dstance panels and inverter

robocop · May 2020

Hi
like to know the type of wire to connect between solar panels to inverter.

Do have 8pcs 500w each panels 12 pcs 250ah batteries and a 5.5kw rated hybrid inverter.

The distance panel to inverter is about 135 feet using mc4 connects.

system voltage is 48v

Awaiting your reply and thanks

Bob

mcgivor · May 2020

Well it depends on the voltage allowable by the inverter, higher voltages results in lower current therefore smaller conductors, how are the panels configured, what are the specs of both the panels and inverters charger? Assuming the hybrid inverter has a MPPT charger built-in.

BB. · May 2020

Bob,

What are you using for the connection from the solar array to the battery bank (MPPT charge controller or GT Inverter or what)?

Basically, need to know the Vmp-array / Imp-array configuration (x series * y parallel connections). What is the Vmp/Imp of the panel?

For example, a 150 Vpanel max input MPPT controller, you can run Vmp-array ~ 100 VDC max, possibly more? (are you in Curaçao, Caribbean Sea?).

For a Vpanel input of 600 volts, a Vmp-array of 400 volts or so is possible... Higher the voltage, lower the current, smaller diameter wire you have to use...

-Bill

PS: I have closed your other discussion... Keep everything in one location. -Bill

robocop · May 2020

hi Bill
panel vmp is 58.95 imp is 10.87 voc 48.63
inverter : max panel array is 4000w pv array mppt voltage is 130vd max pv array open circuit voltage is 145vd

inverter is MUST hybrid 5.5kw and I do live in curacao.

What about the inter panel connections ? Should I use less panel? And what will the thickness be for 35 meter lengt

I do have 12pcs 250ah batteries to form 48v and 750 ah

Thanks for you attention and have a nice day

Bob

MichaelK · May 2020

Here are some specifications I see for your unit

Max Voc =145VDC

PV array voltage 64-130VDC

Max current 80A

I think you have your panel voltage backwards. Voc is always higher than Vmp. Are they Voc=58.95 and Vmp=48.63? Something else is not right. If the panel is 500W, then 500W/48.63V = 10.28A (Imp). Is your amperage actually Isc=10.87?

If the Voc is 58.95, that means you can only have two panels in series to get a Voc of ~118 VDC. Three panels in series would be >176VDC which would exceed the 145V limit of your box.

It's doable to wire these panels in series/parallel, but your unit is limited to 4000W, meaning four strings of 2 panels (2S4P). So 8 total is maximum. Because your working voltage is rather high (118VDC) you can get by with using 10 gauge solar wire. In my own system, I'm going 125' with 10 gauge at 120VDC, and I measure virtually no voltage drop.

Now each of your batteries is 12V? A 250AH 12V battery is very large? I'm guessing that each battery must weigh about 65kg? To wire them for 48V you need to wire them in a 4S3P configuration. You'll need to read up on how to proper wire up three strings so they do not become unbalanced. Assuming each string needs about 25amps to charge, you are looking at 25A x 3 x 52+ volts = 3900Watts, so the panels are in the right ballpark.

I'm interested in hearing about how one of these Chinese all-in-one units actually performs out in the real-world. Please keep us posted on how things turn out?

robocop · May 2020

Hi Bill
Checked with the manufacturer and the label was wrongly printed so you are right
You will hear from me when system is working

thnks and regards

bob

robocop · May 2020

Hi Bill
Another question about cables
Intent using 16mm/ 6awg between each string of batteries ( 4x 12v/250ah) .
each length of cable will be about 8 -9 inhes long.
To interconnect to each string will used 4 awg and from the batteries to the inverter 48v will use 2awg as lengt of 3 meter.
Plse let me know if ok

HAve a nice saterday

Bob

BB. · May 2020

The maximum continuous current from a 5.5 kWatt AC inverter on a 48 volt battery bank would be:

5,500 Watts * 1/0.85 AC inverter eff * 1/42.0 volts batt cutoff = 154 Amps (pretty much worst case)

From a 250 AH battery, the typical maximum current you can draw (reliably over time/state of charge) is around C/5 discharge rate (5 hour rate):

250 AH * 1/5 hour rate = 50 Amps typical max current draw (2x that for a few second surge like starting a well pump)
3x parallel strings * 50 amps = 150 Amps max continuous (math check)

Using the NEC code (relatively conservative):
https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

6 AWG is "good" for ~55 to 75 Amps using the North American Electrical code

4 AWG is "good" for 70-95 Amps... (are you using battery to battery at 6 AWG, and each "string of batteries" at 4 AWG?)

Using a voltage drop calculator... I would suggest around ~2 volts maximum drop (48 volt bus, i.e., 46 volt battery under load - 2 volt drop = 44 volts at load) on all the wiring... For example, 2 feet (one way) of 4 AWG @ 50 Amps:
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.1608&voltage=48&phase=dc&noofconductor=1&distance=2&distanceunit=feet&amperes=50&x=0&y=0

Voltage drop: 0.0098
Voltage drop percentage: 0.020%
Voltage at the end: 47.9902

And 10 feet (3m) @ 150 Amps @ 2 AWG:
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.5127&voltage=48&phase=dc&noofconductor=1&distance=10&distanceunit=feet&amperes=150&x=54&y=18

Voltage drop: 0.47
Voltage drop percentage: 0.98%
Voltage at the end: 47.53

2 AWG is a bit small for 150 amps (NEC 95-130 Amps)--But with exposed cable (not in conduit), I am sure it will not overheat...

2 feet @ 6 AWG @ 48 volts @ 50 amps (battery interconnect):
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=1.296&voltage=48&phase=dc&noofconductor=1&distance=2&distanceunit=feet&amperes=50&x=30&y=12

Voltage drop: 0.079
Voltage drop percentage: 0.16%
Voltage at the end: 47.921

So, your numbers (as I guess at them), look fine.

-Bill

robocop · June 2020

Hi bill

I do have cables awaiting for the las 4 batteries.

concern 12 batteries of 12v 250ah

making 1 string of 4 batt in parrallel/series connecting to another ai 24v 250ah connecting to another string of same
batt parrallel/series to form 48v 500ah and then again to a third string of same batt in parrallel to form 48v 1000ah.
Can you give me in picture how to connect to see if I do have it ok?
Awaiting your reply

Regards

Bob

BB. · June 2020

Personally, I like to run 4x 12 volt batteries in series for 48 volts as a string. 48 volts @ 250 AH capacity per string.

Then take the 3 (?) strings of 48 volts, and connect in parallel. 48 volts @ 750 AH total for bank.

I am not sure your battery connections... Series connections add Voltage (only).

Parallel strings add Amp*Hour (only).

https://engineeringengineashar.wordpress.com/2015/08/23/how-to-make-series-and-parallel-connection/
series and parallel connection

To parallel battery strings, use this website's suggestion:

http://www.smartgauge.co.uk/batt_con.html

A DIY solar setup--The battery bus (one way to parallel):

http://2manytoyz.com/battbank.html

-Bill

dstance panels and inverter

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