Class T fuse Size for two LV6548 Controllers - with 4 48v LiFePO4 batteries

[Mark2014g]

Planning on using a Class T fuse, rated at 300a per controller. is this the correct fuse for use with 4 48v LiFePO4 batteries? And will I be able to add two more batteries later with this fuse?

Thanks for any help, getting a little confused on this issue.
Batteries are "48V 100AH LiFePower4 by EG4 "

 

[John Frum]

Planning on using a Class T fuse, rated at 300a per controller. is this the correct fuse for use with 4 48v LiFePO4 batteries? And will I be able to add two more batteries later with this fuse?

Thanks for any help, getting a little confused on this issue.
Batteries are "48V 100AH LiFePower4 by EG4 "

Fuse size is dependent on wire size.
Wire size is dependent on aggregate load or charge ampacity whichever is greater.
Usually its the inverter which determines this.
With a little more info we can get you a better answer.

 

[Mark2014g]

Fuse size is dependent on wire size.
Wire size is dependent on aggregate load or charge ampacity whichever is greater.
Usually its the inverter which determines this.
With a little more info we can get you a better answer.

The wire size is 4 AWG from the Busbar to the LV6548 controller/Inverters. (4 AWG is recommended in the manual.)

Update 6/14/2022 : 4 AWG is NOT Recommended in the manual for battery connection. 1*2/0AWG is the recommended wire size for battery connection. (4 AWG is the recommended wire size for AC Input/Output Connection.)

 

[John Frum]

The wire size is 4 AWG from the Busbar to the LV6548 controller/Inverters. (4 AWG is recommended in the manual.)

6500 ac watts / .85 conversion factor / 48 volts low cutoff = 159.31372549 service amps
159.31372549 service amps / .8 fuse headroom = 199.142156863 fault amps

2 awg with a 200 amp fuse is bare minimum
0 awg with a 250 amp fuse is what I would suggest

Use pure copper wire with insulation rated for 105C.

Since the eg4 batteries have there own breaker you could have the batteries and inverter in parallel on the same pair of busbars and then you only need to fuse the all_in_one circuit.
If you choose to do it this way then use 4 awg wire and a 150 amp class t per battery.

Its now a question of overall topology.

 

[Mark2014g]

Wow, your quick on this stuff! I have two of these LV6548's and will be running them in Split Phase mode. 2P1 and 2P2. I believe I will switch to at least 2 AWG. I'm definitely using pure copper. Batteries will be in Parallel.

 

[Mark2014g]

Since the eg4 batteries have there own breaker you could have the batteries and inverter in parallel on the same pair of busbars and then you only need to fuse the all_in_one circuit.

I think since I'm using them in Split Phase mode, I'll have to fuse each inverter.

 

[John Frum]

It all depends on topology.
Have you decided on a topology?
That will determine the over-current protection.
Will you being using a shunt based battery monitor?

 

[CamoGreg]

I think since I'm using them in Split Phase mode, I'll have to fuse each inverter.

I think so. A class T fuse close to the bus bar and one for each inverter.

Would you need another Class T close to the battery positive terminal?

 

[wayne530]

6500 ac watts / .85 conversion factor / 48 volts low cutoff = 159.31372549 service amps
159.31372549 service amps / .8 fuse headroom = 199.142156863 fault amps

2 awg with a 200 amp fuse is bare minimum
0 awg with a 250 amp fuse is what I would suggest

Use pure copper wire with insulation rated for 105C.

Since the eg4 batteries have there own breaker you could have the batteries and inverter in parallel on the same pair of busbars and then you only need to fuse the all_in_one circuit.
If you choose to do it this way then use 4 awg wire and a 150 amp class t per battery.

Its now a question of overall topology.

If you have 2 or more inverters connected in parallel with the battery bank, it makes sense that the connection from the bus bar to the inverter should be as you suggested, assuming the topology is battery bank -> bus bar -> fuse -> inverter. How would you go about sizing the conductor from the battery bank to the bus bar, since in theory it might need to carry 2x (or n times, depending on how many inverters) the max current? To make it more concrete, if we use this example of 2x LV6548 in parallel with the battery bank, does that mean the conductors from the battery bank to the bus bar must be capable of carrying 318.6 service amps and that the bus bar must be rated for > 318.6A? If that's the case, would it be recommended to use 0 awg from the bus bar to the fuse and the fuse to the inverter, while using 2/0 for battery bank to bus bar? Apologies if this has been asked before and feel free to point me to existing resources that answer this question! Thanks in advance!

