Measure DC voltage and current at PV panel..

Hello..i mechanical student..i need to get the information about the pv panel to complete my assignmet..from the picture that i attach, it is a true way to get the dc voltage and current??can anybody help me and correct my way if it wrong...thanks..

1 picture = The value that i measure is to get direct dc voltage or just voc??if voc, how to get dc voltage...

2 picture = i need to measure value of current using acs 712 so that i get the sensor value to show in matlab through is a right way??how to get measure value of current??i want to compare value between sensor and measuremet value..

Robert Wall's picture

Re: Measure DC voltage and current at PV panel..

First, is your P.V. panel connected to anything that is not shown on your diagram? I ask because here, P.V. panels are almost always connected to an inverter. I shall assume that as nothing is shown, there is no other connection. If there is another connection, then you must consider what happens when you connect your Arduino, which will probably be earthed via the computer you are using to program it. Get it wrong and you could destroy both Arduino and computer.

Your output voltage is 21.8 V. What is the maximum voltage that the ADC input on your Arduino can accept? Is that a problem, and if so, what are you going to do about it?

Secondly, in your second diagram (IMG_20160319_153523.jpg), what voltage are you actually measuring? I am sure it is not the voltage that you want.

There is always a problem when trying to measure both voltage and current. Either the current you measure includes the current that flows in whatever you measure the voltage with, or the voltage you measure includes the voltage dropped across whatever you measure the current with. You can either make sure that the error is too small to matter, or you can calculate the error and subtract it to give the true value.

hanz's picture

Re: Measure DC voltage and current at PV panel..


i attach here a switch box of standalone system of my pv panel..

firstly, i want to measure vdc..right now, i take the terminal + and - from the pv(at incoming part below) and measure it..i get about 18 v dpend on sun..from this terminal, i connected to voltage divider so that it will drop to 5v and  that value  the arduino can read far, the matlab software can read this value..i still confuse this way i get value vdc or voc??..i will take the sensor value and measure value to make analysis..

secondly, how i can get value of idc??it is simple just i take that terminal + and - and connected to current sensor acs 712(30amp)  and to the arduino?? 

Robert Wall's picture

Re: Measure DC voltage and current at PV panel..

That photograph makes me think that you DO have an inverter connected to the system. If an inverter is connected, it is not a standalone system and therefore my warning about creating a path for a fault stands.

What do you think you mean by "vdc" and "voc"? In normal use, Vo.c. means the open-circuit voltage, and that will be the voltage from your P.V. array with no load. It is sometimes called the "no-load voltage". It has nothing to do with whether the voltage is alternating or direct. (note: we use "V", not "v" for voltage as the unit comes from the name of Alessandro Volta - like Ampere and Kelvin, but don't confuse Kelvin with kilo.)  When we need to be clear that the voltage is alternating, we write Va.c. and when it is direct, we write Vd.c.  You can have and you can measure the open-circuit voltage on both a.c. and d.c. systems.

You should look at the data sheet for the ACS712 to see how to use this device. Application 4 on page 12 is almost exactly what you need, replace the diode D1 with a direct connection and omit resistor R1 and capacitor C1. If your reading is not steady, then see the notes on page 13.  

hanz's picture

Re: Measure DC voltage and current at PV panel..


From you explanation, my understanding is i can divided into 2 part..for d.c system, i can get value for Vo.c,Is.c and Pmax..same like d.c system, in a.c system i can get value for Vo.c,Is.c and Pmax right??

When i do the measurement of Is.c for d.c system, there is a spark when i connected + and - multimeter to the pv terminal..i already setting multimeter to current. I already follow the step from the youtube but still has spark..What the right way to measure Is.c in d.c systems from the pv terminal??

Robert Wall's picture

Re: Measure DC voltage and current at PV panel..

I think I understand now what you are doing. Are you measuring voltage and current under varying load conditions in order to determine the maximum power available from the array?

When you are connecting a circuit and the prospective current is anything more than a few mA, you will get a spark. That is exactly what happens inside a switch, relay, contactor, circuit breaker or indeed any mechanical switching device. If you do not want a spark, cover the panels to prevent the light from falling on them.

You can measure the short-circuit current of your P.V. panels because a photo-voltaic cell is, roughly speaking, a variable current source - it will deliver a current proportional to the light falling upon it.

You must never try to measure the short-circuit current of the inverter's a.c. output. Hopefully, it will sense that there is no connection to the electricity supply and refuse to work. If it is one that is designed to work independently of the mains supply - 'off-grid', then there is a strong possibility that you will blow fuses because it will behave as a voltage source and there is nothing to limit the current that might flow.

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