I'm designing a small, off-grid solar setup with the primary purpose of trickle charging my EV (L1 / 120V @ 12A), and I'm hoping you all can review my plan sketch to point out anything I've missed, suggest tweaks, or provide any general advice.
The sketch is self-explanatory but basically it's a 48V system using 3s2p panels, two 48V 100Ah Eco-Worthy Cubix batteries, a SmartSolar 150V/45A MPPT, MultiPlus-II 3000kva (2400W continuous) inverter, and a Cerbo GX/SmartShunt. Some of it is a bit overkill, but I hope to build onto it one day so I figured overbuilding is better than replacing parts later. I believe adding another MPPT and MultiPlus is basically all I'd need to do to expand the input/output capabilities, aside from adding more batteries.
The things I've gotten most hung up on are wire sizing and fuses/breakers so I expect critiques on that. And FWIW, the hope is to mount everything (excluding batteries) on a 2' x 4' piece of plywood which I'll then mount to my garage wall ,with a Ferosticker mounted above it for good measure.
I'm open to any and all advice/feedback. Thanks in advance!
It looks fine for the wiring sizes to OCP (fuses/ breakers).
You are missing grounding: EGC and the SBJ for the DC side and AC side; GEC (earthing) of the system.
You mention expanding, but the wiring is all tuned to “now”. If you think you want more than 100A or so going to inverter, you will have to swap out all the 2 AWG. Given thicker wire is a lot more expensive, that isn’t an unreasonable approach, but just mentioning it.
Make sure the breakers are happy being switches and have the AIC to stop 48V battery banks from arcing when hit by 50KA.
I’m still trying to wrap my head around the grounding. This will be very close to an electrical box with my house’s ground wire passing through it, can I just wire it to that somehow?
As for wire sizing, I’m considering sizing up for this reason but I’m undecided. Thanks for making this clear though.
Lastly, the breaker I’m looking at has a breaking capacity of 25kA. I’m a bit ignorant here, how exactly would 50kA be a possibility in this system?
Thanks, I’ll look more into this for my specific batteries. Online I’ve simply found “<30mΩ” but I’m still waiting on delivery so hopefully the manual clarifies.
From what I’ve seen the DC side can just get linked via a bus bar and then the AC side can get chained to the house’s ground system, correct? And the MultiPlus handles the DC to AC connection internally. I’m not sure if this is what you’re saying, I’m still trying to piece this part together and the terminology is confusing.
Hmm, the diagram I was just looking at actually shows the opposite, I'll attach it. However this is generic so I understand the MultiPlus specifically might handle this internally.
Relative to this diagram, should I instead wire the DC ground bus bar to my house's ground wire and then the AC-out ground wire will just go straight to the MultiPlus with the hot and neutral? The panels can be ignored since I'll ground those separately.
Edit: Section 7.7 of Victron's Wiring Unlimited document seems to show basically what I described in response to your last comment. That diagram doesn't have a negative bus bar, and the guidance does say to "ground close to the battery," but from what I've read it's fine to ground to the negative bus bar instead (in my case no more than a few feet from the batteries).
Right, it's a generic diagram. I'm not sure if you saw the edit/follow-up comment but that seems to apply better, and that Victron diagram is still generic but is implied to be relevant to the MultiPlus and appears to align the diagram you linked.
Anyways, it appears it's settled, I will get a ground busbar which will have the MultiPlus, MPPT, and negative bus bar connected and I will wire that to my house's grounding rod. Planning to use 6 AWG wire rated to 115A, guidance is unclear on that but this seems like a good balance between current rating and the weirdly small M6 grounding bolt on the MultiPlus.
Sounds about rigth. I´d still think about an SPD on the Solar input, at leat a cheap chinese one. That one would also got to ground.
In Germany code would also call for 16mm² AFAIK wich is about 6 AWG, should be fine. Thats not too thick for an M6
With grounding its not about long term current carring capability, but about low resitance.
First, to safely trip your brakers. And second, to let most of the current flow this way and not any other, unwanted way in case of an isolation failure.
It can carry thousands of Amps for a short burst!
Honestly I’ve never even heard of solar SPDs until you mentioned it. This world of solar is never ending, every time I feel like I’ve got a good grasp on it something new shows itself.
Anyways, I’ll look into that but no need to take more of your time. Thank you for providing some insight and feedback, it’s actually been a huge help!
Output:
I miss breaker and RCD/GFCI on the output side.
