Hmm, if I was more ambitious, or just wanted to make my layout look like a power plant control center, I'd get 4 of Rob's circuits and use the guts out of 4 of the $2.99 Harbor Freight specials and just mount them behind the fascia, with a little cutout for the display. More than adequate and plenty accurate. And cheap.
I'll have to pull the back off one of my meters and check - I bet the guts could be trimmed back enough to make a portable version that has Rob's circuit inside the case. A little careful rewiring of the probe sockets, or just putting in some other connections that run to clip leads and you'd have a handheld portable DCC ammeter.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Below is a link to a DCC amp meter I installed for less than a Ramp meter since I lie to work at the component level. I am using the voltmeter option.
http://cs.trains.com/trccs/forums/p/173404/1902749.aspx#1902749
The fellow I bought the parts from has a simpler one that uses the 20ma scale of a cheap digital multimeter. I have three of that style meter and they are very close to an expensive meter. Rivet counters will tell you to use an expensive meter. If you misuse a meter, guess which one is a less costly mixtake.
His site has facts, not opinions about measuring DCC current.
Below is a link to his site with different options. The is a link for the device that actually samples the DCC current. Read everything. Don't assume.
http://home.cogeco.ca/~rpaisley4/DCCammeter10.html
Rich
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.
Unfortunately, I don't have a DCC system here on which to test this, so it is just a suggestion.
Cut a break in one of your DCC power lines and connect the two wires to the AC inputs of a full-wave rectifier. Then connect the DC outputs of the rectifier to a DC ammeter. I'm thinking that an old fashioned analog ammeter will work better than a digital one because of the effects of sampling in the digital one, as noted in one of the above posts.
The rating of the rectifier should be about 50 watts because the total voltage drop across it will be about 1.5 volts and your power supply has a capacity of 20 amps. Maximum power dissipated in the rectifier will be about 1.5 X 20 = 30 watts. I recommend 50 watts for the rectifier to include a margin of safety.
I'm figuring that, no matter which way the electricity is flowing in the DCC power line, the rectifier will direct it through the ammeter in the same, correct direction.
Two questions that testing may answer:
Will the rectifier work well at the high frequencies that DCC uses?
Will the high-speed rectification cause unacceptable electrical noise?
CSX Robertnorcalmodelerthanks, this is the answer i was looking for. but, you said AC amp meter. wouldnt it be DC. doesn't the power supply convert to DC before it goes into the booster? You have to match the ammeter to the power supply. The booster will run off of a DC or an AC supply.
norcalmodelerthanks, this is the answer i was looking for. but, you said AC amp meter. wouldnt it be DC. doesn't the power supply convert to DC before it goes into the booster?
Yeah, I keep forgetting some DCC controllers/boosters have a full wave bridge rectifier inside so the devices can be powered by just a AC transformer or a DC power supply. Then you can use a standard AC amp meter or DC amp meter.
The cheap multimeters can have a 10 amp or 20 amp max scale. MIne have 10 amp max scales.
Do some Internet searching and reading for DCC.
If you measure the DC current that is used to power the booster, you need a DC amp meter.
If you measure the DCC current feeding the track, you need an AC amp meter that can read the DCC current frequency. Many AC amp meters are good for low frequency AC.
DCC frequencies are quite higher.
Like I said, do some DCC research first. Links have been provided. Do not make assumptions.
The DCC amp meter circuit I provided has a couple tiny IC's that do real time sampling and makes the samples available for a voltmeter in the circuit I use and a 20ma meter in the newest version.
You can buy the Rampmeter from Tony's if you cannot work at the component level.
60YOKID selectorYour $8 multimeter will give a close enough approximation to the true values being drawn by the system that any reading above 12 volts, say, is going to be a solid, bankable, indication that you are getting the designed throughput. I think the OP is asking about current load, and I'm not sure measuring track voltage will help him much to determine his current load. It is very easy to confuse voltage, current, and power, however, they are different electrical parameters. My suggestion is to provide 4 simple 60Hz AC ammeters wired into the input side of each booster. This will enable you to balance the load more or less equally between boosters. As far as how many sound locos your 5 amp boosters will handle, this is usually determined by how many come on-line at the same time. Many of the sound decoders exhibit high inrush currents when first powered up. If you notice sound restarts for no apparent reason, you are probably a little above your limit. The restarts often happen when you go through a turnout, a reversing section, or some place where a slight momentary current increase occurs. Your booster needs enough reserve current capacity to hold the track voltage at normal levels even during a normal reverser operation. Just my thoughts.
selectorYour $8 multimeter will give a close enough approximation to the true values being drawn by the system that any reading above 12 volts, say, is going to be a solid, bankable, indication that you are getting the designed throughput.
