8s2p with two BMS Q

[Devo1982]

Yes, you need over current protection there also. Could be a breaker, could be a fuse. We don't often have to isolate the inverter, so a circuit breaker isn't as necessary in that position as it is in other circuits. A fuse is normally what you see in that position. High amperage circuit breakers are expensive. At least the good quality ones are. Fuses are less expensive.

Yes, put it on the positive cable.

I guess I'm leaning towards a breaker so I can "switch off" my batteries if ever?

 

[Rednecktek]

That's about the use case for it. The fuses are there to protect the wires, breakers are there as a means to shut off power that hapens to also provide an additional layer of protection.

It's the same concept as putting a breaker on your incoming PV wires, so you can easily disconnect power if you need to fiddle with panels at all.

 

[Devo1982]

Battery-1 Positive -> Fuse -> + Bus Bar -> Inverter Pos
Battery-2 Positive -> Fuse -> + Bus Bar

Battery-1 Negative (P-) -> Shunt B- ( if applicable) -> Neg Bus Bar -> Inverter Neg
Battery-2 Negative (P-) -> shunt B- -> Neg Bus Bar

SCC Positive -> Fuse -> + Bus Bar
SCC Negative -> Neg Bus Bar

Wire size will be 1awg all the way around for anything below about 6ft distance. 150a fuses for each battery.

Just looked at this again and was wondering if the shunt can go after the negative busbar, so between the negative busbar and the AIO inverter?

 

[HRTKD]

Just looked at this again and was wondering if the shunt can go after the negative busbar, so between the negative busbar and the AIO inverter?

I suppose you could, but is your all-in-one the ONLY device in your system that is a load/charge? I know in my system, even if I did have an all-in-one that wouldn't be the case. There always seems to be some other device that is a load. If that load isn't seen by the shunt then the state of charge it reports will be wrong.

 

[Devo1982]

I suppose you could, but is your all-in-one the ONLY device in your system that is a load/charge? I know in my system, even if I did have an all-in-one that wouldn't be the case. There always seems to be some other device that is a load. If that load isn't seen by the shunt then the state of charge it reports will be wrong.

It's the only load/charge. My reasoning is that I can just use one cable then from the busbar to the shunt and then another to the circuit breaker before the AIO. If I put the shunt before the busbar, I'll need to connect both my P- to it which will be a tad messier?

 

[Devo1982]

Something like that (please excuse my drawing skills). All the wires will be identical lengths.

 

[HRTKD]

It's the only load/charge. My reasoning is that I can just use one cable then from the busbar to the shunt and then another to the circuit breaker before the AIO. If I put the shunt before the busbar, I'll need to connect both my P- to it which will be a tad messier?

If it's the only load/charge device then you don't need a busbar at all. Run cables from the batteries to the shunt, stacking the lugs on the shunt's stud. Then run a cable from the shunt to the all-in-one.

Should you grow the system, you may find that a set of common busbars is easier to work with.

 

[Devo1982]

If it's the only load/charge device then you don't need a busbar at all. Run cables from the batteries to the shunt, stacking the lugs on the shunt's stud. Then run a cable from the shunt to the all-in-one.

Should you grow the system, you may find that a set of common busbars is easier to work with.

Already ordered the busbar

 

[Rednecktek]

The reason we were saying to wire it otherwise is that if you add anything to the negative bus bar (battery charger, solar controller, MargaritaMaster-1000DC, etc) then the shunt will have no idea that it's there and your measurements will be completely useless.

Also, Class-T or MRBF fuses, not ANL. The amperage dump from a LFP battery can jump right across the gap of a blown ANL fuse. Class-T and MRBF open much larger gaps inside so the arc inside has to work MUCH harder to jump across.

 

[Devo1982]

I'm trying to get my head around how the shunt can determine information about the battery when it is only connected to the negative side?

 

[Rednecktek]

I'm trying to get my head around how the shunt can determine information about the battery when it is only connected to the negative side?

The shunt is programmed when you install it to know how big your batteries are and it keeps track of how many amps pass in and out of the battery.

Example:

You have 100ah of battery when it's full, the shunt shows 100% remaining, 100ah.

You plug in the inverter and power up the fridge for an hour. The inverter and fridge are drawing 10 amps so your shunt will show -10a, and after an hour it will have seen 10 amp hours go out, so it'll show 90% remaining, 90ah.

The sun comes up and starts pumping 20 amps into the system. The inverter is pushing 10a into the fridge and 10a into the battery, so the shunt shows 90% capacity, 90ah, and +10a. After an hour it will show 100% capacity, 100ah, and the charge controller will only draw in the 10a it needs to feed the fridge and not push anymore into the battery.

The sun goes down and you turn on the laptop to p0wn some n00bs online. The laptop and router and 7.1 speaker system need 50a worth of power from the battery to run, so the shunt will show 100%, 100ah, and -50a. After a half hour of spawn camping, you've used up 25a out of the battery so the shunt will show that you've got 75% capacity remaining, 75ah, and -50a of draw on the system.

The shunt just does the math on your batteries and keeps track of how much goes in, how much has gone out, and how much you have left.

 

[Devo1982]

The shunt is programmed when you install it to know how big your batteries are and it keeps track of how many amps pass in and out of the battery.

Example:

You have 100ah of battery when it's full, the shunt shows 100% remaining, 100ah.

You plug in the inverter and power up the fridge for an hour. The inverter and fridge are drawing 10 amps so your shunt will show -10a, and after an hour it will have seen 10 amp hours go out, so it'll show 90% remaining, 90ah.

The sun comes up and starts pumping 20 amps into the system. The inverter is pushing 10a into the fridge and 10a into the battery, so the shunt shows 90% capacity, 90ah, and +10a. After an hour it will show 100% capacity, 100ah, and the charge controller will only draw in the 10a it needs to feed the fridge and not push anymore into the battery.

The sun goes down and you turn on the laptop to p0wn some n00bs online. The laptop and router and 7.1 speaker system need 50a worth of power from the battery to run, so the shunt will show 100%, 100ah, and -50a. After a half hour of spawn camping, you've used up 25a out of the battery so the shunt will show that you've got 75% capacity remaining, 75ah, and -50a of draw on the system.

The shunt just does the math on your batteries and keeps track of how much goes in, how much has gone out, and how much you have left.

That's the best reply I've ever read on any forum ever. You're a

 

[Devo1982]

A couple of update pictures