Voltage drop is a common problem in model railways, especially when you start adding more track and accessories and is one of the most common causes of trains to run slowly or even stop altogether.
Luckily, they are often easy to find and maintain consistent power and keep your locos running smoothly all the away the way round a layout. Regardless of whether it’s OO, HO, N or other gauge this technique will help you overcome voltage drops.
How to prevent voltage drops
Before getting into troubleshooting voltage drops, it’s probably worth recapping a few basic measures that should be followed to prevent them happening in the first place.
Get a good power supply
First up, use a good quality power supply.
Once you move beyond a basic single oval train set, I recommend investing in an upgraded power supply. The standard kit supplied with Hornby train sets isn’t up to much beyond one oval and a one or two small trains.
The output is consistent, reliable and with 4 track control plus one 16v AC and 2 x 12v DC outputs, it should be enough for your needs for some time. I’ve used GaugeMaster units for years and can’t recommend them highly enough.
Use the right wire gauge
Next up is to use the right gauge of wire. The gauge of wire you use will affect voltage drop. The thicker the wire, the less voltage drop you’ll experience and, for this reason, I recommend wire that is at least 16 or 14 UK gauge, for most model railway layouts.
With the right power supply and wire, it’s then a matter of securely connecting the wires to the track. Ideally, I’d solder the wires directly to the track but if you can’t do this, use soldered rail joiners and connect these to the wires from the power supply using snap connectors. Read my guide to soldering wires to rails for more on this topic.
Add additional power supplies and controllers
If you have a large layout, it maybe worth adding additional controllers to different sections. This however also involves splitting the layout into control blocks which is beyond the scope of this article.
Regularly clean the track
When everything is set up, clean your track. Dirty track will prevent the smooth flow of current from the rails to the locomotive wheels and in all my years of model railway engineering has been the number one cause of voltage drops.
Using a multimeter to find voltage drops
So assuming you’ve done everything above, but your trains are slowing down or even stopping on a section of track, here’s how to troubleshoot it.
Get a digital multimeter, this one has all the features you’ll need for track testing and electrics on model railways without breaking the bank.
Remove all your trains and rolling stock from the rails and turn on the power supply setting it to its maximum level.
How to use a multimeter to measure voltage
If the wires for the meter aren’t prewired into it, plug the black one in the terminal marked COM (for Common) and the red into the terminal marked with a V.
Now turn on the multimeter and turn the dial to the Voltage setting and the appropriate level. Given we’re testing model railway voltages, we’ll be measuring voltages around 12V DC, so set the dial to the closest number above with the V- above it. On mine, this is 20. (The V sign with a squiggle is for measuring AC voltages, don’t use this.
Now touch the rails of section of track (where the the locomotives stall or stop) with the probes from the multimeter. For digital multimeters, it doesn’t matter which way around you you connect the red and black leads to the rails.
The display should now show 12.00 (as in the first picture above, taken when measuring a section of track on my layout) or within 10% of this, around 11V.
Model railroad rails aren’t perfect conductors; however, there will often be some drop but you want this to be minimal and enough to power the motors of the locomotives. If I see a loss more than 10 per cent, I consider that a problem and start troubleshooting.
Fixing rail voltage drops
It’s now a case of working backwards to identify where are volts are disappearing to fix the voltage drops.
Identify where the power feeds connect to the track, and measure each section of track from there to where the multimeter showed the voltage drop.
When you find one section of track that has 12V and the next drops, check the fish plates of the rails between these sections. It’s often the case that they have worked lose and aren’t making a good connection with the rails and so the current isn’t being passed between the rails.
In most cases, I will do either two things when faced with this.
If this problem is with a model train set that I’m just playing with, such as on a table or floor, I’ll lift the track, slide off the old joiners and then reconnect the track with new ones.
Once in place, I then squeeze the sides of the fish plates with pliers so they clamp the rails and make a solid connection. This fixes 90 per cent of voltage drop issues with train set setups.
If you later need to pack the train set away, the track can still be pulled part; it just needs a little more pull than normal.
Fixing fishplates on laid track
If, however, the problem is with a layout where the track is laid, glued down and ballasted, it’s much harder to life the track to replace the fishplates. In this case, I’ll see if I can get a sheet of fine sand paper (600 to 800 grit) between the fishplate sides and rails to scrape off any glue or paint that might have got in. Then the outer edges of the fishplate are squeezed with pliers, as above, and finally, a drop of solder is applied to the sides of the fishplate and rail to secure them in place and increase the connection between them and the rails.
> A tip if you do this is to solder on the far side of the rails to the viewing side, so the solder isn’t as visible.
With that done, retest with the multimeter and hopefully you’ll find the section of the track no longer has the voltage drop. As a final test, run your trains and make sure they make it all the way around without slowing down or stopping.
By following these tips, you can prevent voltage drops and maintain consistent power across your model railway layout. This will help your trains to run smoothly.
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Andy is a lifelong modeler, writer, and founder of modelrailwayengineer.com. He has been building model railways, dioramas, and miniatures for over 20 years. His passion for model making and railways began when he was a child, building his first layout at the age of seven.
Andy’s particular passion is making scenery and structures in 4mm scale, which he sells commercially. He is particularly interested in modelling the railways of South West England during the late Victorian/early Edwardian era, although he also enjoys making sci-fi and fantasy figures and dioramas. His website has won several awards, and he is a member of MERG (Model Railway Electronics Group) and the 009 Society.
When not making models, Andy lives in Surrey with his wife and teenage son. Other interests include history, science fiction, photography, and programming. Read more about Andy.