I think the OP is asking about current load, and I'm not sure measuring track voltage will help him much to determine his current load. It is very easy to confuse voltage, current, and power, however, they are different electrical parameters.
My suggestion is to provide 4 simple 60Hz AC ammeters wired into the input side of each booster. This will enable you to balance the load more or less equally between boosters.
As far as how many sound locos your 5 amp boosters will handle, this is usually determined by how many come on-line at the same time. Many of the sound decoders exhibit high inrush currents when first powered up. If you notice sound restarts for no apparent reason, you are probably a little above your limit. The restarts often happen when you go through a turnout, a reversing section, or some place where a slight momentary current increase occurs. Your booster needs enough reserve current capacity to hold the track voltage at normal levels even during a normal reverser operation.
Just my thoughts.
thanks, this is the answer i was looking for. but, you said AC amp meter. wouldnt it be DC. doesn't the power supply convert to DC before it goes into the booster?
As far far and to many boosters. I have the boosters already. i figured i would use them. yes a little overkill, but it is not going to hurt anything to break the layout up. I will have a lot of older locos that draw more amps than the new ones. also the fewer amp you run on each booster the less heat.
thanks to everyone, the input has been great. going to pick up a couple more testers also
Measuring voltage can be important. If a booster section has a poor connection, too small wire size, you will have voltage drop and not enough current. Happened in our club that had DC blocks with #22 wire when we just switched over to DCC without re-wiring.
Also, a couple weeks ago we had a problem in an area that had a poor connection at a track joiner. Voltage measurement show quite a few volts drop.
It is rare we have to measure DCC volts anymore once we had #14 wire and good feeders.
I built a DCC voltmeter that shows our cheap multimeter are in the ball park for readings.
Some of you need to study the relationship between voltage, amps and resistance. With the Internet, there is no reason you cannot find the info.
As I said before, we have a good size club layout and use the NCE 5 amp Power Pro. We run as many as twelve sound locos, diesel and steam, and the current is around 3 amps. When we get a short and then remove the short, all sounds start right up. We use four different brands of sound decoders.
Watch for sales, I have 4 of the HF multimeters stashed in various places so I don't have to go hunting for one when I need it - at $2.99 each I can afford to do this.
I have a multi-hundred dolalr FLuke benchtop meter that I got for free if I need to do any crazy stuff. It's good to withint .5 volt for sine or square wave AC up to 10KHz and within 1ma on the 2 amp range sine or square wave up to 10KHz. And it has an ultra low ohms range that can tell me the resistance of a 10 foot piece of #12 wire - sort of. I need good clip leads to do it properly as at that range it can measure your body's resistance and just varying your pressure on the probes it will alter the reading. There's also an ultra-low volts range - if you short the probes and wave a magnet near the wire it can detect it.
TOTALLY unecessary for model railroad work - or even simple electronics. I certainly never would have purchased a meter like this. The HF ones are more than adequate for model railroad and basic electronics.
Here is a simple solution. The below circuit. Read all the info. You use one for each section. He has different options. A lot less than $55.00 for each section.
Use a cheap digital multimeter from ebay or Harbor Freight. They go for about $10.00 or less. I have three of these multimeters and they all read very close to each other. I have bought meters from both sources.
You could use one multimeter if you so choose.
I use that fellows older circuit at our club with a voltmeter.
rrinker Another option is to use some sort of plugs and make up some jumper cables. Get just ONE RR-Ampmeter. To measure amps it has to go in series, so what you have on the panel are two sets of plugs and sockets for each booster. FOr operation without the meter, a jumper connect the two sets of connectors so current gets to the rails. WHen you you want to monitor a district, pull the jumper and insert the meter. One meter can then serve multiple duties since it's not a permanent part of the circuit. --Randy
Another option is to use some sort of plugs and make up some jumper cables. Get just ONE RR-Ampmeter. To measure amps it has to go in series, so what you have on the panel are two sets of plugs and sockets for each booster. FOr operation without the meter, a jumper connect the two sets of connectors so current gets to the rails. WHen you you want to monitor a district, pull the jumper and insert the meter. One meter can then serve multiple duties since it's not a permanent part of the circuit.
never thought of that, might be able to put it on a switch.
got the brain working now
i think i will play with the tester a little to see what i can come up with.
thanks to everyone for the input
Your $8 multimeter will give a close enough approximation to the true values being drawn by the system that any reading above 12 volts, say, is going to be a solid, bankable, indication that you are getting the designed throughput...assuming your scale is HO. My multimeter generally shows about the same as yours when my Digitrax DB150 is powered up...somewhere near 14 volts, give or take 0.5 volts.
