I just acquired a portable RRampMeter to test voltage along the tracks throughout my layout. I am testing for voltage drops under load by connecting an 1156 automotive bulb to the RRampMeter.
The layout is divided into two booster districts and further divided into seven power districts, three of which are controlled by PSX units and four of which are controlled by PSX-AR units.
All seven power districts perform as expected. However, one power district controlled by a PSX unit shorts when I test voltage under load. But, if I test voltage without load, I get normal voltage readings, no short.
I do not understand what is happening here. Any ideas or thoughts as to why this one power district shorts under load when measuring voltage with the RRampMeter under load? I can run locos in this power district with no problems.
Rich
Alton Junction
Its possible that the load is drawing more amps than the setting on the PSX unit. This unit may be more sensitive than the others.
Joe
Going to have to check the settings on that PSX. It must be at a lower setting than the others. A loco or two will draw less than an 1156 bulb, so thweey will run fine, but the 2.1 amps or so of an 1156 bulb may trip if the breaker is set to something less than that. The 2.54 amp option could be marginal.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
JoeinPA Rich Its possible that the load is drawing more amps than the setting on the PSX unit. This unit may be more sensitive than the others. Joe
rrinker Going to have to check the settings on that PSX. It must be at a lower setting than the others. A loco or two will draw less than an 1156 bulb, so thweey will run fine, but the 2.1 amps or so of an 1156 bulb may trip if the breaker is set to something less than that. The 2.54 amp option could be marginal. --Randy
I checked the PSX unit in question. The trip current setting is set at 3.81 amps, just like all of the other PSX and PSX-AR units.
I was able to watch the PSX that controls the engine servicing facility while I tested that power district under load. The PSX shorted out, while the booster showed no adverse effect. So, it appears that the PSX recognized the short in timely fashion before the booster could short.
I then did the quarter test at various points inside the engine servicing facility. It shorted that power district at each and every point tested, momentarily shutting down the PSX, while the booster remained unaffected by the short.
So, here is what I am thinking. The effect of the load from the 1156 bulb, combined with the number of locos sitting in the engine servicing facility must exceed 3.81 amps. Wouldn't this make sense if the load produced by the 1156 bulb is 2.1 amps plus the 1.65 amps reading without load on the in-line RRampMeter?
richhotrainWouldn't this make sense if the load produced by the 1156 bulb is 2.1 amps plus the 1.65 amps reading without load on the in-line RRampMeter?
are you suggesting that the combined load of 3.75 (2.1 + 1.65) shouldn't trip the breaker since it is less that the 3.81A value stated in the manual by 0.06A?
do you believe the circuit breaker and RRampMeter are that accurate?
the lamp may momentarily draw more that 2.1A as the filaments heat up
greg - Philadelphia & Reading / Reading
gregc richhotrain Wouldn't this make sense if the load produced by the 1156 bulb is 2.1 amps plus the 1.65 amps reading without load on the in-line RRampMeter? are you suggesting that the combined load of 3.75 (2.1 + 1.65) shouldn't trip the breaker since it is less that the 3.81A value stated in the manual by 0.06A? do you believe the circuit breaker and RRampMeter are that accurate? the lamp may momentarily draw more that 2.1A as the filaments heat up
richhotrain Wouldn't this make sense if the load produced by the 1156 bulb is 2.1 amps plus the 1.65 amps reading without load on the in-line RRampMeter?
The RRampMeter will draw a bit of current its self. My digital LED panel meters draw 10ma. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
Got to thinking about this a bit more, so I just went down to the layout and powered it up. Pulled a couple of locos off the tracks in the engine servicing facility and applied load with that 1156 bulb. The power district shorted out. So, I kept on removing more locos until I reached 11 locos off the tracks and the PSX no longer shorted whenI applied the 1156 bulb load.
I took one of those locos and placed it on the mainline which increased the current draw by 0.05 amps. Using that measurement, when I pulled 11 locos off the tracks in the engine servicing facility, I reduced current draw by 0.55 amps. That was enough to prevent the controlling PSX from shorting.
