What amperage for battery wire? Parallel inverters, parallel packs

[CVCPJared]

Ok, so I am trying to get my wire order all sorted out and have some questions regarding wiring size. I will have 5x parallel sets of 16S cells (LF280K) going to a busbar, going to 2x 15kVA Quattros in parallel. What is the wiring sized to? Quattros combined continous is 24kW or ~500a 48v. But peak is 50kW or >1000a 48v. Am I supposed to take the continuous number, spread it across the 5 cables going to the 5 packs (AKA 100a per cable), or do I just assume the full 280a "could" flow across the cable and size to that (i guess if 3 packs were simultaneously disconnected for maintenance)? My cables will probably be around 15-16 feet to the busbar due to CA requiring 3' between batteries and matching cable length.

On that same note, I know I need to not oversize the cables from the busbar to the parallel inverters to increase the resisitance to each inverter, but it's still desirable to oversize from the busbar to batteries correct?

Also, unrelated question but I feel like posting 2 seperate threads is greedy of me being a newbie here lol. The 2 Quattro 15kVA, I plan to run in parallel, 240v 60hz output, into a transformer to get me 2x 120v 100a lines into the main. I had ordered the Victron 100a autotransformer, then recently read only 32a max can be step up or step down, 100a is just the pass-through current allowed (luckily still within the return window). Is there a recommended transformer that others have used for this? I found these online but it's about 10x the size of the Victron and seems possibly commercial/overkill and is $1k more than I was expecting to spend there.

1-Phase 240x480 - 120/240

This transformer converts either 240V 1-Phase or 480V 1-Phase to 120/240V. This unit is great for lighting, CNC machines, and other business machines.

store.maddoxtransformer.com

Thanks in advanced for the advice/help, I really appreciate it!

 

[Brucey]

I had ordered the Victron 100a autotransformer, then recently read only 32a max can be step up or step down, 100a is just the pass-through current allowed (luckily still within the return window).

@sunshine_eggo would have to confirm but that 32A refers to the max neutral current. so you can't exceed 32A difference between the legs. Other than that, you def aren't restricted to 32A overall.

 

[sunshine_eggo]

@sunshine_eggo would have to confirm but that 32A refers to the max neutral current. so you can't exceed 32A difference between the legs. Other than that, you def aren't restricted to 32A overall.

Correct. 100A on the hots, 28/32A on the neutral.

Ok, so I am trying to get my wire order all sorted out and have some questions regarding wiring size. I will have 5x parallel sets of 16S cells (LF280K) going to a busbar, going to 2x 15kVA Quattros in parallel.

I see you're from California. I presume you are in no way subject to or concerned with code compliance. Not only does CA require UL listed components, but you can only select components from the approved list.

Victron EU inverters are not UL listed, nor are your DIY batteries.

What is the wiring sized to? Quattros combined continous is 24kW or ~500a 48v. But peak is 50kW or >1000a 48v. Am I supposed to take the continuous number, spread it across the 5 cables going to the 5 packs (AKA 100a per cable), or do I just assume the full 280a "could" flow across the cable and size to that (i guess if 3 packs were simultaneously disconnected for maintenance)? My cables will probably be around 15-16 feet to the busbar due to CA requiring 3' between batteries and matching cable length.

The manuals give AC and DC wire sizes.

On that same note, I know I need to not oversize the cables from the busbar to the parallel inverters to increase the resisitance to each inverter,

You have stated it backwards. Oversizing the cables would DECREASE resistance to the inverters. Since they are in parallel, the total DC + and - wire length connecting the inverters to the bus bar need to be identical.

but it's still desirable to oversize from the busbar to batteries correct?

Bigger wires never hurt nobody... except on the AC side.

As with DC cables, the AC cables need to be as identical as possible, but it's important they not be oversized.

Please consult line #6 in my signature.

