Need Help: Solar panels used in two different system with voltage concerns

[Firetodd]

Last year the forum assisted me in setting up a solar system for new 5th wheel. It works great and was able to power both my 5th wheel and my father-in-law's 5th wheel! So now I am building him a system, but we will not be adding solar panels... Here is the background, before I get to the questions:

I have a MPP LV6548 and a 48V 280ah battery with 3500 watts of solar. I have 6 panels on my camper, with 4 more on a patio next to the camper. But sometimes I am not at the lake and he would like to have power and use the 4 panels that are at the lake, when I am not there. He doesn't need much power.

So, I will be building him a system with a Growatt 3000 watt all-in-one and a 24V 230ah battery. This will run his camper. When I am there, it will be supplied by my system and store more solar power that I have not been able to capture as my batteries are full in the early afternoon each day. But when I am not there, he can hook up the mc4 cables from the solar panels on the patio and hook them up to the pigtail I will have connected to his Growatt unit.

The question I have is, the 4 panels (1100 watts) are in a series array so they output 133 volts, which is great for my MPPLV6548. But his Growatt unit lists a solar voltage input rating of 30-115 volts with 145 max. Is this too much voltage?

Also, if it is too high of voltage, could I put something to limit the voltage when it enters his camper, like a buck converter before the Growatt?
Or are my options: get him to add Three 200 watt panels to his roof, or take one panel off my patio array?

 

[sunshine_eggo]

The question I have is, the 4 panels (1100 watts) are in a series array so they output 133 volts, which is great for my MPPLV6548. But his Growatt unit lists a solar voltage input rating of 30-115 volts with 145 max. Is this too much voltage?

30-115 is the MPPT operating range, i.e., where you want your Vmp to fall. If 133V is Voc, then should be about right. If 133V is Vmp, then no. It won't work.

 

[Firetodd]

My panels list a VMP of 38.9 with a VOC of 46.7, so a series of 4 would be VMP of 155.6 and VOC of 186.8 !! But that doesn’t jive with real world numbers I’m seeing on my MPP LV6548.

PV1 Input is the 4s configuration on the patio. PV Input 2 is the 3s2p on my camper.

 

[Firetodd]

I guess I cant just use the 4th panels as-is. What are my options? Hmm

 

[sunshine_eggo]

My panels list a VMP of 38.9 with a VOC of 46.7, so a series of 4 would be VMP of 155.6 and VOC of 186.8 !! But that doesn’t jive with real world numbers I’m seeing on my MPP LV6548.

PV1 Input is the 4s configuration on the patio. PV Input 2 is the 3s2p on my camper.

I trust panel specs over readouts. An MPPT won't often show you Voc.

4S of those panels will destroy the Growatt. For ~150Voc PV input limits, 72 cell panels must be limited to 2S.

There's really very little advantage to having high Voc. MPPT charging actually loses efficiency as the Voc increases.

A permanent reconfig to 2S2P would permit both of you to use the array, though you would have to reconfigure your rooftop as well unless it's on a separate MPPT.

 

[DJSmiley]

You can make a switch which enables to switch between 4S and 2P2S. But that allows for user error. If he forgets so set to 2P2S before connecting, he might fry his Growatt

Other options are a seperate MPPT which charges the batteries (an 40A will do) but lots of them also don't allow >100/150V as well.

Another option is getting another 48V system for the old man as well, and instead of 24V / 230Ah building a 48V / 120Ah pack. That will give you the same setup, more available power, and no issues/risk with the voltages.
Additionally, it allows an easy upgrade in case of more demand in the future.

I think 8x120Ah isn't much more expensive compared to 4x230Ah, and it makes BMS sizing / wires even easier (lower currents)
Not sure about the price difference between a 3k / 24V growatt and a bigger MPP but it might be worth something to have it equally.

