This is the third page full of Bill Williams Stories in the Think Small & Tall series.

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Part XIV

DO YOU HAVE "OHM BUGS"?

Hobby time is fun time. Often we forget the fundamentals. Caution -- electrical laws are simple but always enforced. The same rules apply for the 4x8 with a Tyco power pack or a fully scenicked layout with DCC, custom painted locomotives and prototype signaling. LAW: Available voltage divided by the ohms in the circuit determines amperage.

Motors turn when amperes flow through their coils. Power supplies are the source of the voltage that pushes the amps along. Our problems lie along the path between supply and motor. Too much resistance between motor and source means that too few amperes flow through the motor's coils. Does your train slow down, then resume speed without your hand touching the throttle? You have ohm bugs and they can spoil your fun. Your train should slow down or speed up only at YOUR command.

Twelve volts at the power pack does not cut it when too much of the voltage is lost of the path to the motor. The "Techies" say "too much IR drop". I say "Ohm bugs" since resistance is measured in ohms. Let us check some of the places where ohm bugs may lurk on the path between power pack and motor.

Rule number one: clean your track AND wheels. Dirt and oxides add resistance (ohm bugs). Nickel silver's oxide is a fair conductor (few ohms) while brass oxide is a poor conductor (lots of ohms), so we use nickel silver rails. There is a catch: nickel silver rail has more ohms per foot than brass rail. I measured the voltage across thirty-five inches of variousn rails while my power pack pushed one ampere through the rail. This is not Bureau of Standards stuff, but interesting nonetheless.

Figure A

Different lots of rail will vary in resistance per length, but not by much.

Think about prototype rail sizes. Narrow gauges ran on 40 pound rail. 140 pound rail is common on main lines today. 100 pounds per yard was normal during steam days. As ourt scale sense improves, we notice that giant-size rails look silly and we use the smaller sizes. Therefore, the ohm bugs can become more common as we grow more perceptive. Fortunately, this problem is easy to solve.

Generous size copper feeder wire with frequent connections to the rails is the answer. Example: one fair size club layout has 12 gauge feeders with connections to code 83 rails every six feet or less. This may be overkill, but they have no voltage drop problems. My Willow Creek Railway gets along with 19 gauge feeders to code 55 and 70 rails. However, the layout is wired common rail; throttles trip their overload controls at less than one ampere; and all trains run with just one engine. Remember: I THINK SMALL. If you run long trains, lighted cars and multi-engine lashups, a more robust feeder system would be wise. When you opt for DCC, several trains may draw current from a single section of track at the same time. To avoid excess loss of voltage, you may need heavy gauge feeder wires. Just two wires from power pack to layout rails is a myth.

The ohms should increase gradually as we add lengths of rail. BUT...there may be a small problem. Rail joiners (fishplates) often grow loose or oxidize as a layout matures. Ohm bugs! Look at each rail joiner as a future high-resistance connection. Rail joiners allow for expansion and contraction as room temperature changes. This is important. Here in California, we build layouts in garages where 35 degrees in winter and 100 degrees in summer is common. However, the savvy roadmaster solders all joiners not needed for expansion. All sections of rail between expansion joints should have a solid connection to a feeder.

How do you find the spots where ohm bugs lurk? You need a device that draws about the same current as a locomotive or two and gives you an indication of voltage level. An automotive stop light bulb should do the job. I tried a G-E 1157. One filament drew half an ampere at twelve volts; the other filament drew a full ampere at five volts. Bingo! Low tech test gear. Any light bulb that draws an ampere or so at five to eight volts will do. (see Figure B)

Solder two flexible wires with test clips at their other end to the light bulb so the filament lights up when you clip to the rails near your power pack. Adjust the throttle to give a brightness easy to recognize, not too bright. Move your test clips along the track. When the bulb is noticeably dimmer, you have a problem. Perhaps a rail joiner is loose, or your power is just flowing through too many lengths of rail. A feed wire not connected to a rail could be the problem. Move the test clips around. Trace the path those amperes must follow from power source to locomotive wheels. You will find the trouble. Once identified, an ohm bug is easy to conquer.

