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Questions on wire/fuse between batteries and inverter

jsl10

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Building new solar setup... Have four EG4 LifePower4 48V 100AH batteries connected in parallel in a rack. I also have a Growatt 12kW 48V off-grid inverter. I've completed the A/C connections on inverter. So now it's time to connect the battery array to the inverter. A few quick questions...

1) I'm planning A/C draw from inverter to be about 6kW (240V). On the battery side (say 50V to make math quick), would that translate to 120 Amp so maybe a 150A Class T fuse?

2) Part of my power draw is a well with a quick in-rush current of about 73A at 240V. Does that short lived in-rush current translate to a short lived current draw exceeding the 150A current from question 1? (73A*240V)/50V = 350A! Or does in-rush current not factor in?

3) What gauge wire from battery bank to inverter? The manual says 3*2 gauge. I assume this means THREE sets of 2 gauge wire for each connection? That's probably assuming running the inverter at absolute maximum. Would 2 sets of 2 gauge wire be adequate? Or is 1 set of wires enough?

4) While I figure out the wire/fuse and get it ordered, would it be ok to just use some 10 gauge Romex I have to TEMPORARILY hook the batteries to the inverter (WITHOUT ANY INVERTER LOAD)? I just want to power up the inverter so I can take some time to setup it's settings, wifi, etc. while I wait for the permanent wire and fuse. I think the inverter only draws 250V when no load.
 
For some high inrush currents a slo-blo fuse is recommended.

Some HVAC equipment without the "soft-start" option asks for special panel breakers.

The trick for any fuse/breaker is to let thru the high but normal inrush current but still decide if the current is excessive for too many milliseconds.
 
Building new solar setup... Have four EG4 LifePower4 48V 100AH batteries connected in parallel in a rack. I also have a Growatt 12kW 48V off-grid inverter. I've completed the A/C connections on inverter. So now it's time to connect the battery array to the inverter. A few quick questions...

1) I'm planning A/C draw from inverter to be about 6kW (240V). On the battery side (say 50V to make math quick), would that translate to 120 Amp so maybe a 150A Class T fuse?
I'm assuming that the battery rack has busbars down the sides.

12000 ac watts / .85 conversion factor / 48 volts = 294.12 service amps
294.12 service amps / .8 fuse headroom = 367.65 fault amps
I suggest you fuse each battery individually as close to the positive terminal as possible with 150 amp fuse.
That means each battery gets 4 awg pure copper wire with insulation rated for 105C.
2) Part of my power draw is a well with a quick in-rush current of about 73A at 240V. Does that short lived in-rush current translate to a short lived current draw exceeding the 150A current from question 1? (73A*240V)/50V = 350A! Or does in-rush current not factor in?
One or more of the bms might trip but I doubt it.
The fuses won't care.
3) What gauge wire from battery bank to inverter?
4/0 awg pure copper with 105C insulation and 400 amp fuse as close to the start of the branch as possible.
The inverter should tap the busbars at opposite ends to balance the resistance across the batteries.
The manual says 3*2 gauge. I assume this means THREE sets of 2 gauge wire for each connection?
Probably, but that is weird way to do things.
That's probably assuming running the inverter at absolute maximum. Would 2 sets of 2 gauge wire be adequate? Or is 1 set of wires enough?
As above 1 * 4/0 awg is fine for the inverter circuit.
4) While I figure out the wire/fuse and get it ordered, would it be ok to just use some 10 gauge Romex I have to TEMPORARILY hook the batteries to the inverter (WITHOUT ANY INVERTER LOAD)? I just want to power up the inverter so I can take some time to setup it's settings, wifi, etc. while I wait for the permanent wire and fuse. I think the inverter only draws 250V when no load.
Every wire should be fused no higher than 30 amps.
 
Just to be clear each battery should be connected to the busbars individually.
I don't suggest daisy chaining the batteries.
 
1) I'm planning A/C draw from inverter to be about 6kW (240V). On the battery side (say 50V to make math quick), would that translate to 120 Amp so maybe a 150A Class T fuse?
This has been answered pretty good. The only thing I’ll add to what you said is you will need to shut the microwave off when the AC is running and VIce versa.

On a 24 volt system I have 4/0 wire and a 225 amp CLass T for a 3000 watt inverter.
The manual says 3*2 gauge
Do you think that meant 3 pair 2 gauge wire? There is ROmex that comes with a 4th bare ground wire and this three pair SOOW. I found wire hunting for my inverter AC side pretty frustrating. My inverter accepts up to 8 AWG for 3000 watts Onthe AC side.
690CC2E9-9A6C-4013-B0B3-5CF3395BE5C1.jpeg
 
perhaps I didn't read properly, but how else can you make a series arrangement of cells (say, taking 12V to 48V)

The batteries are 48 volt rack mount.
They just need to be sensibly paralleled.
 
To answer the questions above...

o Yes, each battery has it's own set of wires that connect to two busbars in the rack. The busbars have heavier (room for three) connection bolts for the combined power to go to inverter.

o Each battery has it's own built-in 100A breaker.
 
