N gauge "power-on board" question

[sahansen]

I am trying a dead rail approach to N gauge steam. I need some data which I can't seem to get. I need the figures for volts and milli-amps at the motor when the loco is creeping, at speed [scale 30mph], and when stalled [as in can't pull the cars up an incline or drivers spinning]. The very small radio receiving and motor controlling chips needed are delicate.
I have Bachmann 0-6-0 [with motor out the back of the cab] and Bachmann 2-6-0 with motor more recessed. I tried Bachmann repair department by phone and they didn't know; referred me to the forum. I hope you can help. Thanks, sahansen

[James in FL]

Why don't you check yours with a multi-meter?

[sahansen]

Hi James--My multimeter attempts showed a range, depending on speed of 3 to 6 volts. This was with the loco upside down on the bench. Any measurement while running on a track I thought might not be applicable because the voltage lost in the track and through the pick ups is not an issue with power-on-board. My multimeter didn't registure any amps; my smallest scale is 1-10 milleamps. If the amps are in the range of 0.1-0.2 milli amps I may not be able to register them--but will still need to know what they are. Thanks for your reply. sahansen

[James in FL]

Hi sahansen,

I'm not sure the best way to measure is with your lokie belly up.
The dead weight of your lokie from "standing stop" to "in motion" while on the track, will measure different.
Newton's Second law you know.
It will take more energy to start it moving than to keep it moving, regardless of where the power is coming from, the track or the battery.
Provided you have sound connections between track sections, and feeders spaced properly, the voltage will remain fairly constant, when measuring on the track.
Using batteries makes that a moot point, but the Second law is still in effect.

A battery will supply a fairly consistent voltage from fully charged to nearly drained depending on the type of battery you are using. (NiCad, NiMH, Li-ion, Li-ion polymer, or a straight up Reusable Alkaline.
A quarter amp is 250 milliamps.
Figure an n scale lokie to be drawing anywhere from about a quarter amp (sometimes less) to a third amp, you should be able to measure that. (DCC excluded).
When measuring current, the probes must be in series with the current measured.
Are you measuring this way?
Your meter should be able to read that.
What batteries are you using and what are their ratings?

[sahansen]

Hi James--I still have not made satisfactory readings on my belly up 0-6-0. The problem may be my multimeter. There are several contact points on the underside of the Loco and tender. Two copper strip leads from the tender coupler to the engine are visible, and the pick ups from the wheels on the tender are accessible. I think I did the amp. measurement properly. In spite of my poor technique and equipment, a consensus seems to be emerging! Your estimated stall value of about 250-300 milliamps [high side] is bourn out by my researching some old Modelrailroader magazine new- products- test columns. Incidentally, that magazine stopped giving amp draw figures about 2014, while still giving voltages. The good news is that the radio receiver/motor controller which will fit in the tender is rated 1 Amp-safe! The bad news is that its voltage ceiling is 4volts. Do you agree that the loco pulling 3-4 cars at speed can exceed 4 V? There is a Lipo battery [model airplanes] which is 7.4V and will fit in a modified tender. It will need recharging at 300 milliamp hours. Do you agree that would probably be several hours of running without engine stalling? My task now is to find a small receiver rated for at least 6-8 volts. Thanks for your interest.  sahansen

[James in FL]

I have a 0-6-0 (visible motor) last release before the new motor release, which I have added a Spectrum Slope back tender to.
I will try to get some readings tomorrow night.

[James in FL]

The values I am posting may, or may not be the same you experience.
Lots of variables, therefore, this should not be considered benchmarks between your lokies and mine.
This should be regarded as "Ballpark", at best, for those very reasons.

All measurements made with lokie running on track.
The slowest I can get it to creep is 12 inches in 12 seconds which is scale 9.09 mph, 2v @ 30mA.
It will actually run slightly slower but cogs too much to get any accurate measurements.
At 12 in. in 3.5 sec. is scale 31.17 mph, 3.9v @ 48mA.
At 12 in. in 0.7 sec is scale 155.84 mph, 12v @ 59mA.
Dead stall at 12v, @ 360mA.

I should have stated that was without pulling any cars, just the lokie and tender only.

Do you agree that the loco pulling 3-4 cars at speed can exceed 4 V?

Not sure what you are asking here?
Adding cars, or more cars, does not cause an increase (or decrease) in voltage, but rather an increase in amp draw.

Do you agree that would probably be several hours of running without engine stalling?

Depends on current draw.

Let's say for instance, you had a 7.4v battery that was rated at 300 mAh.
If your lokie, with consist, is drawing 100mA, and you ran it without stopping, it would run for 3 hours.


This link may be of some help when using your multimeter;
http://www.trainelectronics.com/Meter_Workshop/index.htm

[sahansen]

James in Florida--thank you so much . these figures really help. I will use a radio receiver/motor controller chip with a ceiling of 550 milliamps. The battery will be 4.7 volts with energy storage of 350 milliamp hours. I am hoping to put these items inside a modified tender. Two further questions, if I may: Your measurements were on the track. In thinking about what the items in the tender and loco will "see", in which directions should I nudge your figures? Would the nudge be significant? Lastly, in the traditional model railroad, if I can cause just the loco and tender to go 28 scale mph by applying 4 volts to the track, won't I have to turn up the rheostat on the power source to make the loco, tender and 6 cars go 28 scale mph?  Thanks again, James.--sahansen

[James in FL]

thank you so much . these figures really help

You are very welcome, glad I could be of some help.

I will use a radio receiver/motor controller chip with a ceiling of 550 milliamps.

I think that is a good choice, you should be very safe with a ½+ amp rating.

I am hoping to put these items inside a modified tender.

If it all won't fit in your modified tender, you might consider using a dedicated box car to hold the battery.
You could make several so as when one is in service the other is charging.
You could use disconnects from each other with these or something similar;
https://www.tcsdcc.com/Customer_Content/Products/Supplies/Connectors/QuickPlugConnectors.htm

Your measurements were on the track. In thinking about what the items in the tender and loco will "see", in which directions should I nudge your figures? Would the nudge be significant?

Let me say my lokie was thoroughly cleaned (including commutator) and lubed less than 5 run hours before this test.
The mechanism is smooth and freewheeling, the tender is a Spectrum Slope Back which is very freewheeling and efficient at power pick-up.
So my figures might be slightly lower than yours, so nudge up if it makes you more comfortable.
The battery and receiver will add weight, increasing amp draw.
I do not think the "nudge" would be terribly significant probably less than 10mA or so.

Lastly, in the traditional model railroad, if I can cause just the loco and tender to go 28 scale mph by applying 4 volts to the track, won't I have to turn up the rheostat on the power source to make the loco, tender and 6 cars go 28 scale mph?

Yes, you would.
An increase in voltage will result in an increase in speed.
You don't have a lot of leeway here, your battery is only 4.7 volts, that's all you will get out of it.
0.7 volts is not that much to get any real speed out of.

Measuring your lokie belly up in a cradle is fine for measuring current draw and voltage at the motor brushes.
A better way to measure is with load applied, even if just testing a battery.

Thanks again, James.

Again, you're welcome.