4/0 cable and M6 studs?

MrM1

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I'm about to build up an off grid homestead using a 48v Growatt 12kw and 32 EVE LF280 ah cells.

My estimate is for 250 amps DC. Maybe it's overkill, but I was thinking of using 4/0 cable for going the 6-8 ft between the battery and the inverter.

But then I thought how tiny those M6 studs are on the EVE cells.

Will 4/0 cable play nice with M6 studs? Do I really need 4/0? Maybe I could run it with 2/0?

And what about the AC output terminals on the Growatt? Will they even take 6awg? I was planning to go out to a 50amp double pole ac
 

RobertGreen

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Well, the M6 stud is less of the current path than the rest of the flat face of the round aluminum terminal. There's someone selling soft aluminum washers which are laser cut to fit onto these cells to provide a better contact face.
 

MrM1

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Yeah on the cells I have now those aluminum surfaces aren't very large of a contact area.
 

HRTKD

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I'm running 2/0 cable to M6 terminals, but I have the older EVE 280 Ah cells with larger terminals (drilled, not welded). The 2/0 1/4" lugs work fine for me.

Are you planning a 16s2p or 2p16s battery bank? 250 amps @ 48v is a lot of watts.
 

jtvt

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I use 4/0 with 1/4" lugs with 4 48v banks. So 4 4/0 cables from main pos busbar and 4 4/0 cables to main neg busbar.

IMO, the big thing with 4/0 is you really need some cable support. The cable is a lot of weight and likely there will be some strain due to twisting. I have welded and non-welded studs. There hasn't been a difference between banks.

Make sure you get 1/4" lugs on battery side to maximize surface contact. You can get them made to order.
 

MrM1

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I'm running 2/0 cable to M6 terminals, but I have the older EVE 280 Ah cells with larger terminals (drilled, not welded). The 2/0 1/4" lugs work fine for me.

Are you planning a 16s2p or 2p16s battery bank? 250 amps @ 48v is a lot of watts.
I plan to run two 16s series strings each with it's own BMS (JK/Heltec 200amp) and then put them in parallel at the battery busbar. This will give me essentially 2 working battery packs so if one goes down for maintenance, I still have functioning system.

The inverter is the Growatt SPF 12kw. It has a surge capacity of 19kw. So I am seeing the possibility of a continuous load (rarely but possible) of 12000kw / 48vdc = 250amps with even greater if there was a momentary surge. The Growatt is a a split phase 240vac with 120vac on each L1 and L2. So I believe it to be 6000 watts on each leg (L1 and L2) for a total of 12,000 watts ac.

Do I need 4/0 (0000) battery cable for that? I think maybe. But I'd rather run 2/0 (00) if it will handle the load for less than 10 ft.

I will be using a 250 amp dc breaker between the battery and inverter AND two 250A Class T Fuses and Fuse Holders (one on each series string) before the battery breaker.
 

MrM1

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I use 4/0 with 1/4" lugs with 4 48v banks. So 4 4/0 cables from main pos busbar and 4 4/0 cables to main neg busbar.

IMO, the big thing with 4/0 is you really need some cable support. The cable is a lot of weight and likely there will be some strain due to twisting. I have welded and non-welded studs. There hasn't been a difference between banks.

Make sure you get 1/4" lugs on battery side to maximize surface contact. You can get them made to order.
Thanks. I wonder if for 250amps at less than 10 ft if I even need 4/0. Maybe 2/0 would work?
 

HRTKD

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My preferred wire gauge calculator is offline at this time. The answer I'm getting from other calculators vary. but 2/0 appears to provide a 1% or better voltage loss at 10' for 250 amps @ 48v.

If you know the sustained current will be 250 amps, then you want a circuit breaker rated for 250 x 1.25 = 312.5 amps. Round up to what you can get, to avoid nuisance trips.
 

MrM1

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My preferred wire gauge calculator is offline at this time. The answer I'm getting from other calculators vary. but 2/0 appears to provide a 1% or better voltage loss at 10' for 250 amps @ 48v.

If you know the sustained current will be 250 amps, then you want a circuit breaker rated for 250 x 1.25 = 312.5 amps. Round up to what you can get, to avoid nuisance trips.
Can you post a link to your "preferred wire gauge calculator"? Thx
 

Bleedingblue

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I'm about to build up an off grid homestead using a 48v Growatt 12kw and 32 EVE LF280 ah cells.

