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I finally got round to having a play with my controllers and my
multimeter.
PUTTING TWO CONTROLLERS ON THE SAME TRACK
-----------------------------------------
Firstly, apologies to Ben, who suggested if you connect two
controllers to the same track, then they'd short only if the
controllers had opposite polarities. Ben was actually correct.
What I actually found was the voltage on the track is the BIGGER
of the two voltages that the two controllers puts out, if they
have the same polarity. If they have opposite polarities, then they
always short out and there's a small residual voltage (about 0.3V)
on the track. I'm a bit puzzled as to what can be going on in
the controllers to cause this behaviour.
Incidently there doesn't seem to be any effect on the speed the train
goes at if you put an extra controller on the track. (I wondered if
there might have been because the controllers could supply more current)
CHARACTERISTICS OF ONE CONTROLLER
---------------------------------
As I suspected the controller supplies a variable voltage. As you move the
speed regulater from zero to the first of the 6 marks the voltage suddenly
jumps up to about 3V. It then increases linearly up to about 9V for the
maximum speed. I say roughly because my controllers, both newish, differ
by 0.2V, so I guess Lego's quality control for this stuff isn't too exact (it
doesn't really need to be).
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).
In more detail, for one of my controllers, the readings were
open circuit voltage with which means
voltage train running internal resistance is
Full power 9.24V 9.04V 0.09ohms
Minimum speed 3.04V 2.99V 0.02ohms
I'm surprised that the internal resistance varies with voltage. I guess
I'll have to go and read up on my basic electronics again to figure out
what's going on.
Simon
http://www.SimonRobinson.com
Simon Robinson writes:
> > > 4) Lastly, what would happen if I had both controllers running at the
> > > same time with the switch connecting them is active (both would be
> > > connected.)
> >
> > ben>> You have essentially connect both loops in parallel with two parallel
> > power supplies. If the two controllers have opposite polarity you have a
> > problem, which will cause a fault and stop the motor and possibly damage the
> > motor if the situation lingers.
>
> I suspect the short would happen even if the two controllers have the
> same polarity, but are set to different speeds. I'm guessing it's the voltage
> they put out which increases as you up the speed. If that's the case and
> you have the controllers set to different speeds then you're still directly
> connecting terminals which will be at different voltages -
> effectively creating a short.
>
> > If both controllers have the same polarity,
> > both trains will run with an amount of voltage from summing the addative • powers
> > of the two power supplies. Note: since they are in parallel it is not a • simple
> > 1+2=3 scenario. The formula escapes me but is a little more complicated.
>
> It's quite a bit more complicated. You're right in that you can't just add
> the voltages. My guess is that if an effective short occurs because of what
> I just said above, then the voltage the trains will see will be the smaller
> of the two voltages being applied by the controller (the bit that's left
> after the difference has shorted). But then how much current the trains
> can draw from that will be different from what they could draw from just
> one controller at that voltage, because you're having to combine the
> internal resistances of the controllers - which are in parallel.
>
> Simon
> http://www.SimonRobinson.com
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Simon Robinson wrote:
>
> CHARACTERISTICS OF ONE CONTROLLER
> ---------------------------------
> As I suspected the controller supplies a variable voltage. As you move the
> speed regulater from zero to the first of the 6 marks the voltage suddenly
> jumps up to about 3V. It then increases linearly up to about 9V for the
> maximum speed. I say roughly because my controllers, both newish, differ
> by 0.2V, so I guess Lego's quality control for this stuff isn't too exact (it
> doesn't really need to be).
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.
>
> 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).
How did you measure that resistance? Ohmmeter across an unpowered motor?
I don't think an amp sounds right. You can battery power these motors
for a good long while on 6 AA batteries. I bet the resistance is a bit
higher with voltage applied.
Disclaimer, I'm not an EE, I never could get past Electromagnetic Fields
class. :-) So I could be all wet.
--
Larry Pieniazek http://my.voyager.net/lar
Stop the FDIC from spying on us! Go to
http://www.defendyourprivacy.com and sign the petition.
For me: No voyager e-mail please. All snail-mail to Ada, please.
- Posting Binaries to RTL causes flamage... Don't do it, please.
- Stick to the facts when posting about others, please.
- This is a family newsgroup, thanks.
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> 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.
> > 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).
>
> How did you measure that resistance? Ohmmeter across an unpowered motor?
> I don't think an amp sounds right. You can battery power these motors
> for a good long while on 6 AA batteries. I bet the resistance is a bit
> higher with voltage applied.
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 rating of 0.2A - so the voltage and resistance readings
I was getting were kinda suggesting I'd probably trash my multimeter if I
did that :) If the resistance does increase with an applied voltage, that
might explain why I couldn't get a consistent calculation for the
transformer's internal resistance.
Simon
http://www.SimonRobinson.com
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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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Simon Robinson writes:
> I finally got round to having a play with my controllers and my
> multimeter.
