I am in the final stages of completing my new layout. It is landscaped and ballasted, and I have repeatedly checked my trackwork for derailments and unintended uncouplings. I do notice a few spots along the mainlines where locomotives seem to slow down a bit.
I understand that voltage under load is critical for accurate voltage testing. So, my question is, what is the most accurate way to check voltage under load along the mainlines?
Rich
I use a 15Ω 10 watt resistor across the track which is 800ma at 12 volts. For higher current I use a 1156 automotive bulb, 2 amps at 12 volts.
Mel
My Model Railroad
http://melvineperry.blogspot.com/
Bakersfield, California
I’m beginning to realize that aging is not for wimps.
And then apply your multi meter to the rails set for 25v DC or whatever the closest setting to 14v your multi meter reads?
OK, guys, thanks for the replies. But I am afraid in this case that I need to be treated as electronically illiterate. So, bear with me.
What you are telling me is that I should set my multimeter to a DC setting of, say, 25 volts and take a reading after doing one of two things.
One, I could lay a 15Ω 10 watt resistor across the two rails.
-or-
Two, use an 1156 automotive bulb, wired across the two rails.
Do I understand that correctly? Is the key here to wire a device, a resistor or an incandescent bulb, across the two rails in order to measure voltage under load at a specific point on the layout?
Rich
Just thought of something that I should have mentioned in my initial post. I am running my layout under DCC power.
So, should my multimeter be set using DCV or ACV?
Rich
At our club we have a dedicated track tester that shows voltage. I don’t know who makes it – I’ll try to remember to nab a picture of it when I get to the club on Sat.
I do have a RRampMeter wired in-line for each of my two boosters. But, those two meters show constant voltage as locos move around the layout. I need to test voltage under load at specific points on the layout.
Rich
The automotive bulb is my favorite for testing wiring. I test with an Amp Meter measuring current through the bulb, which (as Mel stated) should be about 2 amps with both the brake light and tail light filaments illuminated.
I used my eyeballs to see if the lamp is bright.
This is called a dynamic electrical test, and it gives a much more complete picture than just checking the voltage (static electrical pressure) appllied to an open circuit, like track without a locomotive.
-Kevin
So, using the eyeball method, the brighter the bulb, the higher the voltage, the dimmer the bulb, the lower the voltage?
Rich
Yes. The bulbs are designed to operate on 14.5 volts, so it will be plenty bright at full normal track voltage.
Mel will need to confirm how the bulbs behave on DCC.
I have only built a couple of DCC layouts, but we always used a normal DC power pack to test the wiring as it was installed.
-Kevin
not sure how you tell from current if the voltage has dropped below your minimum.
it’s certainly easy to measure the voltage instead of current. if you measure 14.5VAC where the booster connects to the track and want a no less than a 2% drop, you want to measure 14.2VAC or better.
using circuit breakers or a lower power DCC system (PowerCab), wouldn’t you need to be able to test with something that draws less than 2A. i use a #211-2 T3 bulb that draws ~1A with my PowerCab
Rich
Use one of your HF meters on AC to check the DCC voltage. The voltage should be the same anywhere you check it on your layout.
The 1156 Automotive bulb is a single filament 12.8 volt 2.1 amp incandescent lamp.
Brand Philips Lighting
Model Number 1156B2
Energy Used 26.9 Watts
Volts 12.8
Base Single Contact Bayonet (BA15s)
Bulb Shape S-8
Candle Power 32
Bulb Finish Clear
Bulb Technology Incandescent
Average Rated Life (hr) 1200
Class and Filament C-6
Length (in) 2
Diameter (in) 1
GE 1156
Osram Sylvania 1156
Attach the bulb to the rails (I solder a short 2” piece of #18 AWG stranded wire to the bulb with alligator clips) then check the track voltage with a cheapo multimeter, AC range for DCC and DC range for DC layout.
Been using the same bulb for around 20 years.
Mel
My Model Railroad
http://melvineperry.blogspot.com/
Bakersfield, California
I’m beginning to realize that aging is not for wimps.
Somebody posted elsewhere that an ordinary multi meter won’t measure DCC voltage. You can’t use the DC measuring setting. I had understood that the type of AC delivered by DCC also won’t show up on the AC setting of a regular multi meter.
Using a fixed resistance with a known value like a light bulb won’t tell you the actual voltage drop. You need a measuring device for that.
And apparently you can measure DCC voltage using the AC setting on a multi meter.
The cheapo multimeters (HF freebies) are very close using the AC range measuring DCC voltage.
For less current draw use a 15Ω 10 watt resistor, it will draw just under 1 amp.
Mel
My Model Railroad
http://melvineperry.blogspot.com/
Bakersfield, California
I’m beginning to realize that aging is not for wimps.
all you need is a relative measurement. in this case that the voltage is less than some value relative to some other measurement made on the RR with the same meter - as you also suggest (?!)
OK, great, this is all very helpful info guys.
Golf takes priority this morning, but I will do some testing this afternoon and get back to all of you. Thanks again.
Rich
So for DC you apply a load and measure actual voltage with the multi meter on DC voltage setting to measure the voltage drop I.e. actual track voltage after load is applied.
For DCC you can use a multi meter on AC voltage setting to get a relative voltage drop but not actual track voltage. You measure without load and then with load. The difference is the drop even though you don’t have actual voltage in either case.
For DCC you need to get a reference voltage first, I.e. on a piece of track not subject to any load and known to be in good continuity with the power supply (booster) feeding that track section.
With a cheapy meter you more than likely do have the actual DCC voltage, or close enough, anyway. Lack of any sort of RMS processing on the AC voltage setting results in an accurate reading of the square wave. Peak of a square wave = RMS, so a simple peak readign meter will show the proper voltage. A basic RMS meter will not read correctly, as it is calibrated for 60Hz sine waves, and peak is square root of 2 times RMS for a sine. And fancier True RMS meters that can handle multiple wave shapes instead of just sine also report incorrectly because with few rare exceptions, they generally are only good to 100Hz. Way under the DCC frequency.
DC voltage on DCC track had best be as close to 0 as it gets - otherwise one of two things is happening. One, you are using a system that allows running a DC loco using address 00, and address 00 is selected on a throttle and the speed is not set to stop, or two, something is causing the booster to put out an offset signal - either the output drivers are failing, or the input signal is bad and the booster is simply faithfully amplifying the bad signal.
Digitrax recommends measuring DC between one rail and the common terminal (labeled ground on the systems) and adding the two. Both should be equal anless, as above, address 00 is not at speed 0, or something is broken, added together, they should equal the DCC voltage. But that can be difficult to do in the middle of the layout where a connection to the common might not be readily available.
–Randy
Ramp meter! Yes, that’s the device we use.
My four Harbor Freight multimeters read about 13.6 VAC with my NCE Power Cab.
With a small added circuit and using one meter on the 20ma scale, I had a five amp DCC amp meter. for the club.
Rich