Solar Cell Dumb Question

[andyman5002]

Hi guys, OK so my solar interconnect ribbon has arrived thanks to the help from a previous thread. Now I can begin making the strings. So I started soldering a few all went well. Then I remembered I should measure the open volts and short circuit current. I can manage the voltage fine, im getting about 0.53 volts from each cell in poor sun light. Now the current, I just can't seem to get a reading at all. From short circuit I figured I should just measure the current from positive to negative?? But this doesn't seem to give a reading.

So how do you measure it??

Excuse the stupidity

Thanks Guys

Andy

[tecker]

Is this a digital meter? You might break out the book on the meter and double check your hook ups or post a pic with the connection.

[AbyssUnderground]

Check you have changed the leads to the Amps socket on your meter and set it to mA or A if your meter is accurate enough at that setting. If its low sunlight you might not get any reading. I get virtually nothing in low sun on my 6w array, maybe 10mA on the whole array, thats a few mA per cell.

[andyman5002]

My meter only has two sockets one for common and one for positive. There are different ranges, I just presumed I would see about an amp as they are supposed to do 3.85 amps per cell. The cells may be faulty I think, or maybe they just need very strong sunlight, they are the ebay solar cells.

The panel is going to hopefully be 60W, ive just soldered 12 cells which will form 1 string. I will try changing to mili amps and report back.

Thanks Andy

[andyman5002]

Ok, ive tried changing the range but no luck, it does amps (0) and then 0.00 amps either one there is no change. The meter is a digital clamp meter. It has leads and a clamp on the top. I think I will have to borrow a better meter from someone.

Andy

[Countryboy]

To measure amps, you need to have a load on the cells.  Run wires from the cells to a battery and measure the amps running thru the wires.

[drdongle]

Most of these meters have an amp scale fuse inside, make sure that it has not been blowm, if it is you will get no reading, been thee done that.

[andyman5002]

Can I not measure short circuit current? I thought i read somewhere before you build the panel you should measure voltage and short circuit current to try and get evenly matched cells? Also If I do connect them to a battery will it damage them as they are only 0.5 volts and the battery will be 12V?

Andy

[Countryboy]

Current is flow.  If you short circuit, there is no flow to measure.  You have to have somewhere the current can flow to if you want to measure current.

Unless your solar cell voltage is above battery voltage, you won't have any current flow.  Use a AA battery if necessary to load the solar cell.  They are like 1.5V.  You can use small resistors or LEDs for testing too.

[ghurd]

Don't connect a single cell to a battery. That can't be good.

Just set the meter for DC amps, one lead on +, the other on -.

Sun light is needed. Home lighting wont do much.

With 36 cells, the short circuit amps X 90% will be about the operating point on a 12V system.

I also bet the meter fuse is blown if you get no amp reading.

G-

[stephent]

And it could be that it only reads the amps through the "clamp" part instead of the leads.  Lower amp readings can be "multiplied" by using a couple of turns around one of the clamp arms and dividing by 2 or 3 for three turns--etc..

Make sure the "clamp" is completely closed for the most accurate readings.

[andyman5002]

I had thought that this might be the case. I took it apart and had a quick look around and couldn't find any visible fuse, it could have been on the other side of the board. I think I will borrow one from somewhere. I cant really do anymore testing today as the suns gone, was cloudy anyway.

Andy

[willib]

i bet you are right ghurd , he probably has a blown fuse in the meter.

good call

[willib]

usually the short circuit current is flowing through the Ammeter

so just connect the plus of the Ammeter to the cell plus

 and the minus of the ammeter to the cell minus

[veewee77]

The clamp-on meter will ONLY measure AC amps. It will NOT measure DC ams of any sort.

Get a different meter. Do not set it for miliamps! Set it for AMS first and then if the meter readss a low current, then try a lower range. If you set it for miliamps and the cell produces more, bad things might happen to the meter.

Doug

[Darren73]

some clamp meeters WILL read DC amps, please do not give the impression that all clamp meters are ac only they are not, it depends on the meter.

Darren

[Darren73]

Andy,

Whereabouts in the UK are you? i'm in South Wales

Regards

Darren

[andyman5002]

Darren Im in the northwest of england. Probably not the best for either of my projects. But its interesting so why not. The clamp meter reads DC amps as well as AC as it has the two settings on the dial. How much of a problem would it be if i just assembled the panel without measuring each cell individually?

Andy

[pepa]

to test and size those solar cells you need to have the same amount of solar light at the same angle on each cell. find an old projecter bulb and set it over your work space. these bulbs come as close to natural sun light as you can get and the reading that you get will be close to the reading you get out side in full sun, makes it a lot easier to check connections as you build each string. pepa

[inode buddha]

I would use the leads from the meter to make the complete circuit, hook the pos and neg meter leads directly to the pos and neg cell leads. Set the meter to read "amps". The "clamp" type meters are usually for a much higher power level. As it is, my $50 digital Radio-Shack meter will handle up to 10 amps all by itself.