 

[John Frum]

If you have 2 or more inverters connected in parallel with the battery bank, it makes sense that the connection from the bus bar to the inverter should be as you suggested, assuming the topology is battery bank -> bus bar -> fuse -> inverter. How would you go about sizing the conductor from the battery bank to the bus bar, since in theory it might need to carry 2x (or n times, depending on how many inverters) the max current? To make it more concrete, if we use this example of 2x LV6548 in parallel with the battery bank, does that mean the conductors from the battery bank to the bus bar must be capable of carrying 318.6 service amps and that the bus bar must be rated for > 318.6A?

318.62745098 service amps / .8 fuse headroom = 398.284313725 fault amps.
The main wire from the battery to the busbar needs to be able to handle 400 amps minimum.
The main fuse should be 400 amps.
The busbar needs to be able to handle 400 amps minimum.

If that's the case, would it be recommended to use 0 awg from the bus bar to the fuse and the fuse to the inverter, while using 2/0 for battery bank to bus bar?

4/0 awg pure copper wire with insulation rated for 105c is the minimum for the battery to busbar connections.
Depending on your batteries I would suggest a different topo.
What batteries are you using?

 

[wayne530]

318.62745098 service amps / .8 fuse headroom = 398.284313725 fault amps.
The main wire from the battery to the busbar needs to be able to handle 400 amps minimum.
The main fuse should be 400 amps.
The busbar needs to be able to handle 400 amps minimum.


4/0 awg pure copper wire with insulation rated for 105c is the minimum for the battery to busbar connections.
Depending on your batteries I would suggest a different topo.
What batteries are you using?

6 48V EG4s. There isn't a lot of space in the cabinet to add a fuse for each battery, but I saw another recent thread about whether the BMS disconnect/breaker built into the EG4s might be sufficient without fusing each battery. I'd love your thoughts though if there's a better topology I should consider. Thanks!

 

[John Frum]

6 48V EG4s. There isn't a lot of space in the cabinet to add a fuse for each battery, but I saw another recent thread about whether the BMS disconnect/breaker built into the EG4s might be sufficient without fusing each battery. I'd love your thoughts though if there's a better topology I should consider. Thanks!

@RichardfromSignatureSolar has successfully dead short tested the breaker.
No additional over-current protection is required for these batteries.

Here is the topo I suggest.
There first functional block is a legend that describes all the primitives.
The basic idea is the whole system hangs off positive and negative busbars.

dc_domain {
    busbar.positive {
        004|UUU|<->battery.1.positive
        004|UUU|<->battery.2.positive
        004|UUU|<->battery.3.positive
        004|UUU|<->battery.4.positive
        004|UUU|<->battery.5.positive
        004|UUU|<->battery.6.positive
        002|200|<->inverter.1.positive
        002|200|<->inverter.2.positive
        016|001|->shunt.positive
    }
    busbar.negative {
        4/0|UUU|<->shunt.negative.line
        004|UUU|<->battery.1.negative
        004|UUU|<->battery.2.negative
        004|UUU|<->battery.3.negative
        004|UUU|<->battery.4.negative
        004|UUU|<->battery.5.negative
        004|UUU|<->battery.6.negative
        002|UUU|<->inverter.1.egc
        002|UUU|<->inverter.2.egc
        002|UUU|<->premesis_bond
    }
    shunt {
        positive@
        negative {
            line@
            load {
                002|UUU|<->inverter.1.negative
                002|UUU|<->inverter.2.negative
            }
        }
    }
}

 

[wayne530]

@RichardfromSignatureSolar has successfully dead short tested the breaker.
No additional over-current protection is required for these batteries.

