Subject:
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Re: Electrical Things (was: Railroad Dilemma)
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Newsgroups:
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lugnet.trains
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Date:
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Mon, 8 Mar 1999 15:30:03 GMT
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Viewed:
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3047 times
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Simon Robinson writes:
> > I'm not sure I agree that the voltage is variable. People have reported
> > (via oscilloscope analysis) that it's pulse width modulated 9V instead.
> > This will read on an analog meter like a low voltage, because it's
> > taking the average across time.
>
> If you have any URL's where people have reported on this, I'd be interested.
So would I, because it's not true! As I've said this many times, it's plain
and simple variable DC voltage with 6 steps. Look at...
http://ourworld.compuserve.com/homepages/train_depot/current.htm
>
> > > The motor power unit has a resistance of 8.7 ohms, so at max. speed, it's
> > > eating up about an amp. (or about 9 watts of power).
Also not true. The resistance of the motor is not enough to determine the
current it will draw because you are forgetting the back EMF generated by the
motor (which depends on speed and load). Again, look at my page.
Matt
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Message has 1 Reply:
 | | Re: Electrical Things (was: Railroad Dilemma)
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| (...) it on a scope. If we have a PWM voltage with a 50% duty cycle and 10 millisecond period An analog voltmeter will report the average voltage of 4.5, not 5 milliseconds DC 9V and 5 milliseconds DC 0V because it does not have the timescale (...) (26 years ago, 8-Mar-99, to lugnet.trains)
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Message is in Reply To:
| | Re: Electrical Things (was: Railroad Dilemma)
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| (...) If you have any URL's where people have reported on this, I'd be interested. (...) Yep - it was ohmmeter across unpowered moter. I did think about directly measuring the current with the motor running, but my multimeter has a maximum current (...) (26 years ago, 8-Mar-99, to lugnet.trains)
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