Help with PV wire size on rv! Maybe mistake ?

[Benihanas]

Well, unless the label says Voc should be 18V. That's not what the website shows, but maybe you have a slightly earlier version with different specs. It's tedious to nail down every single detail like this, but as they say the devil is usually in the details.

So I tested this morning in early sun. I get 73 on one and 72 on another. Will test again at noon for hopefully higher readings

 

[Benihanas]

Any chance I’m only getting 18 volts because of the time of year? I’m in south Florida not sure if it would make a huge difference

 

[Vigo]

If you don't plan to upgrade your 40a charge controller to get 'the rest' of the panel capabilities out (in the narrow conditions where it would exceed the 600w it can already do), i wouldn't chase down the last few volts, personally.

 

[Benihanas]

If you don't plan to upgrade your 40a charge controller to get 'the rest' of the panel capabilities out (in the narrow conditions where it would exceed the 600w it can already do), i wouldn't chase down the last few volts, personally.

I’m going to get that 60 amp and see what happens

 

[Doggydogworld]

Any chance I’m only getting 18 volts because of the time of year? I’m in south Florida not sure if it would make a huge difference

Most panels will get close to Voc even at half sun. Temperature has a bigger effect. Can you disconnect a single panel, measure it while pointed straight at the sun and compare it to the actual label on the back? That'd eliminate a lot of guesswork. Otherwise just let us know what happens when you hook up the 60A unit.

 

[Benihanas]

Most panels will get close to Voc even at half sun. Temperature has a bigger effect. Can you disconnect a single panel, measure it while pointed straight at the sun and compare it to the actual label on the back? That'd eliminate a lot of guesswork. Otherwise just let us know what happens when you hook up the 60A unit.

I disconnected each of them this morning and they were reading close to 17.5 / 18 each. Some a bit over.

 

[Doggydogworld]

I disconnected each of them this morning and they were reading close to 17.5 / 18 each. Some a bit over.

Good info. Did you happen to snap a pic of the labels on the back? Besides the voltage and current specs they sometimes have other useful info, e.g. lot numbers, which help in tracking things down.

 

[Benihanas]

Good info. Did you happen to snap a pic of the labels on the back? Besides the voltage and current specs they sometimes have other useful info, e.g. lot numbers, which help in tracking things down.

Can’t get to the bottom of panels but to my recollection they’re the same as the label online. Tech support today backtracked on the claim yesterday. Said my charger might just think the batteries are full and batteries need to be balanced. I guess we’ll see. They said that the charger will cut the PV voltage as well when it needs to slow. They also said reading 18 and up is fine and the VOC is simply the ultimate max that as long as they’re reading at least 18 I should be ok

 

[Benihanas]

Do these renogy people know anything or are they just Throwing out buzz words? Why would I need to balance two lithium batteries with BMS connected in parallel that are working fine ? Wouldn’t they have balanced themselves in the year of use lol

 

[Vigo]

Yeah, from one battery to the other they should be fairly balanced as long as the connections to each are equally good. As far as the cells inside each batt, balancing those is the BMS's job although i've heard some BMS's balance so slowly that they can't accomplish it in the time available when the batteries are constantly in use. So inside the batt could be an issue but even so, it's probably a red herring to bring it up unless the charge controller is actually in communication with the bms's in the first place.

 

[Benihanas]

Yeah, from one battery to the other they should be fairly balanced as long as the connections to each are equally good. As far as the cells inside each batt, balancing those is the BMS's job although i've heard some BMS's balance so slowly that they can't accomplish it in the time available when the batteries are constantly in use. So inside the batt could be an issue but even so, it's probably a red herring to bring it up unless the charge controller is actually in communication with the bms's in the first place.

I tested them and they’re within 10 mv of eachother so probably not the issue. Oh well we’ll get the big boy and update you guys. Appreciate everyone’s help on this!

-ps renogy knows literally nothing about any of their products tech support, customer service etc. you’re best off asking online or looking at pictures because their promotional material is contradictory and vague as well.

 

[RVLiFe]

Update. May be an issue with the charge controller? As soon as I connect the controller to my panels it cuts the voltage from the 70 or so down to about 55. Not sure what the heck is going on. Is this the 13.6 charging the battery? So weird and confusing

Once again, It is common for a MPPT controller to drop the MAX voltage of the panels to provide you with a Max Amperage. Just wanted to show you a picture to prove it. My battery is nearly full but yet the voltage drops and the amperage increases due to the time of the day and the charge curve. Not sure why you are getting so confused about this and faulting the MPPT. A newer one will do the same thing. See the big drop in voltage at the beginning?

 

[Benihanas]

Once again, It is common for a MPPT controller to drop the MAX voltage of the panels to provide you with a Max Amperage. Just wanted to show you a picture to prove it. My battery is nearly full but yet the voltage drops and the amperage increases due to the time of the day and the charge curve. Not sure why you are getting so confused about this and faulting the MPPT. A newer one will do the same thing. See the big drop in voltage at the beginning?

Interesting. You’re running a similar 18vx4 pattern? Ok good to know! I honestly had no clue

 

[RVLiFe]

Interesting. You’re running a similar 18vx4 pattern? Ok good to know! I honestly had no clue

The Watts don’t drop, only the voltage drops a little but that is to optimize the amp output. Volts * Amps = Watts. It doesn’t matter how the MPPT slices and dices the Voltage and Amp numbers as long as it’s giving you the maximum Amp output based off the current Watts that the panels are producing. If your panels are only rated at 8 Amps each and you have four of them, that’s a maximum of 32Amps that they can produce on a perfect day(not just clear skies either, you have to consider the solar radiance in your area as well.)
However, your MPPT will try to give you as many Amps as it can(up to 40). In order to do that, it lowers the voltage to increase the Amps. THAT is the voltage drop you’re seeing. Now, if you have 10 panels capable of 8 amps each, a 40 Amp MPPT isn’t going to be able to maximize the theoretical output of your panels no matter what.

 

[Doggydogworld]

However, your MPPT will try to give you as many Amps as it can(up to 40).

Good info overall, but just to be clear the 40A limit refers to current going to the battery. Amps coming from the panels will typically be lower. Sometimes much lower, depending on panel configuration.

 

[RVLiFe]

Good info overall, but just to be clear the 40A limit refers to current going to the battery. Amps coming from the panels will typically be lower. Sometimes much lower, depending on panel configuration.

Correct!