[Vwdiesel] Different GP monitoring cct stuff

[Gavrik Peterson]

I read the data sheet for the Allegro hall-effect current 
sensor. The output is referenced to half the supply 
voltage. This allows it to only have three terminals but 
makes it somewhat more complicated to use. In addition it 
needs to be inserted in the current path which is not very 
convenient.

What about some scheme where a toroidal core is slipped 
over each glow-plug and the current in each is measured. 
This could be quite accurate and does not require anything 
to be inserted in the current path. It might be possible 
to 
use a c-core and eliminate the need to disconnect each 
glow-plug from the copper bus. Schemes like this for 
measuring dc current are not difficult to build. If anyone 
is interested I could create a schematic.

   --  Gavrik


On Wed, 5 Jan 2005 11:14:53 -0400  "Smith, Michael" 
<Michael.Smith at rvh.nb.ca> wrote:
>Hi Dieselheads ! Clatter clatter clatter (marbles in a 
>glass bowl)
>
>Well, I finally got my 5 Allegro Hall-Effect current 
>sensors (ACS750xCA-050)
>in the mail here today and tried them out. (free samples 
>btw !)
>Output voltage swing is very slight.  For 2.5A of current 
>(I used a 12v/100w
>light bulb) @ ~12VDC, the output is about 3.2V....
>Even w/o any current being drawn (lightbulb off)  the 
>output is about 2.5V
>According to the spec sheet, even at 10A (what a GP might 
>draw) I am
>probably only looking at a very slight increase....aprox 
>3.5V I think.
>(they also require a Vcc of 5Vdc....I can use 16Vdc max, 
>but the outputs are
>very squirrely to say the least, even @ 12Vdc)
>
>If I were to put one inline with each GP, I'd still be 
>down into the mV
>range of variance w/o using some kind of op-amp cct to 
>boost the overall
>output swing.
>
>I suppose we could say, if I read *anything* over the 
>resting output voltage
>of 2.5V, then we have current flow, thus the GP *is* 
>working.
>
>They are rated @ 50A each, so I could stick just one in 
>the main line, just
>after the fuse and would see a 2.5V-4.0V (40A) swing if 
>all plugs were
>working, however the voltage swing is so slight you 
>probably wouldn't notice
>if only 3GP's were working.  Of course, this theory is all 
>out the window on
>the second attempt to crank,  when your battery is weak, 
>or you're cranking,
>the dome light is on....anything to change the Vcc from 
>its
>nominal(original) 12Vdc before you touch the key !
>
>Hmmmmmmmm...maybe I'll just go back to the big honkin' 
>blocking diodes and
>LED's (Mark the Miser)....or a cheapie $10 multimeter and 
>a 4P switch like
>Hagar... Was it Val who used Hall-Effect sensors in the 
>past? (I forget)
>
>11 pages- Data Sheet 
>http://www.allegromicro.com/datafile/0750-050.pdf Main 
>page http://www.allegromicro.com/sf/0750/
>
>Mike in NB, Canada
>
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