Siberia Racing
Tech Pages

Track Wiring Performance Standards

This article discusses three favorite topics. Batteries, track wiring and rules that either cannot be enforced or have no basis in reality. There are a lot of misconceptions about batteries. We discuss a few important ones. Track wiring has been a topic of mine ever since the track power switch melted at a race twenty some years ago when a controller faulted freshly charged batteries and there was no main fuse. Of course, rules are always a subject for discussion.

Iím not talking about selective (or non) enforcement of a rule or letting somebody slide "this time". I am talking about rules and criteria that conflict with known physical properties.

The following article examines a trackís wiring in detail and shows why track wiring must be short and stout and why multiple power taps are a necessity if good power is the goal. The article also debunks a myth about battery power supplies and pokes a hole in a rule that has been on the rulebooks forever. Unfortunately, the rule appears to conflict with known physical properties. Read on and judge for yourself.

 

Introduction

Is a wiring standard necessary? In my opinion, yes. Itís no fun to race on a track that has a bad lane or bad sections in a lane. A poor track detracts from the experience and can dampen a good day of racing, especially if a portion of the track goes dead during the race. These problems primarily occur with sectional plastic tracks. The continuous rail tracks and tracks with minimal joints such as Maxtrax donít seem to have much of a problem. But problems can occur and some form of standard or criteria is necessary to ensure a good racing and a problem free track.

The national rulebooks had (and may still have) a standard that states that tracks must have battery power and have a track voltage of 18VDC at a minimum load of six amps per lane. A regulated power supply may be added in addition to the batteries.

That sounds stout and a track built to that standard should provide enough power for anyone. However, there is no performance test specified. A standard or criteria without a performance test to verify the criteria is for the most part useless. Letís take the standard apart, turn it upside down and compare the standard against some real world tests. Then we have facts that can be used to evaluate or develop a criteria.

 

Test Track

After a year and two races CRR had no identified voltage drop problems, felt like a high power track and was the natural guinea pig for the test. Figure 1 shows the wiring at CRR. The track is wired with a short set of 10 AWG leads from the power supply to the relay/breaker panel. Individual 14 AWG positive and negative leads are routed from the relay/breaker panel to the drivers stations, a set of reversing switches and finally to each power tap. At that time CRR had a 20 Amp single-pole automotive type power relay, a 6 Amp breaker protecting each lane and a reversing switch for each lane rated at 15 Amps.

CRR is a Maxtrax layout with a 46-foot lap length. At this time the track had two power taps. The main power tap is located on the main straight in front of the relay/breaker panel and just above the reversing switches. This power tap came with the track and 14 AWG wires routed from the reversing switches terminate directly at the section. The other power tap is custom made and consists of 12" long 16 AWG jumpers soldered to the underside of the rails. These 16 AWG jumpers connect to 14 AWG wires routed directly from the reversing switches. All connection are soldered or terminated using screw type terminals and crimp on lugs.

 



Figure1

CRR Wiring Diagram

Test Methodology

The following test was used to determine the variation in power supply voltage from no load to full load and to determine the voltage drop from the power supply to the track rails. The test used four 10-Ohm 10-Watt resistors. A 10-Ohm resistor was connected across the white and red terminals of each lane with the exception of the lane being tested. This lane has its 10-Ohm resistor connected across the rails at points approximately halfway between the power taps. The power was turned on and voltage at the power supply, driverís stations and track rails was measured. The test was repeated between each set of jumpers. Finally the resistors are removed and the no-load power supply voltage was measured. CRR is 4-lane track with two jumpers per lane. This required eight measurements plus the no-load measurement.

The goal was to determine the variance of the power supply from no-load to full load and verify that the maximum voltage drop between power supply and track rails. The total load on the track power supply during the test was approximately 7.2 Amps (1.8 Amps per lane) at 18 VDC. This is 30% of the 6-Amps per lane mentioned in the above standard.

The 10-Ohm resistors got extremely hot during the test and care was taken to protect the table, track and fingers. The test was performed such that the resistors were energized for no more than 30-seconds at a time.

 

Results

The results were a real surprise and an eye opener. The results for a typical lane were as follows:

 

Measurement Description

Volts DC

% Drop

     

No-Load Power Supply Voltage

18.140

100.443%

Power Supply Voltage (7.2A Load)

18.060

100%

Voltage drop from Power Supply to Breaker/Relay Panel. (6.5í 10 AWG Wire)

0.112

0.620%

Voltage Drop Across 20A Track Relay

0.029

 

Voltage Drop Across 6A Circuit Breaker

0.070

 

Voltage at Drivers Stations

17.830

-1.270%

Voltage drop across reversing switches and wiring from Driverís Stations to Track Jumpers (10í 14AWG Wire)

0.250

 

Voltage at track power taps.

17.580

-2.66%

Voltage at midpoint between track power taps.

17.280

-4.32%

Total Voltage Drop from Power Supply to Track Midpoints

0.780

4.32%

The test shows that the 10 Amp power supply will droop less than 0.08 VDC (0.45%) from no load to 75% of full load. It also shows that the power supplies will have to be set at 18.78 VDC to supply 18 VDC at the midpoints between jumpers using the test load. Extrapolating upward, CRRs power supplies will have to deliver approximately 20.6 volts at 24 Amps to supply 18 VDC at the midpoints using the 6 Amps per lane criteria.

As most tracks donít have reversing switches or circuit breakers the CRR test results need to be revised to accurately model a typical track without these items. Excluding the reversing switches and breakers, but including the wiring from the drivers station to the power taps, CRR has a voltage drop of approximately 0.335 VDC with a 10-Ohm load per lane and a drop of 1.116 VDC with a load of 6 Amps per lane.

