need some help with cheap panels

[jenkinswt]

Well....I bought 4 - 240 watt panels for a off grid 24 volt system off eBay. They were unbranded and quite cheap. The seller appears to be out of business. They have been in storage until now while building our house.

I started messing with them yesterday and it was very cloudy but 2 panels showed about 14 volts and 2 showed zero. Today was very sunny and all 4 showed about 14 volts. I was wondering at first if they were 12 volt panels but I don't think they make 12 volt that size. Am I out of luck or can they be fixed? I looked all over internet but can't find anything. I was wondering if its a diode problem or something.

I've learned my lesson and will buy nicer panels but can't afford right now.

[RandomJoe]

Did you check short-circuit current?  If they really are 14V open-circuit panels then their short-circuit current (Isc) should be at least 17A, probably more like 27A.  Can't measure directly with most standard multimeters, as they usually top out at 10A.

A proper 12V panel should have an open-circuit voltage (Voc) around 21-24V, and a max-power voltage (Vmp) around 17V, so either they aren't proper 12V panels or they're duds.

*IF* they really are working and just have a low voltage / high current configuration you could series all four together.  14Voc would probably mean a Vmp somewhere around 8-9V?  Giving a series voltage of 32-36V, which would just work for a 24V battery bank (might have trouble equalizing).

Just checking, you did have the panels outside in the sun facing toward it? 

[jenkinswt]

The multi meter I have is a cheap one I couldn't check current and I hooked them in series yesterday and was getting close to 30 volts. Again cheap analog meter makes it hard to get exact voltage. I have a mppt charge controller and was getting a charge but don't know how much yet. I will get a different meter in a day or so but is there a quick fix to this? I believe they were supposed to be like 31 volts. The only info I find is a barcode on the back of them.

Ya they are in the sun, not on roof yet until I know what's going on.

[Bruce S]

There could be a couple ideas on these. When you can send up a pic of at least one so we can tell which type they are.
The really cheap ones (like to sets from H.F.) actually will not start doing much until they are in the sun and what I call "settle".
Get them out in the sun, securely so they don't blow over and crack when you're not looking  .
Grab some kind of battery that is discharged , and attach it with a few clamps, then start taking readings of each panel. Even the cheaper and sometimes free DMMs from HF have a 10A range. Hook it up correctly and look to see what you have.
Cheap meters can certainly help, I get them and use them to determine the initial health of batts and panels.
Best of Luck

[Simen]

Count the cells on one panel. Your open voltage should be a volt or two above half the cell-count. (if there's 36 cells, the open voltage should be around 19-20V, for example)
If the voltage are half of that, i'd suspect a diode...

[mab]

I would suspect fried bypass diodes - if the junction box on the back of the panel can be opened you should see some diodes - try removing them and check the voltage again.

[jenkinswt]

It can be opened and I only see 1 diode. I checked all over and only got voltage on one spot. If I remove the diode do I need to replace it or will the charge controller take care of it? They are hooked in series right now so I can get some charge. I have 12 2 volt C&D batteries that I bought used that seem to work quite well. Charge controller is windy nation trakmax and can have a maximum of 55 vdc. The panels have 60 cells I believe. I will try to get a few pictures.

[dnix71]

Take a jumper clip (alligator clips on a short piece of wire) and jumper across the diode you see. Check the voltage in full sun again. If it is still the same, then one of the ribbon connectors is probably torn from thermal expansion and contraction so you only have 1/2 of each panel working. That's why they were inexpensive panels.

If you can find the break and it is accessible from the back of the panel, with a sharp hobby knife you could cut and lift the laminate and solder across the break and reseal the cut to restore the panel to full output. If one of the cells has failed open, then you would need to get rid of the bypass diode and bypass the failed cell and have a panel with one less cell (and about 1/2 volt lower Voc.).

[jenkinswt]

Well I messed with it a bit today but didn't find any voltage from the other tabs just the one on the right side in the junction box. I only tried one panel and was in direct sun. I looked all over the cells to see if I could spot a break and didn't. When I crossed that diode the voltage dropped to zero. I took pictures but their too big to upload. I think unless I figure it out I'm just gonna use these at their lower output and start trying to get my wind generator finished up hopefully by winter. I will have to get parts welded somewhere since I moved back to Iowa I don't have access to a welder.

[dnix71]

Go here: http://www.picresize.com/
Upload your picture and accept the default resize options, except enter 150kb as the max size. The online resize will make it 640x480 and reduce the quality enough to post it here.

The Gimp is free. http://www.gimp.org/  It is an open source photo manipulation program for all modern operating systems.
It's a large download, but worth the effort to get and learn. I have a Mac and do not use Photoshop.

[jenkinswt]

Here are a few pictures. Thanks for help everyone.

[Simen]

There are 2 more diodes in those junction boxes; those two square surface mounted ones. i'd guess one in each panels have short circuited!

(Edit;
The round one are probably a blocking diode, while the two square ones are bypass diodes; one for each half of the cells...)

[mab]

I'd expect 30-35v from those panels - can't see the junction box too well but would try removing the diodes.

[dnix71]

Go out in direct sun with some pieces of cardboard. Put the volt meter on the main output screws and cover pieces of the panel until you see a voltage drop. You will probably be able to cover 1/2 of each panel without affecting the output.

Show us what that looks like. There has to be a broken cell or solder ribbon break. If it was only bad diodes the panels would have been repaired. Once you know which half of the panel is bad, the break will be easier to find.

Is it okay to ask how much you paid for the panels?

[Mary B]

I would test diodes first, simple ohmmeter test is all it takes.

[jenkinswt]

 Got a better meter the other day while we had good sun. One panel is completely dead, then the other three were approx 10, 12, and 30 volts but when ran in series and charging I was getting around 46 volts. I can't remember amps but I was getting approx 254 watts. I'm sure on the roof they'd do better but I'm going to try and find the break using cardboard when it gets sunny again.

Its been raining a lot here lately but I will update if anything changes.

[tecker]

Remove the diodes from each and test the voltage from each panel individually  full sun .  Put an electrolytic capacitor across the +- leads and see if it will hold voltage . The cap may leak down but it should hold in circuit , take care not to short the cap . They should have current full short with an Ammeter make sure the meter can take the current . Those diodes are in circuit to put them in series .  active by pass diodes are there to be in effect during shading There's a good chance one has gone bad . Order some more they are probably schottkys I'll attache blocking and active bypass

[tecker]

Here's the active bypass explanation