Power?

Jonathan
There are good suggestions from f1rem0uth, RichD and John - You should be fine if you go with one of those

QUOTE (RikoRocket @ 2 Apr 2012, 16:01) <{POST_SNAPBACK}>I'm not quite in agreement with Screwneck, if you use power taps at every straight you will have perfect power. If you have power drops then yes you should sort the connectors but a power tap will bypass the bad joint and give you smooth power.
Slot car track power, like some much else in life, is never truly perfect. The important thing is to make the imperfections small enough so they don't inconvenience you.
There is some drop in power on all tracks away from the power feeds, even if every joint is as good as it can possibly be. Fortunately that power drop is too small to notice on short tracks, as you go to longer tracks it gets worse. How much lap length before something beyond fixing the joints needs to be done depends on how much the driver is concerned about power drop, and how much power your cars are taking. For Screwneck that length is 80ft, others may have different views.

QUOTE (John Cahill @ 3 Apr 2012, 11:05) <{POST_SNAPBACK}>So here's what I'm thinking as we wrap this issue up...in what way is copper tape, run full circle around the track, with conductive adhesive...in what way is that not simply a semi-infinite series of power taps?
John
Tape is quite different from a semi-infinite series of power taps, I'll try and explain why.

The resistance of a track is made up of the resistance at the joints plus the resistance of the rails.
The most common power drop problem with plastic track is when the joints are in poor condition, in this case the resistance at the joints is much larger than the resistance of the rails.
When the track joints are in good condition, their resistance is quite a lot smaller than the resistance of the rails.
(I've just measured the voltage drop on some very old Scalex classic track, and the resistance of the joints is less than 20% of the resistance of the rails.)
Length for length, the resistance of copper tape is typically about 2/3 the resistance of Scalextric track rails. (The exact numbers depend on the thickness of tape used.)
So copper tape on a track with all the joints in good condition will reduce the track resistance by about 60%.
Another way of looking at it is you can have somewhat over twice the lap length for a given resistance.
If the joints are not all that good (which is probably rather common) the copper tape will produce a larger improvement.

Power taps are really quite different, how much they reduce resistance depends on the layout and the thickness of wire used. In some circumstances the track resistance can be reduced by better than 60% with 2 or 3 taps.

QUOTE (RichD @ 3 Apr 2012, 18:11) <{POST_SNAPBACK}>If you can make all of the joints perfect there is a way to even out the voltage drop due to the resistance of the rails themselves. If you connect all of your positive taps in one location and all of your negative taps half way around the track from there the voltage will have to be the same all around the track.
Indeed that does make the voltage drops more even. That's a trick sometimes used on routed tracks where the joint resistance can be negligible compared with the tape / braid resistance.
What it's doing is making the drop worse on the good parts of the lap and better on the worst parts of the lap (hence more even).
If the rails are connected as a complete loop (which is how they are intended to be on most tracks), it doesn't make the drop exactly the same all the way round.
It is possible to make it exactly the same all the way round by putting breaks in the rails at the appropriate places, but it's rather doubtful that's a good idea as it would make the drops worse in nearly all parts of the track.

QUOTE (RichD @ 4 Apr 2012, 00:17) <{POST_SNAPBACK}>The trick that I have proposed is commonly used on braided tracks in the US. The voltage has to be the same all around the track because there is always the same lenth of track braid in the circuit no matter where the car is on the track. There is a voltage drop due to the resistance of the braid of course.
Indeed that trick is used on a good many braided tracks. How that changes the the voltage drop round the lap is more complicated than you suggest.

If (and only if) there are breaks in the braids at the appropriate places, the voltage will be the same all around the track because there is always the same length of track braid in the circuit no matter where the car is on the track.
However, braided tracks are almost always designed with the braid as a loop - without a break part way round. That gives more power virtually the whole way round the lap length. (In the simplest case the improvement of using a loop varies between 25% and 50% round the circuit where the trick is used.)

