Subject:
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Re: External Power Port Problem..?
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 9 Dec 1999 23:12:03 GMT
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Viewed:
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605 times
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Roger Hamlett wrote:
>
> In lugnet.robotics, Nick Taylor writes:
> > Jonathan Perret wrote:
> > [snip]
> > > Did the 1.0 RCX really take AC input, btw ??? I've never seen
> > > anything but DC being supplied through plugs like that...
> > >
> > > Cheers,
> > > --Jonathan
> >
> > Hi Jonathan ... yep, the 1.0 RCX can take AC or either polarity
> > DC. The LEGO wall wart supplied with their train delivers 10 or
> > 11 volts AC ... and works fine on the RCX.
> Yes, but this may be the very reason it has been dropped. A lot of people have
> connected DC supplies capable of delivering far more current than the correct
> transformer. The problems are that when using a DC supply, only two of the
> diodes in the rectification bridge are in use, and will fail at a lower
> current than when fed with AC, and with the higher current available from some
> supplies, there have been failures...
> The best way to go with the 'rear supply', would be to rectify yourself if
> required, and have a fuse to provide protection against a short - look at a
> fast blow 3A design.
>
> Best Wishes
This is my take on the problem: Many (most?) DC wall warts supply a
voltage as much as 200% of the rated output when lightly loaded ... so
a really big 12VDC wall wart may supply as much as 20+ volts to the
RCX. As careful as TLG is in designing their electrical products, I
seriously doubt that they used diodes that cannot handle a great deal of
current in excess of what the RCX demands ... even with three stalled
motors and three light sensors.
BTW ... a wall wart rating of 9V @ 2A does NOT mean that it supplies
2 amps! It only delivers the current demanded by the load. The 2A
rating means that the wall wart will supply near the rated voltage
at a 2A load and should not fail at that load. Today most of us have
many wall warts lying around while the device they were supposed to
be used with has long since gone into the trash. It is *good* practice
to not use a wall wart that has a current rating greater than about
130% of the anticipated load ... not because it will deliver too
much current, but because it will most certainly deliver a voltage
much higher than its rated output if lightly loaded. Better to buy
a supply of the proper rating ... they're usually under US$10.
Have fun and play safely,
- Nick -
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Message is in Reply To:
 | | Re: External Power Port Problem..?
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| (...) Yes, but this may be the very reason it has been dropped. A lot of people have connected DC supplies capable of delivering far more current than the correct transformer. The problems are that when using a DC supply, only two of the diodes in (...) (25 years ago, 9-Dec-99, to lugnet.robotics)
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