So, to recap, the engine servicing facility was measuring 1.65 amps without the 1156 bulb load. When I removed 11 locos, the amps dropped from 1.65 to 1.10. Add 2.10 amps for the 1156 bulb load, and I get 3.20 amps in the engine servicing facility - - less than the 3.81 trip current setting on the PSX.
If all of this is accurate, and if my reasoning is correct, I am a little surprised that I needed to remove as many as 11 locos to end the shorting.
when i worked, our lab equipment was recalibrated every year.
you might want to compare you RRampMeter with a more professional meter such as a fluke.
I have always considered the parked locomotive current draw one of the problems with DCC.
If I was using DCC, I would still kill tracks where locos are just "stored" and I would have a large engine terminal on its own booster - a big one.
But what do I know, none of my trains have little brains.......
Sheldon
gregc when i worked, our lab equipment was recalibrated every year. you might want to compare you RRampMeter with a more professional meter such as a fluke.
ATLANTIC CENTRAL I have always considered the parked locomotive current draw one of the problems with DCC. If I was using DCC, I would still kill tracks where locos are just "stored" and I would have a large engine terminal on its own booster - a big one.
richhotrainWill a fluke give accurate readings for DCC?
i was think more in terms of current. voltage measurements can be relative
if you want an accurate DCC voltage measurement, an oscilloscope would be unequivocal
I would think that the DCC Specialties specs are close enough for model railroading. Measures true RMS Volts/Amps, +/- 2%.I calibrated my Rob Paisley DCC ammeter using a cheapo meter then later on checked the calibration with my scope and it was dead on. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
RR_MelMeasures true RMS Volts/Amps
but isn't it including the current its drawing. if the loco is drawing 50 ma, 10ma drawn by the RRampMeter is a lot more than 2%
richhotrain gregc when i worked, our lab equipment was recalibrated every year. you might want to compare you RRampMeter with a more professional meter such as a fluke. Will a fluke give accurate readings for DCC? Rich
Will a fluke give accurate readings for DCC?
The only one that MIGHT is an old 8060, it's one of those old classics with the buttons ont he side to select the ranges. It's TrueRMS but up to 100KHz. The specs show the accuracy dropping way off as you appreach the limit though. I need to clean mine up again, the LCD started acting up again so I can't really read it - it worked for a while after I cleaned it up last time.
A cheap meter with absolutely NO RMS compensation will give the best results for DCC square wave signals. Or an oscilloscope.
If a meter says RMS - those are generally only calibrated to work for sine wave, 60Hz or maybe a little extra. True RMS, they can handle sine, square, and triangle waves, but for the most part are still limited in frequency. If limited to a few hundred Hz at most, to test DCC it might as well not even have the True RMS feature, it's going to be way off at the far higher DCC frequency.
As far as accuracy at low current levels - that's another one of those, does it really matter that much kind of things. It's not like we're designing the loco ourselves (and the decoder) so that it draws the absolute lowest current. Designers of some things are concerned with that - sleep mode on some microcontrollers can be in the nanoamp range, and that requires specialized equipment to measure, since even .5ma swamps that out by several orders of magnitude. But really, if the meter says the loco is drawing 25ma, and the meter itself adds another 10ma - who's designing their booster network with that tight a tolerance where that extra 10ma is the difference between the district having enough power and the breaker tripping? It just doesn't seem worth the effort to chase it down to so fine a point when simply moving some accessories off to a cheap accessory booster might reduce the load on the track driving booster by an amp or more.
I would HOPE the reading on the Rrampmeter shows only the output side of it, not including the load of the meter itself.
In the intermediate level, when you don't quite need down to the nanopamps, there are "low burden voltage" meters for taking low amp readings without causing as much as a voltage drop in the circuit as a more traditional meter (the 10 ampo range in a typical meter is typically done by measuring the voltage drop across a loop of thick wire).
I was referring to the accuracy of the RRampMeter, 2% should be close enough for model railroading. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
rrinkerI would HOPE the reading on the Rrampmeter shows only the output side of it, not including the load of the meter itself.
then it would have to know how much current it draws and subtract that from the measured value. a fluke, for example, is powered from batteries.