The braid as a loop doesn't give the same voltage drop all the way round the track.
With a loop there isn't simply one length of braid from the feed to the car (each side), there are two parallel paths from the feed to the car. For example, as the car goes clockwise round the track the length of the clockwise braid carrying current to the car increases and the length of the braid carrying current anticlockwise to the car decreases. In the worst case the trick with the braids connected as a loop gives 50% more drop at the worst points (1/4 and 3/4 way round the lap) than at the best points (start and 1/2 way round the lap).

QUOTE (John Cahill @ 3 Apr 2012, 21:38) <{POST_SNAPBACK}>re: "The resistance of a track is made up of the resistance at the joints plus the resistance of the rails."

See, the thing is, you have to start by imagining the copper tape on top of the rails all the around to get my point. If so...at any small section along the rail...the effective resistance in that section is the least of the following actually: the copper itself, the rail (and/or joint) itself or the combination of copper and rail and/or joint. That's one. The second point comes from extending this idea. Suppose you have amazingly good conductivity (low resistance) along the rail for 40% of the way and then suddenly have a bad joint...and of course the copper tape is on top of the rail all along...at the very point where the rail voltage would drop dramatically, the copper tape "kicks in" and delivers higher voltage, effectively becoming a power tap. And because it is right there, all along the rail, just waiting until it becomes the path of least resistance at any point...is effectively a semi-infinite power tap. That's the point I was trying to make.
So you are saying the copper tape bridges a bad joint in the rails, pretty much eliminating the resistance at the joints problem.
Yes that's true assuming the tape is in good contact with the rails.

QUOTE (John Cahill @ 3 Apr 2012, 21:38) <{POST_SNAPBACK}>One other point...I'm not sure what copper tape you guys are using, or how amazing your rail steel is, amazing joints, huge cross-section etc...but in my experience (and i prefer thick and wide copper tape personally), the copper tape alone is superior to the steel and/or joints anywhere and everywhere. I used to run it on my Carrera track (which admittedly has more nickel and chromium content and less conductivity than Scalex steel) and now run it on a wood track with no parallel run of steel at all (and no power taps)...and I get no noticeable voltage drop, and actually run at significantly lower voltages than I used to (partly because of so much less mechanical resistance from eliminating the joints, and less hysteresis at the tire/track interface).
The resistance of 1/4 inch wide 0.004 inch thick copper tape is about 2/3 the resistance of Scalextric Classic track rails.
It would be interesting to see measurements for other types of track.
There is a power drop in copper tape, with short tracks and low powered cars this is unlikely to be noticeable. With longer tracks and/or more powerful cars it is often noticeable, taps are often added to reduce this problem.

QUOTE (John Cahill @ 3 Apr 2012, 21:38) <{POST_SNAPBACK}>PS I'm tempted to pose another question...why do you think your power taps help? Is it (more) because they are shorter runs, or because you are using continuous, copper wire? *grin*
Power taps work by reducing the resistance from the power feed to the distant parts of the track.
Power taps work better if their resistance is lower. That can be achieved by reducing the length or increasing the cross section of the conductor. For example the resistance of a conductor can be halved either by halving its length or by doubling its cross section.
The effect on a real track can be calculated or measured. Do both and you'll know this is correct rather than just think it is.

To recap what I was saying (and I think John was saying rather the same thing?)
The first place to look for power drop problems on plastic track is the joints, and joint problems frequently give much larger power drops than the resistance of the rails. We seem to agree that copper tape laid on top of the rails acts as a loop and that the joint problem pretty much disappears once the loop is in place.

Not sure if there is real disagreement over the "semi-infinite power tap" thing, or if we are just saying the same thing in different ways.

The effect of a loop conductor is the same as a pair of power taps to wherever the car is on the track. In a sense that is a "semi infinite" number of power taps, but with only two of them working at once. The resistance is these power taps is the resistance of the length of tape travelling clockwise round the lap to the car in parallel with the length of tape travelling clockwise to the car. The effect of a "semi infinite" number of connections between the copper tape and the rails underneath is to make them conduct in parallel. As the number of connections increases, they more precisely approach running perfectly in parallel at whatever point on the lap the measurement is made.