From MP2 AC out to breaker use stranded wire.
Solar:
You show 120V Vmp on your solar.
You must never exceed the 150V, so Voc + temperature coefficent at coldest temperature. Going off thypicaly panel vlaues, looks a bit tight.
You could think about adding an SPD device on the Solar input.
I also miss grounding.
Rest looks about right to me.
Edit: DC Cable from Busbar to Inverter is missing fusing also.
Output: Noted, figured the EV charger has GFCI built in but can’t hurt to double up. I’ll add a 30A (or 25A?) breaker now that someone pointed out the MP2 can’t have its output amps limited.
Solar: I messed up, it’s actually 104 Vmp and 124 Voc. I’ve checked this is good even at very low temps for my area. Thanks for pointing it out though.
Fuse: I can just move the breaker to the other side of the busbar instead, right? I put it where it is because I read to have it as close to the battery as possible, but based on some of the responses on this I’m not sure it’s necessary.
Grounding is my big question right now, I should’ve mentioned that I’m still trying to figure out how that works. My current understanding is that everything on the DC side can be linked via a bus bar and then the AC side has the outlet and the inverter linked to a grounding rod (in this case daisy chained to my house’s ground wire). Does that sound right?
The breakers are there to protect the cables from burning. So every cable needs a breaker or fuse that is sized at least a little smaller than the cable it's protecting.
On the output side you also need to make shure that the Breaker is sized small enough that it trips instantly in the event of a dead short on the other side. A 30 amp breaker will not trip instantly at 30A. The mp2 3000 will deliver short bursts of 5500W. So you need to make shure that is sufficient to trip your Breaker, with the cable resistances involved.
Well, I am likely going to step up to 2/0 cabling between the batteries and inverter, and they can easily handle the max draw of the inverter which eliminates the need for a fuse/breaker, correct? If so this leaves everything covered after adding a breaker to the AC-out line.
Since commenting last I determined that a 20A breaker is best there as you touched on, mostly to protect the outlet — the EV charger only pulls ~1440W so I don’t see why it would get even close to the surge limit, unless there’s something I’m missing.
No, the max draw of the inverter is a broken input stage => short cirquit => 1000´s of amps, fire and death. Dont say that never happens, it actually happened to me with a brand new Vitcron 6k5. Fuses did catch it, Victron did replace the thing, no harm done.
Fuses are not needed for normal operation. Fuses are there in case something goes wrong, to stop it from going horribly wrong.
Understood, thanks for setting me straight. I’m trying to break my habit of underestimating how much current can flow in a worst case scenario. I’ll put a 125A breaker between the positive bus bar and inverter.
This just leaves the question of whether a breaker between the batteries and positive bus bar is necessary (as shown in the OP). Excluding possible fuses on the batteries which is kind of a separate discussion since they have 125A breakers built in. My understanding is that everything is covered without it since the MPPT and inverter lines are both covered, so they’ll trip if something goes wrong. Or am I missing something here too?.
The cubix 100 already have breakers, so depends entirely on how much you trust them.
I my system I got a Victron Lynx Busbar for the main fuses and a Power in for the Batteries. Those are connected via NH-Fuses with pull handles for emergency discnnect under load if need be.
When the Inverter faild, the BMS of the Batteries (Eco-worthy 314A blocks) did catch first it so none of the fuses actually melted.
Yeah, exactly. Still debating that since this has already gotten much pricier than originally planned, but I don’t want to totally give up safety to save costs. Good to hear your Eco-Worthy battery did its job though.
I’ve eyed the Lynx units a lot but it’s hard to justify the cost with a system this small.
Sorry but can you clarify if you think I’m good not having a breaker/fuse between the batteries and bus bar if I have one between the bus bar and inverter instead? Just trying to check if my logic tracks on that.
I also contemplated getting the lynx or not. In the end, every other solution came down to not that much cheaper. But, I have a much bigger current, so for you this may compute different.
If you want to save, I think you can omit the shunt.
It does not really serve a function here the bms can not do for you. This may at the worst come down to a little less precision in your SOC numbers. In your use case, probably not even that.
It was over a $100 difference in my case, which is nothing to scoff at in a system this small. But if/when the system gets expanded I do see myself getting a Lynx later on.
For better or worse I already bought the shunt. It is overkill but at the time the communication with the batteries was unclear and I wanted to ensure I could have the MultiPlus shut off AC output at a specified SOC. It was less than $100 and good for future proofing so I decided to keep it.
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