# am I experiencing voltage drop



## njitgrad

Complete newbie here. New to this site, new to Lionel, and new to model trains.

My family received the NY Central Flyer as a gift last year and I just finished setting it up around my Christmas tree for my kids. I am trying to understand the physics behind voltage drops and how they relate to model trains. I have an engineering degree but my EE courses were taken 15 years ago so most of that has faded from my memory (but will easily come back with a simple tutorial if someone wouldn't mind).

Here's my issue...after creating a layout (rounded square) around our tree, I noticed that the train would slow down around one particular turn. I went to a local train shop and was told that I needed another terminal connected to the transformer. So I placed the second connection opposite the first and saw no change in behavior. I even tested the two terminals independently one-by-one and saw no change in performance from both being connected simultaneously.

I then decided to measure voltage across the track. At 100% throttle I was reading ~13V uniformly across the entire length of the track, both with a single terminal connected, and with both terminals connected, essentially confirming that I didn't really need a second terminal connection. 

I then decided to test out just the locomotive without tender or any other cars. It went around the entire track several times at a constant speed. I then added the tender and that's when I noticed the slow down. When I asked the train shop owner he said that what I was observing was not intentional...basically something is causing it to slow down.

Coincidentally today I was shopping for Christmas decorations when I happened to noticed a similar Lionel train set on display circling a tree. It too was slowing down around one of the turns. Was this coincidence or expected behavior?

I'm hoping someone knows why I am experiencing this.


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## sstlaure

It's possible that the track in that area has some corrosion/dirt on it causing a loss of voltage.


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## njitgrad

sstlaure said:


> It's possible that the track in that area has some corrosion/dirt on it causing a loss of voltage.


That's exactly what the train shop owner said, but...

1) it doesn't happen unless the tender is attached
2) the voltage measured with my meter was uniform
3) I saw a similar train behave in the same manner today

Unless none of that matters if the track is not clean? 

Could one bad spot on a track cause a brief sudden voltage drop to slow the train down through an entire turn? I will experiment tonight by swapping my curved tracks randomly throughout the run.


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## sstlaure

I think moving the suspect track around and seeing if the behavior follows that is the best route to see if it's the track or the power supply. (mechanical engineer speaking here.)

Possibly the addition of the tender adds just enough resistance to make the difference.


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## mr_x_ite_ment

Yes, Scott has a good point. I would think it is possible for that piece of track to be slightly too tight for the train/tender combo to navigate. Could the track be slightly out of gauge as well? The track could be off in more than one way...either curved slightly too much, or slightly out of gauge...or both maybe.

Chad


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## sstlaure

Or maybe the wheels on the tender are out of gauge and only drag in a certain spot.


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## njitgrad

I will try swapping sections tonight...if this is indeed the culprit, is there a way to repair the bad section, or should I just replace it?


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## NIMT

Does the tender have power pickup for a horn, bell or whistle?
Push the tender around the track by hand and see if it binds in any curves?
Check to make sure that the link between the engine and the tender is not binding in the curves.
Check that all the wheels on the tender move freely.
Reverse the direction of the engine, does it have the same problem in the same area?
Pull the other cars without the tender (tie them to the engine with a piece of string if need be) does it still slow down in the same area?
Voltage drops will change when the train is actually pulling power from the rails, measure the voltage when the train is running around the loop.
check all pins and connections in the area of the slow down and check the tracks for bends or kinks.


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## njitgrad

Can one of you guys paint me a picture of how voltage drops across an A/C train track? 

How does adding a terminal section alleviate any drop? 

If I measured the same exact voltage of ~13V throughout the run, does this mean I have zero voltage drop (assuming the wheels always make good contact)?

An "A/C Trains 101" lesson is what I really need here. I Googled but didn't get the explanation I was looking for.


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## sstlaure

The farther you get from where the power goes into the track, the lower the voltage will become. Typically it's not a big problem unless you're talking long runs of track. (My experience is with HO, but I have to think electrons work the same in O gauge) To alleviate this you create multiple spots around the track for the power to go straight into the track. By using a large enough buss wire, you can minimize the voltage drop. (I use #14 for HO)


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## tjcruiser

I'm stretching a bit beyond my true understanding of electronics, but ...

An old-school Lionel AC transformer was a simple beast ... dial up the throttle, and it kicked out a certain amount of voltage. You could measure that same voltage (abeit with some resistance losses) at the track, regardless of whether a train was on the track and/or running on the track.