>
> PUTTING TWO CONTROLLERS ON THE SAME TRACK
> -----------------------------------------
> Firstly, apologies to Ben, who suggested if you connect two
> controllers to the same track, then they'd short only if the
> controllers had opposite polarities. Ben was actually correct.
>
> What I actually found was the voltage on the track is the BIGGER
> of the two voltages that the two controllers puts out, if they
> have the same polarity. If they have opposite polarities, then they
> always short out and there's a small residual voltage (about 0.3V)
> on the track. I'm a bit puzzled as to what can be going on in
> the controllers to cause this behaviour.
That is because there is a diode to protect from reverse voltage and the
voltage drop is about 0.3V
>
> Incidently there doesn't seem to be any effect on the speed the train
> goes at if you put an extra controller on the track. (I wondered if
> there might have been because the controllers could supply more current)
>
> CHARACTERISTICS OF ONE CONTROLLER
> ---------------------------------
> As I suspected the controller supplies a variable voltage. As you move the
> speed regulater from zero to the first of the 6 marks the voltage suddenly
> jumps up to about 3V. It then increases linearly up to about 9V for the
> maximum speed. I say roughly because my controllers, both newish, differ
> by 0.2V, so I guess Lego's quality control for this stuff isn't too exact (it
> doesn't really need to be).
>
> 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).
The maximum current is about 0.7A MAXIMUM ( maximum voltage and whell not
turning) with one controller
> In more detail, for one of my controllers, the readings were
>
> open circuit voltage with which means
> voltage train running internal resistance is
> Full power 9.24V 9.04V 0.09ohms
> Minimum speed 3.04V 2.99V 0.02ohms
>
> I'm surprised that the internal resistance varies with voltage. I guess
> I'll have to go and read up on my basic electronics again to figure out
> what's going on.
the internal resistance will vary with voltage apply ( or will look to) because
at full speed the voltage is not realy constant there is a little variation
(ripple) du to the voltage regulator (the box you plug into the wall) that
is near is maximum capacity, and because there is a semiconductor voltage
regulator inside the controller.
> Simon
> http://www.SimonRobinson.com
<snip>
if there is two controller, then you will be able to draw about twice the
current of a single controller or about 1.4A
Martin
Electronic technitian
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Matthew Bates wrote:
>
> Simon Robinson writes:
> > 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
Your page says you used a voltmeter. That is insufficient evidence. Put
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 resolution to show that variation. The needle can't move that
fast. Now, I COULD be wrong, but I seem to remember someone reporting
that they did put it on a scope and saw PWM waveforms. Those are rather
striking as they look like square waves.
Put a DC voltmeter on an AC mains (don't try this at home, please, it's
a thought experiment) and you will see 0V. Yet the voltage is going to
110, back to 0, to -110V and back to 0 (RMS) 60 times a second.
While I did not pass electromagnetic fields :-), I DID have 4 years of
vocational electronics in high school and still remember a bit of it.
I will not argue whether this power supply uses PWM or not, as I said, I
don't recall exactly. But I will argue that an analog volt meter is
insufficient to determine if it does or not. So are all but the most
sophisticated digital meters.
--
Larry Pieniazek http://my.voyager.net/lar
Stop the FDIC from spying on us! Go to
http://www.defendyourprivacy.com and sign the petition.
For me: No voyager e-mail please. All snail-mail to Ada, please.
- Posting Binaries to RTL causes flamage... Don't do it, please.
- Stick to the facts when posting about others, please.
- This is a family newsgroup, thanks.
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Larry Pieniazek writes:
> Matthew Bates wrote:
> >
> > Simon Robinson writes:
>
> > > 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
>
> Your page says you used a voltmeter. That is insufficient evidence. Put
> it on a scope.
True, I used a voltmeter to generate the data on that page, but I didn't claim
anywhere on my page or previous posts that that was what I used to prove it is
not PWM. Proof is obtained by opening the controller, getting the number of
the chip used and looking it up in a databook. Turns out to be a simple
variable voltage regulator.
Matt
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Matthew Bates wrote:
>
> Larry Pieniazek writes:
> > Matthew Bates wrote:
> > >
> > > Simon Robinson writes:
> >
> > > > 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
> >
> > Your page says you used a voltmeter. That is insufficient evidence. Put
> > it on a scope.
>
> True, I used a voltmeter to generate the data on that page, but I didn't claim
> anywhere on my page or previous posts that that was what I used to prove it is
> not PWM.
But (pedant mode on) your wording in the post above does make that
implication. ;-)
> Proof is obtained by opening the controller, getting the number of
> the chip used and looking it up in a databook. Turns out to be a simple
> variable voltage regulator.
No fair. :-) That's a white box test. Much more fun to drag out a scope.
OK, I give.
--
Larry Pieniazek http://my.voyager.net/lar
Stop the FDIC from spying on us! Go to
http://www.defendyourprivacy.com and sign the petition.
For me: No voyager e-mail please. All snail-mail to Ada, please.
- Posting Binaries to RTL causes flamage... Don't do it, please.
- Stick to the facts when posting about others, please.
- This is a family newsgroup, thanks.
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