To me, that is like the cold engine indication on your dipstick that you have oil in the crankcase when only the bottom 1/4" of the dipper shows shiny black oil. You would be greatly concerned if you dipped a cold engine and found no indication of oil...at all!!! Similarly, your non-defective few-bucks multimeter showing only 8 volts in HO scale mode would suggest you have a real deficit for some potentially serious reason. Anywhere above 12 volts indicated should be a good sign, and 14 volts indicated should be an even fuzzier and warmer sign that you probably have a decent meter, as well.
-Crandell
With the DCC amp meter that I posted here a few weeks ago, our club runs sometimes twelve sound locos and the current is usually around three amps. We run the NCE 5 amp Power Pro. DCC voltage at the tracks is around 13.5 volts. When we get a short, the amp meter indicates 4.98 amps for almost a second and the system cuts out.
A SoundTraxx rep at a show once told us we should use a booster. We have never found a reason for more power.
CSX RobertPhoebe Vet" i was planning on running a digitrax dcs-100 (command / booster) and 3 db150's. " Wow, I guess i need another cup of coffee because I completely missed that line!
Phoebe Vet" i was planning on running a digitrax dcs-100 (command / booster) and 3 db150's. "
It's probably just the heat. lol.
Poeple new to DCC often greatly over estimate how much power their trains draw.
Dave
Lackawanna Route of the Phoebe Snow
Wow, thanks everyone for the response. Just to fill you in. My layout is about 27 x 15 with an additional 10 foot "L". it is three levels. I am modeling northern California, where i live and grew up. Just started using DCC a few months ago. Lots of questions
bottom level is a 10 track staging yard, plus a double main (when finished will be a loop) that winds up to the 2nd level which will be Mt. Shasta & Dunsmuir. i plan to run two double headed trains on each mainline. (that is 8 locos). then there is a single line (point to point) from Mt. Shasta to the the 3rd level Mccloud lumber area. i want to be able to run two trains on the mccloud level, single line (loop also). (3 more loco) I do like to watch the trains run but will be set up for operations also. while these 6 trains are running you will be able to run cars from Mt Shasta to Mccloud without interfering with the main line. (1 to 2 loco) then the Dunsimuir yard running switchers.
so i figure that could be 14 to 20 locos with sound and others in the yards with just sound. i may just use the dcs100 and two boosters and keep the third for a spare. i will add circuit breakers down the road and am trying to wire for occupancy and signaling. can get expensive fast. will see how it goes.
i am in the construction stage, just bench work and track, no scenery. have most of the lower level complete up to Mt. Shasta and part of the 3rd level bench work. need to move a hot water heater be for i move forward and it gets really hot in Redding, don't work much on it in the summer. it is in a my garage, insulated and sheet rocked.
Always happy to have fellow model railroaders stop by and see. not much to see right now but i do enjoy advise and input. if anyone has a layout in the area i would also like to visit. How do you post photos?
i still have one question, everything has been very helpful. i wast planning on getting a ramp meet from Toney's. but to do what i wanted i would have to buy 4 @ $55 each. if i can put the amp meter before the booster, i can get just an inexpensive amp meter for around 10 each. $40 vs $200. that is another loco with sound.
CSX RobertPhoebe Vet That must be some layout you are building that requires 20 amps of power. You should be able to run 40 or 50 engines at a time with that much power. Will it be open to the public for displays? PM 42s are a lot cheaper than boosters if you just want multiple power districts. I did not see where anyone here mentioned needing 20 amps. The original poster only mentioned the Digitrax 20 amp power supply because of the built-in amp meter and was wondering if you could do something similar to measure current draw with other power supplies.
Phoebe Vet That must be some layout you are building that requires 20 amps of power. You should be able to run 40 or 50 engines at a time with that much power. Will it be open to the public for displays? PM 42s are a lot cheaper than boosters if you just want multiple power districts.
That must be some layout you are building that requires 20 amps of power. You should be able to run 40 or 50 engines at a time with that much power. Will it be open to the public for displays?
PM 42s are a lot cheaper than boosters if you just want multiple power districts.
" i was planning on running a digitrax dcs-100 (command / booster) and 3 db150's. "
That's 20 amps.
