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Old 02-26-2018, 07:51 PM   #1
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Wire Sizes

Was hoping to get some validation on wire sizes for a solar / lithium setup. I am most fuzzy if everything from controller to battery and then to bus bars should be 2/0 vs. 4 gauge

Roof Panels - 2 200watt panels 6.65amps each ( 600 future )
Portable panels - 2 125 watt panels 9.87amps each
600ah lithium - 200amp continuous
Victron 150/85 Controller
Factory charger disconnected ( upgrade later )
Factory inverter ( upgrade later )


Battery Parallel connections - 2/0 1'

Roof Run to Blue Sea on/off - 4 AWG approx. 20' run

Blue Sea on/off to controller - 4 AWG approx. 18"

Controller to Pos - Neg Posts - 4 AWG approx. 18"

Pos - Neg Posts to Bus Bars - 4 AWG approx. 18"
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Old 02-26-2018, 08:17 PM   #2
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I don't know your planned configuration so perhaps these questions are off base.

What are the panel voltages? I am confused by the 200 watt panels at 6.65 amps each v. 125 watt panels at 9.87 A each. Are the voltages different? How are the panels wired, series or parallel? I'm assuming parallel since you specified currents for "each". If parallel, the voltages for the panels should be the same.

Is the 20' run length you list the physical length, or the round trip? Wire should be sized for the round trip distance.

Why are the battery parallel connections larger than the battery to buss bar wires? Why would the battery to battery current be so much larger than the current to the buss bars?

You don't mention any fuses. There should be fuses protecting the wiring from potential current sources, i.e. converter/charger (when connected) and batteries. The solar panels are self limiting, so if the wire size is adequate for the Isc, you probably can get away without fusing that run.

Al
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Old 02-26-2018, 08:42 PM   #3
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Thanks Al

I transposed the amps on the panels 9.87 on the 200s and 6.65 on the 125's. They will all be wired parallel.

20' run is physical. Roof combiner to controller under the bed

No specific reason, if it can all be 4 gauge I am ok with that.

Fuses are planned for battery side of controller, pos-post to bus bar, Inverter to Pos-post.

Thanks!
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Old 02-27-2018, 05:00 AM   #4
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Quote:
Originally Posted by wponder View Post
Was hoping to get some validation on wire sizes for a solar / lithium setup. I am most fuzzy if everything from controller to battery and then to bus bars should be 2/0 vs. 4 gauge

Roof Panels - 2 200watt panels 6.65amps each ( 600 future )
Portable panels - 2 125 watt panels 9.87amps each
600ah lithium - 200amp continuous
Victron 150/85 Controller
Factory charger disconnected ( upgrade later )
Factory inverter ( upgrade later )


Battery Parallel connections - 2/0 1'

Roof Run to Blue Sea on/off - 4 AWG approx. 20' run

Blue Sea on/off to controller - 4 AWG approx. 18"

Controller to Pos - Neg Posts - 4 AWG approx. 18"

Pos - Neg Posts to Bus Bars - 4 AWG approx. 18"
Are you using the Victron 150/85 Controller because you want to be able to expand your solar later? That will handle a lot of amps!
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Old 02-27-2018, 06:53 AM   #5
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I would think the only run you might need to be concerned with is the 20' run from the panels. Let's say you upgrade to your 600W capacity. That would triple your current, so 3x9.87 = 29.87A, call it 30. #4AWG wire resistance is .00025 ohms per foot. So the drop in that run would be V = .00025 x 40 x 30 = 0.3 volts. 0.3 volts x 30A = 9 watts lost out of 600. That would seem to be acceptable.

On the other hand, you don't speak to the inverter current. That is the largest current in the system, so the battery cables should be sized for that. I was basing my previous comment on the fact that the cables from the batteries to the buss bar are #4. Is that adequate for your inverter? What is it currently wired with?

If it is a 1000 watt inverter, it could draw around 1000/12/.8 or just over 100 amps. The runs are all short, so ampacity would probably drive the selection. #4 with 90 degree C insulation is rated for 95 amps. 00 with 60 degree C insulation would get you 145 amp rating. So your selection of 00 for the parallel cables might be appropriate for all the 12V wiring that inverter current would travel through.

Just my opinion.....

Al
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Old 02-27-2018, 07:54 AM   #6
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Hey Al -

I am using the 100/85. The 50 is to close for my future solar potential.

The inverter is the stock AS 1000 watt inverter. It's currently wired inverter to buss bar with the stock 4 gauge. I was planning to leave it in place as it works for us for now. I will also simply disconnect the charger that is not lithium friendly. In the future if / when I upgrade that. I will likely go to the Magnum MS2012. It seems to be the most programable and would work just fine. Even if I picked something else I do not envision going over 2000watts or hybrid.

So, I was planning on just leaving it as is for now but do want to make sure not to box myself in for the possible future upgrade.
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Old 02-27-2018, 05:41 PM   #7
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Hey Al -

Just to confirm. I think this is what your suggesting.

Battery Parallel connections - 0 AWG 1'

Roof Run to Blue Sea on/off - 4 AWG approx. 20' run

Blue Sea on/off to controller - 4 AWG approx. 18"

Controller to Pos - Neg Posts - 4 AWG approx. 18"

Pos - Neg Posts to Bus Bars - 0 AWG approx. 18"

Replace existing 4 Gauge from inverter to neg bus bar / pos post with 0 AWG

Thanks!
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Old 02-27-2018, 06:40 PM   #8
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Is there a reason why you aren't considering wiring the solar panels in series-parallel pairs? Doing so would cut your voltage drop in half, or would let you use smaller wire. It would also let your MPPT solar controller work more efficiently, as these controllers thrive on higher-than-18V voltages.

For reference, I have 600 W of Renogy Eclipse panels on the roof, wired as three series-parallel pairs for a (rated) total of 35.5 V at 17.1 amps, feeding a Victron 100/50 solar controller and 320 amp hours of Victron Smart Lithium batteries. Right now in February, this yields about 350 W maximum, and my batteries normally hit 95% around noon. (In fact, they went from 75% to 95% by 1:00 p.m. today in spite of a solid overcast.) In short, even in wintertime his setup produces more power than I need.

Optionally I can also connect a couple of series-wired 100 W portable panels (rated total of 35.5 V at 5.7 amps) that I prop up on the ground at the end of a 30' length of AWG 10/2 cable. Series-wiring the ground panels is especially important--if they were in parallel, the voltage drop in that long umbilical would be much higher than I want.

I'm not saying you should copy my setup; I just mention it to give an example of a somewhat similar setup to what you have in mind. But I do recommend seriously thinking about using series-parallel wiring for your solar panels. As mentioned, it has many advantages.
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