Over-paneling Victron MPPT controllers.

[Zwy]

If you've got 16, why not 4s2p in 2 home runs back to the inverter /SCC and go one each into pv1 and pv2? Couldn't u then skip the extra SCC?

You're right, Isc is 13.43a x 2=26.86 on PV1 and PV2 each at 198V. Not sure where I came up with over 120a total. Even at 4S4P it would be only 107a.

Thanks.

All same direction unfortunately (design constraints). Two 4s4p arrays, one in to PV1, the other into PV2. 370w panels: voc 47.46 (4s = 190vdc) / isc 11.07 (4p = 44.28).

At 2 times the 4P, that's 177a. Does Ian think it will just clip it off? Or will the SCC be able to feed loads in addition to charging battery bank?

I wish you would write Ian. I'd be curious to hear his response to your query.

It's better bouncing it off you.

What I don't quite understand is the SCC is rated at 3500w per PV1 and PV2. Each of my strings alone comes to 4240w using Isc and Imp (530w x 8). I guess I'll have to ask him.

 

[MrM1]

At 2 times the 4P, that's 177a. Does Ian think it will just clip it off? Or will the SCC be able to feed loads in addition to charging battery bank?

Sorry if I'm not understanding. My math can be fuzzy, but I thought 2 x my 4p would be 88.56a

44.28 from one array and 44.28 from the other array would be 88.56a.

It's also a question mark if the excess can be used for loads. Look back in this thread, I think that has already been debated.

 

[MrM1]

It's better bouncing it off you.

? Bad plan. I know very little. I pretty much just paint by the numbers. So this would be a blind following the blind scenario ?

 

[Zwy]

Sorry if I'm not understanding. My math can be fuzzy, but I thought 2 x my 4p would be 88.56a

44.28 from one array and 44.28 from the other array would be 88.56a.

That would be correct, I took the 88.56 times 2.

It's also a question mark if the excess can be used for loads. Look back in this thread, I think that has already been debated.

I see Hedges questioned the 4000w of charging but unit could convert all of the PV to usable power. And Robert questioned the ability to convert high PV voltage thru the inverter. I didn't see any clear answer on that, my thinking is all PV would need to go thru the SCC before the inverter. Who was the installer where he made the video?

 

[MrM1]

Saw your question on my other thread. I'll wait for some one to respond, but my thought is it does not/cannot use additional power for loads additional is wasted . But that assumes that the panels hit max. To me 'waste' in pv is relative. If it's cloudy, it's not actually wasted and your making a lot more than if you didn't over panel

 

[Zwy]

Saw your question on my other thread. I'll wait for some one to respond, but my thought is it does not/cannot use additional power for loads additional is wasted . But that assumes that the panels hit max. To me 'waste' in pv is relative. If it's cloudy, it's not actually wasted and your making a lot more than if you didn't over panel

At this point, I'm comparing the GW SPF 12000T DPW to 2 MPP LV6548's instead. I actually think you might be better off with the same. LV6548 is high frequency compared to the low frequency 12000T. You can't stack the 12000T, you can stack up to 6 LV6548.

Also, I sent Ian an email, haven't heard back.

 

[MrM1]

I definitely need low frequency with a nice big copper coil and iron core. We will be starting power tools, AC units and pumps so I'd be afraid hi frequency just wouldn't be up to repeated tasks

 

[Zwy]

I definitely need low frequency with a nice big copper coil and iron core. We will be starting power tools, AC units and pumps so I'd be afraid hi frequency just wouldn't be up to repeated tasks

I understand, I do have a well pump to run and I am researching on whether I can use the LV6548 or will need to go with a low frequency inverter. The LV6548 might be a better choice with over paneling however. Combined with parallel up to 6 units makes expansion down the road easier.

I have no intentions of powering my shop with solar at this time. It's a power hog and would require a very large PV array.

 

[MrM1]

You might want to consider an auto transformer if you go HF

 

[ShedLab!]