 

[CVCPJared]

@sunshine_eggo would have to confirm but that 32A refers to the max neutral current. so you can't exceed 32A difference between the legs. Other than that, you def aren't restricted to 32A overall.

That's what I thought at first, but I read in the manual that they limited step-up neutral forming voltage to 32a as well, then later saw in a video that limit applied to step-down as well. It would be amazing if the Victron AT still worked for 100a 240v to 200a 120v

 

[sunshine_eggo]

That's what I thought at first, but I read in the manual

what manual?

4. Specifications

www.victronenergy.com

that they limited step-up neutral forming voltage to 32a as well,

Yes.

then later saw in a video that limit applied to step-down as well.

That's technically true, but you may be misinterpreting it. It's a neutral limit.

On a split phase panel, the neutral only carries the imbalance between the two 120V legs.

If you're using 5000W on each 120V leg, you have 0A on the neutral.

What this ultimately means is that your 120V legs can't be more than 32A * 120V = 3840W for 30 minutes and 28A * 120V = 3360W continuously imbalanced.

It would be amazing if the Victron AT still worked for 100a 240v to 200a 120v

Again, It works at 100A on the hots and up to 28A cont/32A 30 min on the Neutral. If you're using 100A on each 120V leg, you're good.

 

[CVCPJared]

I see you're from California. I presume you are in no way subject to or concerned with code compliance. Not only does CA require UL listed components, but you can only select components from the approved list.

Victron EU inverters are not UL listed, nor are your DIY batteries.

I have been issued permits, the datasheets were in the permit application and stamped approved, obviously not to the point of inspection yet though. Eve 280k themselves are UL listed (not BMS tho), and code does say they MAY allow similar standards but didnt require it to be allowed (I can dig it up if that's contestable)

You have stated it backwards. Oversizing the cables would DECREASE resistance to the inverters.

Sorry, I think I double negatived it "I need to not oversize to increase resistance"

Please consult line #6 in my signature.

Yup, got it printed and binded and read through 2x, so naturally I comprehend about 30% so far

 

[CVCPJared]

That's technically true, but you may be misinterpreting it. It's a neutral limit.

Ok, understood. The 32a imbalance rating is on the output side then (120v) from what you're saying. I'm going to assume that # will be broken often. AC/heater, well, water heater when not on heat pump all come in that ballpark alone. I won't be able to tell my wife "wait, let me turn on the toaster before you take a shower".

Is there a general direction for transformers that would not have the 32a limit on neutral?

Thanks again!

 

[CVCPJared]

what manual?

https://www.victronenergy.com/upload/documents/Autotransformer/37571-Autotransformer-pdf-en.pdf

"The transformer itself is equal in both models and has a 32A capacity (peak) and 28A nominal. This is the maximal current that can be used to transfer energy from leg to leg or from 120Vac to 240Vac."

But yeah, you already cleared that up, thank you

 

[Brucey]

Ok, understood. The 32a imbalance rating is on the output side then (120v) from what you're saying. I'm going to assume that # will be broken often. AC/heater, well, water heater when not on heat pump all come in that ballpark alone. I won't be able to tell my wife "wait, let me turn on the toaster before you take a shower".

Is there a general direction for transformers that would not have the 32a limit on neutral?

Thanks again!

Your well and ac and other larger loads are prob 240V loads, where an imbalance won't occur. any remaining large 120V AC loads can be put on opposite legs.

I would put all your diy batteries under a tarp or out of sight and just have a single UL 9540 approved battery with UL mark for inspection. The cell level UL approval is of absolutely no significance for CA or I think any other authority.

 

[CVCPJared]

The manuals give AC and DC wire sizes.

Sorry, I was asking about the size of the wiring from the DIYs to the busbar. I dont see anything in any Victron manuals about the wire size across multiple parallel batteries. I guess I'm asking more what best practice is? Theoretically it should pull fairly equally across all batteries if all connectors/wires are identical, right? I'd hate to get 4/0 welding cable if 2 AWG is sufficient and 1 AWG is sufficiently oversized

 

[CVCPJared]

Your well and ac and other larger loads are prob 240V loads, where an imbalance won't occur. any remaining large 120V AC loads can be put on opposite legs.

