Solar Panel Voltage Drop Once Connected to Controller

[Schtevie]

Hi and thanks for taking time to read this! Not sure how much specifics are needed, but I have 12 100 watt panels paired up in parallel, and then six pairs linked together in series. These go into a 100 amp circuit breaker, and then into a 60 amp charge controller. That charges up three 100ah 12 volt Lifepo4 batteries wired in parallel.

This setup has been working without issue for almost two years. Two days ago, it stopped charging the system. After some troubleshooting, I realized that if I check voltage between the input of the circuit breaker, and the solar panel input of the charge controller, I get an appropriate voltage. As in like 118 volts depending on the sun. If I check the voltage at the circuit breaker output, and the solar panel input of the charge controller, I get only 12 volts. I've replaced both the circuit breaker leading into the charge controller, and the charge controller itself. Same issue as it only registers 12 volts after the circuit breaker going into the charge controller.

Any ideas would be greatly appreciated!

 

[robbob2112]

So you have them wires 2p6s = what are the specs on the panels? Should be a sticker on the back of a panel - or may need to find a link to your panels and get the specs from there.

12v panels just means they are suitable for use with a PWM controller that shorts the panel voltage to the battery terminals and release quickly to charge a 12v battery.

So working from the values provides - these may be a bit off but are probably in the ballpark
Putting them in parallel series means the voltage from 6 are added and the current is the same as if you only had 2 in parallel that adds.

You see 118v at times - 118v / 6 = 19.6v per panel.
100w / 19.6v = 5.1amps each

So on a normal basis your charge controller would see 118v at 10.2amps

From the description it sounds like your problem is a bad connection out where your panels are. Something corroded a bit so it allows full voltage through but as soon as there is a demand for current it won't pass anymore. Easy check - in full sun either measure the temp of each connection or just feel them. If any are noticably hotter than the others you found your problem. Try taking them apart and inspecting all the connectors between panels (cover with a towel/cardboard or do it at night or a cloudy day) Remember they will all have voltage on them and 118v can really bite or be lethal if there is any current behind it... Insulated gloves are recommended.

Need links to the MPPT and breaker to check those, but I suspect a bad connection

 

[HRTKD]

After some troubleshooting, I realized that if I check voltage between the input of the circuit breaker, and the solar panel input of the charge controller, I get an appropriate voltage. As in like 118 volts depending on the sun. If I check the voltage at the circuit breaker output, and the solar panel input of the charge controller, I get only 12 volts.

This doesn't make any sense.

---- + (A) breaker (+) (B) --------- solar charge controller
---- - -------------------------- (C) solar charge controller

118 volts between A and C but only 12 volts between B and C?

Are you sure you weren't testing using the battery connection side of the solar charge controller?

 

[MisterSandals]

I realized that if I check voltage between the input of the circuit breaker, and the solar panel input of the charge controller, I get an appropriate voltage. As in like 118 volts depending on the sun. If I check the voltage at the circuit breaker output, and the solar panel input of the charge controller, I get only 12 volts.

Can you post a pic of your wiring? Bonus points for showing how you measured voltages.

 

[MichaelK]

So you have them wires 2p6s

I think you got that backwards. I would interpret "six pairs linked together in series" as 2S6P.

That being said, it is a mistake to be wiring one array of panels running at maybe 18V, and a second set running at ~36V. All the parallel strings should be running at the same voltage.

 

[Schtevie]

Sorry for the delay in response, but thank you for all the feedback on this! The first thing I did after reading these were to go back and check all of my connections. One further point of clarification: The solar array gets moved in the winter months to an area 150 feet away from where it is in the summer time due to trees. From the solar array location to the house, I buried a 12/2 underground wire years ago for 'winter location' usage.

The solar array has been in it's 'winter location' for about a month and working fine before this issue started. I checked all of the connections and voltage on the solar array, and they appeared to be fine up to the point where the 12/2 wire entered the ground. Checking connections and voltage where the 12/2 wire emerged from the ground at the house, and the voltage was 0. After seeing this, I rigged together a few 12 awg exterior extension cords, and the charge controller is now getting power as shown on the image below:



Since this 'winter location' setup is only in use for three months or so out of the year, is there any issue with continuing to use exterior extension cords like this? Here are the specs of the current extension cord:



Also, can I get away with less then a 12 awg extension cord for this? Here are the specs for the cheaper 14 awg:

 

[robbob2112]

Can you? yeah... should you? probably not.... It works, but it is subject to damage and carries voltage that could be lethal if someone/something got across a bare wire. And critters do love to chew on wires, the sheath tends to make a tasty meal.

Were it me I would get some stranded THWN - 3 strands (red, black, green) 12awg - and some 1/2 PVC conduit - pull the wire through a section at a time, when you are done, glue it all together... and come spring if none of the conduit is damaged dig a trench and drop it in.

Then you should be good from now on. The UF direct bury cable is quick, but critters really like to eat the sheath on that so it has a lifespan that can be pretty short, the THWN in conduit should last as long as you do.

 

[Schtevie]

Can you? yeah... should you? probably not.... It works, but it is subject to damage and carries voltage that could be lethal if someone/something got across a bare wire. And critters do love to chew on wires, the sheath tends to make a tasty meal.

Were it me I would get some stranded THWN - 3 strands (red, black, green) 12awg - and some 1/2 PVC conduit - pull the wire through a section at a time, when you are done, glue it all together... and come spring if none of the conduit is damaged dig a trench and drop it in.

Then you should be good from now on. The UF direct bury cable is quick, but critters really like to eat the sheath on that so it has a lifespan that can be pretty short, the THWN in conduit should last as long as you do.

Thanks for the advice. I'm looking to be cost effective here, so is 12 awg the minimum gauge wire you would recommend? What exactly am I looking at in the specifications of the wire to make sure it will be safe given my average load on the charge controller screen shot above?

 

[robbob2112]

DC Voltage Drop Calculator | Mangan Power Distribution Group

Among leading power distribution companies, we offer a DC Voltage Drop Calculator to calculate the voltage drop as per the IEEE standard. Call 310-835-8080.

manganpower.com

Here are the specs for 12, 14, and 16awg wire - you double the length because the circuit is in and out.

For an AC circuit you want less than 3% loss. For a DC MPPT circuit you can do anything you want to. All smaller wire means is more wasted power and less charge in the batteries.

For this the max at the panels is 576w....
if you use 16awg you get 524w at the MPPT,
for 14awg you get 544w at the MPPT,
and for 12awg you get 556w at the MPPT.

Multiply that times the hours of the day you get full sun and you can figure what you are loosing due to wire resistance.

 

[Schtevie]

DC Voltage Drop Calculator | Mangan Power Distribution Group

Among leading power distribution companies, we offer a DC Voltage Drop Calculator to calculate the voltage drop as per the IEEE standard. Call 310-835-8080.

manganpower.com

Here are the specs for 12, 14, and 16awg wire - you double the length because the circuit is in and out.

For an AC circuit you want less than 3% loss. For a DC MPPT circuit you can do anything you want to. All smaller wire means is more wasted power and less charge in the batteries.

For this the max at the panels is 576w....
if you use 16awg you get 524w at the MPPT,
for 14awg you get 544w at the MPPT,
and for 12awg you get 556w at the MPPT.

Multiply that times the hours of the day you get full sun and you can figure what you are loosing due to wire resistance.



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Thank you so much! The link, you sharing your knowledge, and your screen shots are incredibly helpful.