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'[EE:] Current sensor'
2004\02\12@155047 by Dmitriy Fitisov

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Hello everyone,
I think about measuring current in car.
The problem I see - current is big enough and impulses
may go really high and measure voltage drop on resistor I see chalenging.
Another thing I'd like to have -
indication of current direction to or from battery.
Anybody has any thoughts? Current transformator, Hall sensor (??)
anything else?
Thanks.
Dmitriy Fitisov.

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2004\02\12@162413 by Larry Bradley

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Dimitri, I've built a rather complete battery monitoring system for my
sailboat. I used a standard shunt (50 millivolt, 100 amp), amplified the
voltage up to + or - 2 volts, then fed it to a  MAX186 A/D converter, which
is connected to a PIC.

The shunt in my case goes in the -ve battery lead, as this makes life a bit
easier. I used an external A/D that can handle bipolar input voltages. This
one I had on hand - it is an 8 channel, 12 bit converter - I also needed
the 12 bit resolution.

I originally tried a "absolute value" circuit, right out of "The Art of
Electronics", to convert the + or- 2 volts into a positive only voltage,
and a comparator to detect +ve or -ve. This worked fine, but I eventually
went to the external A/D as I had one on hand, and I wanted the higher
resolution.

The shunt I used was from Blue Seas Systems (they have a web site, and any
boating supply place should have their stuff.


At 03:48 PM 2/12/2004 -0500, you wrote:
{Quote hidden}

Larry Bradley
Orleans (Ottawa), Ontario, CANADA

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2004\02\12@163041 by Richard.Prosser

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Dmitriy,

The "traditional" answer to this question is using the bond wire to chassis
(or the live feed wire to the battery) as a current shunt. This works OK
but can be improved by adding temperature compensation. Adding logrithmic
amplifiers (one for each direction) may also be desirable if you are
wanting to cover the whole range.
Are you including cranking current for  example? - or just normal charge &
discharge?.

Embedding a temperature sensor in the bond wire & using it to correct for
wire resistance is probably going to be enough. You will need to figure out
a way of calibrating it however.

An opamp can perform the amplification, filtering  & any level shift
required.

Richard P





Hello everyone,
I think about measuring current in car.
The problem I see - current is big enough and impulses
may go really high and measure voltage drop on resistor I see chalenging.
Another thing I'd like to have -
indication of current direction to or from battery.
Anybody has any thoughts? Current transformator, Hall sensor (??)
anything else?
Thanks.
Dmitriy Fitisov.

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2004\02\12@164114 by David Minkler

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Dmitriy,

Measure the voltage drop across the main ground cable between the
battery negative terminal and its point of attachment to the chassis
(I'm assuming negative ground here).  Amplitude will need to be
calibrated but signals are small and direction of current flow is
preserved.  The cable is your sense resistor; it has to be there
anyway.  This was (may still be for all I know) a common technique used
in the old uncalibrated dash displays.

Best regards,

Dave

Dmitriy Fitisov wrote:

{Quote hidden}

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2004\02\12@164734 by David Schmidt
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I believe there are off the shelf hall effect current sensors (pass the wire
through a loop) that will output a conditioned signal.
Just in case you didn't want to buy and add in your own current shunt.

Dave

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2004\02\12@201555 by Dmitriy Fitisov

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Thanks everyone.
Hall effect sensors from http://www.lem.com look nice,
otherwise decided on 50W 0.01 Ohm resistor from Vishay.



{Original Message removed}

2004\02\12@211105 by Jinx

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Silicon Chip 6/2002. 80A, 3-digit LED, Hall Effect sensor

http://www.siliconchip.com.au/cms/A_30551/article.html

Uses an F84

The code

http://www.siliconchip.com.au/software/jun02/ammeter.zip

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2004\02\12@211933 by Denny Esterline

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Look into the hall effect current sensors from allegro.
http://www.allegromicro.com/sf/0750/

Very low insertion loss, currents to 100A, isolated output, magnitude and
direction information out.

-Denny


> Hello everyone,
>  I think about measuring current in car.
>  The problem I see - current is big enough and impulses
>  may go really high and measure voltage drop on resistor I see
chalenging.
{Quote hidden}

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