Here is the topo I suggest.
There first functional block is a legend that describes all the primitives.
The basic idea is the whole system hangs off positive and negative busbars.

legend {
    {} { functional block }
    nnn|NNN| { fused busbar position where nnn is the wire guage in awg and NNN is the fuse rating in amps }
    nnn|UUU| { un-fused busbar position where nnn is the wire guage in awg }
    <-> { bi-directional current flow }
    -> { uni-directional current flow }
    <- { uni-directional current flow }
    @ { back reference
}
dc_domain {
    busbar.positive {
        004|UUU|<->battery.1.positive
        004|UUU|<->battery.2.positive
        004|UUU|<->battery.3.positive
        004|UUU|<->battery.4.positive
        004|UUU|<->battery.5.positive
        004|UUU|<->battery.6.positive
        002|200|<->inverter.1.positive
        002|200|<->inverter.2.positive
        016|001|<->shunt.positive
    }
    busbar.negative {
        4/0|UUU|<->shunt.negative.line
        004|UUU|<->battery.1.negative
        004|UUU|<->battery.2.negative
        004|UUU|<->battery.3.negative
        004|UUU|<->battery.4.negative
        004|UUU|<->battery.5.negative
        004|UUU|<->battery.6.negative
        002|UUU|<->inverter.1.egc
        002|UUU|<->inverter.2.egc
        002|UUU|<->premesis_bond
    }
    shunt {
        positive@
        negative {
            line@
            load {
                002|UUU|<->inverter.1.negative
                002|UUU|<->inverter.2.negative
            }
        }
    }
}

Thanks, I'll investigate this further! I had come up with the original topology because the cabinet housing the batteries has built-in bus bars so it felt easier to treat the cabinet is one big DC source as opposed to individual batteries. I do like eliminating the 4/0 run on the positive side though.

 

[John Frum]

Thanks, I'll investigate this further! I had come up with the original topology because the cabinet housing the batteries has built-in bus bars so it felt easier to treat the cabinet is one big DC source as opposed to individual batteries. I do like eliminating the 4/0 run on the positive side though.

Someone mentioned that the feeders on both busbars are on top.
The solution is to re-install one of the busbars rotated 180 degrees so that the path resistance is equal across both the batteries.
In other words connect the inverters to the busbars at opposite ends.

 

[wayne530]

Someone mentioned that the feeders on both busbars are on top.
The solution is to re-install one of the busbars rotated 180 degrees so that the path resistance is equal across both the batteries.
In other words connect the inverters to the busbars at opposite ends.

Yep, I (thankfully) read that in another thread and I installed the negative bus bar upside down. I might rotate them in your topology though since that would shorten the 4/0 run. Thanks again for the suggestions!

 

[John Frum]

Yep, I (thankfully) read that in another thread and I installed the negative bus bar upside down. I might rotate them in your topology though since that would shorten the 4/0 run. Thanks again for the suggestions!

My pleasure.
Please share pics when done.

 

[THISISME]

Hello,

I don't intend to hijack this thread, but my questions are very similar to this topic without starting a new topic. My question is sizing the T class fuses. and or circuit breakers. I've read a lot, watched a lot of videos, and still don't have a clear understanding. I watched Wills video where he installed the same inverters with 150amp marine breakers, but since he increased his batteries he re-wired his setup with T class fuses but didnt really go over any details on how it was set up. My system will be this: 2 x LV6548s wired in parallel for split phase output. My batteries will be 2 banks of 48V 304AH EVE DIY batteries. combined in parallel for a total of 608AH. Ihave a Victron 500AMP SMartshunt to connect from the main Battery negative lead to the negative bus bar. I will have a 600amp bus bar for both negative and positive connections. My solar panels are 390w bifacial Canadian Solar with Max Voc of 46.8Vs and max circuit amps of 10.74. they will be wired in series of 5 for 234V or 3900w(possibly 4 depending on actual total volt output). 20 panels total will be hooked up (10 for each inverter). I'm a complete solar noobie but not a stoopy. I'm just confused on how to measure my current draw.
I'll plan to use for my system to power a travel trailer off grid as well as some GPU miners drawing about 15-20 amps. My travel trailer requires a 50amp hookup with 2x 15k btu a/c units, plus some other odds and ends. at full draw the trailer will be around 40amps(not constant). I plan to only GPU mine during the day while I have actual solar power. My confusion is if you have to go up in fuse or breaker size when you go up in battery AH size? Or because the system power of 6500w / .8 /48 is constant then a 250amp fuse on each inverter will be fine?

