Voltage Drop Calculation 230' & # of panels

[sabo]

I am trying to figure out how many panels to put in a string. I have 20 San Tan 250 W panels. (specs below) and a MPP Solar LV 6548V (specs below)
How many should i put in series and what gague wire should I run 230ft. Unclear on # of conductors and Load Current amps. Is my calculation good and accurate? Should I use 10 Ga wire from the panels to the inverter?











Likely Mfg Trina Solar
Open circuit voltage (VOC): 37.6 V
VOC 37.8
VMP 30.3
ISC 8.85 amps
IMP 8.27 AMP
FUSE RATING 15 AMP
Junction Box IP 65
Poly Crystalline
Max V 600 V

 

[sunshine_eggo]

Hello again. Why another thread?

To use all 20 panels:

7S2P on MPPT 1
6S on MPPT 2

In the calculator, voltage is the series Vmp of the panels. Current is the current of the array, so:

7S = 30.3V * 7
2P = 2 * 8.85A

Calculate the numbers and enter into the voltage and current fields of the calculator. Select 1 pair of conductors. That's the voltage drop for array on MPPT 1.

6S = 30.3V * 6
1P = 1 * 8.85A

Calculate the numbers and enter into the voltage and current fields of the calculator. Select 1 pair of conductors. That's the voltage drop for array on MPPT 2.

Play with wire size. 10awg may be fine.

 

[sabo]

7S = 30.3V * 7 = 212.1 Volt
2P = 2 * 8.85A = 17.0 amp

Voltage drop: 3.91
Voltage drop percentage: 1.84%
Voltage at the end: 208.09

—---------------
6S = 30.3V * 6 = 181.8
1P = 1 * 8.85A = 8.85

Voltage drop: 2.03
Voltage drop percentage: 1.12%
Voltage at the end: 179.77

The key is to keep VOC near the max VOC rating of the MPPT and amps down



LV 6548V Max. PV Array Open Circuit Voltage is VOC 390Vdc

208 + 179 = 387



P.S. I wanted a new thread because I changed my Inverter and for clarity because the last thread move in a few different directions.
I hope this makes the thread very clear for future new solar enthusiasts. ( Like Me )

Thanks for your assistance

 

[sunshine_eggo]

The 2 conductors in parallel means you're running a total of 4 wires for each array. Switch this to 1 pair (1 conductor per phase). Loss will double. You might want to go 8awg on the 7S2P array.

 

[Ampster]

Voltage drop may be less of an issue with panel output because you can always add a panel and that may be more cost effective than increasing wire size, within reason.

 

[sunshine_eggo]

Oh, and you don't add the two voltages. The 390V limit is per MPPT.

 

[Zwy]

I am trying to figure out how many panels to put in a string. I have 20 San Tan 250 W panels. (specs below) and a MPP Solar LV 6548V (specs below)
How many should i put in series and what gague wire should I run 230ft. Unclear on # of conductors and Load Current amps. Is my calculation good and accurate? Should I use 10 Ga wire from the panels to the inverter?

View attachment 144143





View attachment 144142



Likely Mfg Trina Solar
Open circuit voltage (VOC): 37.6 V
VOC 37.8
VMP 30.3
ISC 8.85 amps
IMP 8.27 AMP
FUSE RATING 15 AMP
Junction Box IP 65
Poly Crystalline
Max V 600 V

You could go 10S per string but it cuts pretty close to the 390VOC limits when temps get low.
I would go 9S per string. You could use the extra 2 panels on another MPPT, you have a total of 4. Or buy 7 more panels and have another string of 9S with the ability to add one more string.
10AWG will work fine, it's if you parallel 2 strings you will find there will be more voltage drop and power loss. 8AWG gets expensive compared to 10AWG.

Like I said above, I'd go 3 strings of 9S. The idle consumption of the LV6548V is high, Lithium Solar tested 125W at idle. That extra 1750W from the 7 panels will help with the overhead.

I don't know why you feel you need to parallel strings, just because you have a combiner box, doesn't mean you need to use it to parallel strings. I'd look at different panels if you want to maximize PV input to each MPPT. The problem is the 390VOC limit doesn't help with reaching the wattage limit. A panel like this 410W in 9S strings would be a better choice. https://www.santansolar.com/product/new-solarever-410w-solar-panel-palllet-31/

The 455W here doesn't work well with the 390VOC max, you get more watts per string with the 410W. The 455W would limit you to 7S. https://www.santansolar.com/product/new-solarever-455w-panel/

 

[sabo]

I am located in Sunny Southern Cali. How low of temps are we talking about? I do plan on getting more panels and I do want panels 350 W +. At some point in the not too distant future I plan on having 2-3 inverters.