Mfg Isc limits, i.e. the over-paneling limit, are a function of what device has been tested and certified for. Parts of this testing involves short circuiting or fault testing the internals so the max Isc flows through the connectors and PCBs etc and the unit doesn't burn up. You can imagine what might happen if you have 10x the Isc and then have a shorted FET inside the SCC. Keep in mind that you can perhaps limit the Isc available from of your array by using a fuse.

I suppose there could also be switching transient concerns too when connecting the large array. An appropriately designed fuse may mitigate safety concerns but there's no guarantee about the switching transients because not tested. Could be fine tho.

 

[MrM1]

Mfg Isc limits, i.e. the over-paneling limit, are a function of what device has been tested and certified for.

I believe that is the problem though. Growatt does not publish ISC limits. They merely state max array size as 7000watts with no explanation - which I do not interpret as an Isc limit. To complicate the matter, every vendor (who also serve as tech support for the Growatt 12kw's) and 1 installer of the 12kw unit I have spoken with says Overpaneling is not a problem, it's simply wasted power. I reached out to growatt over a week ago and got no response.

 

[jamiegreen]

Appreciate all the info in this thread, especially the litterature from @FilterGuy Made me wonder a little more about my plan to switch my controller(s) over to victron. Currently I run a single Morningstar Tristar 60a MPPT, which I'm very hesitant to change because it's an amazing bit of kit. But all of my equipment bar that is victron, and I love the integration and for everything to talk to eachother.

I'm currently running an 8s 24v 270ah setup with a 3k Multiplus, and around 2kw of panels (limited to 1.6 by the controller) But I'm definitely thinking of adding another 2.5kw array to combat with long winter weather which I'm struggling in (completely off grid)

I'd want to run a seperate SCC for this, tempted to grab another TriStar 60 but also tempted to sell that and grab 2 150/45 Victrons. My reason for the 45s is I will upgrade to 48v.. at some point, another 8 batteries and a 5k multi ain't cheap!

I don't think it'll be an issue but this thread certainly made me think about whether it's a good thing putting about 2.5kw into each Victron MPPT and letting them limit to around 1.3kw. Having now have time to have a sit down and a proper read through and not just a skim, I'm a little less hesitant, my ISC would never get near the 50a limit of the controller, with 3s3p it would see an absolute max of 30a ISC. Obviously once it's upgrades to 48v it won't be limiting anymore, but it may be a year before then running at 24v.

I'd like to think the victron MPPTs are of a very high standard like the rest of their equipment, admittedly I've read the odd post saying "they wanted into the MPPT game so relabelled a Chinese controller" but I doubt those accusations given their reputation and warranties. I'm not sure they maybe live up to Morningstar's quality but I'd really like the MPPTs to talk to the rest of my system, I'm aware these some coding that can be done to achieve this but that's a bit beyond me. Tough decisions..

 

[SniperX]

Ian says that if you want to overpanel the unit but want to harvest as much PV as possible, it would make more sense to just add another SCC. Makes sense, the inverter is large enough for needs but the SCC is limited on input to 7Kw total. With adding a SC48120 MPV, you add another 6.6Kw at 250V.

Most likely this is the route I'll be taking on my residential system, one GW 48V 12000T MPV with an SC48120 due to over 8Kw of panels. You have to keep under PV 150V max and with larger panels around 50VOC it can make it complicated to keep amps per string down. The GW 48V 12000T MPV I believe is 250V total but each SCC is limited to 145VOC. Ian has 4S listed on 40VOC panels but I think that might exceed to rated MaxVDC says 150V. If you look at the SC48120 MPV, it lists 145V max. My guess is the SCC in both units is the same, with dual inputs.

If you run 4x47V panels in series as he indicates, there might be smoke. I'd surely want to know if it's true or not.

I am about to install my system (same growatt as is being discussed) and I did buy the separate SCC from Ian thinking I would do just what is being suggested here, but I cannot find a diagram on how to insert this extra SCC to the batteries. Will it interfere with the main Growatt 12kw supplying the pv or will it work in conjunction? I may not be understanding how this works together and that is why I am asking for someone to diagram it simply so I can see it. I am more of a visual vs reading.