1. WIll I need a fuse or circuit breaker between batteries before shunt?
2. What size circuit breaker or T class Fuse for this setup. I'm guessing single 600amp t fuse or 2x300amp for each bank of 48v batteries?
3. I'm estimating 2/0 ga welding wire from batteries to bus bar is this correct?
4. planning to expand the system for whole home and mining once I get house built

 

[John Frum]

My confusion is if you have to go up in fuse or breaker size when you go up in battery AH size?

Fuse ampacity is based on the maximum load.
For most systems that is the continuous rating of the inverter.
For you setup
6500 ac watts / .85 inverter efficiency / 48 volts low cutoff = 159.31372549 inverter amps
159.31372549 inverter amps / .8 fuse headroom = 199.142156863 fault amps.

That means each inverter circuit should have minimum 2 awg with a 200 amp fuse.
If it were me I would use 1/0 awg and a 250 amp fuse for each inverter circuit.

Based on the above we can determine that you you battery subsystem will need to supply 318.62745098 service amps.
The details depend on the exact system topology.
318.62745098 service amps is a big deal.
What batteries are you planning for and how many?

The often overlooked fuse parameter is AIC=arc interrupt capacity.
Since LFP batteries can dump so much energy into a dead short we often suggest class-t fuses as they have a very high AIC rating.

1. WIll I need a fuse or circuit breaker between batteries before shunt?

No.
The shunt goes between the main battery negative and the rest of the system.
Orthodox design has the fuses on the positive side of the circuit.

2. What size circuit breaker or T class Fuse for this setup. I'm guessing single 600amp t fuse or 2x300amp for each bank of 48v batteries?

Depends on the batteries and topology.

3. I'm estimating 2/0 ga welding wire from batteries to bus bar is this correct?

Depends on the batteries, topology and fuse size.

4. planning to expand the system for whole home and mining once I get house built

You should consider the final form during the design phase.

The first issue I see is the BMS.
What BMS are you planning to use?
You need BMSs that can handle at least ~160 amps each.
We can figure out a topo for you after we figure out your bms solution.

 

[THISISME]

What batteries are you planning for and how many?

My batteries will be 2 banks of 48V 304AH EVE DIY batteries. combined in parallel for a total of 608AH.

The first issue I see is the BMS.
What BMS are you planning to use?

I order 2x 16S 100amp BMS from overkill solar but now I see that wont be enough. I'll have to order the Daly 200amp from amazon. I wasnt able to find another option on a quick search.

 

[John Frum]

My batteries will be 2 banks of 48V 304AH EVE DIY batteries. combined in parallel for a total of 608AH.

I suggest this topo using a lynx power-in that is hacked to have 2 fused positions and 2 un-fused.

Lynx Power In - Victron Energy

Connect batteries to the Lynx DC distribution system with the Lynx Power In, a modular DC busbar. Find a dealer nearby.

www.victronenergy.com

legend {
    {} { functional block }
    nnn|NNN| { fused busbar position where nnn is the wire guage in awg and NNN is the fuse rating in amps }
    nnn|UUU| { un-fused busbar position where nnn is the wire guage in awg }
    <-> { bi-directional current flow }
    -> { uni-directional current flow }
    <- { uni-directional current flow }
    @ { back reference }
}
dc_domain {
    busbar.positive {
        1/0|UUU|<->250amp_class_t<->battery.1.positive
        1/0|UUU|<->250amp_class_t<->battery.2.positive
        1/0|250|<->inverter.1.positive
        1/0|250|<->inverter.2.positive
        016|001|->shunt.positive
    }
    busbar.negative {
        4/0|UUU|<->shunt.negative.load
        1/0|UUU|<->battery.1.negative
        1/0|UUU|<->battery.2.negative
        1/0|UUU|<->inverter.1.egc
        1/0|UUU|<->inverter.2.egc
        1/0|UUU|<->premesis.bond
    }
    shunt {
        positive@
        negative {
            line@
            load {
                1/0|UUU|<->inverter.1.negative
                1/0|UUU|<->inverter.2.negative
            }
        }
    }
}