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Old 10-03-2009, 07:13 AM   #2337 (permalink)
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Join Date: Jul 2009
Location: Vallejo,CA
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49state 4door - '91 Geo Metro 4 door
90 day: 59.31 mpg (US)

old blue - '91 Geo Metro base CA
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you wrote:
Hey Bob! I'm using 5/16" holes in the bus bars. If it is a thin manganin
sheet, how does the mounting usually work? Could it just replace the
section where the LEM usually is? I've never seen a shunt. Is it sturdy
for bolting?
I am supposed to get a 4x4 inch or so piece of .060 annealed manganin (Cu, Mn, Ni), which should saw and drill easily, and might just answer to my biggest tinsnips.
as I work it out, a 1 inch wide strip, with the current uniformly distributed, has an area of .387 cm squared. Manganin has a specific resistance of 38 microohms . cm, and a temperature coefficient of plus minus 15 ppm. That is the reason this alloy is used for metal resistors. Anyway, dividing 38 by .387 gives 98 microohms per centimeter.

So for a 0.1 milliohm shunt, the voltage taps need to be 1 cm apart. The bolt holes for connection to the busbar and cable can be at the diagonal corners of a square an inch on a side. I'll either bolt or silver solder one or two pairs of sense leads near the centerline, spaced 1 cm apart. Filing or grinding the opposite corners should allow calibration at around 200 amps with standards traceable to a wastebasket in Guandong, China. No lab standards around my shop these days.

The resistance was chosen to allow for 1000 A full scale, with 100 watts dissipated in the portion between the sense points. Think you can fit such a piece inside the controller, to replace the noisy Hall sensor? I'll put on two pairs of leads, to allow for a 200 mv panel meter and the current feedback to be separately hooked up. Check my figures and reasoning if it comes handy.
We will know about two productive hours after the stuff comes in the mail.
Better allow a week.
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