 

[Zwy]

I am about to install my system (same growatt as is being discussed) and I did buy the separate SCC from Ian thinking I would do just what is being suggested here, but I cannot find a diagram on how to insert this extra SCC to the batteries. Will it interfere with the main Growatt 12kw supplying the pv or will it work in conjunction? I may not be understanding how this works together and that is why I am asking for someone to diagram it simply so I can see it. I am more of a visual vs reading.

The SCC output is simply ran to the battery busbars. I'm currently in the process of adding 2 SCC's to my LV6548's although in my case I won't be using the SCC's in the LV6548's. But it would still be hooked up the same.

 

[Hedges]

Does that use battery BMS to track SoC?
Or does system operate not knowing SoC?

 

[SniperX]

Does that use battery BMS to track SoC?
Or does system operate not knowing SoC?

I have the EG4's with the screen and I bought a solar assistant for monitoring when not around but I have not set this up at all. As I understand it, the growatt can communicate with the EG4 batteries.

 

[SniperX]

The SCC output is simply ran to the battery busbars. I'm currently in the process of adding 2 SCC's to my LV6548's although in my case I won't be using the SCC's in the LV6548's. But it would still be hooked up the same.

Will this interfere with the main growatt inverter? I figured with 6 of the EG4's, I would need at least 6 hours of pv to keep the batteries full and that does not even include any draws so I figured this would help some. Can you come back and post or start another thread and tag me when you do your set-up so I can see? I would really appreciate it.

 

[fafrd]

One thing I almost hate to bring up is that the wording of the Err38/Err39 kinda resurfaces the old debate about damaging an SCC by disconnecting the battery before disconnecting the PV.

I just want to point out that this is exactly what happens whenever BMS protection kicks in.

I fried a grid-tied battery inverter because I did not see / digest the warning to always disconnect AC before disconnecting DC.

If significant DC current was flowing through the inverter to generate AC when connection to battery is disconnected, transistors (or whatever can fry).

It does not say disconnecting the battery first will damage the controller, but it implies it will throw an error.

That was a cheap Chinese inverter and I am pretty sure Victron would have added some protection circuitry to prevent that.

But if an SCC is pushing a high charge current into a battery based on a maximum solar current, when that charge current is abruptly cut off, solar current cannot be stopped instantaneously and internal voltages are likely to increase somewhere while string voltage increases to Voc. Whatever protection circuit has been built is likely to have maximum current and voltage ratings whether based on diodes or transistors or both.

So even for an SCC, I would take any spec on maximum Isc more seriously than any spec on maximum overpanelling in terms of Watts or Imp…

 

[FilterGuy]

I just want to point out that this is exactly what happens whenever BMS protection kicks in.

I fried a grid-tied battery inverter because I did not see / digest the warning to always disconnect AC before disconnecting DC.

If significant DC current was flowing through the inverter to generate AC when connection to battery is disconnected, transistors (or whatever can fry).


That was a cheap Chinese inverter and I am pretty sure Victron would have added some protection circuitry to prevent that.

But if an SCC is pushing a high charge current into a battery based on a maximum solar current, when that charge current is abruptly cut off, solar current cannot be stopped instantaneously and internal voltages are likely to increase somewhere while string voltage increases to Voc. Whatever protection circuit has been built is likely to have maximum current and voltage ratings whether based on diodes or transistors or both.

So even for an SCC, I would take any spec on maximum Isc more seriously than any spec on maximum overpanelling in terms of Watts or Imp…

Victron has said their charge controllers can handle DC disconnect while charging, but some folks say have smoked other SCCs that way

 

[fafrd]

Victron has said their charge controllers can handle DC disconnect while charging, but some folks say have smoked other SCCs that way

That’s what I would have expected of Victron.

But do you agree that their limit on Isc max could be related to the design limits of whatever protection circuitry they implemented?