Flash forward ...

Today's modern-chip transformers are different beasts. The voltage they produce is created in response to demand needs. If you try to measure the voltage at the transformer (or on the track) with the throttle in one position but with no train on the rails (i.e., no current draw), you'll get a very different result than that by having a loco on the track demanding power (current).

Separately ...

Voltage drop around a track is simply due to resistance losses associated with non-perfect conductors ... track rail, end pins, etc. Also, electricity wants to do its job (power the train) in the easiest-possible manner. That means that when the loco is in one position on the track, current will flow from the LockOn clip say clockwise to the train, whereas when the loco is in a different position on the track, current will flow counterclockwise to the train.

TJ


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## gunrunnerjohn

Actually, you'll get voltage droop from any transformer, modern or ancient. The amount will be a product of the design of the specific transformer, not to mention it's power capacity.


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## njitgrad

tjcruiser said:


> I'm stretching a bit beyond my true understanding of electronics, but ...
> 
> An old-school Lionel AC transformer was a simple beast ... dial up the throttle, and it kicked out a certain amount of voltage. You could measure that same voltage (abeit with some resistance losses) at the track, regardless of whether a train was on the track and/or running on the track.
> 
> Flash forward ...
> 
> Today's modern-chip transformers are different beasts. The voltage they produce is created in response to demand needs. If you try to measure the voltage at the transformer (or on the track) with the throttle in one position but with no train on the rails (i.e., no current draw), you'll get a very different result than that by having a loco on the track demanding power (current).
> 
> Separately ...
> 
> Voltage drop around a track is simply due to resistance losses associated with non-perfect conductors ... track rail, end pins, etc. Also, electricity wants to do its job (power the train) in the easiest-possible manner. That means that when the loco is in one position on the track, current will flow from the LockOn clip say clockwise to the train, whereas when the loco is in a different position on the track, current will flow counterclockwise to the train.
> 
> TJ


Thanks TJ. This was the type of explanation I was looking for.


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## njitgrad

I take back what I said about the tender causing the problem. Tonight I tried a few different troubleshooting steps and realized the problem originates with the locomotive. I don't know how else to describe what I'm seeing, so what I decided to do was post a couple videos of the locomotive in action and try to get some feedback from all of you. 

In the two videos below, the throttle was set to about 20%-25% so that you could actually see (and hear...turn your speakers up) a significant change in velocity. The first video has the locomotive going counter clockwise. The second video has the train going clockwise. 

You can see in the first video that it slows down just as it approached the cars stored under the tree, speeds up briefly, slows down again, then proceeds normally.
Ironically it seems to slow down as it approaches each of the two terminal tracks.

In the second video, it seems to slow down significantly on the backside of the tree.

Re-locating track sections did not result in any difference in behavior.

Thoughts?


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## TONOFFUN80

Looks like ethier dirty track or dirty pick ups on the locomotive. the head light 
flashes as it comes at you in vid one i had some ho that did that. good cleaning took care of it.


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## mr_x_ite_ment

I would tend to agree with TON...it could very easily be dirty track and/or loco wheels. Maybe try giving a cleaning to the track, and the wheels of the loco if possible. Any grime on the track and/or wheels will cause poor electrical conductivity. Keeping these items clean is a MUST for the success of any model train. Let us know how it comes out.

Chad


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## deboardfam

+1 to what they said.. I have a basic set temporarily in my dusty attic... it does the same on the voltage connection points unless I clean it off.


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## T-Man

I would think "Track connections" You have a CW on a small circle there should be no drop. Running will help. The engine may need some use, but the track appaears to impede the engine so take apart the track connections, maybe switch them around. I don't have anything specific since I do not use fast track.


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## njitgrad

Okay, i'll try cleaning everything tonight...I assume rubbing alcohol pads work just fine?

But does this explain why the locomotive slows down at different sections simply by turning it around to travel in a different direction? I would think that if a section of track was not clean it would cause a slowdown in either direction. The slowdown on the backside of the tree only occured in the 2nd video.

I also moved track sections around. I moved the 4 contiguous sections (2 straight, 2 curved) where the locomotive first slowed down (in the first video) to the back of the tree and I still saw the slow down at the front of the tree.

