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, 2 Dec 1999 16:59:16 GMT
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Viewed:
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589 times
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In lugnet.robotics, "Tilman Sporkert" <tilman@activesw.com> writes:
> To be safe, you could use a small 1A fuse. You can buy in-line fuse holders
> in electronics parts stores. It's a little black tube with a screw on cap,
> and wires or solder tabs on both ends. Just tape it to your battery pack.
> Another possibility is an 12V automotive light bulb in series with the
> battery pack. You will have to try a few to find one that doesn't light up
> under normal operating conditions. The resistance of a light bulb is almost
> zero if cold (not lit), but goes up significantly when it gets hot (lights
> up). That limits the current and protects your RCX, and at the same time
> gives you a visual indication that something is wrong. This setup is
> sometimes used by Model Railroaders where shorts are a frequent occurence.
>
> I believe the motor drivers are protected. But if the motor drivers limit
> the current to 1A each, then if you short all three at full power, the RCX
> can draw 3A input current total - if you are using it with a power supply
> that can deliver that much power. I suspect that the AC rectifier in the old
> RCX bricks wasn't dimensioned for that.
Yes. It is also worth realising that the rectifier has a lower rating, when
running from DC, than when AC is used (with DC one pair of diodes does all the
work, and will fail earlier than with AC).
> You might not need this with the new RCX brick if you use the battery
> terminals. I believe there's no component in the path between the terminals
> and the protected motor drivers than can get fried.
I think a fuse is still the best idea, one of the little 'thermal' self
resetting designs could probably be used.
>
> Tilman
>
> > I own a 1.5 RCX (still wondering why it's marked 'RCX 1.0' when obviously
> > there are two different versions, with and without the AC plug)
> > and I've been
> > contemplating retrofitting an AC plug with a couple of wires inserted in
> > the battery compartment. This thread makes me wonder if I should
> > include some
> > kind of current-limiting circuitry to prevent the RCX from blowing up
> > (suggestions are welcome as to how to do this, since I don't have the
> > slightest idea).
Best Wishes
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Message is in Reply To:
 | | RE: External Power Port Problem..?
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| To be safe, you could use a small 1A fuse. You can buy in-line fuse holders in electronics parts stores. It's a little black tube with a screw on cap, and wires or solder tabs on both ends. Just tape it to your battery pack. Another possibility is (...) (25 years ago, 2-Dec-99, to lugnet.robotics)
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