Measuring Amps on an Isolated Section of DCC Track

[richhotrain]

I have a coach yard, consisting of several tracks, that is gapped and isolated from the rest of the layout.

What type of instrument can I use to measure the amps within that section?

I have an RRampMeter, but it cannot measure amps on the track if you use it as a portable instrument rather than in line.

Rich

[N6VC]

Hi Rich,

Are you after a dedicated meter for that location or are you just wanting to sample periodically?

Jon

[tstage]

Rich,

Do you have a Power Cab or a ProCab throttle?  (I'm thinking the latter.)  The Power Cab has a built-in amp meter.  If you had a Power Cab and could hook up the isolated coach yard (or section of track) to a PCP panel, you could use the amp meter in the Power Cab.

Tom

[rrinker]

 You can't, really, without cutting into the bus line for that section an inserting a meter.

You can try a clamp on type meter, but they may not be sensitive enough for the relatively low currents of model trains.

You could probably adapt a current transformer and build a simple circuit to go with it - however this still will require cutting the bus line to thread it through the transformer.

           --Randy

 

[betamax]

You could use an RRampmeter for this, with a little extra wiring.  You would need two pairs of binding posts so you could connect to the circuit, and just short them together to complete the circuit whenever you don't have the RRampmeter in the circuit.

The other options require breaking one wire so the ammeter can be inserted into the circuit.  You would need a rectified AC ammeter, since your typical AC ammeter or DMM is designed and calibrated for 60 Hz operation.

A current transformer is another option, either a 5-5A, or a 5-0.08A or 5-0.1A bushing type. They can be quite accurate, but again, you need a rectified AC Ammeter, and the CT is designed and built for 60Hz. Which just makes it a little more complex because you need to get it tested and calibrated for the much higher DCC frequencies.

Maybe someone needs to design a simple Hall Effect device that can be inserted into the circuit and provides a known DC voltage or current in relation to the current flowing through the shunt.  If it can work for a 200A house meter, no reason it can't work here…

[N6VC]

Any kind of ammeter requires a shunt. The shunt is where you adjust the reading for the meter. The meter is just a volt meter that measures the voltage drop across the shunt.

Ammeters that are already scaled have a built in shunt. You can buy a volt meter and calculate the scale. Dry transfers are available to mark the values, so you can place a shunt in parallel with the meter and the shunt in series with the load and get whatever sensitivity you require.

Ohms Law will help in setting it up. The meter has its internal resistance that figures in.I haven't set one up in more than 30 years, but the last one I set up on a power supply is still working. I set it up with a switch so I can toggle between volts and amps.

Jon

[richhotrain]

Nuts, the coach yard is an isolated reversing section of track controlled by a Digitrax AR-1. 

The AR-1 has a Tunable Trip Current (TTC) Adjustment which can be adjusted from .25 amps to 8 amps.

That got me to wondering how many amps are present when one or more locos are sitting in the coach yard.

So, I was hoping that there might be an easy way to measure amps inside this reversing section.

I wanted to do it periodically, not continuously.

I use a Pro Cab which is part of my NCE PH-Pro 5 amp wireless system.

Doesn't sound like I can do this, at least not very easily.

Rich

[N6VC]

Hi Rich,

I use a Fluke 87V True RMS Multimeter to measure mine. It requires opening the circuit to get the reading. This meter is fused for 10 amps, so it's a pain if I accidentally exceed this value and have to replace the fuse.

Jon

[mfm37]

Cut your bus and install a plug and socket. Make up a set of leads with corresponding plugs and sockets to be able to cut in a meter when needed.

AR1 gets adjusted to trip before the 5 amp booster. No reading is really needed. When a dead short occurs at the gap the current draw will be more then 5 amps. Phase to phase shorts always are. AR1 trips first and corrected phase before the booster circuit breaker can react.

Martin Myers

[richg1998]

You can do this with the below two devices. The PC board and the meter from Harbor Freight. I have three of these meters. He does not show the meter but all these multimeter's have a 20ma DC current selection.

These meters show about 14 VAC at the booster terminal using a NCE system. I have not checked them on any other system.

http://home.cogeco.ca/~rpaisley4/DCCammeter10.html

http://www.harborfreight.com/7-function-multimeter-98025.html

Two ZXCT1009 devices convert the DCC signal to DC and that DC is measured by the cheap digital meter. I made two of the devices. One for the club I belong to and one for my home layout.

The only people who say it will not work are those who have never used it.

Compares very close to my NCE Power Cab at home. At the club, the device indicates 4.9 amps when the NCE Power Pro 5 amp booster shuts down.

]Rich