Measuring Current of a Moving Object???

Off hand I would say you have another path back to the transformer that the current is flowing through.

What are you using to measure current? I use a clamp meter for around the house, and some goofy panel meters on the layout that I never look at.

Does your meter capture ALL the current going from the transformer to the track?  Since the engine can draw current from either track direction, I'm imagining a scenario where multiple power feeds can create such a situation if you only measure current going into one feed.

Is your power source chopped-sine?  Some AC meters indicate lower measurements in such situations.  Furthermore, even if presented with a "pure" sine power source, modern electronics draws current near the peaks of the AC signal.  So even if the voltage is pure sine, the current is quite "chopped".

On level track and constant speed, the current reading should remain the same irregardless of where the train is on the track.

First, are you hard wiring an ammeter in series with the power wire feeding the track?

Second, are you reading AC current and not DC?

Are there any other loads, such as lights or accessories that may be operating at the same time?

Lastly, are the connections between tracks clean and tight? Bad connections will give you a false reading.

Larry

I'm using a Powerhouse 180 for track power and a Radio Shack 22-813 Digital Multimeter connected in series with the red lead in the 10amp connection and the black lead in common, set on the mA/A AC setting, as per directions for the meter.

I would think I'd get a higher reading the farther away from the meter connection (due to amount of track the current is going thru), but it shouldn't be a lot of difference.

Here's my layout diagram, the meter is connected to the right end of the drop-down "Wye" bridge (where there's gaps in the track so I can drop the bridge):

Trains run fine, I'm just curious about the readings.  Is 350 milliamps about normal for 2 MTH motors?

Measure the current directly at the locomotive.

Take the loco off the layout and put it upside down in a cradle. Hook one power lead to the chassis/frame or wheels, and the other power lead through the ammeter to the pickup roller. The reading you get is the power draw of the loco.

I would think that you should be getting more current draw than 350ma. Even a couple of incandescent light bulbs draw more than that.

Larry

The current would remain exactly the same no matter where the locomotive is, unless the locomotive actually starts drawing less current.

There's no way you're drawing that little power, something else is afoot.

Connect the meter in series with on the leads off the transformer.    Do this ahead of any splits to various parts of the track.   If you have multiple leads to the track, who knows what you are measuring at that wye.

Most of my newer 2 motor locos draw about 700 milliamps (.7 amps) give or take .1.

The fact that the current drops to nothing at times indicates parallel current paths, so that should give a more accurate reading.

The Radio Shack manual says the AC current is "RMS calibrated"...rather than true-RMS.  As such it will produce lower than actual AC-current readings when measuring the pulsed AC (not sinusoidal) current going into bridge-rectified electronics as the MTH engines have.  

This kinda' screams at me that there's a connection error somewhere.

I placed my Atlas GP9 (MTH motors and PS2, headlight, marker lights, and sound are the only things drawing current) on my layout with a 6-car train.  At 30smph I measured the current and read between .001 and .350 amps.

Reading no current at any point doesn't make sense.

That's why I posted, I'm thinking it's either operator error or the meter.  Like I said, the trains run fine.

It could be the way I'm connecting the meter leads, just touching them against the side of the rails.  I could stick the probes in the ends of the track as an easy test.  If I get the same results I'll try near the power supply and then get a clamp-on meter.

How exactly are you hooking up the test leads to get a current reading?

One wire from the transformer to the lockon needs to be disconnected at the lockon, the black meter lead gets connected to the wire, and the red meter lead gets connected back to the lockon.

Any additional transformer feeds to the track need to be disconnected so that all current goes through the meter.

Larry

You do realize that the meter has to be in SERIES with the transformer lead in order to measure current, right?  prrjim mentioned that previously, and he's of course correct.

You can't get a series connection by just touching the sides of the rails. Hook it up like TrainLarry says.

Before hooking up your meter in series, make sure it can take at least 10 amps of current,some of them are limited to DC only and limited amperage draw.

Dale H

I do not know enough about Lionel electronics to lick a stamp.  That qualifier said, what about reading your amps upstream of the transformer?  Between the wall socket and the plug.  Read the amps when the transformer is not doing anything and then read the amps when the engine is running.  Maybe the difference, if there is one, might give you a clue as to how many amps or whatever your engine is pulling.  Again, I don't know what I am talking about and this could be a stupid, time wasting effort that will lead nowhere.  Include the danger in playing with this kind of voltage I would think long and hard about it and exercise every safety measure at you disposal.  Above all, remember I do not know anything about this.  It is merely an out of the box suggestion.