To answer the questions above...

o Yes, each battery has it's own set of wires that connect to two busbars in the rack. The busbars have heavier (room for three) connection bolts for the combined power to go to inverter.

o Each battery has it's own built-in 100A breaker.
Dont trust the breaker until the company behind it does.
Add a class-t fuse as close to the positive terminal as possible.
If/when @RichardfromSignatureSolar says that breaker is guaranteed to protect against a dead short then its ok to forgo the class-t fuse.
 
@jsl10 Forgot to mention voltage drop as a factor in determining wire size.
If the all_in_one is more than a few away from the battery rack then we need to be factored.
Here is a calculator to address voltage drop https://baymarinesupply.com/calculator
The battery rack is literally right in front of and below the inverter (which is mounted to the wall). So even with some extra wire length for looping around it's probably no more than 4-5 feet of wire length.
 
The battery rack is literally right in front of and below the inverter (which is mounted to the wall). So even with some extra wire length for looping around it's probably no more than 4-5 feet of wire length.
Lets call that 12 feet round trip.
According to the calculator the voltage drop is 0.38% which is excellent.
The constraint in your use case is dominated by amperage.
 
Building new solar setup... Have four EG4 LifePower4 48V 100AH batteries connected in parallel in a rack. I also have a Growatt 12kW 48V off-grid inverter. I've completed the A/C connections on inverter. So now it's time to connect the battery array to the inverter. A few quick questions...

1) I'm planning A/C draw from inverter to be about 6kW (240V). On the battery side (say 50V to make math quick), would that translate to 120 Amp so maybe a 150A Class T fuse?

2) Part of my power draw is a well with a quick in-rush current of about 73A at 240V. Does that short lived in-rush current translate to a short lived current draw exceeding the 150A current from question 1? (73A*240V)/50V = 350A! Or does in-rush current not factor in?

3) What gauge wire from battery bank to inverter? The manual says 3*2 gauge. I assume this means THREE sets of 2 gauge wire for each connection? That's probably assuming running the inverter at absolute maximum. Would 2 sets of 2 gauge wire be adequate? Or is 1 set of wires enough?

4) While I figure out the wire/fuse and get it ordered, would it be ok to just use some 10 gauge Romex I have to TEMPORARILY hook the batteries to the inverter (WITHOUT ANY INVERTER LOAD)? I just want to power up the inverter so I can take some time to setup it's settings, wifi, etc. while I wait for the permanent wire and fuse. I think the inverter only draws 250V when no load.
My new setup (still installing) is very similar to yours, but I have the 6K version of the inverter and I will occasionally be pulling 6K (for short periods of time, like when using an electric tea kettle or toaster in the summer). What size ware and fuse combo did you end up with?
 
I ended up using a single set of 4/0 cables from the battery rack to the inverter. I also used a 400A Class T fuse. Fuse is probably larger than I need but everything else was out of stock everywhere at the time. Since I'm not making up sets of 4/0 cables all the time, I simply purchased the length I needed with good quality lugs pre-crimped on. The wire was a little more expensive that way but I didn't want to purchase tools I'd probably not need again. I purchased the Blue Sea Class T fuse mount from Amazon and the fuse from SolarPenny since they had it in stock (they even called on the phone to make sure I knew the fuse didn't come with a mount!). Bought the cables from Amazon - Windy Nation. Looked like good quality solid copper cables and plated copper lugs. I wasn't disappointed in the quality when I got them. They seem like good cables and sized plenty big enough.
 
Thanks! I am interested to hear how your setup is working and what kind of loads you are running. Is this now providing power to your home, or part of?
 
Thanks! I am interested to hear how your setup is working and what kind of loads you are running. Is this now providing power to your home, or part of?
I'm embarrassed to say it but I'm still working on my solar system! Got the ground mount rack (rigging for high wind) almost done and then it's mounting the actual panels. I've got everything else done at least! :) Regarding loads... I'm targeting two different use cases for the solar system. On a daily basis, want to use it to charge the plug-in-hybrid (hopefully twice - once during the day and once at night). Each charge takes 3.6kW for about 3 to 4 hours (so about 11-14kWh). The other use case for the solar system is if we have a power outage. In that case, will power most of the house by back-feeding a generator ready panel (receptacles, micro-wave, refrigerator and well pump). All the high power stuff like HVAC, stove/oven, etc. are on a different panel and will not be run on solar during outages. I've got 16 - 440W panels so a moderate size (7kW max) system. I've also got 25kWh of battery storage. What are you building and how will you be using it?
 
I have an existing net-metered solar array and I am moving approx. 6 circuits from my main panel to a sub panel that will be powered by the new off-grid system. These are the critical circuits in the house that are already connected to a transfer switch so I can run them off a little genny when the power is out (which happens frequently). I wanted to move to an automatic battery backup for these circuits and add more solar production, partly with an EV in mind, but didn't want to give the utility the opportunity to "reclassify" my system and change my net-metering deal to one that is less advantageous to me. At the same time I want to keep my little genny as a back-up to the back-up in case we lose power over a period of very cloudy days. And I decided to put in a transfer switch on the load side of the new sub-panel so I can revert to grid power for these critical circuits in case the off-grid system goes down for any reason. I am attaching a diagram and will probably post the finished project with pics in a few weeks.
 

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