Two classics with three wires

[qrper]

Gang...

I'm thinking of adding onto my solar array this summer.

The other day, it was cool and sunny and i maxed out the Classic 150 at around 86A. What I want to do is add more panels so during the winter months, I can get the battery fully charged even on an overcast days. However in the summer, I'll clearly overtax one Classic.

So, I am going to install new wires from the array to the controller. Thinking the new panels will be on one feed, the second classic on another feed, and with ONE ground between the two.

One classic 150 to one array @ 7kW
another classic 150 to another array @4kW.
one common negative lead for both.

The idea is to save some $$$ because of the length of the wire run, about 200' give or take, and I plan using #2 wire.
Both controllers will charge the same battery.

Will I end up creating the ground loop from hell?

Mike

[boB]

There will be a bit of difference of voltage across the one wire when running at high current but SHOULD be OK I think.

What is the typical PV input voltage at around 7 kW  and the wire gauge of the 200 foot run ?  That should tell us how much voltage drop in that single wire.  Vdrop = I X R  of course....   And I =  Pwr / V   of the input.

What are the two PV voltages ?   Voc or Vmp or nominal should be good enough for that question.

[qrper]

Bob,

I have three 250 W panels in series and I see 85 V pv on the input to the classic right now under full current going into the batteries

I'm thinking of 2 gauge wire for the run of 200 feet.

Will need to do some voltage checks at the array and then at the battery end of the wire run as I have it now. The current wire is underground, but barely. As a matter of fact, it's entrance cable that's not even suppose to be used underground. That needs to be fixed this coming spring/summer. The cable is aluminum. Game plan is to replace that wire now and then replace the whole shebang with new copper wire. Of course, expanding so I can use two Classics

mike

[mike90045]

Each PV array should have it's own + & - wires going to it's own controller, and the controller should have it's own wires going to the battery (rated for 90amps)

No technical reason to join the - wires at the controllers.

For every amp coming out of a PV panel, it has to use the other wire to get back, both + & - wires need to be the same gauge
often 10 ga from array to combiner, and then 8 or 6ga from combiner to controller, and 2ga from controller to battery.

[qrper]

Each PV array should have it's own + & - wires going to it's own controller, and the controller should have it's own wires going to the battery (rated for 90amps)

No technical reason to join the - wires at the controllers.

For every amp coming out of a PV panel, it has to use the other wire to get back, both + & - wires need to be the same gauge
often 10 ga from array to combiner, and then 8 or 6ga from combiner to controller, and 2ga from controller to battery.

It was a feeble attempt to same some money on the wire. I know it's best to run four wires, each controller on its separate feed. Two gauge wire is about $1.35 a foot from the local electrical supply house. I need 200+ feet. Times four. So $5.40 a foot (all three wires). Or $1080 for the run. That hurts!

mike

[boB]

200 feet  (60.96 meters)  of 2 gauge wire would have about   0.03127248  Ohms of resistance.

Let's say you have half the current on the PV side that is going into the batteries.  We'll call it
50 amps...

E = IXR = 50A X  0.03127248  = 1.6  volts  of drop  and   around  I^2 X R = 78 watts of loss in the wire.

One day, hopefully this year, virus cooperating, we'll be able to just change the controller to a higher power and higher input voltage charge controller and then you can just wire the input PV array for several hundred volts and all would be well again.

boB

[qrper]

200 feet  (60.96 meters)  of 2 gauge wire would have about   0.03127248  Ohms of resistance.

Let's say you have half the current on the PV side that is going into the batteries.  We'll call it
50 amps...

E = IXR = 50A X  0.03127248  = 1.6  volts  of drop  and   around  I^2 X R = 78 watts of loss in the wire.

One day, hopefully this year, virus cooperating, we'll be able to just change the controller to a higher power and higher input voltage charge controller and then you can just wire the input PV array for several hundred volts and all would be well again.

boB

Oh, don't make me re-wire the array again!

mike

[boB]

200 feet  (60.96 meters)  of 2 gauge wire would have about   0.03127248  Ohms of resistance.

Let's say you have half the current on the PV side that is going into the batteries.  We'll call it
50 amps...

E = IXR = 50A X  0.03127248  = 1.6  volts  of drop  and   around  I^2 X R = 78 watts of loss in the wire.

One day, hopefully this year, virus cooperating, we'll be able to just change the controller to a higher power and higher input voltage charge controller and then you can just wire the input PV array for several hundred volts and all would be well again.

boB

Oh, don't make me re-wire the array again!

mike

I wouldn't dream of making you wire anything in a way that is uncomfortable to you 

[qrper]

200 feet  (60.96 meters)  of 2 gauge wire would have about   0.03127248  Ohms of resistance.

Let's say you have half the current on the PV side that is going into the batteries.  We'll call it
50 amps...

E = IXR = 50A X  0.03127248  = 1.6  volts  of drop  and   around  I^2 X R = 78 watts of loss in the wire.

One day, hopefully this year, virus cooperating, we'll be able to just change the controller to a higher power and higher input voltage charge controller and then you can just wire the input PV array for several hundred volts and all would be well again.

boB

Oh, don't make me re-wire the array again!

mike

I wouldn't dream of making you wire anything in a way that is uncomfortable to you 

Bob... any idea how far down the road I might have to rewire the array for a high voltage input controller?

mike

[boB]

Bob... any idea how far down the road I might have to rewire the array for a high voltage input controller?

mike

Less than a year but more than 4 or 5 months ?

Realistically speaking...

[bee88man]

No Free Lunch, 2 controllers need 2 wires for each to the PV...no sharing.
For DC sgaring would be 2 times the current!!!
This is not like split-phase AC where a neutral only carries the unbalanced current of the 2 oposite AC phases.