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
Alton Junction
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.
RR_Mel 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.
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.
Lastspikemike And then apply your multi meter to the rails set for 25v DC or whatever the closest setting to 14v your multi meter reads?
And then apply your multi meter to the rails set for 25v DC or whatever the closest setting to 14v your multi meter reads?
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?
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?
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.
richhotrain use an 1156 automotive bulb, wired across the two rails.
RR_MelFor higher current I use a 1156 automotive bulb, 2 amps at 12 volts.
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
Living the dream.
SeeYou190 The automotive bulb is my favorite for testing wiring. I used my eyeballs to see if the lamp is bright.
The automotive bulb is my favorite for testing wiring.
richhotrainSo, using the eyeball method, the brighter the bulb, the higher the voltage, the dimmer the bulb, the lower the voltage?
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.
SeeYou190I 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.
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
greg - Philadelphia & Reading / Reading
RichUse 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 LightingModel Number 1156B2Energy Used 26.9 WattsVolts 12.8Base Single Contact Bayonet (BA15s)Bulb Shape S-8Candle Power 32 Bulb Finish ClearBulb Technology IncandescentAverage Rated Life (hr) 1200Class and Filament C-6Length (in) 2Diameter (in) 1GE 1156Osram Sylvania 1156Attach 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.
LastspikemikeSomebody posted elsewhere that an ordinary multi meter won't measure DCC voltage.
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.
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
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
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.
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
I have two Cen-Tech A830L meters and over ten of the Harbor Freight Cen-Tech freebie meters and all check within ¼ volt of my scope measuring DCC voltages.Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
LastspikemikeFor 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.
in all case (DC, DCC) make all measurements (reference and point) with the load
measuring the voltage drop across a length of rail due to wiring and/or rail resistance.
for that, you need the "loaded" voltage that you're starting with.
it might also make sense to measure the loaded voltage at the booster itself to make sure it's at spec, as well as compare that to the loaded track voltage at the point closest (electrically) to the booster.
I thought that was obvious. I did not mention that in my previous post.
Unless you've got a complete break in the wire, the cumulative effect of bad joints, loose joiners, too long a wire run with too thin a wire, etc. is an increased resistance. Voltage drop is proportional to resistance and current flow - with practically no current, even a realtively high amount of resistance will show little to no voltage drop.
Multimeters are specifically designed to place as little load (low amp draw) on the circuit under test precisely to not influence the circuit under test. The meter's resistance may be 10 megaohms or more - 10 million ohms. Even at 120 volts, 10 MOhm will only allow .000012 amps to flow. That's .012mA - this is why when using an anti-static wrist strap, you never connect it directly to a ground, it runs through a large value resistor. Accidently touch a hot wire at 120V if the wrist strap is connected directly to ground, and you could experience a lethal shock. At best, it's not going to be pleasant. With the proper resistor, you won't even notice it.
So to get an accurate indication of what happens when a train runs through a section of the layout, you need to apply a load across the rails equivalent to what is expected when the train runs through. If the wiring is all up to snuff, there should be little to no voltage drop, if the wiring is inadequate and there is a lot of resistance due to long runs of wire, or poor connections, there will be a proportionally larger voltage drop.
Here are my initial test results.
Let me first say that I have two DCC boosters, and voltage/amps are read for each booster by a separate RRampMeter wired in-line.
My initial results have been measured on the mainlines which are controlled by a separate booster. The mainlines are 160' long, and the mainline bus is divided 80' in each direction, a little long at 80', but at the moment it is what it is.
I am using an 1156 automotive bulb to simulate load.
Using a digital voltmeter, without load, I get consistent readings of 13.9 volts across the entire mainline. My RRampMeter shows 13.3 volts.
When I measure near the booster, I get 12.0 volts under load. Approximately 40' down the mainline from the booster, I get 11.3 volts under load with no apparent slow down by any loco. About 70' down the mainline from the booster, where I do notice loco slow downs, I get a reading of 11.1 volts.
