Subject:
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Re: AC Adapter Specs?
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 26 Jan 1999 00:26:16 GMT
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Original-From:
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Al Thiele <agthiele@san.rr.ANTISPAMcom>
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Viewed:
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1179 times
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I believe that you should, indeed, be wary of oversizing an AC adapter.
The simple "wall cube" is unregulated and typically employs a "just-big-
enough" transformer. Voltage under light loading rises considerably
above nominal, and poses a threat of damage.
To illustrate, I've just taken DC measurements on an aging Radio Shack
500mA "universal" AC adapter. At its 9V setting, no-load voltage is
13.6Vdc, and V = 11.9V @ 80mA. At its 12V (max) setting, no-load
voltage is 18.3V, and V = 15.9V @ 110mA. A "fixed-voltage" adapter
may exhibit somewhat-better fidelity, but caution remains in order.
My RCX (with a 7.5~9.0Vdc supply and 2 motors running) draws less
than 100mA with medium mechanical loading on both motors. I've not
seen more than 200mA total drain with both motors nearly stalled (each
at its max power setting of 8, i.e; 100% "on" time).
I'd choose a 9V 200~300mA adapter and (for peace of mind) measure
its output with the RCX powered on, but nothing running (30~40mA
load), hoping to see less than 12V (unless we can obtain some insight
into LEGO's design margins).
Al Thiele
Dinosauric EE
Jasper Janssen wrote:
> On Sun, 24 Jan 1999 17:35:11 GMT, lego-robotics@crynwr.com (Peter
> Thorup) wrote:
>
> > I have looked on the RCX and I've noticed it does say "9-12V ~". From
> > what I've gathered the "~" means polarity doesn't matter. My concern is
> > the mA rating of 9 volt adapters. Radio Shack has about 6 different
> > types each with a unique mA rating. (eg. 300 mA, 500 mA, 800 mA, etc.)
> > My question is, could the wrong mA rating damage an RCX?
>
> No. If you take one with too small a current rating, however, you
> could overload the Power Supply and fry that. Or, maybe, you'll find
> that oyur batteries still drain even with the RCX plugged in :)
>
> I would think 800 mAmps should be enough, but you can never have too
> large a current-rating.
>
> Jasper
> --
> Did you check the web site first?: http://www.crynwr.com/lego-robotics
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message has 1 Reply:
 | | Re: AC Adapter Specs?
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| I had posed this question to Fred Martin at MIT who was involved in the designing of the Programmable Brick/RCX and this was his response; (...) This is by no means an official response from The Lego Group. Pete (...) -- Did you check the web site (...) (26 years ago, 26-Jan-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: AC Adapter Specs?
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| (...) No. If you take one with too small a current rating, however, you could overload the Power Supply and fry that. Or, maybe, you'll find that oyur batteries still drain even with the RCX plugged in :) I would think 800 mAmps should be enough, (...) (26 years ago, 24-Jan-99, to lugnet.robotics)
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