Build a test lamp and chase some ohm bugs. We have just started down this trail. We will squash some more ohm bugs next time.

Figure A	Figure B

Bill Williams (The Ancient One)

From the September 1999 CALLBOARD

Part XV

OHM BUGS II

Think about this: a good part of the superior running we experience with can motors is because quality motors are more efficient and therefore run on less current. This means less voltage is lost between power source and motor. That law again: Amperes times Ohms equals Volts. Reduce either amperes or ohms in a path and you reduce the volts lost. When we remove ohm bugs from the track circuit the performance of ALL trains running on that track is better. Does your budget have limits? Reducing amperes can be expensive. Reducing ohms usually cost less. Find and squash those ohm bugs to improve your rail fun at minimum cost.

Locating ohm bugs is easier if we have the tools to do the job. A simple test lamp keeps me happy most of the time, but I am the Ancient One. Most of you live in a high tech world. You can build a handy device that makes the stalking of ohm bugs quicker and easier. This device avoids the archaic light bulb and uses some of the more stylish contemporary stuff. Diodes in a bridge rectifier plus a zener and a light emitting diode make the gadget more technical than a mere test lamp. The circuit is really simple.

Figure C.

The bridge rectifier unscrambles track polarity. The zener holds the LED dark until a threshold is available. The ten ohm resistor is a load that looks like a locomotive to the power pack..

Why not build the gadget as shown in Figure D. You will need a chunk of 3/4" wood, two strips of metal (copper, brass, phosphor bronze or nickel silver) and the following electronic parts: Resistor – 10 ohm 10 watt Radio Shack part # 271-132, Resistor 330 ohm 1/4 watt RS # 271-1315, Small bridge rectifier RS # 276-1161, 6 volt Zeener diode RS # 276-561, and any handy LED RS #s 276-021 or 022 or 041.

Figure D.

The load resistor is tucked inside the wood block where it can get quite hot doing its job without any chance of frying your fingers. The bridge rectifier finds safe haven for its tender wires in its own hole in the wood. To keep everything neat, the metal shoes vary depending upon your track gauge. Shoes about 3/8" wide spaced about 3/16" apart do the job for HO and N. If your railroad is O or S, shoes 5/8" wide spaced 1/2" apart should work fine.

The Ohm Bug Locator is easy to use. On a section of track with known good power feed, press the metal shoes of Figure D to the rails with a firm touch. Slowly advance your throttle until the LED just turns on. Each advance of the throttle past the turn-on point reduces the sensitivity of the Ohm Bug Locator. Apply the shoes to the rails at various places around the layout. If the LED dims or is dark, crank up the throttle to turn it on. The amount of throttle advance is a measure of the voltage loss in your track circuit. Slide this palm sized gadget along your rails to find where you should do a bit of maintenance or perhaps add a feeder or two. The Ohm bug Locator does the job of a test lamp in a more sophisticated manner. Also, you have another gadget for your collection. Isn’t the winner in today’s world the person with the most gadgets?

Next time we will hunt for more of those SMALL problems called OHM BUGS that lurk around your layout.

Bill Williams

The Ancient One

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Part XVI

OHM Bugs III

Last time we chased OHM bugs on the main line. Did you found any loose rail joiners? I found a cold solder joint at a feeder. Now the time is here to look at our turnouts. They can harbor nasty OHM bugs.

We clean track. We polish wheels. Still our trains slow or stall on some of our turnouts. Flywheels help. All wheel pickup helps. However, we are living with problems instead of fixing them. Grit your teeth. Prove your courage. Most likely, there are only one or two turnouts with OHM bugs. Squash those bugs!!

When there are only one or two problems to fix, you do have the time to eliminate weak points designed into commercial products. You can modify your turnouts to eliminate the OHM bugs found at eyelet rivets and point to rail contacts. DCC glitches may diminish also. Try a bit of model rail gandy dancing - you might enjoy it.

