J-Box and Bypass Diode wiring help

[fredster]

Hi,
I am new to forums and to the DIY Panel building. I am building 5 panels each with 60- 6 x 6 cells and I need help with how I should wire up the J-box and bypass diodes. I can wire either for 12 volt or for 24 volt. I am flexible with that at this point. I have attached a drawing of my layout and would appreciate input and wisdom from those of you have more knowledge of this then me. I am regulated to the size and layout of my design due to glass and frame material that I already have on hand. I am very flexible as to the wiring layout. I have not purchased the J-boxes yet until I am sure I have a clear understanding of how to wire them, and know exactly which J-boxes I should be using. Thank you

[inetdog]

Hi,
I am new to forums and to the DIY Panel building. I am building 5 panels each with 60- 6 x 6 cells and I need help with how I should wire up the J-box and bypass diodes. I can wire either for 12 volt or for 24 volt. I am flexible with that at this point. I have attached a drawing of my layout and would appreciate input and wisdom from those of you have more knowledge of this then me. I am regulated to the size and layout of my design due to glass and frame material that I already have on hand. I am very flexible as to the wiring layout. I have not purchased the J-boxes yet until I am sure I have a clear understanding of how to wire them, and know exactly which J-boxes I should be using. Thank you

You have not described what you would be using these panels for, but it looks like you have two 12-volt strings of 24 cells, with an additional 6 volt string of 12 cells.
This is not compatible with charging either a 12 volt or 24 volt battery directly through a PWM controller, since a panel Vmp of about 18 volts (36 cells) is considered to be the minimum practical for this application. If you put your 6 volt string in series with one of the 12 volt strings you could effectively charge a 12 volt lead acid battery, with 24 cells remaining totally unused. Or by putting all three in series you would get 30 volts, which is low for charging a 24 volt battery.

That part of your design seems to be flawed, but if you have specific plans for using these panels (such as putting them in series to be used with an MPPT CC), then please let us know.

[fredster]

You have not described what you would be using these panels for, but it looks like you have two 12-volt strings of 24 cells, with an additional 6 volt string of 12 cells.
This is not compatible with charging either a 12 volt or 24 volt battery directly through a PWM controller, since a panel Vmp of about 18 volts (36 cells) is considered to be the minimum practical for this application. If you put your 6 volt string in series with one of the 12 volt strings you could effectively charge a 12 volt lead acid battery, with 24 cells remaining totally unused. Or by putting all three in series you would get 30 volts, which is low for charging a 24 volt battery.

That part of your design seems to be flawed, but if you have specific plans for using these panels (such as putting them in series to be used with an MPPT CC), then please let us know.

Thanks for responding. My goal is off grid stand alone for a small cabin to charge batteries. With using the size glass I have on hand this is the only configuration that I can come up with, with my 6 x 6 cells. Is there a different wiring configuration that I can use? Like I said, I can do 12 or 24 volts if needed. As for my plan being flawed... that is quite possible. That is why I am in the paper planning phase and info gathering and learning. Thanks for your input.

[Naptown]

A 60 cell panel is OK for charging 12V batteries. It really boils down to what type charge controller you use. A 60 cell MPPT controller will charge a 12V battery no problem and with little losses as it will down convert the voltage to the appropriate level for the state of the battery. A pwm controller will reduce the wattage dramatically on a panel with higher voltage than panel charging voltage.

[fredster]

Diode wiring still the issue....

A 60 cell panel is OK for charging 12V batteries. It really boils down to what type charge controller you use. A 60 cell MPPT controller will charge a 12V battery no problem and with little losses as it will down convert the voltage to the appropriate level for the state of the battery. A pwm controller will reduce the wattage dramatically on a panel with higher voltage than panel charging voltage.

Right. I don't have a problem using a MPPT controller, but I am still in the dark as to the proper wiring of my cell strings in relation to the diodes. I attached a drawing to my first post. Can anyone help with that????

Thanks

[inetdog]

Right. I don't have a problem using a MPPT controller, but I am still in the dark as to the proper wiring of my cell strings in relation to the diodes. I attached a drawing to my first post. Can anyone help with that????

Thanks

Sure. In your drawing there are 4 bus inputs into the j-box, with three sets of diodes in place already.
If you connect the + of each string to the - of the string immediately to the left of it, you will be left with exactly 4 distinct outputs from the cell array (instead of the six tab ends you have with them unconnected). Connect each of those outputs, in order from right to left, to the j-box inputs above them, also going from right to left.

[fredster]

J-Box Diode Wiring

Sure. In your drawing there are 4 bus inputs into the j-box, with three sets of diodes in place already.
If you connect the + of each string to the - of the string immediately to the left of it, you will be left with exactly 4 distinct outputs from the cell array (instead of the six tab ends you have with them unconnected). Connect each of those outputs, in order from right to left, to the j-box inputs above them, also going from right to left.

Ok inetdog. Lets see if I understand. I have attached another drawing. If I am understanding you correctly, the red lines are what you are saying, and this configuration with 60 cells should give me 30 Volts and 240 watts. Am I correct? Thanks for your help and patience.

[inetdog]

Ok inetdog. Lets see if I understand. I have attached another drawing. If I am understanding you correctly, the red lines are what you are saying, and this configuration with 60 cells should give me 30 Volts and 240 watts. Am I correct? Thanks for your help and patience.

By George, I think you've got it! Yes, that is what you should do and 30 volts (nominal) is what you will get out. But since you have not said anything about the Imp of the cells, I can't confirm that you will get 240 watts. Not all 6x6 cells are the same.
If they were sold as 4 watt cells, then a 240 watt panel is what you should compare them to. But the difference between standard conditions and realistic conditions will mean that neither a commercial 240 watt panel nor yours (if 240 watt) will actually produce that much power other than on the brightest coldest days.

[fredster]

By George, I think you've got it! Yes, that is what you should do and 30 volts (nominal) is what you will get out. But since you have not said anything about the Imp of the cells, I can't confirm that you will get 240 watts. Not all 6x6 cells are the same.
If they were sold as 4 watt cells, then a 240 watt panel is what you should compare them to. But the difference between standard conditions and realistic conditions will mean that neither a commercial 240 watt panel nor yours (if 240 watt) will actually produce that much power other than on the brightest coldest days.

Great! Now I can move forward. I do appreciate your time and patients with me. Yes these are 6 x 6 cells that are rated at 4 Watts each., and I was figuring 240 Watts, but I also realize that is optimal output under optimal perfect conditions. Thanks again. God Bless.

Fredster

[sunscreen]

Need help too in wiring to Jbox

I hope you can help me too here. since I have the same problem.
I got this solar panel kit for a very cheap price at an auction in ebay and it came with a junction box with 4 input connections. I wonder if my drawing is correct on how to connect the solar cells to the junction box.
diagram solar panel.jpg

thanks in advance for those who will reply

[Mike90250]

It looks OK to me, but shouldn't the seller be the authority for their kit?

[sunscreen]

Thanks for the reply. The kit was bought last year when somehow I got so interested in building my own panel for experience purposes but then due to so many reasons I didn't find the time to build it until now. I guess I should contact the seller if I can still find him in ebay. Thanks again.