728Re: Locomotive current demands
- Dec 31, 1999Jeffrey and Bim:
>Jeffrey: I suppose I'm not quite clear on what we're checking here though.There are two nightmares you can have with any model train in any scale:
1. Burn out the motor (with too high a voltage, or some types of pulse power)
2. Have a dysfunctional mechanism that gives you frustrating performance and
overloads the motor until it burns out, or tears up the gears.
The question at hand addresses the detection of # 2 before it is too late.
With all my 12% knowledge I claim to have, I calmly put a brand new Marklin
steamer on the tracks a year ago and watched it tear itself apart at a show.
Dumb. Dumber than dumb. I "assumed" a brand new loco was properly oiled. I
What are some of the things that we have found inside locos:
- - - - - - - - -
Dirt and grime
Excessive grease/oil - or - No oil at all
Oil that has turned into concrete from age
Strings, pieces of wire and springs
Ballast, pieces of scenery, rolling stock, or even parts of the loco itself
Unidentified gummy "stuff"
Misassembled gear stacks, idlers, worms
Brushes completely worn out
Brushes far too tight on the commutator (acts like a brake on the motor)
Bent shafts and gears
Bad electrical connections
, etc., etc., etc.
No, we do not store our equipment rolling loose in the trunk (boot) of our
cars. While they have clean storage, they run on layouts. Layouts always
have some kind of loose "stuff" on them. There is no better track cleaning
device known than a loco itself. If its loose, the loco will pick it up and
I have bought locos from others which appeared to have been stored outside in
a horse barn.
The amazing thing, is that locos will desperately try to run with all this
"stuff" inside of them. Or at least for a while. Until the motor or the
gears give up.
Anything on the list above, will try to prevent the motor from turning at its
normal speed. This will cause the motor to draw more current. That can be
seen on a meter, without a disassembly of the loco to check for all these
The idea is to see if a "benchmark" for normal current, at a specific
voltage, under repeatable load conditions can be established for a quick
check BEFORE someone puts a loco on the track.
> Bim: What do you use to measure current???Most folks know that a volt meter measures electrical pressure expressed in
volts. In order to make that measurement one puts the meter in PARALLEL with
the power pack, the rails or the loco.
In order to measure current, one has to put a meter in SERIES with the power
pack. Since the polarity of the power back can be reversed, a "zero center"
meter is appropriate. That means a meter that at rest, will have its pointer
in the middle of the scale, and not off to the left side like most meters. A
meter with 1amp-zero-1amp offers a usable reading, but can survive a dead
short across the rails. Remember, any current (including a short) will pass
through the meter on the way to the rails in a series connection.
Likewise, a "zero center" voltmeter is quite appropriate too. Again, because
the power pack can reverse the polarity to the rails.
If interest develops, any one of several of us on the list can put together a
list of parts from common (cheap) resources that folks can buy and use, with
little or no electrical knowledge. A number of how-to books already have
But let's see if anyone agrees with the "normal" readings and the "test
procedure" before we advance to that step.
Who's next at the keyboard on this topic?
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