(And, in case of problems, easy to diagnose by just swapping inverters)

 

[Ozark Tinkering]

So I've been watching all these folks driving around the country living in their rigs and producing their own power for a long time. Did it myself full-time for over a decade. In recent years y'all have stepped up your game and gone beyond the simple 12-24 vdc system or the genset supplied by the rv manufacterer that were popular just a few years ago and have begun to upgrade to 120vac and higher off-grid portable stand alone systems (Kudos!!!) that actually produce voltage that is deadly to the touch. At that point the NEC should be followed when establishing your grounded neutral and equipment bonding.
In your particular situation I think I would also be asking what are the ramifications to the neutral ground when 2 separately derived sources get combined from an operational safety perspective?
The RVers here might think I'm being silly and often am but anyone running their own powerplant needs to establish a "True Earth Ground". That usually involves driving an 8' ground rod in a residential setting. That close to the water you could likely do it with a 4' rod, imo but testing can be done there too. I'd at least be carrying a 4' ground rod around for setting up my tramp camp.
Here's a conversation about that...

Does Your System Qualify as a "Separately Derived Source"?

Recently there's been a lot of talk around grounding and neutral issues on some of these AIOs coming from China without any UL testing. Here's a start to the conversation that I think any DIYer needs to pay very close attention to prior to embarking on a build that attempts to act as their...

diysolarforum.com

That's a really nice spot, btw!

Last year the forum assisted me in setting up a solar system for new 5th wheel. It works great and was able to power both my 5th wheel and my father-in-law's 5th wheel! So now I am building him a system, but we will not be adding solar panels... Here is the background, before I get to the questions:

I have a MPP LV6548 and a 48V 280ah battery with 3500 watts of solar. I have 6 panels on my camper, with 4 more on a patio next to the camper. But sometimes I am not at the lake and he would like to have power and use the 4 panels that are at the lake, when I am not there. He doesn't need much power.

So, I will be building him a system with a Growatt 3000 watt all-in-one and a 24V 230ah battery. This will run his camper. When I am there, it will be supplied by my system and store more solar power that I have not been able to capture as my batteries are full in the early afternoon each day. But when I am not there, he can hook up the mc4 cables from the solar panels on the patio and hook them up to the pigtail I will have connected to his Growatt unit.

The question I have is, the 4 panels (1100 watts) are in a series array so they output 133 volts, which is great for my MPPLV6548. But his Growatt unit lists a solar voltage input rating of 30-115 volts with 145 max. Is this too much voltage?

Also, if it is too high of voltage, could I put something to limit the voltage when it enters his camper, like a buck converter before the Growatt?
Or are my options: get him to add Three 200 watt panels to his roof, or take one panel off my patio array?

 

[Firetodd]

I guess I’ll either take a panel off the patio, or ask him if we can put some panels on his camper….

 

[sunshine_eggo]

I guess I’ll either take a panel off the patio, or ask him if we can put some panels on his camper….

3S is not safe on that controller unless it's warm. 2S is the only option.

 

[Firetodd]

Argh... My LV 6548 needs at least 90 volts. MPPT range is 90-230. So i have a narrow window of 90-115...

 

[MisterSandals]

It looks like you should have easy access to the MC4 connectors of the 4 panels. Adding/removing a pair of Y connectors is the difference between a 4S and 2S2P array. If this is required only a couple times a year, it would be high on my list of solutions.

 

[sunshine_eggo]

It looks like you should have easy access to the MC4 connectors of the 4 panels. Adding/removing a pair of Y connectors is the difference between a 4S and 2S2P array. If this is required only a couple times a year, it would be high on my list of solutions.

Agree. Reconfig should take about 2 minutes

 

[Ozark Tinkering]

How about this...buy a 24vdc battery charger and when you are there you can charge his battery bank from the ac output side of your 6548? Then wire his growatt 3000 and the 230ah battery in a semi permanent configuration? down and dirty and simple

 

[Firetodd]

How about this...buy a 24vdc battery charger and when you are there you can charge his battery bank from the ac output side of your 6548? Then wire his growatt 3000 and the 230ah battery in a semi permanent configuration? down and dirty and simple

That is what I was planning on doing when I'm there. The problem is when I am not there.

 

[Ozark Tinkering]

Oh okayyy I see I did misread your op...so presently all 10 of the panels in the photo you provided are configured to run your trailer in a parallel configuration to the 6548 and when you aren't there they don't get used at all?

 

[Firetodd]

Yes, the MPP LV 6548 has two separate charge controllers. So I have PV2 connected to the roof port which is wired 3s2p and provides 2100 watts. PV1 is connected to a pigtail. When I get to the lake, I pull the cord out and connect to the 4s panels on the patio and add 1400 watts.