Current Sensors

[AdamHeard]

for a project I'm working on I need three different, ideally very cheap, current sensors.

One from 0-30 Amp, one from 0-75, and one from 0-150.

I can't use a jaguar due to size and cost. I've heard of teams using ~$10 sensors for this before, but wouldn't know where to find them or what brands work well. I did a bit of googling and found these, which cover the range nicely and are in stock at a few places.

[EricVanWyk]

I spent a lot of time looking for current sensors in this range while designing the PI (the PD's predecessor). You'll be hard pressed to find an easier solution than Allegro's hall effect based sensors (e.g ACS758) . I really like their funky-space-ship looking ones, as they combine low resistance, isolation, and buffering into one odd looking package. The accuracy is decent, but not best-in-class. If you are making less than a hundred of whatever device you are designing, grab the appropriate Allegro sensor and be done with it.

If you are making more, I'll need more information on what your requirements are.

Your other options are
* Some other hall sensor
* Current sense resistor
* Current sens transformer (for AC current only)
* Some magnetoresistive sensor (yuck).

"Some other hall sensor" will be mostly a test of your google-fu.
"Current Sense Resistor" takes a bit more thought than a hall sensor, because it isn't isolated. This means that you need to be careful about protecting your delicate circuitry from your 100 amp path. It isn't difficult, it is just time consuming.

EDIT / PS:
If you go with the allegros, bear in mind that they are ratiometric. If at all possible, sample them with a ratiometric ADC. Otherwise, your power supply noise is going to wind up in your measurement.

PPS: What sort of accuracy do you need?

[AdamHeard]

They'll be hooked up to a vex controller,

+/- .5 amps for the 30 would be good, +/-1 for the rest is probably good as well.

[Al Skierkiewicz]

Adam,
When we did Stangesense a number of years ago we used a Maxim Chip. The resistor needed was a .001 ohm which is perfect as it is 1 foot of #10 wire. We added it in the negative power lead of the Victor but you can really put it anywhere. If you search on CD you will find the circuits and chips.

[Gdeaver]

One possible solution on a board ready to go.http://www.pololu.com/catalog/product/1187

[AdamHeard]

Originally Posted by Gdeaver

One possible solution on a board ready to go.http://www.pololu.com/catalog/product/1187

I do like that!

I am not completely opposed to making a circuit, but I would prefer something already mounted and good to go (attaching wire leads is fine).