into the siding and then set the points for the mainline route. We could rest assured that the locomotive wouldn't creep away on us - assuming there were no additional track power feeds to the siding. The turnout would function as an electrical switch in addition to its duty as a track switch.
We could then flick the points on another turnout which held another locomotive on that siding, then we could then operate that new locomotive. This ability had everything to do with how the Electrofrog was wired - By a combination of the rails and wire bonds on the underside, the points acted as an electrical switch that routed power to either the mainline or diverging route.
While it wasn't obvious, if the points were set for the mainline route, a whole lot more than just the mainline route was electrified. In the bottom half of the photo below, we've traced the electrical polarity in blue and red. Take a look at the red rails. Hard to believe that all of these rails, particularly the point and diverging rails on the diverging route are also powered when the points are set for the mainline route!
Digital Command Control eliminated the requirement for power-routing switches. Locomotives only moved when told to move (via the throttle). When parked, they stayed parked, even though there was still power in all the rails. We also added all kinds of track feeds because we didn't have to worry about power-routing to sidings, particularly around turnouts.
Good DCC wiring practice requires track feeds before the switch and after the frog on both the mainline and diverging routes. Which caused problems with the Peco Electrofrogs. Because the points routed the power, depending on how things were wired, Electrofrogs shorted the DCC power bus.
Shorting In the Electrofrog
In the photo, the track power bus and feeds before the points and after the frog with the points aligned for the mainline route.
You can see that doing this creates a major short at the frog where the red current on the inside mainline rail crashes into the blue current of the inside diverging rail - electrically speaking, that is.
Making the Electrofrog DCC Friendly
- These modifications are recommended by PECO, and illustrated in their data sheet. See the links at the end of this page for links to various PECO documents.
Insulated Rail Joiners After The Frog - Mandatory
In addition to adding track feeds before the points and after the frog on both the mainline and diverging routes, the first step is to use insulated rail joiners on the inside mainline rail and the inside diverging rail. (If your turnouts are already installed, simply cut gaps in the rails after the frog and fill the gaps with epoxy.)
When you set the points for the mainline route, the points of the Electrofrog continue to power-route the power as before. However, because we've added an insulated rail joiner on the inside diverging rail, we no longer have a short, notwithstanding that both point rails, the straight closure rail and curved closure rail have the same red polarity.
When you set the points for the diverging route, the points of the Electrofrog continue to power-route the power into the diverging route. And, because we've added an insulated rail joiner to the inside mainline rail, we no longer have a short, notwithstanding that both point rails, the straight closure rail and the curved closure rail have the same blue polarity.
As a minimum, if you are using Peco Electrofrogs, you must install insulated rail joiners on the inside mainline rail and the inside diverging rail. Or gap these rails and fill the gaps with epoxy or styrene. NO EXCEPTIONS!
We still have the problem, where the wheels of our locomotives may create a short between the stock and point rails. This is especially true for steam locomotives and 6-axle diesels. This wasn't an issue with Analog operation, but DCC is very sensitive to even the shortest period where an issue like this occurs.
Taking a look at the above two photos, the red point rail shorts out on the mainline blue rail as the loco goes through and the wheels span the gap between the two. OR, the blue point rail shorts out on the red diverging rail as the loco goes through and the wheels span the gap between the two. If you still don't see how this happens, take a look at the graphic below.
As part of the process, verify the wheels are in gauge with an NMRA gauge.
This is what makes a turnout incompatible with DCC.
Peco Electrofrog - Modifications for DCC
So far, you've taken care of Step 1: Adding insulated rail joiners beyond the frog. This gets rid of the "built-in" short. We may still have an intermittent short as our locomotives go through the points and the inside and mainline diverging rails. To get rid of this short, we're going to disable some of the circuitry (NOT the rails) and make modifications to the wiring.
This will be done in 3 extra steps and will all be done on the underside of the Peco Electrofrog.
- Cut the wire bonds between the frog and the inside mainline and diverging rails. This disconnects all power to the frog. Depending on which way the turnout is thrown, it also cuts power to either the inside mainline rail or the inside diverging rail.
- Solder some wire bonds between the outside mainline rail and the inside diverging rail; and between the outside diverging rail and the inside mainline rail. This restores power (with the correct polarity) to the inside mainline and diverging rails.
- Add a Tam Valley Frog Juicer (or a switch) to power the frog. This restores power to the frog and sets up a control mechanism which gives the correct polarity to the frog as a train goes through the turnout.
Let's take a look at the underside of the Peco Insufrog.
Cutting The Wire Bonds on the Peco Electrofrog
The first thing you will notice on the underside are a pair of wires on the inside diverging rail and the inside mainline rail. These wires bond the frog with either "blue" electricity or "red" electricity, depending on which way the points are thrown. This means the points are not DCC Friendly as they are both energized through the frog to the stock or diverging rails, depending on the position of the points. This makes it possible for a metal wheel to bridge between the point and adjacent rail through the tread and backside of the wheel.
Cut the wire bonds so that the frog is no longer powered by the point rails. (If your Electrofrog turnout is already installed, you can cut the wire bonds from the top with an Atlas snapsaw inserted between the rails.) This is a simple matter of snipping the wires with a pair of cutters and then twisting the wires off of the rail. They should come off very easily. You now have a "dead" frog.
This adds power with the correct polarity to the point rails, the inside mainline and inside diverging rails, regardless of how the points are thrown! This prevents our locomotives from shorting out if the wheels contact the point rails as the point rails and inside mainline and diverging rails are the same polarity as their respective outside mainline or diverging rails.
Solder Wire Bonds Onto The Point Rails
Our next step is to bring the points and inside mainline and diverging rails "back to life". To do this, we solder wire bonds between the outside mainline rail and the inside mainline rail; and between the outside diverging rail and the inside diverging rail as shown.
- Strip about 2" of insulation off a track feed wire
- Flux and tin the track feed wire
- Flux and tin the undersides of the rails shown in the photo below
- Solder the tinned track feed wire between the outside and inside mainline rails
- Cut the excess wire off.
- Solder the tinned track feed wire between the outside and inside diverging rails
- Cut the excess wire off.
Notice that, regardless of which direction the points are set, the polarity of the points and the inside main and diverging rails remains unchanged.
This leaves us next to get power into the frog rails.
Correct Polarity for the Frog
If you turn your Peco Electrofrog over, you will notice a short piece of wire embedded in a groove in the plastic ties near the frog. Pry the end of this wire up. If you follow the route of this wire, you'll find that it's connected to the four frog rails. We can use this wire to power the frog with either "red" or "blue" power, depending on which way the points are thrown. This can be done with a Tam Valley Frog Juicer, the auxiliary contacts on a switch machine (such as a Tortoise or a Tam Valley servo motor) or a SPDT switch that is connected to the throw bar of the turnout. In our case, we're going to use the Tam Valley Frog Juicer.
As we're going to place the Frog Juicer under the table, we're first going to solder a single-wire track feed, it will be the "frog feed". We only need one "frog feed" as either the outside mainline rail or the outside diverging rail will be the "return" on our circuit.
- Strip about 1/2" of insulation off one end of 12"-18" piece of track feed wire.
- Wrap the wire around the wire from the Electrofrog relatively close to the base of the turnout.
- Flux and solder the wires. (Cut the excess wire from the frog.)
There are a number of data sheets, in various languages, available on the PECO Technical Page. This link goes to the English Code 83 Electrofrog turnout. OO/HO Gauge Electrofrog Turnouts/Crossings (Code 83)