What is the tolerance of mppt maximum voltage

[tbaleno]

My maximum voltage including temperature Coefficient appears to be 324.3 and the mppt 6548 has a max input of 250. Would this cause it to cause an over voltage alarm on the inverter (if it has one). For temperature I'm using outside air temp. Is this the correct way to do it? Would this actually cause harm to the inverter? This is the math I used in case I messed up.

voc = 46.8v
# of panels 5
Temperature Coefficient (Voc) -0.28 % / °C
Lowest temp will be around -15 F / -26.11C
Nominal operating temperature rated at 41 ± 3°
I calculated 67c difference from nominal operating temperature to max lowest temperature as 67.41C
So 67.41*.28 is 18.8748 voltage increase so 5 panels voc 18.8748 * 5 panels is 94.35 extra volts.

Total voltage 324.3

Specs to the panels can be found here: https://store.santansolar.com/wp-co...dian_Solar-Datasheet-BiHiKu_CS3W-PB-AG_EN.pdf The 390w panel.

 

[Mattb4]

With a combined VoC of 234vDC (5 X 46.8) from wiring the panels in series you are below the 250vDC max input but by not much. As you mention in vary cold conditions and direct sunlight you could exceed the 250vDC and damage your inverter.

Probably better to go with 4 panels (187.2Voc) or buy another panel to do a 3S2P (140.4Voc) depending on your inverters lower voltage specs.

 

[HRTKD]

Nope. No way would I run 5s with those panels and that solar charge controller. Matt's recommendation is solid. If you can't find another panel then consider a different solar charge controller.

 

[tbaleno]

Thanks guys. It sounds like I did the math right. I will probably buy another panel and go 3s2p. Seems like that would be 259.44v and it would have to be a perfect storm type deal to hit that and it is only 3% over. I suspect the circut has a bit of leway due to variences in part tolerances. So going over by 3% in this situation shouldn't be bad right? It probably would only happen rarely and probably for a short period of time like probably less than an hour since getting temps that low and having the sun out is pretty hard.

 

[HRTKD]

You never, ever want to exceed the Max PV Input Voltage of a solar charge controller. Unless you really like seeing the magic smoke come out.

3s should max out at 194.58 volts if I used your numbers correctly. That's well under the 250 volt limit of the MPPT.

 

[jasonhc73]

I've been using the LV6548s since released. I can confirm that if you have a 265V VOC they will refuse to work, SOMETIMES.

When I first set up the inverters I made 6S strings (12 Panels). The inverters worked fine, until one early day they didn't. The protection on the 6548s is robust and works great. Nothing happened to my 6548s other than the over-voltage alarm came on and they refused to operate.

I rewired the 12 panels, 4s and 4s2p and all is happy. Same 12 panels, same 3.5 kWp. This VOC is 183.2, and the normal operating voltage is 112V to 130V

The LV6548 has to have 80V to startup. You might be able to get by with a 3s and 2s set of strings. If you cannot get another panel to get two strings of 3, I would go with a single 5s string, 229 is your VOC. Yes, the string will make 229V when the sun first starts the day, but the moment the MPPTs pull a load(current) the voltage will probably be in the 155V~180V range.

1 MPPT on 1 LV6548 Inverter
2 STRINGS - 4s and 4s2p, 12 panels 3.5 kWp



2 MPPT on the other LV6548

2 strings, both 5S, 10 panels, 3.4 kWp

Rated Power: 340W
Open circuit voltage (VOC): 45.9 V
Max power voltage (VMP): 38.4 V
Short circuit current (ISC): 9.36 A
Max power current: 8.86
Maximum system voltage: 1500V DC
Fuse Rating: 30 A
IP67 Junction Box with bypass diodes and industry-standard solar connectors
Weight: 22.4 kg (49.4 lbs)
Dimensions: 2000 ˣ 992 ˣ 40 mm (78.7 ˣ 39.1 ˣ 1.57 in)