Subject:
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Re: when they say "fresh" batteries, they mean it!
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 13 Aug 1999 22:39:02 GMT
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Original-From:
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Jacob Schultz <anne.jacob@get2net.SPAMLESSdk>
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Reply-To:
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C948605@STUDENT.DTU.saynotospamDK
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Viewed:
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596 times
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> So if you're only measuring 8.75 volts, it's probably time to replace the
> battery.
Yep. The measured voltage is the idle voltage. The normal approximation to a
battery is an ideal voltage source at 9V and a Thevenin resisance of some ohms,
say 7 ohms, in series. This will give a stall current of about 1,25A at a
terminal voltage of 0V! The problem is this internal resistor. I do not know how
much current the tower draws from the battery, but I assume it is arround 100mA
to 200mA, giving a voltage drop of 0,7V to 1,4V at the terminal, or is your case
between 7,3V and 8V. This is probably in the lower end of what is necerary.
By the way, the idle voltage of a fresh battery is somewhat above the labeled
voltage.
Jacob
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message is in Reply To:
 | | Re: when they say "fresh" batteries, they mean it!
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| (...) Actually it is common practice these days to power small peripherals off of the supply voltage pins on RS-232 ports as long as you're not trying to pull tooooo much juice. And even a device with a 9-volt power supply can produce higher (...) (25 years ago, 13-Aug-99, to lugnet.robotics)
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