Re: Reducing voltage

In lugnet.trains, Martin Legault wrote:
> 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. ...


> 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.


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. That's more than enough for a train motor or 2. Also the interal circuit
including the diodes will drop ~2v no matter what. I'd use a 9v transformer,
thus giving you a maximum of 7v for that last 3 notches on the controller.
Which shouldn't be to fast.

Mat