Minimum Volts DC for a charge controller

[cyberfranklin]

Hi all,

Beginners Question: I am working to design a small (12 panel) ground mounted system with an EG4 6.5kw Off-grid inverter and charge controller and a 48 V LiPo4 battery. My question has to do with putting panels in a Series-Parallel configuration. My backyard where the panels will be installed is about 75 feet from where I plan to install the Inverter-Charge Controller and Battery. I am currently planning to use Trina 250W (Data Sheet attached). I want to take advantage of the lower amperage of configuring in-series (lighter gauge copper) and also minimize the wider-array degradation that is less likely to be invoked when a panel is shaded in a parallel configuration. So, I am configuring this way:

2 Trina 250W panels in series

Open Circuit Voltage (VoC)-volts= 37.6 * 2 (panels) = 75.2 volts
Maximum Power Current (amp)= 8.27
6 (series) Pairs of those panels in parallel
volts=volts in a parallel configuration 75.2=75.2 volts
8.27 amps * 6 (pairs) of panels in parallel = 49.62 amps
So, connecting with the charge controller we have:
75.2 volts
49.2 amps
Looking at the data sheet of the EG4 charge controller we understand that the max PV input is:
500 VDC
120 Max current (amp)
So, we are well below those thresholds with our series-parallel configuration.
Here is my question: the data sheet says that the charge controller range is 90VDC - 450VDC
And, as I show above, my array will only produce 75.2 volts. So, do I have to meet a 90 volts (DC) threshold to meet the requirements of the charge controller? Follow-up question, would I need to put MORE panels in series to increase the voltage?

As a newbie, am missing some fundamental concept?

Humbly willing to listen and learn. Thank you for your knowledge and time in-advance?

-G

​

​

 

[MisterSandals]

max PV input is:
500 VDC

From the spec sheet, this must be the MPPT range (optimized voltage range):
PV Array 90VDC - 450VDC

This is what you should use first to configure your array.
450V / 37.6Voc = 11.96 panels

You could almost put all 12 in series but temp correction would put you over. So 6S2P is likely the best option.
This would give you 6x 37.6V = 225V and combine 2 in parallel for about 16A (whatever 2x panel Isc is).

As you have specified with 6 pairs in parallel (2S6P), the 42A exceeds the MC4 connector current rating of 30A so you'd need a combiner box and fuses for each array. Not a very well designed array.

 

[Rednecktek]

Like he said, your best bet is a 6s2p setup to make all the numbers happy.

 

[cyberfranklin]

From the spec sheet, this must be the MPPT range (optimized voltage range):
PV Array 90VDC - 450VDC

This is what you should use first to configure your array.
450V / 37.6Voc = 11.96 panels

You could almost put all 12 in series but temp correction would put you over. So 6S2P is likely the best option.
This would give you 6x 37.6V = 225V and combine 2 in parallel for about 16A (whatever 2x panel Isc is).

As you have specified with 6 pairs in parallel (2S6P), the 42A exceeds the MC4 connector current rating of 30A so you'd need a combiner box and fuses for each array. Not a very well designed array.

Thank you, very much a appreciated. I was thinking that I would need a combiner box, but why introduce more complexity and expense into the system when you can keep it simple. Thank you for the perspective, knowledge and assistance.

 

[chrisski]

I bought a combiner box in a tough metal enclosure made for the outdoors through these guys:

MidNite Solar's

MidNite Solar manufactures E-Panels, combiners, charge controllers, pre-wired renewable energy systems, surge protection devices and other quality Renewable Energy System electrical components.

www.midnitesolar.com

I have also built my own combiner boxes out of plastic project boxes, circuit breakers, and DIN Rails, gang box connector blocks for 1/3 to 1/2 the cost, but I doubt the plastic would last for year, after year in the sun.

I am looking at a bigger build and I am noticing it is difficult to match bigger panels to these without going over amperage or voltage with temperature compensation and get very close to the max rating.