Using the RRAmpmeter

The RRAmpmeter from DCC Specialties is a great device for measuring track voltage and amperage. Because the DCC signal has such a high frequency your everyday volt ohm meter doesn’t provide accurate values but the RRAmpmeter is designed specifically for that job.

However one thing to be aware of is that you do have to have a load on the track when using it. A single locomotive sitting on the tracks may not be enough of a load for consistently reliable results. However the load can be something as simple as a 12 volt automobile tail light bulb clipped to the tracks. Be careful in choosing the bulb since a large taillight bulb like the #1156 may pull in so much current that it can shut down a small booster or command station. The reason being that light bulbs draw as much as 10 times their rated current when they are cold compared to after they have been on a short while.

Another thing to watch out for is the heat generated by a bulb–don’t let the light bulb flop over onto foam scenery. I did just that while I was taking a photo and it got hot enough to actually melt a hole in my foam scenery! I don’t know whether it could have gotten hot enough to start a fire if left there long enough, but I learned my lesson from that experience.

For convenience, you can quickly make up a fixture with the light bulb soldered to two wires having alligator clips on their ends. Attach it to the tracks you are measuring or clip it to the contacts on the opposite end of the RRAmpmeter from the track contacts. This arrangement makes it much easier to move the RRAmpmeter along the tracks making measurements as you go.

When measuring track amperage you must have the RRAmpmeter wired in line with the track feeders so it is basically a stationary measurement device for amperage. If you have your layout broken into a number of blocks using a PM42 or PSX4, you can move the RRAmpmeter from one to the other but that will get old fast. Some folks mount the RRAmpmeter into the fascia or adjacent to the booster to montior voltage and amperage for all the blocks powered by the specific booster. In that configuration the standard RRAmpmeter is rated at 23 volts and 10 amps–a more robust unit can be ordered that can take up to 20 amps.

If you have several boosters it get expensive to purchase a RRAmpmeter for each of them. There are plans available on the internet for building circuits that allow you to measure DCC voltage and amperage using a standard volt ohm meter. You also can buy standalone meters for voltage and amperage to install with these circuits. Having a way to reliably measure track voltage and amperage is a useful tool when you need to debug a problem.

6 comments

  • When the RRampmeter is set into the fascia and wired in parallel (?) to the booster, is it still necessary to add a load/bulb to the block being measured after or at the PSX?

    Also, can you please recommend an appropriate bulb to use. Thank you Larry.

    • Robert—that depends on what you are using it for. The bulb is typically used when you are checking out things like the voltage drop around the layout and probably don’t have many if any locos on the tracks. Most folks who install one in the fascia are using it to monitor voltage and amperage draw during normal operations when there are several locos running and they provide sufficient load for the readings to be accurate. As for the bulbs, a #912 draws about 1 amp, a #1141 about 1.5 amps, and the #1156 about 2.25 amps. For test purposes I’d use the #912 as that should be enough of a test load while keeping heat under control to prevent burns. These little bulbs can get hot so don’t touch one until it cools off.

  • Would it be possible (and still be accurate) to mount the Rrampmeter in a central location and switch it between boosters with a rotary switch of some kind? Would the extra wiring between the mounted location and the actual booster being measured create a problem?

    • That shouldn’t be a problem if you can find the right rotary. Just use heavy enough wiring so you don’t build in any voltage drops.

  • Larry does the bulb need to be clipped to the section of track you are checking or can it be clipped to the other side of the RRampmeter?

    David

    • I have dine it both ways. If you clip it to the track you are less likely to burn your hand, but don’t burn the scenery or melt ties.