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Sensing DC current- HELP

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I need a way to sense DC current (up to 200A). I don't need to actually "measure" it, so accuracy is not important. I just want to know if it's there or not. The ability to do this is critical to the project I'm working on.

I've been checking out Hall effect ic's from Allegro, Micronas (and others) and they seem like they're what I'm looking for. Have any of you done anything similar or used these hall effect ic's? Any suggestions or recommendations?

ZeroSkillz

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I don't need to actually "measure" it, so accuracy is not important. I just want to know if it's there or not.

Sounds like what you're really sensing is a closed circuit. Can you just use a common ground?

I'm sure there are much more elegant ways, so I'll pipe down and let the adults (i.e. EEs) talk now.

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You can use a shunt/sense resistor in the line you are measuring. Connect a sense resistor( 0.1 ohms or 1ohm ) between your load and ground. Measure the voltage across the shunt resistor, it should give you a voltage. With Ohms lay I = V/R

You can also try a current sensor breakout board from Sparkfun.

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Sheesh,

I typed up a nice description of what my plans are and before I could submit it I got booted....SO...

Condensed version:

Yes DOC, it's a closed circuit.

36V battery on an industrial charger. I want a sensor to let me know:

Is it charging? Yes or No.

and build on it from there.

Thanks again!

ZeroSkillz

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@bluehash

I would prefer a totally non-invasive way. My goal is to eventually have a device that can be marketed as a "Just clip it on and let it go" device. But thanks for the input!

ZeroSkillz

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It is not easy to handle 200A.

A "shunt resistor" of 0.1 Ohm will generate 4000W of heat.

W = I * I * R = 200 * 200 * 0.1 = 4000

http://www.rc-electronics-usa.com/buy-c ... shunt.html will sell you a "shunt resistor" of 0.0002 Ohm. This will only generate 8W of heat and 100mV output. Take a look at the picture and the price tag.

http://www.allegromicro.com/en/Products ... /index.asp will sell you a "shunt resistor" of 0.0001 Ohm with an integrated Hall effect sensor. But you cannot "clip-on" to anything. You need to integrate it to the charger.

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How long is the wire? Is it long enough to wind it few times around a magnetic core?

200A is a lot and attaching Hall sensor to the wire might be enough, but you may have to create a small coil.

Checkout UGN3503's datasheet from Futurlec.com. You don't have to use round core, I think couple of wounds around rod should be enough. Hall sensor would then go at one end of the rod.

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uh-oh, I was thinking 200mA.

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Thanks for all the input guys!

@RobG - The cables are probably about 6 feet long 2 gauge with heavy connectors on the ends:

http://www.allbatterysalesandservice.co ... 4,644.html

As I said in the OP, I've been looking at sensors such as these:

http://www.semiconductorstore.com/cart/ ... HAL401SF-A

(Here's a selection guide for Micronas)

http://www.semiconductorstore.com/pdf/n ... G_2010.pdf

Allegro:

http://www.allegromicro.com/en/Products ... s/Sensors/

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Oh, so if you have a connector then why not to use shunt resistor method.

You can get a short version of that cable to plug between battery and charger, connect wires to both ends and measure voltage drop. Cheaper solution would be to run a thin wire from one end (battery side) all the way to the charger and measure the drop that way ( I am assuming you can also attach wire on the charger side.)

You should get enough voltage drop for MSP430's ADC or you can add an op amp, like TI's TLV2772.

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Again, thanks for all the input guys (and/or Gals! I'm sure there are girls on the interweb, no matter what everyone says!)

Using a shunt IS an option but one that for some reason I'm dead set against...LOL

I KNOW it will work, but it doesn't play nice with my plans... I'm eventually planning on MASS production (Just for MY application I'll need 30 of these puppies! With plans of SELLING more, HUNDREDS more.) and I really want a FOOLPROOF way to do this... Adding to the connectors is an option as well, but these connectors aren't cheap. I would need 2 connectors to "splice in" for each device which just adds to the materials cost. A device that snaps over the cables, or straps onto them, is my cheapest/safest option.

I've seen the sensors at Seeed..and HOLY CARP! 11.50 (plus shipping) and it's AC 100A max... I'm looking for something along the lines of 1 to 2 dollars per unit... The whole reason I was attracted to the LaunchPad...can't beat 4.30 for a complete kit with 2 MCU's to play with!

ZeroSkillz

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Awe come on. What's \$11.50 in the face of earning 1 ZILLION dollars?!?!

Seriously, if you don't want to interrupt the charging circuit then you're going to HAVE to sense the magnetic field generated in the charging circuit.

Option 1: Sense the current coming out of the charger.

Option 2: Sense the current supplied to the charger.

What's it going to be? The easy way or the hard way?

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Seriously, if you don't want to interrupt the charging circuit then you're going to HAVE to sense the magnetic field generated in the charging circuit.

I know 99-cent stores often have toy compass. If you hold it near a wire that carries 100A, the needle sure will tilt. You just need to label "North" as "Charging" and give some good instructions of how to use it.

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Seriously, if you don't want to interrupt the charging circuit then you're going to HAVE to sense the magnetic field generated in the charging circuit.

I know 99-cent stores often have toy compass. If you hold it near a wire that carries 100A, the needle sure will tilt. You just need to label "North" as "Charging" and give some good instructions of how to use it.

Hilarious!

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