 

[sunshine_eggo]

I am located in Sunny Southern Cali. How low of temps are we talking about? I do plan on getting more panels and I do want panels 350 W +. At some point in the not too distant future I plan on having 2-3 inverters.

My recommendations were based on you having 20 of the listed panels.

You can safely get 9S of those panels on each MPPT and be good down to about -10°C.

Mixing panels on the same array can get tricky. If you plan to use a single panel brand/size on each MPPT, that's fine.

If you have a final configuration in mind, you should finalize it and create a roadmap on how you're going to get there. Piecemealing it without a plan usually means you make a misstep along the way.

 

[Zwy]

I am located in Sunny Southern Cali. How low of temps are we talking about?

You input the data here. https://www.midnitesolar.com/sizingTool/

Colder weather is higher VOC. The max VOC for the MPPT is not to be exceeded.

I do plan on getting more panels and I do want panels 350 W +. At some point in the not too distant future I plan on having 2-3 inverters.

If you do plan on moving to higher wattage panels then you should probably start with panels that can maximize the input per MPPT.

If the plan is eventually moving to 2 inverters for 240V split phase, I'd purchase both inverters at the same time. This allows greater flexibility to build the PV array as you gain 2 MPPT's. Then you can build your array larger as time and money allow. It also helps with installation as you won't have to make changes down the road.

 

[sabo]

You input the data here. https://www.midnitesolar.com/sizingTool/

Colder weather is higher VOC. The max VOC for the MPPT is not to be exceeded.

If you do plan on moving to higher wattage panels then you should probably start with panels that can maximize the input per MPPT.

If the plan is eventually moving to 2 inverters for 240V split phase, I'd purchase both inverters at the same time. This allows greater flexibility to build the PV array as you gain 2 MPPT's. Then you can build your array larger as time and money allow. It also helps with installation as you won't have to make changes down the road.

I use 240 / 220 off breakers in my Grid Subpanel to reduce the amp draw. I assume reducing amp draw on a solar supplied subpanel is the same benefit of a subpanel from an inverter. Are there other benefits of 240v split phase on a solar supplied subpanel?

 

[sabo]

Since the LV 6548 has 2 MPPT's, which Solar PV DC Quick Disconnect Switch is a good choice?
Will Prouse recommends a 32 amp IMO DC Disconnect Rooftop Isolator Switch
in this setup

48V Offgrid Solar Power System

If you wish to build the ultimate offgrid solar power system, look no further: All-in-one units make setup a breeze. Each unit has it's own Inverter, MPPT, Transfer Switch and Battery Charger. Budget...

www.mobile-solarpower.com

The EG4 appears to have one MPPT per inverter. I am wondering if I need a 64 amp since there are two MPPTs on the LV 6548V?

 

[Ampster]

I am wondering if I need a 64 amp since there are two MPPTs on the LV 6548V?

What size is your wire and what is the current on each string? You need separate over current protection on each string.

 

[sabo]

What size is your wire and what is the current on each string? You need separate over current protection on each string.

I plan on running 10 ga from the panels to the inverter 9S . 9S 30.3 * 9 = 272 Volts ; 1P = 1 * 8.85A = 8.85 amps
Was considering this one:

https://www.amazon.com/gp/product/B0761WZXXR/ref=ppx_od_dt_b_slice_asin_title?ie=UTF8&psc=1

But then realized maybe would need to double the amperage protection to this one?

https://www.amazon.com/Aims-Power-DC1600V32A2IO-Disconnect-Switch/dp/B07C8VF2J8/ref=pd_vtp_h_pd_vtp_h_sccl_1/147-7163176-0021317?pd_rd_w=DnOa5&content-id=amzn1.sym.a5610dee-0db9-4ad9-a7a9-14285a430f83&pf_rd_p=a5610dee-0db9-4ad9-a7a9-14285a430f83&pf_rd_r=2EGX18KETPFSA8TP6RTJ&pd_rd_wg=NyFwp&pd_rd_r=dc1c34e2-74d3-4384-b372-422495d5f93d&pd_rd_i=B07C8VF2J8&psc=1

 

[Ampster]

.....plan on running 10 ga from the panels to the inverter 9S . 9S 30.3 * 9 = 272 Volts ; 1P = 1 * 8.85A = 8.85 amps

10 AWG is good for 30 Amps. The over current protection is to protect the wire so a 20 or 30 Amp fuse should be sufficient since teh max current is under 10 Amps.

