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In lugnet.trains, David Laswell wrote:
> Our club lets kids run the controller for one of the lines when we do certain
> events (like, right now, with Detroit Festival of Trees), but we could use a way
> to forcibly limit the speed on the line that they're allowed to run. One way
> that's really easy is to just build physical stops onto the top of the regulator
> so the dial won't turn as far in either direction, but that makes it difficult
> to actually operate the dial and won't be much fun for the kids. The other
> solution I just came up with would be to maybe limit the voltage going into the
> regulator. And that's where there's a problem. LEGO power adapters, for some
> odd reason, output in ~9vAC, not DC. Finding an AC-AC power adapter is
> difficult at best, and the only two that I can find through Radio Shack (the one
> place I knew of that _does_ sell them) run 9-13vAC or 18-24vAC, which is not
> going to help at all. They do sell an adapter that goes as low as 3v, but it
> outputs in DC instead of AC, and I'm not having much luck doing a generic
> internet search for adapters that output in AC below 9v. Does anyone know where
> I might be able to find such a beast?
>
> Also, is it safe to run LEGO trains on a regulator that's putting out DC voltage
> when all LEGO devices are designed with the expectation of AC power input? I
> know this is an issue that caused a lot of people to burn out the power busses
> on the RCX 1.0, which then led to the outright removal of the built-in power
> adapter port on the RCX brick (and probably directly influenced the transition
> to a power port that's built right into a battery pack for the NXT).
>
> Failing that, would there be a safe way to step the power down _after_ it comes
> out of the regulator? Say, running the power to a 9v TECHNIC motor and then
> gearing the speed down a bit before having a second 9v TECHNIC motor act as a
> low-power generator? The motor bogeys have to get a few rest periods throughout
> the day or they'll overheat, which makes me really cautious about hooking up two
> 9v TECHNIC motors and forcing them to run 8-9 hours at a time.
Hello,
you can put AC or DC voltage at the input of the regulator with no problem as
long as you don't put more than 9VAC~14VDC. The internal circuit will take
both.
So a quick fix that put 4.5~5V DC at the input will ouput about 3~3.2VDC at the
output.
Another option would be to modify the internal circuit so the position 4-8 are
limited to about 3.1V as position 3. Need a (small) soldering iron and some
instruction. You can possibly find info on the web somewhere. I could put detail
later this week.
As for thr resistor inline with the wire, you would have to calculate for
position 8 and always use position 8 as other will be really really slow (ie not
moving).
for this a 22 or 24 ohm resistor should do 6W minimum and it will get warm.
2 12 ohm in series would also work (3W each).
For the RCX, the problem was that the internal component where not strong enough
to feed all the power giving by the power adaptor, so at full power, those
component burned before the adaptor was at it's limit which is not the case
with the regulator.
Martin
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Message has 1 Reply:
 | | Re: Reducing voltage
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| (...) You have to be careful here. The controller is designed to take AC or DC, but the input diodes that that convert the AC to DC are only rated for 1 Amp (1000 milliampres). Make sure your transformer/wallwart is not rated for more than this. (...) (15 years ago, 24-Nov-09, to lugnet.trains, lugnet.robotics)
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Message is in Reply To:
| | Reducing voltage
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| Our club lets kids run the controller for one of the lines when we do certain events (like, right now, with Detroit Festival of Trees), but we could use a way to forcibly limit the speed on the line that they're allowed to run. One way that's really (...) (15 years ago, 23-Nov-09, to lugnet.trains, lugnet.robotics)
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