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16s Lifepo4 48v - T fuse rating? - ..and bus bar cable awg size?

Spikeuk

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Any advice on the following would be greatly appreciated....

I have inverter running 6000w 48v and have ordered 16s lifepo4 cells 48v to make a diy battery.

System will be used to run computer servers - Initially I will be drawing 1200w of power, hopefully upto max in future as I expand - so want to spec wires/fuse as if its under full load.

Two questions I want to create some flexible bus bars - crimping ring terminals onto wire, and I understand I need to install a t class fuse for protection.

1) What AWG wire should I be using for my busbars?

I was looking at 1/0 AWG? - but I cant find a definitive amp rating? Found a chart showing 1/0 Awg Kapton PTFE Silicone Kapton PTFE Silicone @ 325Amps

but everywhere I look I see different AMP ratings for 1/0 AWG...

Found a ebay listing - 0 GAUGE OFC 65mm² 0 AWG RED POWER CABLE WIRE PER METRE OXYGEN FREE COPPER 400+ AMPS

I just realised that the different amp rating for same size wire is due to more copper strands internally? is this correct? - I think 250amp 1/0 gage wire would work for the busbars?

What size t-class fuse should I use?
6000w/48v = 125a + 25% = 156a so a 200a t class fuse?

Thanks for comments/replies in advance!
 
I have inverter running 6000w 48v and have ordered 16s lifepo4 cells 48v to make a diy battery.

System will be used to run computer servers - Initially I will be drawing 1200w of power, hopefully upto max in future as I expand - so want to spec wires/fuse as if its under full load.

Two questions I want to create some flexible bus bars - crimping ring terminals onto wire, and I understand I need to install a t class fuse for protection.

1) What AWG wire should I be using for my busbars?
By busbars I assume you mean the connects between the cells to make a 16s battery.
6000 ac watts / .85 conversion factor / 48 volts low cutoff = 147.058823529 service amps
147.058823529 service amps / .8 fuse headroom = 183.823529412 fault amps.

I was looking at 1/0 AWG? - but I cant find a definitive amp rating?
Typically the wire we use for this application is fine stranded copper with insulation rated for 105C.
The most common choice is welding cable.
1/0 awg pure copper with insulation rated for 105C is rated for 285 amps as per AYBC standards.

I would use a 250 amp class t-fuse.
I just realised that the different amp rating for same size wire is due to more copper strands internally? is this correct? - I think 250amp 1/0 gage wire would work for the busbars?
Nope its not the strands.
The technical reason for the differences are the temperature rating of the insulation.
The other common reason is disreputable vendors praying on the noobs.
Other reason is different regulatory standards and environmental factors.
Wires can carry more current in free air at 25C ambient as opposed to being stuffed in a conduit with other wires.

What size t-class fuse should I use?
6000w/48v = 125a + 25% = 156a so a 200a t class fuse?
For 1/0 awg I suggest a 250 amp class-t fuse.
The fuse size needs to be larger than the calculated fault current and lower than the wire rating so that the fuse protects the wire and not the other way around.
Since higher rated fuses generally have lower resistance I tend toward the upper bound.
 
Hello @smoothJoey,

I'm also having some difficulties to achieve the cable size from my battery to the inverter.
My system will be used 24/7 as a main source in a house.
At this moment the consume peak was 3000W powered by the grid, but in the future I could have more loads, so let's assume I could need for some hours (4h) 5000W from my inverter.

My system is:
  • Battery: 16s lifepo4 cells 272Ah
  • Inverter: 5600W (Voltronic Axpert MKS IV 5.6KVA)
  • Already bought a T-Fuse - 200A (this was probably a mistake without knowing the cable size)
  • 6x 540W Longi Solar PV

Based on your calculation:
5600 ac watts / .85 conversion factor / 48 volts low cutoff = 137 service amps
137 service amps / .8 fuse headroom = 172 fault amps

Following the Wire Sizing Calculator, this is what I got:
  • Wire Gauge 2|0
1645651553181.png

But based on EXPLORIST.life Wire Sizing Calculator:
  • Wire Gauge 2 AWG

1645651663260.png

From Blue Sea app:
  • Wire Gauge 2 AWG

1645652085219.png

And in from inverter manual:
  • Wire Gauge 2 AWG

1645654763040.png

So, what should I choose?


Thanks
André Magro
 
Hello @smoothJoey,

I'm also having some difficulties to achieve the cable size from my battery to the inverter.
My system will be used 24/7 as a main source in a house.
At this moment the consume peak was 3000W powered by the grid, but in the future I could have more loads, so let's assume I could need for some hours (4h) 5000W from my inverter.

My system is:
  • Battery: 16s lifepo4 cells 272Ah
  • Inverter: 5600W (Voltronic Axpert MKS IV 5.6KVA)
  • Already bought a T-Fuse - 200A (this was probably a mistake without knowing the cable size)
  • 6x 540W Longi Solar PV

Based on your calculation:
5600 ac watts / .85 conversion factor / 48 volts low cutoff = 137 service amps
137 service amps / .8 fuse headroom = 172 fault amps

Following the Wire Sizing Calculator, this is what I got:
  • Wire Gauge 2|0
View attachment 84994

But based on EXPLORIST.life Wire Sizing Calculator:
  • Wire Gauge 2 AWG

View attachment 84995

From Blue Sea app:
  • Wire Gauge 2 AWG

View attachment 84996

And in from inverter manual:
  • Wire Gauge 2 AWG

View attachment 84998

So, what should I choose?


Thanks
André Magro
I'm not going to speak for smooth, but I had been caught up on trying to figure out which cable to go with. I have the 6000 watt version of yours, which is also basically the mpp LVX6048. My inverter manual also said 2 awg. In the end, it basically came down to understanding that going bigger usually isn't going to hurt anything, as long as the physical connection points will fit what you're using. 2 Awg could probably cut it, but the more resistance you have, the more the excess heat is generated. If you have access to 2/0 and you can afford the difference in price, I'd go with 2/0 so you're not pushing the limit. The 200 amp fuse you have will still protect the wire, but a 250 amp wouldn't have hurt. Since you're not using full capacity at the moment, I wouldn't think you'd have any issues with the 200 amp T class fuse.
I'll attach the wire size guide from Temco. Other manufacturers may have different specs, but this is what I used.
Screenshot_20220223-144926_Chrome.jpg
 
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