 

Some Truths About Batteries

The standard stated that batteries have to be used and the power supply is an option. When not being charged, a typical, fully charged 18 Volt slot-car battery pack has a maximum no-load voltage of 19.1 VDC. Using CRRs results and assuming that the battery will supply 18 VDC under a 24 Amp discharge the track voltage would be 16.9 VDC. The battery powered track thus fails the criteria. Unfortunately, it gets worse.

Battery manufactures performance curves indicate that a battery under any significant discharge will not deliver an output voltage greater than 2.00 volts per cell. Battery voltage will vary as the battery is discharged and battery voltage is dependent on the number of amp-hours removed from the battery and the load on the battery. A typical deep cycle battery set under a slot car track has nine cells. The output of a fully charged battery under an initial 24 Amp load is between 17.5 and 17VDC. This voltage will decrease as the battery discharges. The manufacturers consider a battery discharged when its output voltage falls to approximately 90% of its rated voltage. A continuous 24 Amp load will discharge a typical golf-cart deep cycle battery in less than four hours.

 

Results

The testing indicated that track wiring must be short, stout and multiple power taps are required if any kind of sectional track is used. An old rule of thumb for a sectional track is to provide a power tap about every 10-feet of running length. The testing proves the value of this old rule.

CRR currently has two regulated power supplies with a combined continuous output of 32 Amps at 18 VDC. As shown above CRRís regulated power supplies provide nearly constant voltage up to their rated output. As a result of the testing, CRR recieved two more custom power taps. That reduced the total voltage drop to approximately 3% with a 10-Ohm load/lane. Wire lengths were minimized where possible and the 20 Amp relay was replaced with an industrial grade DPDT 40 Amp contactor. The relay was the weak link in the wiring and upgrading it will also helped to minimize the voltage drop from power supply to track.

The criteria listed above is written such that the batteries must be able to provide the necessary power on their own without assistance from any added power supplies. The testing performed indicates that the standard has a problem.

 

Basis?

Where did the 6 Amp per lane criteria come from and what is the basis for it? Good questions, and ones that I donít have an answer to. The above test and the following case studies might help to provide a basis for a future standard.

 

More Real World Results

At two national championship races battery voltage was monitored on the restricted open track. The first year there was no power supply hooked in parallel with the battery. The second year a 1-Amp regulated and filtered power supply was attached in parallel with the battery. The monitoring was being done for a magazine article that remains unfinished. The 1-Amp supply made a difference; however, battery voltage at the end of the main both years was on the south side of 18V. Did anybody complain? No driver at that race, including the six in the main at each race, raised an issue about power. Were the tracks illegal? In my opinion, the tracks were legal. The battery packs were brand new and fully charged before the race. I had also been doing battery analysis work and knew that the battery was doing what it was designed to do as it was designed to do it. In my opinion the rule was bunk. Unfortunately no ammeter was available to measure the power draw during the race.

Another time at a Midwest series race my 10-Amp regulated power supply was hooked in parallel to the tracks batteries. This time track voltage and current contributed by the power supply were monitored throughout the weekend. There was Friday night practice. Saturday featured practice, modified and restricted open races and more practice. Sundayís activities featured four more hours of practice followed by superstock and unlimited races. The battery got about six hours of charge per night. At the end of the last race of the weekend, the unlimited main, voltage was unchanged from the start of the weekend but the power supply was putting between 6 to 8-Amps into the track at the end of the race. That tells me that the power supply was running the show and the battery was along for the ride most of the time. Again no power problems were identified by any of the racers. This was a four-lane track, so the unlimited cars were drawing a maximum of 2-Amps each when they were running. Even at the start of a segment when all four cars were accelerating from a dead stop no noticeable voltage dip was observed.

That same 10-Amp supply has powered restricted open, modified and superstock races on several four-lane tracks for years with no power problems. Well, almost no problems. When the power supply was out of site nobody complained about a lack of power or power supply problems. When it was revealed that a power supply was used, somebody would always use the power supply as an excuse for a poor finish.

 

Why do I do this?

Good question. I started racing 30+ years ago with "Fast" Al Thurman on a two lane layout in Hammond, Indiana. Al and I ran against Carl Dreher in our first real race a few years later. We didnít do so good. We got better and I was fortunate to be in the main event at what was supposed to have been the Super IIís coming out party with a Thurman powered AFX. This race was otherwise known as the first HOPRA national race in Parma Ohio that featured folks like Bill Thayer, Tony Porcelli and Gary Ryder. I screwed the car up during a 3 AM rebuild just before the main and lost a sure third place. I finally won my first HOPRA race in 1975.

I was Race Director (RD) for the Restricted Open class at least three HOPRA Nationals and Modified RD for another. I have also been the series director, technical director and RD for other state and regional races.

With some help I was able to win both the Restricted Open and Modified classes at the 1987 HOPRA Nationals in Jackson, Michigan and follow that victory up with winning the Restricted Open race at the Winternationals approximately six months later. Along the way I was also fortunate to win many other state and regional races resulting in four HOPRA state championships.

I am an electrical engineer working in the power industry. One of my specialties is DC systems and battery analysis. I have a need to know WHY something works. My analytical approach to racing combined with a natural ability to tune and drive a car to its limits has resulted in some advantages and unique solutions. Itís important to me to understand a problem and solve the root cause rather than just treat the symptoms. At times this approach gets in the way as, sometimes in racing, itís faster to treat the symptoms than to cure the problem.

Hopefully this article has shed some light on track performance standards, how the electrical system on a typical track performs under load and why I do what I do.

Steve "Maddman" Medanic

 

Back to the Tech Pages Menu Page


Revised 10/25/2003