Subject:
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Re: Smooth power or PWM for Lego train motors?
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Newsgroups:
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lugnet.trains
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Date:
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Tue, 2 Sep 2003 08:40:47 GMT
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Viewed:
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1294 times
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Mark Bellis wrote:
> I've seen the DCC mod some people have made to motors, and read about
> the overheating problem.
the overheating is not due to the use of PWM, but because the task asked
from those motors was too great. why do you think long trains use 2 or
more engines, with sometimes even engines in the middle or at the end ?
One of the questions I had for those using DCC is, Do you make sure only
9 volts is given out by your DCC system ????
> Does DCC provide smooth DC to the motor or PWM? If it's
> PWM, the motor will heat up twice as much as usual.
that depends.
PWM is the only proper solution but the frequency at which the pwm is
done is very important. also, lego motors are not really adapted.
You see, most high-end model train manufacturers (fleishmann comes to
mind) use Faulhaber 5 poles motors. the lego motor is only 3 pole.
> I once tried a 9V train motor with a 12V transformer up to 9V but the
> buzz was horrible!
the buzz you hear depends on the frequency (you heard the basic 50 or 60
Hz of your mains supply)
> This used full wave rectified power in a similar way to controllers
> from non-Lego railways.
well, duh, that was the 50 or 60 Hz you were hearing. proper pwm is done
at a much higher frequency (10 or 20 KHz).
by the way, this was probably a VERY CHEAP transformer
Ever been on a recent public transportation train ? the (sometimes loud)
high pitched noise is the PWM you are hearing.
> I concluded that 9V motors need smooth power and have used that ever
> since.
the premisses were flawed, hence the conclusion too
> I use a dual 30V 3A smooth DC power supply to power my Lego trains,
> especially since some have four motors and one happily draws 1 Amp
> round the curves.
this sounds like a nice power supply. don't go over 9v though
oh, and by the way, this is where the lego controller fails to deliver...
This thing is designed with an LM317T voltage regulator. This part is
not designed to handle more than 1 amp of *resistive* load. An electric
motor is part resistive, part inductive, and thus, they would have
needed a much larger voltage regulator (national semiconductor makes
some that can handle up to 8 amps). Also, the use of a wall adapter
(just a transformer in a box really) is not proper. True, it makes the
boxes cheaper, because you can ship just a different transformer for the
various countries (100v for japan, 120v for the US and 230 for the rest
of the world). However, this small transformer can only give out about 1
amp max, thus, there's no way it will be able to properly power more
than 2 trains (as you say below, the motor requires 300mA minimum)...
> I reckon the motors are 3 Watt ones, so I allow 300mA per motor when
> running the trains (in proportion to the applied voltage though).
> Some of my steam engines have Technic gearmotors (also 3 Watt motors)
> to turn the driving wheels and I make sure the load on them is small
> as I build.
nice and all, but there is no way you will be able to have realistic
speeds with variable voltage. the lego motor doesn't even start turning
if you feed it less than 2.5v (at least)
quoting from :
http://stage.itp.nyu.edu/~tigoe/pcomp/motors.shtml
The rated voltage of a motor is the voltage at which it operates
at peak efficiency. Most DC motors can be operated somewhat
above or below their range, but it's best to plan to operate
them at their rated voltage. Dropping below rated voltage
reduces the motor's power, and operating above the rated voltage
may burn the motor out. Plan on the motor's top speed being at
rated voltage, and slowest speed at no more than 50% less than
the rated voltage.
you can see that you should not go below 50% of 9v for the lego train
(or technic motor), which is 4.5v
now, acording to:
http://hot.ee/sonnich/lego/9vcontroller.htm
the lego controller has the first 2 steps under those 4.5 volts
(respectively 2.9v and 4.3v).
Now, to put a final nail in the coffin, the RCX uses PWM, and I never
had a motor overheating....
Conclusion:
Your post shows no knowledge of physics whatsoever, and not even
research about it's subject on the web (which has tons of educative
resources at your fingertips...)
PS: google is your friend :D
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Message has 2 Replies:
 | | Re: Smooth power or PWM for Lego train motors?
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| (...) Some model railroad companies actually use that sort of DC to power their trains to make them run more smoothly at low speeds... Fleischmann's "MSF" principle is based around converting 50Hz AC to DC with only diodes, and put the non-smoothed (...) (21 years ago, 2-Sep-03, to lugnet.trains)
| | | Re: Smooth power or PWM for Lego train motors?
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| (...) Being British I'm not too familiar with American trains (yet), Though I know about the multiple engines in real life. I would intend to triple head trains in a similar way when I have made enough American engines! The motor duty limitation is (...) (21 years ago, 4-Sep-03, to lugnet.trains)
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Message is in Reply To:
| | Smooth power or PWM for Lego train motors?
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| I've seen the DCC mod some people have made to motors, and read about the overheating problem. Does DCC provide smooth DC to the motor or PWM? If it's PWM, the motor will heat up twice as much as usual. I once tried a 9V train motor with a 12V (...) (21 years ago, 2-Sep-03, to lugnet.trains)
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