I have been interested in making tight (read low resistance) connections between track sections for some time. I have tried using an ohmmeter with less than accurate or quick results. A few days ago, I rigged up a Kelvin connection for measuring resistance. It will measure as low as 20 micro-ohms. With this I have made the following measurements:
A good connection between track sections is 1.5 milli-ohms. This is with clean pins and clean openings in the two sections. Also, it is necessary to bend the ends of the section where the pins are installed to increase the contact pressure between the pins and the openings in the adjacent section. With the pins of a section pointing away from me, I bend the left rail where the pin is installed to the left and bend the center rail to the right. I also use pliers to form the ends of the open rail back to where they should be if they are bent out of shape.
Resistance of a Lionel O-31 curved section = 0.0035 ohms
Resistance of a good joint between sections = 0.0015 ohms
Resistance of a Lionel O-31 straight section = 0.0032 ohms
Resistance of a Lionel prewar 072 curved section = 0.0048 ohms
Resistance of a Lionel prewar 072 straight section = 0.0058
Resistance of a prewar American Flyer O-40 curved section = 0.0040
Resistance of a prewar American Flyer O-40 straight section = 0.0040
Resistance of a Lionel O-42 curved section = 0.0039 ohms
Resistance of a Lionel prewar 072 (711) switch = 0.0100
About half of the resistance of the 711 switch is the wire that connects from the rivet holding the fat rail to either of the other two center rails. This wire is apparently steel and not copper. Replacing this steel wire with a copper wire would reduce the resistance of the switch by about 0.003 ohms. With the steel wire, the resistance is 0.0047 ohms.
The four 711 switches that I tested had a significant amount of resistance between the rivet that holds the fat rail and the rivet itself. I soldered the rivet to the
I just wanted to verify that one should increase the resistance that you measured by 50 percent, to 4.8 milliohms per section, to account for the entire circuit. I figure that that is approximately equivalent to 18 AWG copper wire. I have advised using no smaller than 14 AWG for feeders, on the basis of CTT’s similar published measurements, that I estimated to be equivalent to 16 AWG. The feeder resistance of course should be lower than the track resistance in order to improve the overall circuit conductance by a significant amount.
Based on my measurements of the joint resistance with and without the rails bent where the pins are, the joint resistance is the problem. It can become quite large if the pins are not clean, the hole in the end of the rail, and there is no side pressure on the pin (rail not bent where the pin is installed). Bob. I know that you solder a jumper between track sections, but with a floor layout I don’t have that option. So I am modifying the track sections to get the joint resistance down very low.
Most of the track that I have is old. Some is 072 prewar, some is AF prewar, and some is O-31 post war but may be 50-60 years old. I am modifying and cleaning the track so I can put it together and not have a lot of poor connections. Adding a feeder is an option I am trying to avoid.
You might think about using a small amount of an electrical inhibitor grease on your track pins. This is a product used by electricians to stop corrosion on electrical joints. It is available at industrial supply stores like Grainger. This would help stop oxidation and the electrical resistance that comes with it. Obviously, keep this stuff off the tops on rails.
I have been interested in making tight (read low resistance) connections between track sections for some time. I have tried using an ohmmeter with less than accurate or quick results. A few days ago, I rigged up a Kelvin connection for measuring resistance. It will measure as low as 20 micro-ohms. With this I have made the following measurements:
A good connection between track sections is 1.5 milli-ohms. This is with clean pins and clean openings in the two sections. Also, it is necessary to bend the ends of the section where the pins are installed to increase the contact pressure between the pins and the openings in the adjacent section. With the pins of a section pointing away from me, I bend the left rail where the pin is installed to the left and bend the center rail to the right. I also use pliers to form the ends of the open rail back to where they should be if they are bent out of shape.
Resistance of a Lionel O-31 curved section = 0.0035 ohms
Resistance of a good joint between sections = 0.0015 ohms
Resistance of a Lionel O-31 straight section = 0.0032 ohms
Resistance of a Lionel prewar 072 curved section = 0.0048 ohms
Resistance of a Lionel prewar 072 straight section = 0.0058
Resistance of a prewar American Flyer O-40 curved section = 0.0040
Resistance of a prewar American Flyer O-40 straight section = 0.0040
Resistance of a Lionel O-42 curved section = 0.0039 ohms
Resistance of a Lionel prewar 072 (711) switch = 0.0100
About half of the resistance of the 711 switch is the wire that connects from the rivet holding the fat rail to either of the other two center rails. This wire is apparently steel and not copper. Replacing this steel wire with a copper wire would reduce the resistance of the switch by about 0.003 ohms. With the steel wire, the resistance is 0.0047 ohms.
