Subject:
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Re: First Trains
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Newsgroups:
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lugnet.trains
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Date:
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Sat, 10 Feb 2001 12:26:03 GMT
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Viewed:
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894 times
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In lugnet.trains, Rich Thompson writes:
> If I run my trains at 3v, then two Lego Solar Panels can provide ~3v. Looks
> like I have another project after this one.
You're forgetting something important - as the load on the motor increases
(e.g. pulling more weight), the current it draws will increase { Power (W) =
Voltage (V) x Current (A) }. You only regulate the voltage with the
controller, not the current. Your solar panels might be able to produce 3V,
but it's unlikely they'll produce anywhere near the current required to move
a train motor. You might (if you're lucky) just get the wheels to turn if
you pick the motor up, but you'd be looking at several square feet of highly
efficient solar panel to provide enough power to shift a LEGO train.
> As for powering the RCX through the train track, I had not thought about
> having to run the controller full tilt to power the RCX. That would surely
> limit putting other trains on the track. I may have to resort to an RCX and
> battery pack for a long session. I have decided to build an 8-wide engine to
> house the RCX instead of a box car using this Amtrak car
> (http://www.robotthoughts.com/article.php?sid=101) as a
> model. I can then put a tender car or passenger car behind with a battery box.
>
> Rich Thompson
I've just checked my (UK) power adaptor, and it's rated at 10V. Being a
fairly small box, I presume it's not too smooth. The output will be DC, but
still have the ripples in it from the mains AC. Unfortunately I don't have
an oscilloscope to put across it's output, but the LEGO train controller
obviously has a capacitor in it to smooth the supply - check how the LED
stays on for a while after you unplug it. Now this 10V could be peak, in
which case it would smooth out to less than that, or it could be RMS (Root
Mean Squared), which is the average voltage when completely smoothed. So,
it may not be ideal for powering your RCX anyway. Digital circuits like
this don't always need the exact voltage to run, but a smooth power supply
is best. Rechargeable batteries are a lower voltage than regular ones, but
still operate most equipment. A slightly higher voltage will probably just
make it run a little warmer.
As for building your own battery box, you've got the same issues as with
mains power. Larger batteries can provide more current when the demand is
there, and this could warm up your RCX too.
I'm not saying don't do it. Just be cautious. When running it,
periodically take out your RCX, take the battery case off the bottom, and
feel all around for signs of heat build up. Don't worry too much if it runs
a little warm, but if it just keeps getting warmer and warmer when running,
stop what you're doing, and go back to AAs.
And it's at your own risk - don't blame me or TLC if it goes horribly wrong!
If anyone's got any experience of doing this with an RCX, or got any kit
they can test the train supply with, please feel free to correct me or help
this guy out.
Jason J Railton.
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Message has 1 Reply:
 | | Re: First Trains
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| (...) Actually, from what has been posted over in .robotics, it is not going to harm the RCX to use the track power, except if you have 2 or 3 of the outputs loaded down. The prefered input to the RCX is AC, because it contains internal diodes, (...) (24 years ago, 10-Feb-01, to lugnet.trains)
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Message is in Reply To:
| | Re: First Trains
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| If I run my trains at 3v, then two Lego Solar Panels can provide ~3v. Looks like I have another project after this one. As for powering the RCX through the train track, I had not thought about having to run the controller full tilt to power the RCX. (...) (24 years ago, 9-Feb-01, to lugnet.trains)
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