Time for a bigger transformer? (DC)

Model Railroader General Discussion (Model Railroader)
1

I’ve got a basic loop, a ceiling train, DC, 17’ X 12’. It’s wired in parallel, using 22 gauge wire, with feeders every 3 feet, using Bachmann EZ track grey roadbed, nickel/steel. All the track connectors are solid; the track is kept clean & clear. Powering the whole layout is a MRC200 Tech4, 15.5VDC transformer. I don’t power any accessories from it, using Spookshow’s Low Voltage lighting circuits for streetlights & some other closed circuit LED controllers for signals.The engines are good quality; IHC/Mantua, a Bachmann Spectrum, a couple of Stewarts, all oiled & clean.

But I have to keep the throttle almost wide open for my consists to get any appreciable speed. I also have a couple of spots that while not ‘dead’, are noticeably slower. These I’ve rewired, replaced track, checked level; but it still happens.

Should I upgrade to a more powerful transformer, or am I missing something else here?

2

You have a loop of track over 50’ long. #22 is good for the feeders from the track to the ‘power bus’ - but there is way too much voltage drop in your ‘bus’ if you are using #22 wire. You also mentioned that you have a feeder every 36" - there are maybe 4 sections of EZ Tack in that 36", and rail joiners that can become corroded where you cannot see(inside). At least you have the ‘grey’ nickel silver EZ Track. Does the train ‘slow down’ in any of these sections of track? If so, you have bad rail joiner connections. With #22 wire, you will have about 1.5v drop on a 50’ wire pair when pulling 1 amp. The more load you pull, the bigger the voltage drop will be.

Your current power pack will put out a little over 1 amp of power. If you are running newer locomotives like P2K, Kato, or Atlas, you should be able to run 2-3 engines with no issues. Older Athearn ‘Blue Box’ engines will draw a lot more current, and you may not be able to run more than one at a time.

I would take a multi-meter and check the voltage at several spots along you layout to see if you have a voltage drop issue. Measure right at the power pack terminals to get a base reading. A larger power pack will be nice, but I think you will need to address the voltage issues first.

Jim

3

So what would be the recommended gauge wire for my power bus? Could I sidestep the connector corrosion issue by soldering the joiners?

4

I would try soldering the joiners at the locations where you see noticible slow downs. If there is corrosion in the joiners, it may be difficult to get a good solder joint. You could drop feeders from every secition of track. However, can you pull the sections apart to look over the joiners? Joiners are cheap and if you find ones with problems, replace them after cleaning the rail where the joiners make contact and then I would solder.

5

Sounds like your wiring might not be sufficient. 22AWG wire is pretty small… according to the vast wealth of information in Google, 22AWG wire has a resistance of 0.0161 ohms per foot (16.14 ohm/1000 feet). Depending on how you’ve wired the controller in, this bit will change a little bit – I’m gonna assume you’ve got the controller 6’ below the tracks, centred on one of the 17’ runs, and it ends somewhere near the centre of the other 17’ run.

Thus, your minimum distance from the powerpack is 7’, where your maximum is 41’ (rounding a bit). Since this is DC, and the electricity has to make a complete circuit, the ACTUAL distance it has to travel is approximately 14 - 82 feet.

Voltage Drop is calculated as V = DIR/1000

where:

D = distance
I = amps (we’ll assume “0.5”. I know most modern locomotives are less than this when running freely, but we’re just using it for illustration)
R = Resistance in ohms/1000 feet

SO

Vl = 140.516.14/1000 = 0.11V at the near end. (or a max voltage of 15.39 VDC to the locomotive)
Vl = 80 *0.5 *16.14/1000 = 0.64V at the far end. (or a max voltage of 14.86 VDC to the locomotive)

Admittedly, this isn’t a whole lot, but that’s the absolute minimum loss you have, before factoring in feeder lengths, track, bad solder joints, poor conductivity between the track sections, etc.

keep the 22AWG feeders to about 6-12" length, and run a 18 or 16AWG bus line (effectively, the speaker wire you can get from Radio Shack) that the feeders tap off of.

using 18 AWG wire, your voltage drop changes to the following:

Vl = 140.56.385/1000 = 0.04V at the near end. (or a max voltage of 15.46 VDC to the locomotive)
Vl = 80 *0.5 *6.385/1000 = 0.25V at the far end. (or a max voltage of 15.25 VDC to the locomotive)

granted, it all depends on what “appreciable speed” is to you. &

6

First a note on terminology: a self-contained DC power source for trains is usually called a “power pack”. A transformer is an AC electrical/electronic component that changes voltages. Trains powered by AC call the power supply (which used to contain a variable voltage transformer) a “transformer”.

The motors in our engines vary their speed by varying the voltage supplied.

The measure of power for a power supply is watts (volts times amps) or volt-amps. Since max voltage is nominally fixed, the current (measured in amps) is the commonly used measure of load or power. According to MRC’s web site, the Tech 4 200 has a maximum output of 1.4 amps or 17VA (volt-amps). This should power at least 3 HO engines in good running condition simultaneously.