Ah, duh Thank you for that. Well...going to have to do some math then I guess

 

[sunshine_eggo]

Same gauge, same length for each battery to bus bar - refer to the aforementioned resource.

I just realized you were confused by Victron's honesty. kVA and kW are the same when power factor = 1. Almost all inverters are rated for kVA even when they say kW.

So you have 2X 15kW inverters.

30,000W / 51.2V / .85 = 689A

689A/5 batt = 138A/batt

That's the absolute minimum assuming your batteries perfectly share the current.

I would allow for 200A per battery with a 250A class-T fuse on each.

 

[Brucey]

I like Windy Nation 1/0 for my batteries. Plenty of margin.

 

[CVCPJared]

689A/5 batt = 138A/batt

That's the absolute minimum assuming your batteries perfectly share the current.

I would allow for 200A per battery with a 250A class-T fuse on each.

Thank you very much, really appreciate this!

 

[zanydroid]

I have been issued permits, the datasheets were in the permit application and stamped approved, obviously not to the point of inspection yet though. Eve 280k themselves are UL listed (not BMS tho), and code does say they MAY allow similar standards but didnt require it to be allowed (I can dig it up if that's contestable)

+1 to being extremely surprised you got a permit approved.

Because California Residential Code specifically calls out UL9540 as required.

I don’t know how you’re going to win a fight about a system level certification like UL9540 being equivalent to the cell level certifications from EVE plus your own design/skills.

NEC requires the inverters to be listed which those are not AFAIK, esp since you are talking about using autotransformer.

I would honestly suggest asking around on some general California homebuilding forum about whether permit approval means all non code compliant stuff apparent in the submission plans is now locked in as legalized. If the approval is conditional you may have taken on some risk of inspector rejecting it.

 

[zanydroid]

Not only does CA require UL listed components, but you can only select components from the approved list.

This is only for grid tie setups AFAIK.

I’ve been operating under the assumption that off grid can use anything, subject only to AHJ

And zero export non NEM has a shot of being approved with non CEC approved components, with some extra approval steps

 

[sunshine_eggo]

I'm concerned that even with approved plans, there's some caveat that doesn't exempt equipment from being listed. I'd bet a nut that the inspector is going to fail you when they can't find the listed labels on the units, and you're going to have an ugly fight on your hands.

 

[CVCPJared]

This is only for grid tie setups AFAIK.

Yeah, this is all off-grid, no NEM, no export, no power pole on the property

They did make me get a CA licensed Engineer stamped approval on the electrical. I think that was their way of saying "we don't fully get this, but if someone with a license will take some level of responsibility for it, OK". Hoping that magical stamp gives me the benefit of the doubt

I'm concerned that even with approved plans, there's some caveat that doesn't exempt equipment from being listed. I'd bet a nut that the inspector is going to fail you when they can't find the listed labels on the units, and you're going to have an ugly fight on your hands.

I go to bed concerned about this every single night, but I hope that you're wrong haha

 

[zanydroid]

What’s the driver for permitting it in presumably a very low density county?

(And that may also be related to why they didn’t check)

 

[CVCPJared]

New house, this will be the only electric to the home so permitting is required for occupancy

 

[sunshine_eggo]

Yeah, this is all off-grid, no NEM, no export, no power pole on the property

They did make me get a CA licensed Engineer stamped approval on the electrical. I think that was their way of saying "we don't fully get this, but if someone with a license will take some level of responsibility for it, OK". Hoping that magical stamp gives me the benefit of the doubt

I go to bed concerned about this every single night, but I hope that you're wrong haha

Me too! Since you got an engineer stamp, I'd be more confident.