Do you have some Atlas turnouts? Most of us know about the fix for those cast frogs that live in splendid isolation. Drill and tap for a brass screw and solder a wire to the screw. Then rig a SPDT switch to provide the frog with a connection to the correct rail as the turnout is thrown. This is a good start. Why not go all the way??

The pivot rivets for the points usually work fine on new turnouts. Apply some dilute white glue to hold the ballast or just change the calendar on the wall a few times. How a point may be energized for the express and dead when a switcher follows the same path two minutes later. The points are less than three inches long but when a point is dead you have OHM bug trouble. Flywheels and multiwheel pickups usually get the trains thru BUT when you have visitors a stall is likely. The fix is simple. Three fourths of a n inch of #30 wire either solid or stranded soldered to rail and point bridging their junction frustrates the OHM bugs in the brass eyelet with a good solid path for those electrons. You tied a SPDT switch to the throwbar to energize the frog. Now finish the job. Make that Atlas selective so you can park an engine on the spur or siding.

See figure "E"

Do this and you will have an Atlas turnout with reliable power feed everywhere in the turnout plus selective control of power as the turnout is thrown

Some of you have more flexible budget and built your trackwork with Shinohara type turnouts. You too can be deviled by OHM bugs (Nastier than Atlas OHM bugs).

See figure "F"

Because the point to stockrail contact is so important, you may have been warned about wimpy turnout actuators. You can modify those Shinoharas to operate reliably with a wimpy throw rod and be DCC friendly too. Two tiny scraps of PC board, a SPDT switch and some jumper wire plus a bit of work do the job.

See figure "G"

You operate five engine lashups and lighted passenger cars. You say my 30 gauge flex connections will vanish with a puff of smoke. Look again. Worst case: No contact from point to rail. Power to less than three inches of point rail flows thru the little wire. Only one locomotive will draw current thru that wire and only for a short period of time. The 30 gauge flexible connection won't even work up a sweat on the occasions when it must do its job. Just as in a modified Atlas turnout, the flex connection carries current only to the point rails.

As a depression kid, I follow the "If it ain't broke, don't fix it" guideline. When some thing "broke" I smile if a repair is possible. Fixes for turnouts make me happy. The end result is usually a turnout a cut above a new replacement and at a minimum cost. A big plus is that the fix usually requires less work than fitting a replacement into the layout.

There are more OHM bugs to hunt down but it is time to run trains. Next time we will hunt the little rascals on different grounds.

Bill Williams – The Ancient One

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Part XVII From the January 2000 CALLBOARD

OHM Bugs IV

Think Small -- OHM BUGS IV

We began the OHM Bug odyssey where the wheels meet the rails. Rule number one is: "Clean your track and wheels." A Think Small from the summer of 1998 gave us low cost roller cars to clean the grime off our rails. With a wet roller ahead of the train and a dry roller as the last car, we can swab the goo off our rails and clean the wheels at the same time.

Today we face the question: Why do my rails get dirty so quick? NMRA Bulletins of over twenty-five years ago had an answer. Back then our hobby was less, "Where do I buy it?" and more, "How do I make it or fix it?" Those model railroaders of years past did some serious research. They found that the weakest link in the path from power pack to motor is the contact between wheel and rail. When pickup wheels ride over dirt, dust or oxide the connection at the rail is impaired or lost. If the connection is lost, electrical energy stored in the motor windings is discharged across the gap between wheel and rail. A small arc burns a small pit in the wheel and/or rail. The small pits collect dirt and the problem escalates. More pits collect more dirt. More arcs make still more dirt collectors. Aggressive cleaning removes surface dirt but the pits remain. Have you noticed that the power pickup wheels are the first to collect dirt when the engine does not pick up with all wheels?

