Post by thread:[EE:] Current sensor

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. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

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}>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. > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics Larry Bradley Orleans (Ottawa), Ontario, CANADA -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

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. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

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}>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. > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics > > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

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 -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

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}> 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. > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics