solar panels no current but full voltage

[bhavin66]

I bought 12 used sunpower 435w solar panels from the seller about a year ago. I checked panels on delivery 2 showed some burn damage which the seller refunded promptly. I had checked the voltage at the time and all were within limit of the panel specs. A few weeks ago I decided to test the panels with the inverter and unfortunately 5 out of the remaining 10 show voltage on connection to inverter but no current so the output power is zero.
After much reading I attempted replacing the bypass diodes but no change. The original diodes test fine with multimeter.
Any ideas on how to diagnose the issue and make it usable.

 

[AntronX]

Did you try testing short circuit current?

 

[bhavin66]

Did you try testing short circuit current?

Panels specs approx that I remember
Vmp - 72v
Imp - 5.9a
Voc- 85v
Isc - 6.8a
On faulty panel In full sun I get
Voc - 82-83v
Isc - 5a (with a multimeter)
Vmp -56v
Imp - 0 (when connect to inverter)

On working panels in full sun I get
Voc - 82-83v
Vmp - 65v
Imp - 5a

 

[bhavin66]

Did you try testing short circuit current?

Yes I did

 

[CoolWill]

Maybe your batteries are charged

 

[bhavin66]

Maybe your batteries are charged

PV1 has another set of panels and is pushing full amps. this is on PV2. when i connect this panel(faulty) i see the voltage 56v(a bit lower than working panels) but no amps. when i replace it with another working panel i see 65v-68v and 5a pushing through PV2 same location same elevation angle.

 

[efficientPV]

On the faulty panel attach a 100W incandescent light. That will provide enough load to determine what is wrong. Open circuit voltage and short circuit voltages can be correct on a defective panel. With lamp as a load, you can measure voltage across each bypass diode. If you are running a series string of panels (none in parallel), you could just short out the bypass diode of the the bad section.

 

[bhavin66]

With a day job and crappy weather not much enthusiasm to do anything.
I am leaning towards faulty/cheap MC4 connectors I bought from AliExpress. Hopefully can confirm in a day or two.

 

[Quattrohead]

Yeah I was pondering the state of your connections.

 

[KITROBASKIN]

Hope it is the connections but wonder why only half are faulty if you used the same connections on all.

Testing under load like efficientPV said…

In the ‘90’s I had a solar panel with a flawed spot where the back sheet may have been damaged. It showed normal volts but would not produce.

 

[bhavin66]

So far with a workaround with faulty connectors and a cheap pwm charge controller I can confirm that only two of three strings are producing. I was able to see 54.5v and 2-3a on the charge controller and two strings show voltage the third string is not showing any voltage.
So if I short the third diode I will be bypassing the diode which I believe will not help. I think if I cut out the diode I should get the full voltage and current hopefully. Later I will try to replace the diode and check.
Correct me if my thought process is wrong.

 

[Tomthumb62]

Are your batteries fully charged? If so, you’ll have low to no current. Put a good strong load on your battery, like a heat gun connected to your inverter and see if the amps start to rise.

 

[efficientPV]

You have not said what the panel does with a load. This is not like auto repair where you just keep replacing things till it works.

A load provides a complete circuit. A bypass diode will allow you to bypass a section of panel which does not produce voltage. If there is a bad section of panel, it can stll be used if the array is in series and a MPPT controller is used that can handle the higher voltage.

If that damaged panel is in parallel with other strings in parallel, current will not flow from the lower voltage string to a higher voltage.

A load like a lamp will form a complete circuit. You will likely find across one of the bypass diodes the voltage is very low compared to the other diodes.

Whether or not that panel with a bad section can ever be used depends on how your strings are arranged in parallel and in series. You might as well short out the diode of the bad section as sooner or later the current will cause it to short out anyway. Shorting the diode out will also protect some electronics if used for some other low voltage application from too high a voltage. A lower voltage panel can be used for some separate projects. I have a bad panel which runs a fan for my wife when she lounges outside.

 

[SeaGal]

I have a bad panel which runs a fan for my wife when she lounges outside.

... now I have this image of your poor wife carrying a half-broken 2m x 1m PV panel around with her as she moves her lounger to different parts of your decking or pool, propping it up towards the sun before she can lie down, sip her martini and rest

 

[bhavin66]

You have not said what the panel does with a load. This is not like auto repair where you just keep replacing things till it works.

A load provides a complete circuit. A bypass diode will allow you to bypass a section of panel which does not produce voltage. If there is a bad section of panel, it can stll be used if the array is in series and a MPPT controller is used that can handle the higher voltage.

If that damaged panel is in parallel with other strings in parallel, current will not flow from the lower voltage string to a higher voltage.

A load like a lamp will form a complete circuit. You will likely find across one of the bypass diodes the voltage is very low compared to the other diodes.

Whether or not that panel with a bad section can ever be used depends on how your strings are arranged in parallel and in series. You might as well short out the diode of the bad section as sooner or later the current will cause it to short out anyway. Shorting the diode out will also protect some electronics if used for some other low voltage application from too high a voltage. A lower voltage panel can be used for some separate projects. I have a bad panel which runs a fan for my wife when she lounges outside.

i did go through some parts of the test as you mentioned but not all. so now it has become like auto repair for me to figure out what did i miss and i did find out that the MC4 connectors were faulty which i had a workaround and connected to a PWM charge controller.
Currently some renovations underway so not much time to work on anything else and with busy work schedules for a few weeks.

 

[Tomthumb62]

i did find out that the MC4 connectors were faulty

Will and others shout from the rooftops: most solar system problems come down to wiring problems. Poor wire, too thin of wire, poor joints, poor solder, poor crimps, terminal screws too loose, etc.

When I went through my entire system replacing almost everything with better wire, I found a couple of really bad connections. Terminal screws either I forgot to tighten down or they had loosened with vibrations from the road (camp trailer). No wonder my batteries weren't charging well. I hear a lot about poor MC4 connectors and/or mismatched brands of connectors. Some people remove ALL the MC4 connectors and replace them with new ones. Either new ones all from the same brand or the official but expensive Staubli ones (about $5 each M/F pair). I haven't done this myself yet but so far I haven't seen any problems or reason to do so.

 

[Checkthisout]

It's not possible to have a bad panel that shows full voltage but no amps while under load.

Electrical 99 level stuff here.

 

[Quattrohead]

It's not possible to have a bad panel that shows full voltage but no amps while under load.

Electrical 99 level stuff here.

Absolutely is possible. High resistance connection but no load can show near full voltage with a digital multimeter.
This is also why electronic circuits have pull up and pull down resistors to make sure no data lines are floating. Electronics 101 LOL

 

[Checkthisout]

Absolutely is possible. High resistance connection but no load can show near full voltage with a digital multimeter.
This is also why electronic circuits have pull up and pull down resistors to make sure no data lines are floating. Electronics 101 LOL

Absolutely incorrect.

If your CC shows full panel voltage but no current is flowing then your CC isn't applying a load.

Its possible to have full panel voltage with an open circuit and a poor connection but not under load.

Voltage will drop through a bad connection if current is flowing. This is the most basic test in regards to electrical diag.

 

[Quattrohead]

Pretty sure we are saying the same thing