Could there be other variables at play here? I can only think of two others...the first being the fact that my pre-lit tree is powered from the same power strip as the transformer, and the power strip itself is plugged into the only outlet in the vicinity (which also happens to have a water cooler plugged into it). The second being the fact that it does not appear that my floor (or carpeting) is 100% level. Notice in the first video as the train approaches the first slowdown the tracks actually get pushed down from the weight of the train.


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## T-Man

The engine could be impeding performance. The wheels, rollers, track could all be contributing . Direction could give you a hint but power comes from each direction and will flow the least path of resistance. So your contact will actually switch from one side to the next at the farthest point. I suggest to run it more it will work better. A light buffing with scotchbrite pad will help but the contact may have to be pushed out on the track pieces. IN slot cars this was commmon. Tabs touched each other and if bent too far in they didn't connect. You may be better off removing the outer most track to break the circular connection and run the train from one set of wires and see how the track reacts.


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## gunrunnerjohn

Clean...clean...clean... I have to believe the blinking light is either dirty track or dirty pickups and wheels. The fact that it happens in the same place sure suggests a track issue.


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## Artieiii

I have learned from this forum that wacky symptoms are frequently due to dirty track (or wheels or pickups). I have not always been able to explain exactly why some symptoms occur but when in doubt first step is to clean the track. Don't get too worried about exactly why weird things happen. Just my .02.
-Art


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## mr_x_ite_ment

I am going to add to what Art and John said. My layout is in my un-insulated shop, where it is exposed to extremes in temperature and humidity. Needless to say, I ALWAYS have dirty track. I have to clean track roughly every three operating sessions to maintain the best performance. Anytime I run my fingernail over the track, I have oxidation residue showing up (black crud).

I have two trains that are quite sensitive to that black crud. They will literally come to a dead stop at times. Sometimes they might start up right away again, and sometimes I might have to give them a nudge. Obviously at this point it is time to CLEAN! They don't stop at the same place all the time either...it happens anyplace, and in different spots each lap! I hate cleaning, but it is the only way to keep up good performance. 

Chad


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## njitgrad

Well I finally got around to cleaning the track thoroughly and the pickups on the locomotive. I used plenty of rubbing alcohol pads and each one got black rather quickly. It did not result in any performance change. The locomotive still slowed down at the same points on each loop around the track. 

Any other suggestions for troubleshooting? This is frustrating me.


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## NIMT

How many places are you feeding power to the track?


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## njitgrad

NIMT said:


> How many places are you feeding power to the track?


Currently just one, but I already tried feeding it at two places with no change in performance so I eliminated that as a possible source of the problem.


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## NIMT

If you feed power right to where you had slow downs and had no change then check for bent rails, Pinching the wheels maybe?


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## sstlaure

I'm with NIMT on this one. I think there is a kink or pinch in the track..


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## RyanMac

Sounds like it could be a tract width problem. I had something similar on an O setup I had. One turn was 1/32 narrower than the rest of the track. It was just enough to bind the drive wheels for a second. Do you have a caliper or something you can measure rail to rail.


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## njitgrad

Well now that Christmas is over and the tree has been taken down, I decided to try the track out in a different part of the house. I laid it down on my basement floor and ran just the locomotive. It ran reasonably well without any of the exaggerated slow downs I was previously seeing. I will attach more cars tonight and repeat the test. If it works as I hope it will, I can only come to one conclusion...the culprit was my carpet.

I have a medium-pile plush carpet, age unknown since I only bought the house. I would say at least 5-8 years old. Could the fibers of the carpet be contacting the rails underneath enough to cause non-uniform resistance and as a result create slow spots?

That is the only thing that I could think of. That, and the fact that I plugged the transformer into a different outlet.


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## tjcruiser

Hmmm ... was the carpet wet at all?

Not an electrical comment, but do try to avoid carpet fibers getting into a locos motor, gears, etc. That'll really slow 'em down in the long run.

TJ


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## njitgrad

tjcruiser said:


> Hmmm ... was the carpet wet at all?
> 
> Not an electrical comment, but do try to avoid carpet fibers getting into a locos motor, gears, etc. That'll really slow 'em down in the long run.
> 
> TJ


carpet was dry


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## mwpeber

Another possibility is maybe the padding below the carpet was weak there and when the engine ran across that location, the track flexed down at the joint and maybe either the wheels didn't touch the rail or the center rollers were not touching.


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