Connecting two flexmax 80's with 3 wires to solar

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Connecting two flexmax 80's with 3 wires to solar

Postby david1 on Fri Mar 17, 2017 9:38 am

Hi,

I have 3 4/0 wires running underground 1000 feet, and I want to setup two strings, one facing west, and one facing east, and will be using two flex max 80 charge controllers (one for each string). Can I connect all negatives together and run them through one of the wires, then run the positive from one string through the second and the other positive through the third?

Thanks
David
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Re: Connecting two flexmax 80's with 3 wires to solar

Postby Sandra Herrera on Fri Mar 17, 2017 9:50 am

David,
This is not recommended, the array side of your system must be completely isolated, one positive and negative wire per controller.
Your idea of sharing the negative conductor will seem to work in the beginning; the controllers will seem operational, however, you will affect your total production. The MPPT algorithm will not perform at its maximum efficiency
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Re: Connecting two flexmax 80's with 3 wires to solar

Postby david1 on Fri Mar 17, 2017 11:43 am

Thanks. How much efficiency are we talking about? Just wondering, because the cost of running a 4th wire is too much. If it is just a loss of 1-2% then I will take the loss, otherwise I will probably just put one charge controller with one array.
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Re: Connecting two flexmax 80's with 3 wires to solar

Postby blackswan555 on Fri Mar 17, 2017 12:44 pm

Thinking out loud,,,,,, you may need to get a data connection for temp sensing but possibly put the CCs the panel end ? with 4/0 you should not get that much drop even just using 2 of the three conductors, use the three & I presume you will get morning then afternoon Sun so the neutral will not be too loaded ?

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Re: Connecting two flexmax 80's with 3 wires to solar

Postby david1 on Fri Mar 17, 2017 10:51 pm

since I am using a 24v battery bank, I would end up loosing a lot of power (32.67%) by putting the ccs on the panel end.

I wonder if I could just use one CC and put in some sort of switch to switch back and forth between arrays?

Could you please explain why sharing the negative wire effects the MPPT? Just out of curiosity.
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Re: Connecting two flexmax 80's with 3 wires to solar

Postby david1 on Sat Mar 18, 2017 9:05 am

Another thought, is could I use one charge controller and connect both arrays in parallel with a diode to prevent back current to the shaded array? This may be the simplest solution, and even save money on the second charge controller.
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Re: Connecting two flexmax 80's with 3 wires to solar

Postby blackswan555 on Sat Mar 18, 2017 10:28 am

Fill in your profile, You may get some better answers ?
Tim
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Re: Connecting two flexmax 80's with 3 wires to solar

Postby Mike Swift on Sat Mar 18, 2017 8:20 pm

David, you could try this technique to get the most out of your system without having to run another #4 wire. Using just two panels set them up facing east and west, then with a diode to prevent backflow measure the short circuit current over the day. From these reading you can calculate the max power current over the whole day. Adjust the angles so the peak current never exceeds the CC max amp ratings (with the whole array). You will find that the power output from your system will be much higher in the morning and evening but a little lower at noon than a system with all of the panels set south, (assuming you are in the northern hemisphere). Note that you should also parallel two of the #4 wires, either positive or negative to reduce losses in your wire run.

And as Tim said, please fill in your profile. I don't know if you may be in Australia. :smile:
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Re: Connecting two flexmax 80's with 3 wires to solar

Postby david1 on Wed Mar 22, 2017 7:31 am

@mike Thanks! I think I will do just that.

I live in southern Idaho (USA).
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