Subject:
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Re: WHAT IF? Take a look!
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Newsgroups:
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lugnet.trains
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Date:
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Mon, 31 Jul 2000 20:15:39 GMT
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Viewed:
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1852 times
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> Running a 9V motor at 12 V for extended periods (say with a heavy load so the
> train will not fly off the track) will shorten the lifespan of the 9V motor.
Lets put it this way: I don't think you are going to harm the Lego motor unless
you build it into a special engine that is designed to stand 12 volts around
highly banked corners. I can try it if you want...I have ample 12 volt
supplies and curved track (at present, only curved track...).
> I thought that voltage would matter. I understand that ultimately the strength • of
> the coupler will decide how long the train will be, but a 12 V motor should be
> able to pull a train of say 12 cars faster than a 9 V motor could pull them.
IF the coupler can stand the pull, which it cannot.
The force required to start a train is going to be higher than the force
required to keep it rolling at lego type speeds (say 20 mph at most).
It can be calculated as aproximatly 4 lbs pull/100 lbs of train, on straight
level track.
Pull from a engine can be calculated using 2 formulas, the most relavent one is
that you will manage 1/4th the weight on the driving wheels as a max. tractive
effort.
Assuming you have 4 lbs of weight in your lego engine, and all axles powered (I
doubt your loco is this heavy!), then you will be able to put out a TE of
arould 1 lb, and be able to pull around 25 lbs of load.
Power has nothing to do with this calculation (to this point), in that the
amout of power (force*distance) is 0, up to the point that the train starts to
move. If the coupler is not strong enough, then the limit will be whatever
strain breaks the coupler.
In fact, from a electrical stand point, the most 'power' will flow with 0
RPM...because there is no counter EMF from the motor to disrupt the flow of
electrons-so, assuming a constant voltage source, the most current will flow
through the windings, because the resistance of the windings will be less at
the start.
(hence, the advantage of a Diesel, it can produce all its power at low speed,
whereas a direct drive steam engine has to be moving at a substatial speed to
develop maximum power)
> Since power = current x voltage[1] (work = charge x voltage[2]), one would
think a 12 and 9 V motor should be able to do the same amount of work or
generate the same amount of power. In practice 9 V is not always a high enough
potential to force the required current through the circiut to generate the
power to do the work.
>
> >
Yes, but if the 12 volt is at the source, and the 9V or less is at the motor,
then it will not be able to harm the motor.
(I know, it sounds like I am trying to make a real railway again!...st, I'd
rather do these calcuations for something useful, like my Brit, which, will
haul at least 1000 lbs)
James
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Message is in Reply To:
 | | Re: WHAT IF? Take a look!
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| (...) Running a 9V motor at 12 V for extended periods (say with a heavy load so the train will not fly off the track) will shorten the lifespan of the 9V motor. (...) I thought that voltage would matter. I understand that ultimately the strength of (...) (24 years ago, 31-Jul-00, to lugnet.trains)
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