In a recent GAZETTE article Yuta Susuki, a successful HOn3 operator, traced poor running to poor electrical pickup. He says this is caused by oxidation of the rail generated by constant electrical sparking. He eliminated the sparking (and constant oxidation) by increasing the number of pickup wheels on his locomotives. He also runs dragger cars every day in a special train. If you operate, you probably have dragger cars that slide blocks of cork, Masonite or wood along the rails. Casual dirt and goo is gathered by the slider. Those draggers are great OHM Bug chasers. Users are believers!

THEORY: The motor winding is an inductance thru which the motor current flows. The induced voltage is dependent upon the rate of change of the current flow and motor characteristics. When dirt or oxide blocks the flow of current, the motor's inductance generates a voltage sometimes reaching 100 or even 200 volts. That makes an arc that pits wheel and rail. If the theory is sound, then a snubbing circuit across the motor should reduce the problem.

The electrical committee of years ago ran some tests. Two arc suppression circuits were found to be best of the lot. One was the standard headlight-backup light circuit. (Fig. H)

Since the momentary induced voltage is opposite in polarity from the voltage powering the train, it flows thru the dark, (hence low resistance), light bulb and does not rise high enough to make an arc.

The other effective snubber was an ancient telephone industry circuit that protected contacts from troublesome arcing. (Fig. I)

As the value of the condenser is reduced, the suppression is less effective.

If the current flow is not interrupted there is no arc. Today's diesels usually have all wheel pickup; thus there are fewer interruptions of current flow. However, experience will prove to you that interruptions do occur.

Figure I might be bad news for DCC pulses so be cautious if you are truly modern. The figure H snubber should cause no problems; hundreds of DCC engines are happily running with directional headlights.

The induced voltage theory is a strong voice for lights in our locomotives. If we can reduce track cleaning by lighting our motive power, why not do it and smile?

The simple headlight across the motor helps a little. Directional headlight-backup lights are a quantum improvement. Ditch lights, cab lights; what tempts you? Indulge yourself. This is a new Millennium!!

Part XVIII From the March 2000 CALLBOARD

On my soap box

We all Think Small. The numbers vary; 1:22, 1:48, 1:64, 1:87, or 1:160, but all of us are caught up in attempts to capture the feeling of full size railroading with our models. My small world may be set in the 1930’s era while your time line is today with an eye to the future. The shint rails are our common bond. Variety is one of the strengths of this hobby but we must remember that common bond we all share – the rails.

The NMRA provides standards. Trains made in Italy or China run thru turnouts made in Ukiah. DCC works with a mix of parts from four different suppliers (for that I bless the National). Our Division has an important function that involves YOU. Some of us are Closet Railroaders who feel that this hobby is PRIVATE, your sheltered cave of tranquility when life turns hectic. Having full control can be soothing. However, when we limit our sources of information to books and magazines we cheat ourselves. Division meets are for sharing. Clubs are great.
When three or four work together to solve a problem or meet a deadline everyone gains from the shared experience. The R.E.D. had more than 15 clubs scattered over the map the last time I counted. Most groups welcome visitors infected with the train virus. We can expand our fun by sharing. The Division provides a common meeting ground that should bring us together to make model railroading more fun.

If you come to meets looking on quietly and sharing a few words only with the people you know well, you are cheating yourself. We are all klutzes in one way or another; put away your shyness. I an certain you found some weird conclusions in my past THINK SMALL essays. If you were prompted to think about the problem presented, I was successful. After all, I am "The Ancient One". Senile dementia is always available as a defense if my discussion annoys you.

The burr under my saddle that prompted me to side track the semi-technical stuff I enjoy is your ignoring Howard’s "contests" at our meets. They are really "Show and Tells". We are not asked to fill out any forms – just bring examples of our models. The objective is to share techniques – to learn from each other.

At the November meet, there were just three entries. I saw tiny details added to a kit building that made my eyes pop. But; only three of you were generous enough to bring entries. January’s category; Box Cars, should have produced a table full of entries. Just three "gray heads" were willing to share "Box Cars". Two of us had a common theme – start with a block of wood, then add details to create a box car to run on your railroad. The other exhibit was a parade of paint schemes one railroad used over a period of years. I was surprised by the variety of colors and patterns.

