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Fuses / disconnects / breakers for 2 LV6548 system

Texican

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Feb 8, 2022
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Building a off grid / grid assist system with 2 LV6548 and a bank of 6 EG4 48v batts
using 48 used 250 watt panels. planning 6s2p for 3000 watts to each of the 4 mppt inputs 12kw total
I have a few questions on fuses etc

1. T fuses between inverters and batteries..should I be using 200 amp or 300 ?

2. I have 4 strings of panels, I need 4 dc breakers at 30 amps, what are a lot of you using for this ?

3. A/C input, the inverter manual seems to call for 4ga wire for AC input and output. how many amps are being fed in ? and how is it divided to serve both LV6548s ? separate breakers and wires to each inverter from the main panel ?? should I install a a/c disconnect for the ac input ?

4. what is a shunt ? and do I want or need one ? Ive seen smart shunt that sends battery info


thanks for any advise
 
Building a off grid / grid assist system with 2 LV6548 and a bank of 6 EG4 48v batts
using 48 used 250 watt panels. planning 6s2p for 3000 watts to each of the 4 mppt inputs 12kw total
I have a few questions on fuses etc

1. T fuses between inverters and batteries..should I be using 200 amp or 300 ?
I suggest that you connect the each battery individually to a long set of rack mounted busbars.
Each battery should have class-t fuse as close as possible to the positive terminal of the battery in order to minimize the chance of an upstream short.
I don't trust the built in breaker to quench a dead short.
Each battery should get 4awg pure copper with 105c insulation and a 150 amp class-t fuse.

3. A/C input, the inverter manual seems to call for 4ga wire for AC input and output. how many amps are being fed in ? and how is it divided to serve both LV6548s ?
6500 ac watts / .85 inverter efficiency / 48 volts low cutoff = 159.31 service amps per LV6548.
I would connect each inverter with minimum 2 awg pure copper with 105c insulation and a 200 amp fuse.
Fuse doesn't have to be class-t because you have class-t protection at the source of the most angry pixies.
This fuse is just for fault isolation.


separate breakers and wires to each inverter from the main panel ?? should I install a a/c disconnect for the ac input ?
Is the ac source the grid?
If yes, then won't it be fed from a branch circuit in your master panel?
4. what is a shunt ?
A shunt is a special inline device that measures current.
and do I want or need one ?
Most people would have one for a system of this size.
Ive seen smart shunt that sends battery info
Base on the topology decisions I suggested above I think you should put a shunt on the negative lead for each inverter.
If you want one shunt then we need a common negative for the inverters.
The common negative will have to handle ~350 amps minimum.
 
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thanks Joey
first regarding the T fuses. I have the 6 battery rack with door from sinature solar, it has pos/neg bus bars built in. Am I understanding that I should get 6 T fuses, 1 for each battery ?
 
regarding the AC input, yes it would be fed off a branch circuit from my main panel. I was surprised that the inverter requested 4ga wire and it makes me wonder what the size of this branch off the main panel needs to be to feed both inverters
 
thanks Joey
first regarding the T fuses. I have the 6 battery rack with door from sinature solar, it has pos/neg bus bars built in. Am I understanding that I should get 6 T fuses, 1 for each battery ?
yes
 
Just one, for the entire bank. The batteries, already have individual breakers.
I don't trust those breakers.
I asked their support and he said he would get back with an answer and has not yet replied.
Until he does I will recommend a class t fuse as close as possible to the positive battery terminal.
 
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Thanks Tim. so 1 T fuse for each inverter between it and the batts, and 200 amp is good ?
 
I would bring each inverter feed and the battery bank feed, to a buss bar and install 3 fuses. One fuse for each.
 
1. T fuses between inverters and batteries..should I be using 200 amp or 300 ?
If each inverter is 95% efficient then it will draw up to 6000/.95 = 131.6A when the battery is low (48V).
For the two inverters, it will be 263.2A. The fuse should be 25% larger so 2 x 236.2A = 328.9A. You will probably have to round up t 350A fuses.
3. A/C input, the inverter manual seems to call for 4ga wire for AC input and output. how many amps are being fed in ? and how is it divided to serve both LV6548s ? separate breakers and wires to each inverter from the main panel ?? should I install a a/c disconnect for the ac input ?
The AC input needs to handle all of the pass-through current plus all the current that will be used to charge the batteries.

I do not know what the pass-through rating of the 6548 is, but assuming it is 6KW, that is 60A.
The battery will charge at 120A DC. assuming a 95% efficiency that is 50.5A AC input.

  • The total AC input could be 100A per inverter (You can reduce this by programing the max charge current to something lower than 120A)
  • The Total AC output could be 60A per inverter.
Size your wires accordingly.

4. what is a shunt ? and do I want or need one ? Ive seen smart shunt that sends battery info
A shunt is nothing more that a very low value precision resistor. When current goes through them a voltage shows up across the shunt and this can be used to calculate the current.

This description of the Aili Battery monitor may help explain it:

1646705697479.png

Having a battery monitor is optional. The EG4s have displays that will give state of charge for each EG4 and you can probably use the % state of charge for one of them as a good proxy for the total state of charge. However, if you want to access the SOC from another location, a separate battery monitor might be usefull.
 
thanks Joey
first regarding the T fuses. I have the 6 battery rack with door from sinature solar, it has pos/neg bus bars built in. Am I understanding that I should get 6 T fuses, 1 for each battery ?
Little tip on the rack, typically you'll bring the red wire in on the left bust bar, at the top, and the black to the bottom of the right bus bar. Problem is, the bigger screws on both bus bars are at the top, unless you take one out and flip it over. [the ground / right side] Otherwise you get the batteries all wired up and then realize you can't connect the black to the bottom of the bus bar. Ask me how I know this... :)
 
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