If parts of the track are noticeably slower than others, there is either increased friction for the train, or much more likely, an increased voltage drop in that part of the track. Doesn’t matter what you have done, those are the 2 causes for slowing. Extra friction can occur on curves, and sometimes through turnouts. Voltage drop comes from extra resistance due to insufficient feeders, loose connections, loose rail joiners, dirty track and wheels, etc. Getting a power supply with a bigger current rating will not change the voltage drop or the extra friction.

Top speed of better quality HO model engines is generally around 80 scale MPH. This about 16" per second, which does not come close to “normal” speeds for Lionel and other O gauge trains.

Bottom line: unless you are running more than 3 engines at a time, getting a bigger power pack is not going to fix the symptoms you describe.

my thoughts, your choices

Fred W

7

Well, I used 14 gauge solid copper house wire for my throttle bus. My feeders are 22 gauge. The 14 gauge is gross overkill, but I had the wire just lying around and it’s mechanically rugged. I’d say anything from 18 gauge (speaker wire) thru 16 gauge (lampcord) to 14 gauge house wire will make a fine bus. Actually 22 gauge isn’t impossibly bad for a bus, although I would choose something heavier.

What you really need to do is use a good voltmeter and make sure the track voltage is at least 12 volts at full throttle and at full load (engine on the track, running). Check your voltmeter to make sure it’s reading right. Your car battery ought to read 11.8 to 12.8 volts engine off. An alkaline D-cell ought to read 1.5 volts.

There are various things that can go wrong with power packs causing them to fail to output 12 volts (or more). In which case you need to repair or replace the power pack. But, if it delivers 12 volts under load, its a good power pack and replacement won’t help you.

HO is specified to run at full speed at 12 volts. In actually fact, the power packs all can deliver just a little more than 12 volts, and the locomotives will all acheive full speed at a little less than 12 volts.

Any power pack has enough current output to drive any single HO locomotive to full speed. Not all power packs can handle a four unit lashup, say an Athearn blue box ABBA set of F units. For you initial testing, try just a single locomotive without a train attached. Measure the track voltage with just a single locomotive. See if it runs as fast as you expect. Then add locomotives and a long train. Make sure tha

8

Jim’s suggestions are the way to go, bigpianoguy. And I would suggest at least 18 gauge, but preferably 16 gauge as a minimum feeder size. The biggest issue you have, however, is the sectional track.whether it’s EZ track or any other, each rail joint or contact is a potential source of problems, from total loss of contact to just weak connection. Your best bet to eliminate problems is to relay the track on cork roadbed using flex track and soldering the joints, leaving one or two open for thermal expansion.

9

Let’s not forget that if all the connections allow good continuity, the track’s rail will do a great job of carrying the juice to the train.

10

To follow up on this idea, and many of the other suggestions offered, I have been building DC powered layouts for over 40 years. I have yet to use any sort of bus wire system or multiple track “drops” to one isolated track section (commonly called a block by many). Many of my blocks have been 25-40 feet in length and fed with one 18 GA feeder. That feeder is usually tied into a 12 GA throttle bus for multi train operation.

BUT, as others have suggested, sectional track with joints every 9" is your problem - no doubt in my mind.

Solder all the rail joints and you problems will go away. Or, as suggested rebuild with flex track AND solder the rail joints - then I bet one 18 GA feeder will run that loop of track just fine.

Unless your climate situation is extreme, soldered rail joints seldom cause expansion/contraction issues.

Sheldon

11

Well, thanks, everyone; now I’ve got a game plan, at least. Replacing the joiners on EZ track is not an option, though, as they are manufactured with them already soldered to the sectional track, but I can solder them on the loose joins.Nor is a rebuild to flex track an option right now; but my way ahead will include that at a later date.

So for now, testing, soldering, testing, & replacing the feeder bus with a heavier gauge wire.

Thanks,

Paul &n

12

Like Sheldon, I don’t use a bus wire or multiple feeders. The power is connected to the track at one location only. With all rail joints soldered together, it makes no difference where the locos are running on the over 300’ of in-service track and I’ve run over a dozen locos at one time (grandkids seem to like watching them chase each other around the layout ). [swg]

Wayne

13

OK, then, just one more question: does it matter where I solder the joiners? Inside, outside, or all around the town? (sorry…)

I finally found one of those spiral metal holders for the soldering gun & just have to design a rig that I can safely use on the ladder…

Thanks,

Paul

14

It shouldn’t matter on which side you apply the solder, unless you use too much of it - you don’t want it to affect the wheel flanges as they pass over the joints, so the safest place for the solder is on the outside of the rails.
I use a large capacity iron for soldering rail joints, placing it atop the rail after first cleaning the area to be soldered and applying a little non-acid flux. To avoid melting nearby ties, I use small wads of wet paper towels as heat sinks. The large iron will put heat into the area quicker than it can dissipate along the rails, and a good solid joint can be made in a couple of seconds or less. I soldered all of the track joints on my DC-powered layout, with about 200’ of mainline in service, and over 100’ of passing sidings, staging tracks and industrial spurs. I then used a cut-off disc to place electrical gaps where required. The main line is operated as a single block, with the ability to kill power on either track where passing sidings are in place.

Shown below is the power connection from the MRC Controlmaster 20to the track:

Wayne