But then realized maybe would need to double the amperage protection to this one?

No need to overthink this, just size the fuse or circuit breaker based on wire size, since that is sufficient to carry the current of each string. Neither of those devices are circuit breakers anyway. A circuit breaker offers both over current protection and a means of disconnect for maintenance.

 

[sabo]

This video by Ian shows runnung the LV6548 batteryless. I have the 6548V, checked the manual and I cant find an example running without a battery. I thought I saw a video on Youtube showing the need to charge the inverter with two wires before use. Anyone familiar with this? Pre-charge the capacitor.

 

[Zwy]

Since the LV 6548 has 2 MPPT's, which Solar PV DC Quick Disconnect Switch is a good choice?
Will Prouse recommends a 32 amp IMO DC Disconnect Rooftop Isolator Switch
in this setup

48V Offgrid Solar Power System

If you wish to build the ultimate offgrid solar power system, look no further: All-in-one units make setup a breeze. Each unit has it's own Inverter, MPPT, Transfer Switch and Battery Charger. Budget...

www.mobile-solarpower.com

I use the IMO https://signaturesolar.com/dc-disconnect-rooftop-isolator-switch-by-imo/

The EG4 appears to have one MPPT per inverter. I am wondering if I need a 64 amp since there are two MPPTs on the LV 6548V?

EG4 has 2 MPPT's rated at 450VOC which helps get to max wattage per MPPT.

 

[Zwy]

I use 240 / 220 off breakers in my Grid Subpanel to reduce the amp draw.

Do not understand. If you are stating, for example running a motor, the amp draw per leg will be 1/2 on 240V compared to running the electric motor on 120V.

I assume reducing amp draw on a solar supplied subpanel is the same benefit of a subpanel from an inverter.

I'm not understanding the question other than 240V power is needed for some items such as a heat pump or electric motor and the amps on each leg will be 1/2 the amps of running the heat pump on 120V. It is still the same number of watts, just the load is split between the 2 legs of alternating current.

Are there other benefits of 240v split phase on a solar supplied subpanel?

240V AC split phase is what N America grid runs for electrical service. The current service panel in your house is 240V split phase AC, each leg is 120V.

A LV6548, LV6548V and the EG4 6500EX are all 120V inverters. By running a pair with communication cables between the 2, you can create 240V AC split phase power. One inverter is the master, the second a slave and offsets the master by 180 degrees.

 

[Zwy]

This video by Ian shows runnung the LV6548 batteryless. I have the 6548V, checked the manual and I cant find an example running without a battery. I thought I saw a video on Youtube showing the need to charge the inverter with two wires before use. Anyone familiar with this? Pre-charge the capacitor.

Forget batteryless operation, any cloud cover and the output power of the inverter can drop. The battery smoothes out the AC output of the inverter.

I have a precharge circuit on my control panel. You can see it in the 54Kw Battery Box thread in my signature below. Search the forum for information on precharge resistors.

 

[sabo]

Do not understand. If you are stating, for example running a motor, the amp draw per leg will be 1/2 on 240V compared to running the electric motor on 120V.



I'm not understanding the question other than 240V power is needed for some items such as a heat pump or electric motor and the amps on each leg will be 1/2 the amps of running the heat pump on 120V. It is still the same number of watts, just the load is split between the 2 legs of alternating current.

240V AC split phase is what N America grid runs for electrical service. The current service panel in your house is 240V split phase AC, each leg is 120V.

A LV6548, LV6548V and the EG4 6500EX are all 120V inverters. By running a pair with communication cables between the 2, you can create 240V AC split phase power. One inverter is the master, the second a slave and offsets the master by 180 degrees.

I dont believe I have the need to reduce amps currently. I understand the 240V is for higher power draw devices but in my current application I would not be running any hit draw. only lights and other items that run on 120. I was trying to figure out if when using solar and an off grid inverter it I may be missing some other reason to have 240v