Bob,  The PS engine below pulls about 3 Amps at speed with a few lighted cars.  Perhaps 4 amps when starting to move and 2 amps going really slow at a steady speed.  Doesn't matter where it is on the track but my track is not as large as yours.  Can't see any difference in 3 or 20 cars on my analog meter. Only lighted cars I think would make a noticeable difference and I only have 3 of those.  My junk multi-meter doesn't do AC amps.

Like Larry said, right side of meter is + coming from transformer, left side out to center rail of track.  That 2nd picture below was taken with the engine running at normal speed.

Measuring the input amps to the transformer would not give you a true reading of the current drawn by the trains. The input current reading would be higher due to losses in transformers, most noticeable as heat.

Larry

If I understand this statement, you touch the Red meter lead on one side of the gap, and the Black meter lead on the other side of the gap?  That indeed measures the current flowing in the track (across the gap), but this does not represent the current flowing to the engine.  The engine is running in a loop where you measured the current.  The engine can draw current from track ahead of it or behind in.  Depending on where the engine is on the loop relative to the power feed, there may indeed 0 current flowing across your gap.

Actually, using network theory as taught in first-year college EE you can solve this to determine engine current but better to just do what everyone suggests and choose a different measurement point that reads a constant (or near constant) engine current no matter its location on the loop.

Note that you still have an independent problem that your meter under-reports the type of AC current waveform encountered with modern electronic engines.

I think Jim had the answer, I was connecting the meter at the wrong place to get a good reading.

I connected the meter between the red wire coming from the PH180 to the TIU Input.  At 30smph I'm reading between .8 and .95 amps as the train goes round the layout.  At 45smph it goes up just over 1 amp.

My reason for asking this is because I'm considering making at least one of my engines RC/battery controlled (posted in the RC sub-forum) and wanted to see just how much current was being drawn.  I'm looking at a 4amp decoder and wanted to make sure it was enough.  I'm going to run this check on all of my engines to see the different readings I may get.

I measured 10 of 12 engines (no cars) and here's what I got:

Atlas GP9 with PS2 - .85 amps

MTH RK NW2 with PS2 - .88 amps

Williams brass 2-8-2 with PS2 - .85 amps

MTH RK 2-8-0 with PS2 - .84 amps

MTH 0-6-0 RK Imperial with PS2 - .90 amps

Williams brass 4-6-2 with PS2 - .79 amps

Williams brass 4-8-4 with PS2 - 1.40 amps (1.75 amps with 5-car train, 1 lighted)

I have a slight bind in the 4-8-4 that I can't isolate yet, but it's a heavy engine and with 5 aluminum cars that's still not bad.

Then I checked my TMCC/ERR/Legacy engines at at setting of 60 speed steps (128 spd setting on the DCS handheld):

GGD E7 - 1.4 amps (could be the belt drive)

Lionel GP9 - .87 amps

MTH RK RS3 - 1.0 amps (had to set it to 30 speed steps, the gear ratio must be low because at 60 speed steps the thing was flying around the track).

I wasn't able to test 2 engines, my Williams E7 (no electronics) and my Weaver 4-6-0 with PS2 (derailing for some reason, probably traction tires)

Except for the 4-8-4 (almost 2 amps) the rest are very close.  All diesels have 2 motors and all steamers have 1.

Bob, the ERR Cruise Commander Lite is rated at 4 amps, but I managed to cook one just running a 2-cat K-Line Interurban set when it briefly stalled on a switch.  For a full consist with a decent sized locomotive and cars, the peak currents may be more than you expect.

John,

Was the stall an electrical problem or a mechanical one?

Tony Walsham of RCS in Australia:

http://www.rcs-rc.com/pages/home

has a 5amp system and near the same prices so I need to take a look at what he's got.

Bob, it was mechanical, the engine got hung up in a switch and the stall current of the motors obviously exceeded the 4A maximum of the board.  I've since put a PTC in series with the motors to attempt to protect the board in a similar failure.  So far, it has worked...

Thanks John,

I also have a MTH RK 2-8-0 that will be a guinea pig for battery RC as soon as I get a motor for it.

The RCS system from Australia looks like the one I want, but I have to determine the dimensions to see if it'll fit in the RS3, I have approx 1.25x1.75x5.0 space in the rear of the model that I want to house everything in, including the battery.  I'll have to get a battery from another source, but Tony should be able to give me a lead on what/where.

You could consider tethering a dummy to haul the batteries, makes it easier to fit a decent sized battery.

I detest dummy units, but when I get to my RK NW2 I may have to bite the bullet or keep using DCS/PS2/TMCC.

More later!

If the battery is in there, it won't be a dummy unit!   It'll be the fuel tanker.

I wonder if I can disguise a large round battery to look like a tankcar?!?!?!

Ya know, that may be doable

Well, you can put it in a tank car or a boxcar if that is more desirable.  A tether and a larger battery in an otherwise empty car will give you lots more range.