With a voltmeter (VAC), I read each side’s output at the binding post. “A” was 16.4; “B” was 17.5, the “constant” read 18.2. I disassembled and cleaned off the carbon from the rollers’ tracks. Read again; each was between 19.2 - 19.4. Took it back downstairs and reconnected the wiring. Each read the same as before the cleaning! Voltage readings from the track (FasTrack) were 14.6 on the “A” and 17.2 on the “B.” I am using TMCC so I have both handles pushed to the max at all times. Can anyone help me interpret these numbers?
I don’t know the exact winding ratios on the KW, however let’s assume that it will put out 20 volts with the line voltage at 120(which is pretty consistent with what I measured when I had one). This gives us a winding ratio of 6:1.
If the line voltage drops to 110, the maximum output voltage drops to 18.3 volts.
If your line voltage goes even lower, like say to 100 volts, then the maximum output voltage goes into the 16.6 volt range. It may be a bit of a stretch to think that it would go that low, but it would at least partially explain why you’re getting such low voltage readings.
In addition, could it perhaps be that your roller arms are out of their proper alignment? I sold my KW back in November, and it’s been about two years since I’ve worked on it, but I’m pretty sure that it was possible to adjust the position of the copper roller brackets relative to the coil. In particular, I think that it was possible for them to be bent/set in such a way that they wouldn’t physically contact the highest voltage winding on the coil. It should be possible to determine if this is the case by visual inspection.
Perhaps someone else will come along and tell you whether or not I’m simply making that up(I do seem to recall having to do a similar adjustment, although I don’t recall what exactly I did), and if not what you could possibly do to fix it.
Can you say that the U terminal was connected to the outside rails and the A and B terminals connected to sections of center rails and that there was nothing between those terminals and the rails and nothing being powered from the track? If not, what else was connected and where?
The wires from KW terminals go to a terminal strip and from there to track as you said - U to outside; A and B to center rails. A track has 4 TMCC engines sitting idle and a couple of lit cabeese. B track has 2 TMCC engines idle and 7 lit passenger cars.
I did measure voltage from a number of places on the A section - they range from 14.2 to 15.8, which suggests some connection problems.
Yes, there seems to be some series resistance there, at least some of it between the transformer and the track that those units are on, since the voltage drops are different between the two outputs. What size wire are you using? For safety, 16 AWG is enough with the KW transformer; but you may need heavier to keep the voltage drop reasonable. Track joints are another possible culprit.
It’s 18 gauge wire. I’ve found some variance between pieces of track. Since this track is already scenicked and fairly permanent, are there any options other than pulling it up?
You could solder the rails together. But first try measuring the voltage directly at the transformer terminals with it connected to the layout. If that is not reasonably close to 20 volts, then there might still be something wrong with the transformer itself.
That’s probably all right. I just measured a 1.5-volt drop on a type-Z with a passenger train, so 2 volts on a KW seems not unreasonable. It probably won’t go down much more than that, since the likely cause of the drop is the resistance of the carbon rollers and the resistance of carbon, unlike metal conductors, decreases with increased current.
I would concentrate attention now on the wiring and track joints. You really should have a minimum of 16 AWG for safety; but I would rewire at least to 14 AWG to get the benefit of the lower resistance. To improve the track joints without removing the track, I would solder a small solid wire (18 or 20 AWG) to the rails at the joint, on the less-visible side. Solder about 1/4 inch at the end of a long wire to each rail, then cut off the unsoldered length, so you have a way to hold it in place while soldering.
I switched to 14 gauge wire, which boosted voltage to 17.5 on the tracks, quite
an improvement. Now my 5-car passenger train can get up the hill. That was
apparently the reason my milk car hadnt been operating well, too. Thanks for you
help.
Ya know, the moment I saw that he was using 18 gauge wire, my spidey sense starting tingling “Uh oh!” I always try to use 16 gauge or better on my layouts.