Those are my initial test results. Thoughts, comments, criticisms?
richhotrain Here are my initial test results. Let me first say that I have two DCC boosters, and voltage/amps are read for each booster by a separate RRampMeter wired in-line. My initial results have been measured on the mainlines which are controlled by a separate booster. The mainlines are 160' long, and the mainline bus is divided 80' in each direction, a little long at 80', but at the moment it is what it is. I am using an 1156 automotive bulb to simulate load. Using a digital voltmeter, without load, I get consistent readings of 13.9 volts across the entire mainline. My RRampMeter shows 13.3 volts. When I measure near the booster, I get 12.0 volts under load. Approximately 40' down the mainline from the booster, I get 11.3 volts under load with no apparent slow down by any loco. About 70' down the mainline from the booster, where I do notice loco slow downs, I get a reading of 11.1 volts. Those are my initial test results. Thoughts, comments, criticisms? Rich
What size wire is the buss?
How often are the drops to the buss?
What size wire are the drops?
How long is the average drop?
Are rail joints soldered?
If the answer to the last question is no, or partly, I would change it to yes or mostly.
Sounds like the mainline is one booster and secondary track another booster?
I think I would have been inclined to the divide the layout geographicly (east side/west side) rather than by main/secondary trackage and keep wire runs shorter.
Sheldon
RichI can’t find the size of your bus wires in this post but #14 AWG wire has .12 volts loss at 40’ or 12.19 Meters at 2 amps for one wire or .24 volts for a pair.#14 AWG wire has .22 volts drop at 70’ or 21.336 Meters at 2 amps for one wire or .44 for a pair. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
ATLANTIC CENTRAL What size wire is the buss? How often are the drops to the buss? What size wire are the drops? How long is the average drop? Are rail joints soldered? If the answer to the last question is no, or partly, I would change it to yes or mostly. Sounds like the mainline is one booster and secondary track another booster? I think I would have been inclined to the divide the layout geographicly (east side/west side) rather than by main/secondary trackage and keep wire runs shorter. Sheldon
What size wire is the buss? 14 gauge solid.
How often are the drops to the buss? Every piece of flextrax has a pair of drops.
What size wire are the drops? 22 gauge solid.
How long is the average drop? 12 to 18 inches.
Are rail joints soldered? Only on the curves.
Sounds like the mainline is one booster and secondary track another booster? Correct.
RR_Mel RichI can’t find the size of your bus wires in this post but #14 AWG wire has .12 volts loss at 40’ or 12.19 Meters at 2 amps for one wire or .24 volts for a pair.#14 AWG wire has .22 volts drop at 70’ or 21.336 Meters at 2 amps for one wire or .44 for a pair.
RichI can’t find the size of your bus wires in this post but #14 AWG wire has .12 volts loss at 40’ or 12.19 Meters at 2 amps for one wire or .24 volts for a pair.#14 AWG wire has .22 volts drop at 70’ or 21.336 Meters at 2 amps for one wire or .44 for a pair.
ATLANTIC CENTRAL I think I would have been inclined to the divide the layout geographicly (east side/west side) rather than by main/secondary trackage and keep wire runs shorter.
The two yards (coach and freight) are part of the same power district as the two mainlines. I have separate power districts on the primary booster for (1) the passenger station and (2) the engine servicing facility.
The mainlines power district is an 80' bus running east and an 80' bus running west.
0.9V from 12V is 7.5% which seems high (thought 2% was the target)
i calc a resistance of 3.2 mOhm/ft which is consistent for 14g wire.
12g wire would be half the resistance (1.6 mOhm/ft) and i'd estimate half the voltage drop.
in order to avoid undoing a lot of what you've done, you could add add a 2nd 14g bus wired from the booster to 10' (?) from the end of your existing bus. this would roughly cut the total bus resistance in half. using 12g would be better
RichI bought the Handy Converter from Stan’s Trains and use it for my calcs. When I used a online electrical calculator it double doubles the loss.Just curious, what does the voltage measured at the booster or source do with and without load. A lot of loss could be in the booster its self and not in your wiring.Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps