Page 1 of 1

How to measure amps of a solar panel

Posted: Wed Feb 20, 2013 8:54 pm
by Nannerman
Okay, this is probably a stupid question, but I can't figure it out.

I have a few solar panels that put out more than enough voltage for the raspberry pi. I don't know why, but I can't get the multimeter to read the amps.

Right now, I'm setting my multimeter to read DC amps, and connecting the readers (positive and negative metal prongs) to the corresponding wires on the solar panel, and I get no reading.
I have no issue measuring voltage, just amps.

If someone could tell me what I'm doing wrong, that would be much appreciated.

Re: How to measure amps of a solar panel

Posted: Wed Feb 20, 2013 9:02 pm
by PS1981
Amps, that is current, will be taken by something using it. To measure amps, normally you have to plug in the leads of your multimeter in a different way, then place the multimeter in the circuit, so the current flows through it. This can be dangerous. Try get more experienced help, that is someone who knows what they are doing to actually show you. You cannot measure current in paralell to your circuit.

Re: How to measure amps of a solar panel

Posted: Wed Feb 20, 2013 9:26 pm
by ski522
PS1981 wrote:Amps, that is current, will be taken by something using it. To measure amps, normally you have to plug in the leads of your multimeter in a different way, then place the multimeter in the circuit, so the current flows through it. This can be dangerous. Try get more experienced help, that is someone who knows what they are doing to actually show you. You cannot measure current in paralell to your circuit.
I doubt we're talking that much current here to be dangerous. Essentially you just put the multimeter leads in line with the positive line (break into the positive line with the red and black leads of the multimeter) and read the current being pulled by the device. Of course all you'll see is the amount of current the device is pulling and not the amount of current the solar panels are capable of generating.

But you do need to be careful doing this with a multimeter and not exceed the capacity of the multimeter. I know mine can't go over 10A of current.

Re: How to measure amps of a solar panel

Posted: Wed Feb 20, 2013 9:34 pm
by Nannerman
ski522 wrote:
I doubt we're talking that much current here to be dangerous. Essentially you just put the multimeter leads in line with the positive line (break into the positive line with the red and black leads of the multimeter) and read the current being pulled by the device. Of course all you'll see is the amount of current the device is pulling and not the amount of current the solar panels are capable of generating.

But you do need to be careful doing this with a multimeter and not exceed the capacity of the multimeter. I know mine can't go over 10A of current.
Okay, thanks. I'll mess around with a few different basic circuits to see what I can get.
I'm not at all worried about the saftey of me, since the solar panel's output is only about 6 volts and it's fairly small.

I'll start on this now to see what I can get.

Re: How to measure amps of a solar panel

Posted: Thu Feb 21, 2013 2:33 am
by Squanto
Check that the fuse has not blown in your multimeter!

The Amps / milliamps ranges are normally fuse protected, if you have connected the meter across a voltage source directly when the meter is on its ampere ranges then you might have let the smoke out of the fuse!

Don't forget to measure amps the meter has to 'break into the circuit' to allow the current to flow through the meter from voltage source to load, in other words, it has to be in series between your solar panel and RasPi.

Hope it helps!

Have Fun!

Mark S.

Re: How to measure amps of a solar panel

Posted: Thu Feb 21, 2013 7:44 am
by PS1981
ski522 wrote:I doubt we're talking that much current here to be dangerous.
Yes in this case I do agree. My comment is just a general "be careful", for people who don't know what they are doing. It is not for nothing that multimeters are restricted to certain amperages and are fused, and a maximum of X-seconds measuring etc. Just don't want anyone getting hurt, and if they do please don't say I didn't warn them.

Re: How to measure amps of a solar panel

Posted: Thu Feb 21, 2013 6:00 pm
by Nannerman
After tinkering around with a nine volt and a motor to make sure I was doing it right, I switched the setup to my solar panel and LED. The solar panel didn't have enough amps to even read on the board.

Later on I went to an electronics store and they happened to have the same one. Turns out it only puts out about 75 amps.

Thanks for the help! I might not have as nice of a panel as I'd thought, but now I know how to measure amps.

Re: How to measure amps of a solar panel

Posted: Thu Feb 21, 2013 6:08 pm
by PS1981
Well 75 amps is pretty deadly! It could be that your LED is using 75mA = 0. 075 Amps.

Power is voltsxamps in this case, meaning if you have for example 5 volts and 75 amps, that would amount to 375 watts. That's quite a lot. You could for example run a couple of TV's on that amount of power.

Re: How to measure amps of a solar panel

Posted: Thu Feb 21, 2013 6:41 pm
by Burngate
Also depends on how bright the sun is - you don't get much at night

Re: How to measure amps of a solar panel

Posted: Thu Feb 21, 2013 7:38 pm
by Nannerman
PS1981 wrote:Well 75 amps is pretty deadly! It could be that your LED is using 75mA = 0. 075 Amps.

Power is voltsxamps in this case, meaning if you have for example 5 volts and 75 amps, that would amount to 375 watts. That's quite a lot. You could for example run a couple of TV's on that amount of power.
Oh wow, my mistake. I definitley meant 75mA. Haha, too bad the solar panel doesn't put out 75 amps.

Re: How to measure amps of a solar panel

Posted: Thu Feb 21, 2013 8:32 pm
by PS1981
Nannerman wrote: Oh wow, my mistake. I definitley meant 75mA. Haha, too bad the solar panel doesn't put out 75 amps.
Yep, that would be a pretty mean little panel, I'd like one of those too please!

Re: How to measure amps of a solar panel

Posted: Mon Dec 09, 2013 10:07 pm
by juansmp
Actually the current of your solar panel will depend on the load you use. I suggest you to put different resistors (with known values) and measure the voltage on them in order to get the Voltge vs Curent response. See this link http://www.mtmscientific.com/solarpanel.html

Re: How to measure amps of a solar panel

Posted: Mon Dec 09, 2013 11:43 pm
by mahjongg
yes, actually if you want the maximum possible power output from a solar panel you need a quite complex device called a "maximum power point tracker", but its only useful for very big panels as its complex and expensive.
But the thing is that solar panels are not simple energy sources like batteries, and their output naturally also depend strongly on the amount of light they capture.

Re: How to measure amps of a solar panel

Posted: Tue Dec 10, 2013 2:49 am
by Tage
the way to measure amps of a solar panel is to connect an amperemeter to the wires. this will give the short circuit current value for the solar panel. the important thing to understand is that the current is proportional to the amount of sunlight that hits the panel. so to have any meaning you need to place the solar panel in the sun.
note that because your panel voltage is zero you are not getting any power from the panel in this situation.

the other measurement to make is to use a voltmeter to measure the voltage of the panel. this is called the open circuit voltage.
note that in this situation you will not get any power from the panel either, as the current you draw from the panel is zero.

to get the most power from the panel you should connect a battery to that panel with the battery voltage being 75%-80% of the open circuit voltage. this is the maximum power point voltage of the panel.

the problem is that the open circuit voltage (and the maximum power point voltage) will change a lot with temperature. it will change with more than +/-20% from the room temperature value as the panel temperature changes from -40C to +90C. and if you don't hit the correct voltage you do not get all the available power from the solar panel you paid big money for.

there are both simple and more complicated electronic gadgets that are able to control the panel voltage during battery charging. they are well worth the money as you can use cheaper and smaller panels and your battery will also last longer. these wonders are called MPPT chargers. (this is not the same as the cheap PWM chargers.)

Re: How to measure amps of a solar panel

Posted: Tue Dec 10, 2013 10:40 pm
by mahjongg
these wonders are called MPPT chargers.
yes, MPPT = "maximum Power Point Tracker". they find the point in the curve from "fully shorted, no voltage" to "fully open, maximum voltage" where the combination of the sum of output current and output voltage is maximal, (for maximal output power) and convert that energy to a standard output voltage (12V) at the maximum current possible at the time.

Re: How to measure amps of a solar panel

Posted: Fri Dec 13, 2013 7:51 pm
by realworldnumbers
I have succesfully powered my Pi and done a test on how long it can survive using only 4AA batteries :D
http://realworldnumbers.com/how-to-test ... batteries/. I got about 8.5 hours and there was no damage when pushing 6.52Volts until fully drained.

Re: How to measure amps of a solar panel

Posted: Sat Dec 14, 2013 3:34 pm
by drgeoff
mahjongg wrote: .... where the combination of the sum of output current and output voltage is maximal, ....
More accurately, the product of output current and output voltage.

Re: How to measure amps of a solar panel

Posted: Sat Dec 14, 2013 11:12 pm
by boyoh
There is a another way to check the current (Amps)
Out put of your solar panels , But only do it if you
Consider the out put voltage is at a safe level to work on
Connect a 10 ohm resistor in series with the positive +
Side of the solar panel then measure the voltage drop
Across the resistor , using Ohms to work out the current
Passing through the resistor WARNING select the the
Wattage of the resistor carry the AMPS you
Antsipate it to be

Solar----+------( 10 R)---------LOAD-------------0-Solar

Re: How to measure amps of a solar panel

Posted: Thu Dec 19, 2013 12:01 am
by mahjongg
drgeoff wrote:
mahjongg wrote: .... where the combination of the sum of output current and output voltage is maximal, ....
More accurately, the product of output current and output voltage.
yeah, obviously I meant the product, (the result of a multiplication, not addition ) :oops: must practice my English even more!

Re: How to measure amps of a solar panel

Posted: Mon Jan 06, 2014 3:50 am
by Zachster1996
Check your range on your multimeter. You might have it set too high. Also, are you trying to do this with light bulbs instead of the sun? If you are, leds and cfls won't work as the light must be incandescent, meaning it is heat producing. So if you are going to do this with light bulbs you need the old energy sucking bulbs.