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From: "Boris Nogoodnik"
References: <email@example.com> <firstname.lastname@example.org>
Subject: Re: Limiting total wattage for a constant-current dummy load?
Organization: KGB, Ltd.
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Date: Sun, 10 Nov 2002 02:30:12 GMT
NNTP-Posting-Date: Sat, 09 Nov 2002 21:30:12 EST
"John Muchow" wrote in message
> >>>1. Try putting some kind of temperature sensor on the heat
sink. If the
> >>>pass transistor gets too hot, it could take the circuit out
> >>>current mode or at least show an alarm.
> This was my original idea but I had to reject it. One of the
> wanted to do with the circuit was to measure the "true" AH
> a few battery packs I'm using for electric vehicle drive. If
> circuit went out of CC mode, the numbers would be invalid.
> really wanted to find some way to know in advance if a
> voltage/current combination would exceed my power limits. I
> hate to start the test only to find out a couple of minutes
> it couldn't be finished. :-)
> >>>2. You could probably come up with a comparator and two
> Hmm...interesting idea!
> To sum the voltages, could I do this?:
> V2---/\/\---+---------/\/\---+---+ V-summed (to comparator)
> | |
> | |\ |
> +---|-\ |
> | \---------+
> +---|+ /
> | | /
> | |/
> GND---------+--------------------+ GND
> John Muchow
> P.S. Cool, my first ASCII art piece...and it only took 42
Nice diagram! And it will sum fine. But you still need to
multiply. What meaning 50V + 1 A or 50V + 2A has? Same as
25+26 and 25+27. See what I am saying? What are you going to
compare here? But 50*1 and 50*2 makes a little difference.
This you can compare, as it's directly proportional to power.
Crude singe quadrant multiplier can be made out of 2 opamps and
transistors as non linear elements. I just can't find a circuit
for this. It was too long ago when I worked with this stuff
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