The RRampMeter may be able to measure voltage +/- 2%, but as I said, if the loco draws 40 ma, the meter draws 10 ma, and it reports 50 ma, then the error is +25%. of course, if the loco draws 200 ma, the error is only 5%.
richhotrain Yeah, I need to consider kill switches in the engine servicing facility. Rich
Yeah, I need to consider kill switches in the engine servicing facility.
Every one of my engine terminal tracks have kill switches, especially when there are close to 30 engines down there; some with sound. The engine terminal itself has it's own 5 AMP booster, plus circuit breakers. During an op session I have certain tracks powered that have engines to be used during the session. Otherwise, power is off the other tracks.
Highly recommend adding them. Worth the investment..
Neal
nealknows richhotrain Yeah, I need to consider kill switches in the engine servicing facility. Rich Every one of my engine terminal tracks have kill switches, especially when there are close to 30 engines down there; some with sound. The engine terminal itself has it's own 5 AMP booster, plus circuit breakers. During an op session I have certain tracks powered that have engines to be used during the session. Otherwise, power is off the other tracks. Highly recommend adding them. Worth the investment.. Neal
There is a version of the Rrampmeter that uses a battery, but the marketing blurb on the product page says this is just to allow low voltage measurements when the input voltage drops below 7V, so at normal track voltage it probably is still drawing power from the track.
It wouldn;t be super precise, but it shouldn't be difficult to calibrate the amp reading to read under by the typical current draw of the meter's displays (almost certainly the highest current component of the circuit. Worst case would be if it was displaying 8.88 amps and volts, thus drawing more than average, or displaying 1.11 amps and volts, drawing below average.
I'm no volt nut, with 9 digit meters, I don;t do anythign that needs anywhere near that precision. My best bench meter is a 5 1/2 digit, and even that's overkill, but for the price I got it (surplus closeout of some technical school a few years ago - I got a meter and a power supply) I couldn't pass it up. I have no intention of sending it off for a true calibration, I have a reference standard calibrated with a 10 digit HP/Keysight unit with traceable standards calibration which is more than good enough to keep my gear in check. So while the idea of adjusting a meter to read based on an 'average' power consumption may seem a bit hard to accept from an engineer point of view, the fact that we don't really need anything int he single digits for accuracy in model railroading makes it a bit more reasonable. Butr then, odds are it's not calibrated taking its own draw into account, it's only badly off at low current levels. Kind of the opposite of most multimeters, usually as uyou get intot he higher ranges they get less accurate, the Rrampmeter has less error closer to the current upper limit than it does at nice low power levels.
Have to be a little practical. While it might be nice if it was accurate to .001 volt and .001 amp, the question is, would the increased cost be worth it, based on the intended use?
I have wired my staging yard so that each track is isolated so I can use a kill switch on each one.
BTW, what do you recommend for kill switches to kill power to tracks from the main bus? I need to get some.
I hadn't thought of it for an enigne facility but it makes sense also.
Rio Grande. The Action Road - Focus 1977-1983
I like to break both rails (goes back to not using common rail with DC ) but really you only need to break one. To break both, a DPST toggle would do. Those can be harder to find, a a DPDT WITHOUT center off would work the same. A center off one would result in there being two stops in the toggle where the tracks have no power, and the third one where it did power up, possibly resulting in confusion. A non center-off DPDT only has two positions. One connects one side to the center, the other connects the othjer side to the center, so in one pisiton of the handle, the tracks are powered, in the other they are not, just simple on or off. If you wanted to get fancy, you could get a red light and a lens that says "Track power OFF" and hook that to the opposite side terminals so the light comes on when the track is turned off. Or if I knew a source for the type of buttons they used in Mission Control, as recently demonstrated on one of the YouTube channels I watch - an actual NOS one - where the button is also lighted and split into two different sections, with different colors. Press it, track power off, it glows red. Press it again, track power on, now lights up green. Perfect for something set in the mid 60's through the 80's at least. OK, that's probably overkill - DPDT toggle it is.