My estimate is for 250 amps DC. Maybe it's overkill, but I was thinking of using 4/0 cable for going the 6-8 ft between the battery and the inverter.

But then I thought how tiny those M6 studs are on the EVE cells.

Will 4/0 cable play nice with M6 studs? Do I really need 4/0? Maybe I could run it with 2/0?

And what about the AC output terminals on the Growatt? Will they even take 6awg? I was planning to go out to a 50amp double pole ac


They probably take 6 guage like the MPPs I have but it's a super tight squeeze depending on what brand of wire you use. Also when tightening them up be super super careful because it's plastic and all it takes is finger tightening like 2 ft lbs because those screws will strip out that plastic so easily.

I would use some sort of fuse in between the batteries and 4/0. You can use a distribution block like they use in car audio. Have some 1/0 or 2 guage going to block from batteries fused of course and then the 4/ 0 to distribution block if your dead set on 4/0 then down to 1/0 to battery cable connectors in grow watt. If it can't accept 4/0 those lugs are big. I used 1/0 from MPP to a distribution bar that is fed by 2 runs of 4/0 from battery bank. I'm going to have 6 strings of 280ah. I'm using 6 runs of 4 guage from batteries to copper bar and that copper bar has 2 runs of 4/0 to copper bar and then 4 runs of 4/0 to 4 switches and fuses. Out of switches its 1/0 to 4 MPPs.
That's just the way I did mine.

This isnthe only pic I have in my phone while building it.

20210912_171324.jpg
 

toms

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I would use a solid nickel plated bus bar from the battery terminal to a well mounted single post m8 terminal block. From there you can stack the 4/0 cable to the fuse and there will be no stress on the battery terminal.
 

MrM1

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I'll probable use these between the series stings of batteries and the battery Busbar. Just not sure yet if I'll go 200 or 250 amp

Capture+_2021-10-20-23-18-33~2.png
 

time2roll

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Battery will have two M6 to connect, yes? Maybe a pair of relatively flexible #2 wires from the battery to the bus or the fuse holder.
 

alvirtuoso

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I plan to run two 16s series strings each with it's own BMS (JK/Heltec 200amp) and then put them in parallel at the battery busbar. This will give me essentially 2 working battery packs so if one goes down for maintenance, I still have functioning system.

The inverter is the Growatt SPF 12kw. It has a surge capacity of 19kw. So I am seeing the possibility of a continuous load (rarely but possible) of 12000kw / 48vdc = 250amps with even greater if there was a momentary surge. The Growatt is a a split phase 240vac with 120vac on each L1 and L2. So I believe it to be 6000 watts on each leg (L1 and L2) for a total of 12,000 watts ac.

Do I need 4/0 (0000) battery cable for that? I think maybe. But I'd rather run 2/0 (00) if it will handle the load for less than 10 ft.

I will be using a 250 amp dc breaker between the battery and inverter AND two 250A Class T Fuses and Fuse Holders (one on each series string) before the battery breaker.
A couple of 200a BMS will handle 250a battery load, but what if one of your parallels stops working then you're left with a single 200amp BMS. Just a thought. It's been suggested by people here to derate bms to 60%. Will Prowse prefers 50% more, so I would use 500a BMS each string is the way to go.
 
Last edited:

rmaddy

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A couple of 200a BMS will handle 250a battery load, but what if one of your series stops working then you're left with a single 200amp BMS. Just a thought. It's been suggested by people here to derate bms to 60%. Will Prowse prefers 50% more, so I would use 500a BMS each string is the way to go.
Two 200A BMSes in series will not handle a 250A load. They would have to be in parallel. Then they could handle 400A together.
 

Steve_S

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PLEASE WATCH THIS VIDEO Busbar & Wire Jumper EDUCATION and you really do need to pay attention to this... So many got pooched without understanding why and Ray really covers this point.... AVOID THE ABOVE MISTAKES AS SUGGESTED !


I tested BusBars I've received from Luyuan since Amy took it over. Newest Bars (supplied this summer) at the top to the oldest ones I got last year. Hopefully this will clarify a few questions about causes that can mess with your BMS.

BTW: WE the Collective Seniors on this site, do recommend Derating BMS'.
For FET Based BMS' we generally suggest 20% so a 250A BMS used for a max of 225A.
For Relay/Contactor controlling BMS' 10% derate (with quality) or 20% for cheapo's relays/contactors.

Supplied BusBar Resistance Test.jpg
 
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