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 00:47:50 GMT
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Original-From:
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Tilman Sporkert <tilman@activesw.comNOSPAM>
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Viewed:
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454 times
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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 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.
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.
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).
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Message has 2 Replies:
 | | RE: External Power Port Problem..?
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| (...) Whenever you use a battery pack, use a FUSE!!!!!! I work on products that use the 12V gel cels rated at 4AH or greater, you can find them in security panels etc. Anyways, one day a guy in the drafting department measured the distance between (...) (25 years ago, 2-Dec-99, to lugnet.robotics)
| | | Re: External Power Port Problem..?
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| (...) 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). (...) I think a fuse is still the best idea, (...) (25 years ago, 2-Dec-99, to lugnet.robotics)
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