current sensing options

I am trying to figure out what to use as a current sensor for a project I am working on. I will be connecting to 2 solar panels that output max (17.9VDC, 5.03A) as well Vsc = 22.2VDC and Isc = 5.58A. At first we thought of using the INA168 however, I missed the part where the maximum current at any pin was 10mA which is far too low for my application. I was hoping someone had a part # to someone that would be able to do this.

You might consider Hall effect current sensors. The ones I am familiar with are generally intended for high currents (50 -200 amps) but the low range versions may work for your application. They completely isolate the measuring circuitry from the current-carrying conductor http://www.allegromicro.com/en/Products/Current-Sensor-ICs.aspx

The unidirectional 50 A ACS758 sensor outputs 60 mV/ampere and breakout boards are available cheaply on ebay etc.

look on Ebay for a Hall Effect Current sensor… ACS712ELCTR-30A-T Hall Effect High Current Sensor
http://www.ebay.com/itm/ACS712ELCTR-30A-T-Hall-Effect-High-Current-Sensor-/161045293860?pt=LH_DefaultDomain_0&hash=item257f0c2b24
Is an example of one and is available from Allegro in 5 to 30 A ranges.
The output centers about Vcc and is I believe a 5V device than can measure current bi-directionally Or AC and DC…
The ACS712ELCTR-20A looks ideal for a 10A sensor… I took the liberty of attaching the relevant data sheet…

Doc

ACS712-Datasheet.pdf (643 KB)

I did take a look at the ACS712 earlier and from my understanding it takes a current input? please correct me if i'm wrong I just assume that Ip would be a current input. My main fear is that the voltage would be too high and I would end up damaging the IC.

Not sure what you mean by a "current input"; it's a current sensing device so the current needs to go through the chip. It will allow greater than 184V across its current sense pins (IP+ and IP-) so good luck trying to fry that -- you just need to stay within the current rating. Its logic requires a 5V supply (VCC).

This site might also be of interest to you: http://www.timnolan.com/?page=arduino-ppt-solar-charger

Hi, the current sensor works by magnetic coupling, so as the spec says you have 2.1KV of isolation between the current loop going through the IC and the circuitry of the IC that you will connect to your measuring circuit.

In most cases, you measure the current in the negative of the circuit to minimise any flash over especially DC, the voltage drop through the Ip loop is minimal with 1.2 milli ohms of resistance.

10amps x 1.2mOhms = 12mVolts

Tom....... :)

Thank you Chagrin, that link is actually very useful as I am also exploring maximum power point tracking (MPPT) with this project. The pins being labelled as Ip made me think that it was taking it's reading from a current source as I am used to seeing Vin. Most of my experience has been either in class or industrial applications in the upwards of 120VAC.

Tom, Thank you for clarifying about the 2.1KV isolation as well as the low resistance. With this being a solar application minimizing power loss is important to me.

In case anyone cares and for future reference if anyone searches this topic, I bought the ACS712 5a breakout from sparkfun and bought the 30A ACS712 IC from digikey the breakout board has 5x overcurrent protection so 5x5 25A i'm not suggesting you feed a constant 25A but if you need slightly more than 5A this option should work. I desoldered the ACS712 5A from the breakout board and resoldered the ACS712-30A to it and hopefully the traces will hold up but at most i'm drawing 6A so it shouldn't be a problem in theory.

It seems like a lot of trouble to modify a 5 ampere breakout board, when so many other options are available cheaply. Pololu has a nice collection of current sensors ranging from 5 to +/- 75 amperes, and -- I just checked -- the +/- 12.5 ampere breakout board is currently on sale for only US$ 3.95.

http://www.pololu.com/category/118/current-sensors