[tornado6]

Get another meter as posted early.Clamp meters are NOT RMS,thus very inaccurate for cell testing.Matter of fact,2 point testing(pos`neg)with a multimeter is inherently mas inaccurate with solar cells due to surface area hot spots and AL paste skeleton anomalies.To get a true reading labwise you need a flash strobe tester.Thats just fyi info but the easy fix is get a cheap multimeter to get a general reading.RMS(root mean square) is preferred over mod. sine wave-pricier but if you have a radio shack type place in england,here in the u.s. the cheapos are like 15 bucks.RMS is 60$+ but eventually if you stick with making your own solar you will need it.Also as posted before,the problem you are having with amps is that you do not have a plug that will read up to 10A.That is the limiter on the cheaper models and again why you should probably just go ahead and get a RMS meter.Doubt its a fuse as 9 out of 10 the meter just shuts down after it hits its 2A barrier-thats what happens with radio shack cheapos.Or says OL and then reads 0.Need 10A capacity.And on cell string v~a you dont have to test each cell.If they are the same batch you bought from somewhere they should all be around the same unless you bought some mixed deal.

Isc you dont have to worry about-just V and a.

[Volvo farmer]

This is incorrect advice in his application. You can so measure short-circuit amps, either on a single cell or on an array without using a battery. The current will flow around the cell(s) in a short-circuit configuration and you can measure it. Like others have said, he needs the proper sort of meter set to DC amps, with the leads in the right sockets.

[pyrocasto]

Not really, measuring the cells alone short circuits them(through the meter) making that the load. Should measure just fine if you meter will read that high.

[pepa]

you probably know this already but a weak cell in a string will bring the other cells down to it's level. it is always best to measure the output of each cell and then match them as close as posible in the string. just make sure that each cell is tested exactly the same with the same light the same distance and same angle. pepa.

[andyman5002]

Ok I thought I would just post a quick update on how things are going. I managed to get hold of another digital multimeter. Turns out the other has broke, or the fuse has blown. This one is much more sensitive and works fine. I have taken some readings from various cells, some broke ones and some perfect ones, so far the best reading I have had is 2.3 amps, this was at 11am in england. Now the rated readings should be 3.85 short circuit amps this is probably taken in California in July right? So are these readings about right for my location and time of day and year? The readings were taken on a very rare clear blue sky.

Thanks Andy

[ghurd]

"California in July" at high noon with 0% humidity, aimed perfectly at the sun!

No matter, your solar insolation chart will give hours x 3.4A.

Test them all at the same time, about noon on a clear day, as fast as you can.

Layed flat is easiest so there is no guessing if one had a different angle than the others.

The bad ones will show up.

Might be a good idea if making 2 or more panels to seperate them into very good, good, bad.  Use the seperate batches for seperate panels.

ie: you end up with a 58W and a 47W, instead of a pair of 47W.

Thats how the big boys do it, and why some brands I can think of make PVs the same except for output, like 65 to 90W. ("PW750")

G-

[andyman5002]

Thanks ghurd, I will try to get them measured tomorrow if the weather is good. So what your saying is I should still get 3.4 amps? If thats the case then most of the cells I have measured so far are no good. I think with the amount of 'good' cells I have ie, tabbing not coming off the front I will only be able to make one panel at the moment, and possibly with the other cells a bad one. How does the tabbing affect power output if it has slightly lifted off the surface? If it has no affect then I should have more than enough for one panel.

Thanks a lot Andy

[ghurd]

You "Might" get 3.4A a minute a year if you watch closely when everything is 100% perfect. :-)

If the cells work as rated, then 3.4A is good for figuring how much power they can make in a day, on a fixed mount at the proper angles.  Take 3.4A X you areas solar insolation hours for the time of year.

So if your solar insolation for now is 4.5 Hours, the panels should make 3.4A X 4.5H = 15.3A-H per day, into a battery.

That is for 36 cells per string, no extreme wire losses, etc.

It works out quite well.

England's average worst case winter month is about 1 hour!

Wow! Thats nearly as bad as here, often listed as <0.5H.

I can not find 12 month charts for England.

But its better than that 11 months a year.

Can't help with the loose connections, etc.

Tried DIY a time or 2, it didn't turn out well, I gave up. :/

G-

[andyman5002]

Ok thanks ghurd I understand now So I think the best thing to do is what you said lay them out and try to measure them all at once, then the ones that read below the others call them bad, the ones that are the same or above the average call them good? I think that should be ok. I think for me to see 3 amps now I will have to wait until next summer.

Thanks ghurd for clearing that up.

Andy