That's why I suggested the PM 42s if all he needs is multiple power districts instead of all that horsepower.
fender777When I use my multimeter set to AC'it show's 14.57 or close to that on all my tracks.Does that reading mean anything.My trains run well.But it would be nice to know all the track is getting the right current of DCC.Thanks
When I use my multimeter set to AC'it show's 14.57 or close to that on all my tracks.Does that reading mean anything.My trains run well.But it would be nice to know all the track is getting the right current of DCC.Thanks
It's close enough. The error because of not reading the waveform properly is not going to be huge - your trains aren't getting 20 volts when the rading is below 15. If youhave multiple boosters, as important as the voltage to the rails is, it's more critical that the voltages match in each section so your trains don't speed up and slow down as they pass from oen booster's power district to another. Absolute accuracy in the voltage reading isn't needed to check this. You should get readings within a half volt or better in each power district to avoid noticeable speed changes.
rrinker An amp IS an amp. The problem comes from how you calculate power for various waveforms. Lots of math but this is the full enchilada explanation of root mean square and average vs peak power: http://en.wikipedia.org/wiki/Root_mean_square Note that the square wave works out to be the actual amplitude - however this is ONLY for a fixed wavelength square wave. DCC is NOT fixed length. Zero bits are longer duration that one bits, and the exact makeup of the waveform depends on what commands are beign sent to what locos and stationary decoders, so it really is somewhat complex. Even the circuit from Rob Paisley's site as well as the one in the RR-Ampmeter (probably very similar) are still just close approximations, but defintiely much more accurate than a basic RMS meter which assumes sine wave like the typical AC power in most homes. Honestly there's no way to fully explain it without getting rather technical (see the math on the Wiki page for example). This is one of those things where a non-electricla engineer should probably just treat a device like the RR-Ampmeter as a black box that displays accurate enough results to rely on and not worry about what magic happens inside, just know that if it says 2.4 amps then whatever is on the track it's connected to is really drawing 2.4 amps. On the INPUT side of the booster, that's just standard sine wave AC or in the case of the big Digitrax power supply standard DC, so no special meters are needed to monitor current from that side. --Randy
An amp IS an amp. The problem comes from how you calculate power for various waveforms. Lots of math but this is the full enchilada explanation of root mean square and average vs peak power: http://en.wikipedia.org/wiki/Root_mean_square
Note that the square wave works out to be the actual amplitude - however this is ONLY for a fixed wavelength square wave. DCC is NOT fixed length. Zero bits are longer duration that one bits, and the exact makeup of the waveform depends on what commands are beign sent to what locos and stationary decoders, so it really is somewhat complex. Even the circuit from Rob Paisley's site as well as the one in the RR-Ampmeter (probably very similar) are still just close approximations, but defintiely much more accurate than a basic RMS meter which assumes sine wave like the typical AC power in most homes. Honestly there's no way to fully explain it without getting rather technical (see the math on the Wiki page for example). This is one of those things where a non-electricla engineer should probably just treat a device like the RR-Ampmeter as a black box that displays accurate enough results to rely on and not worry about what magic happens inside, just know that if it says 2.4 amps then whatever is on the track it's connected to is really drawing 2.4 amps.
On the INPUT side of the booster, that's just standard sine wave AC or in the case of the big Digitrax power supply standard DC, so no special meters are needed to monitor current from that side.
All true with respect to calculating RMS values.
But you forgot something else: Sampling rate.
Digital multimeters are limited to a very narrow bandwidth because they sample the signal and calculate it's RMS value. Since the typical line frequency is 50 or 60 Hz, they are built and calibrated for that frequency.
As a result, once you start trying to measure a high frequency signal, you get results that are not true, because the sampling rate isn't high enough for those frequencies.
This where something like the RRAmpmeter comes in. It is designed from the start to work with DCC frequencies and waveforms
Yes, measuring current draw on the power supply under load will work.
I wouldn't worry about evening out the current draw between booster districts because the load is moving between districts. Experience running your trains on your layout would be a better indicator of district boundaries. e.g. A consist pulling a long train up a grade will draw more current than the return trip down grade in the same district.
Martin Myers
rrinkerAn amp IS an amp.
rrinker there's no way to fully explain it without getting rather technical
Randy:
I took a quick look at the link and you are correct...there's no way I'll understand it. But I guess my question still remains: if I hook up a normal amp meter in the circuit, will I see any reading at all, or will the meter show nothing? And if there is a reading, will it be somewhat accurate (as in close enough for what we normally need), or will it be so far off that we can justify the expense of the specialized device?
Thanks
I used the word "sinusoidal" because that was the term used in one of the links I was referred to. Whatever kind of wave it is, there is current involved. My original belief was that an amp was an amp, even though I did understand that there was a difference in the voltage readings one would get if the proper type volt meter was not used.
Since I was corrected on this, which being married I'm used to, my follow up question is "can you not read DCC current with a "normal" amp meter, or is it that you can but won't get the exact reading?" And if the reading is not "correct", how incorrect is it?
I know that you can purchase a DCC volt meter that gives one the correct voltage reading, but in most cases the $2.99 meter you get at Harbor Freight is good enough for what most of us do. And I don't believe that I've ever seen anything that tells me how far off the reading is. So do I have to buy the expensive amp meter from Tony's to get the exact reading, or is the common amp meter good enough for practical purposes?
Thanks.