# Measuring Current of Photo Voltaic cell

Dear Everyone,

Hope every one is in good health.

I am having problem in measuring current of PV module (5 Watt , 21 V) for feeding ARDUINO UNO. I tried by using HALL Current sensor, but it hasn't worked. I want to measure the current something around 200 - 600 mA. Without using any sensor, how do I measure it accurately? Thanks in advance.

Dear Everyone,

Hope every one is in good health.

I am having problem in measuring current of PV module (5 Watt , 21 V) for feeding ARDUINO UNO. I tried by using HALL Current sensor, but it hasn't worked, since it can't measure current below 1A. I want to measure the current something around 200 - 600 mA. Without using any sensor, how do I measure it accurately? Thanks in advance.

There are two common methods:

1. Current shunt resistor.
2. Inductive measurement.

For the current shunt resistor method, a very low resistance current shunt resistor is placed in the circuit you want to measure. Then, you measure the voltage before the resistor and after the resistor. Then, since you know the voltage at each side of the resistor and the resistance value of the resistor, you can calculate the current using I=E/R. Three problems with this method: 1) It adds some resistance to your circuit which decreases its efficiency some. 2) A current shunt resistor of low enough value that it doesn't effect efficiency much, will be very hard to read accurately with a low current circuit. 3) Arduino, on its own, doesn't have highly accurate voltage measurement capability.

For the inductive measurement method, a coil of wire is wrapped around a wire of the circuit you want to measure and a fairly high resistance resistor is placed accross (in series with) that coil of wire. Then, after measuring and calibrating your coil of wire, you again measure the voltage on either side of the resistor and calculate the current using the formula I=E/R * some calibration factor. This method has the advantage over the current sense resistor method in that it can be more accurate for low current circuits and it doesn't reduce the efficiency of the circuit as much. Still, a disadvantage is that an Arduino is not terribly accurate when measuring voltages.

EDIT: Or, of course, I suppose you could put a high resistance resistor directly across the solar cell and measure the current flow through it using I=E/R.

I have already tried to measure the current using Ohm's Law by connecting a 1.5 ohm resistor in series with PV module. Since voltage difference across the resistor is so low, arduino was reading it as zero. What should I do?
Thanks.

Without using any sensor, how do I measure it accurately?

You can't. A sensor of some sort is required. It can be just a resistor.

If this is a one-time measurement, use a multimeter.

If you need to monitor the current as part of your project it's easiest to monitor current on the ground side (measuring voltage across a small resistor*) because the Arduino's ADC reads relative to ground.

And, if you use the optional 1.1V reference you can get-away with a smaller-value resistor (for a smaller voltage "loss").

...Most of the time, we calculate or estimate current because it's kind-of a pain to measure.

I have already tried to apply Ohm's Law in measuring current by using a 1.5 ohm resistor in series with my PV module. However, the problem is the potential difference across resistor is so small, arduino is showing just zero. Any other way?
Thanks.

1.5 ohm * .6 A is 0.9 V - easily read by an arduino.

Time to show your code. My bet is on an integer arithmetic error.

You could try the inductive method by running the photo cell through a transformer or wrapping a photo cell conductor with a coil of wire and see if you can get a decent amount of voltage out of that inductive method which is high enough to measure across a resistor. Basically, itâ€™s quite the same as a shunt resistor except you can amplify the voltage (step up the voltagr through a transformer or a coil wrapped around the conductor) or amplify the current (step down voltage through a transformer) to measure that transformerâ€™s voltage drop across a resistor and calculate the current after calibrating it with a volt meter to determine the efficiency of the transformer/inductive coil. Does that make sense? Need a picture?

Don't Cross post!

You could try the inductive method by running the photo cell through a transformer or wrapping a photo cell conductor with a coil of wire and see if you can get a decent amount of voltage

You could certainly try that, but it equally certainly won't work for direct current.

ty_ger07:
For the inductive measurement method, a coil of wire is wrapped around a wire of the circuit you want to measure and a fairly high resistance resistor is placed accross (in series with) that coil of wire. Then, after measuring and calibrating your coil of wire, you again measure the voltage on either side of the resistor and calculate the current using the formula I=E/R * some calibration factor. This method has the advantage over the current sense resistor method in that it can be more accurate for low current circuits and it doesn't reduce the efficiency of the circuit as much. Still, a disadvantage is that an Arduino is not terribly accurate when measuring voltages.

I think that's an attempt to describe a CT (current transformer) gone badly wrong:

1. You dont wrap a coil around the wire, that would do nothing at all as there would be zero magnetic coupling.
2. A CT only works for AC current.

A current transformer uses a primary with a few turns (usually one), and a secondary with many turns
that is effectively shorted out using a lowish value resistor. The turns ratio means that the current in the
secondary is some small fraction of the current in the primary, but a much larger shunt resistor can be used
to sense it. A CT is typically used for measuring large mains currents, and has the advantage of
being fully isolated.

For DC current measurements of a few 100 mA you should use a 4-wire shunt resistor & precision instrumentation amp for best measurement accuracy (this is how multmeters work). Hall effect
devices are noisy and work best in the 5A up range.

What? You think that you can't measure DC amperage using an inductive technique? Have you seen a \$5 DC analog ammeter? Have you seen \$150 inductive multimeter measuring DC current? But, you are correct about the implementation here. This implementation would require a special hall effect DC current transformer. Otherwise, the current transformer wouldn't measure the total current but would instead only measure the changes in current flow.

What? Wrapping multiple turns of wire around a conductor doesn't create a simple and easy (but less efficient than a transformer) inductive pickup? This is elementary electronics 101. Lenz's Law. But, again, you are correct that this wouldn't work for DC current (unless only trying to measure that change in current instead of the total current).

ty_ger07:
What? You think that you can't measure DC amperage using an inductive technique?

No, I just know that moving-coil ammeters are rare beasts these days, and expensive.

Anyway what's induction got to do with measuring DC current?

What? Wrapping multiple turns of wire around a conductor doesn't create a simple and easy (but less efficient than a transformer) inductive pickup? This is elementary electronics 101. Lenz's Law.

No, that won't work, either for DC or AC current. Back to your textbook!

jremington:
No, that won't work, either for DC or AC current. Back to your textbook!

Maybe I should have specified that it needs to be toroidal wound?

And, yes, it does work for DC if only measuring change in current flow. For total current flow (not measuring only change in flow), for DC, it needs to be a hall effect type DC current inductive loop.

For what it is worth, I never claimed that this was the best solution. I only said that it is a method. I mentioned using a current sensing shunt resistor first and I still think that is the best solution.

Maybe I should have specified that it needs to be toroidal wound?

Correct.

And, yes, it does work for DC if only measuring change in current flow.

Correct. The method, when using a toroidal core, cannot be used to measure steady state DC current flow.

ty_ger07:
And, yes, it does work for DC if only measuring change in current flow.

DC is constant, not changing, that's rather the point...

So no, it does not work for DC, which is what is wanted here.