The four 711 switches that I tested had a significant amount of resistance between the rivet that holds the fat rail and the
I have been interested in making tight (read low resistance) connections between track sections for some time. I have tried using an ohmmeter with less than accurate or quick results. A few days ago, I rigged up a Kelvin connection for measuring resistance. It will measure as low as 20 micro-ohms. With this I have made the following measurements:
A good connection between track sections is 1.5 milli-ohms. This is with clean pins and clean openings in the two sections. Also, it is necessary to bend the ends of the section where the pins are installed to increase the contact pressure between the pins and the openings in the adjacent section. With the pins of a section pointing away from me, I bend the left rail where the pin is installed to the left and bend the center rail to the right. I also use pliers to form the ends of the open rail back to where they should be if they are bent out of shape.
Resistance of a Lionel O-31 curved section = 0.0035 ohms
Resistance of a good joint between sections = 0.0015 ohms
Resistance of a Lionel O-31 straight section = 0.0032 ohms
Resistance of a Lionel prewar 072 curved section = 0.0048 ohms
Resistance of a Lionel prewar 072 straight section = 0.0058
Resistance of a prewar American Flyer O-40 curved section = 0.0040
Resistance of a prewar American Flyer O-40 straight section = 0.0040
Resistance of a Lionel O-42 curved section = 0.0039 ohms
Resistance of a Lionel prewar 072 (711) switch = 0.0100
About half of the resistance of the 711 switch is the wire that connects from the rivet holding the fat rail to either of the other two center rails. This wire is apparently steel and not copper. Replacing this steel wire with a copper wire would reduce the resistance of the switch by about 0.003 ohms. With the steel wire, the resistance is 0.0047 ohms.
The four 711 switches that I tested had a significant amount of resistance betwee
The numbers I published for the joints are for the best joints I have measured. Joint resistance can be a problem and is evidenced by the number of posts where someone is complaining about their train slowing down at some places in the layout. I have seen joints which were not clean with resistances as high as 80 milliohms. If you think this is not a problem, calculate the total resistance for a loop of track with 50 sections and then calculate the voltage drop for loco that pulls 3 amps. You will be amazed how high the voltage drop is.
For the most part you and Nelson are really the only ones worrying about it enough to pull a meter most of us just put drops down every so often and were good with what we get. Its a hobby not a perfection operation where everything must be perfect it’s suppose to be where one comes to relax. Not to cause more headaches. Sorry I just can’t go there.
No one’s asking you to go anywhere. I don’t understand why anyone would think it his place to tell others what they may or may not enjoy about the hobby. Can’t you understand that one man’s “headache” may be another man’s relaxation?
I find the discussion about track and track joint resistance quite interesting. I have also experienced voltage drop due to poor electrical connectivity between track sections and running feeder wires to every section is not a viable option every time. Keep up the good work “servoguy” and “lionelsoni”!
I know one guy who soldered all his track together? Who was that - it was someone who posted on here from time to time back a few years ago…
If the train slows down enough to notice - add a wire. That’s all you need to do. If you do all these calculations and figure it out to these super tolerances, what will you do when you change the plan a little or add another switch etc - calculate the whole thing over again? Just slap on a feeder where needed and run those trains flat out as fast as you can
I would love to chime in here,but wait, who cares? As long as I am here, well here it is. JMHO… As long as they run is good enough for me. I tend to agree with JimmyT’s thoughts, Find a hobby where you can use all those smarts you have that no one cares about anymore now that you are retired. I did. Toy Trains are what I do.
I soldered center rail jumpers between track sections on one of my layouts. Between the work to solder the wires, and the work involved when I broke down the layout, I decided never to do that again. Like some others, I just use extra feeders, both center rail and outside rail. I always put a feeder on each of the three legs coming off of a switch. I also like to use the terminals on each UCS track as feeders too. I was wondering about the meter that Servoguy used to take his measurements. I have a Simpson 657 Milliohmmeter adaptor, which is supposed to measure down to one milliohm, but I have not had occasion to use it. It works with a Simpson 260 VOM.
It doesn’t look like a Kelvin connection. It also doesn’t appear that it gets to a milli ohm or 100 micro ohms. My setup will read down to 20 micro ohms. My setup also gives me instantaneous readings and is not dependent on the connection resistances. If the constant current source has resistance in the clip leads that attach it to the rails, the voltage just goes up until the current is at the set value. The voltmeter has a high impedance and so it doesn’t matter if there is 100 ohms or more in series with the voltmeter. This is the advantage of a Kelvin connection.
Thank you for the thoughts on my adaptor. I am not familiar with it’s construction, and have never found occasion to try to use it. The Simpson documentation states that it measures down to one milliohm.