Where were the Prototype modelers with their box cars that have prototypically accurate doors and ends? Where was the car that had all the tiny letters and numbers correct for a specific car parked at Hopland on March 9, 1952? Most important ! Samples of the research sources that provide this information. Some of you prototype modelers do research worthy of a Doctoral Thesis. Along with providing an education for most of us, you might meet a kindred soul. Isn’t that a worthy gamble?

Did you add detail to a plastic kit to improve its appearance? Why did you decline to share your little improvements with the rest of us guys? Observe our top modelers. They do not look at your models to criticize. As savvy modelers, they know that the new kid on the block often has a superior technique. "Look, ask and learn" is the aim of the game.

If I’m able to make the March 19th meet at Napa, there will be Bodega Western and perhaps Willow Creek passenger equipment for "Show and Tell". What will you bring?

Ohm Bugs V will come with the next CALLBOARD. It should be a good preview of the Vallejo meet. (That is if you bring a sample of your railroad’s MOTIVE POWER for Howard’s "Show and Tell".

Bill Williams "The Ancient One"

Part XIX: OHM Bugs V

Steam locomotives in the smaller gauges are known for Ohm Bug problems. I saved them for the final essay of this series.

When N Gauge was new, the Trix 0-6-0T was touted as a good runner. It is an ugly beast. However, reliable operation on N Gauge was unusual back then. A friend, knowing my quirks, gave me a battered trix found in a piece of old furniture. Yes, its innards were soon exposed. I found lint, a dead spider and guess what? Remember the old telephone arc suppressing circuit of resistor and condenser? Across the motor brushes was a miniature version of Fig I from the last THINK SMALL article in the Jan-Feb CALLBOARD. The condenser and resistor are tiny but they were functional - comutator looked good. Driver wear indicated a generous amount of running. After a quick cleaning, fixing the gauge at one end and a wee bit of oil; the ancient hulk went rattling down the track. That snubber circuit of Fig I is good medicine for motors.

With most steamers we have problems. The common circuit is Fig J.

Tender pickup is usually a weak link. Axle bearings make dubious connections to truck frames. The bolster to frame contact is another possible problem. Connections at both ends of the drawbar are also places for OHM BUGS to lurk. The tender almost always has less weight on the wheels to mash dirt on the rails. Yes, steamers have problems but they can be fixed! That steamer will be a better runner if drivers on both sides of the locomotive are providing a path for current to feed the motor. You can put those left side drivers into the power path with very little effort. (See Fig K).

Wipers can be soldered to a piece of P.C. board fastened to the bottom cover plate. Sometimes it is better to make a new cover plate. Plan your insulating gaps with care. Adjust the wipers to rub gently on the back of driver tires. We want a path for electrons - not brakes! Wipers on the non insulated drivers will balance the lateral thrust on the axle and supplement the path through the bearings. Wipers provide the good pickup we want. Tender pickups provide supplemental paths. You can turn one of the tender trucks to pickup from the right hand rail and pass power to the engine by two flexible wires. Another trick is to rig wipers to the tender axles thus bypassing the journals. With multiple paths for current flow the probability of arc breeding open circuits is reduced. The OHM BUGS are out flanked.

The smooth running of the new Spectrum 2-80 and 4-8-2 prove the effectiveness of all driver pickup.

With a round-house full of old steamers, I have a passel of work waiting for ambition. Perhaps the ancient resistor-capacitor circuit is worth a try. Fitting the headlight-backup wiring into the engine and tender might be worth the effort. Each small aid to a better path for motor current or reduction of arcing improves operation.

The entire path electrons follow from power pack to the locomotive’s motor is important. We have explored cures for problems with track feeds, turnouts and locomotives. Solving problems is satisfying. Look upon the hunt for OHM BUGS as a sport that pays dividends.

May your shiny rails reflect your smile.

Bill Williams "The Ancient One"

Part XX: 

Part XXI:  CULVERTS

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