Expanding my system - does this look right?

[Rhombeus]

I am in the process of expanding my system to add more batteries and a smart shunt. I have a few questions, just to make sure I'm doing this right.

Current system:

• 3000w Victron Quattro inverter/charger (6000 w peak)
• 1 x 16s chevy volt battery module (don't worry - in a fire safe cabinet
  • Each cell group is 3.7v nominal.
  • Each module is 3.7v x 16 = 59.2v nominal
• charging from a 7000w Honda generator

New system:

• adding 3 more chevy volt batteries for a total of 4 = 3.1 kwh x 4 = 12.4 kwh
• adding a Victron Lynx distributor in the battery cabinet
• adding a battery switch to the battery cabinet (mounted on the outside)
• adding a BMV 712 Shunt

Note: in the future I will likely add a 2nd 3000w Victron Quattro, and would like to avoid rewiring the battery cabinet if possible.

My questions:

• What fuse sizes for the Victron Lynx? 4 x 100amp? Would increase fuse size when adding a 2nd Quattro
• What wiring size? Online calculators say 1/0 if I don't want to rewire when adding the 2nd Quattro
• Should I add another fuse between the Victron Lynx and the Inverter?
• Any suggestions for the battery shutoff switch? I was looking at the Victron Battery Switch, but max voltage is 48v

Lastly, I am also adding a BMS but will post separately on that. A whole other kettle of fish there and didn't want to confuse the post.

Appreciate the help.

 

[Rhombeus]

Anyone? Advice is appreciated.

Steve

 

[John Frum]

3000 ac watts / .85 inverter efficiency / 48 volts low cutoff = 73.529411765 service amps
73.529411765 service amps / .8 fuse headroom = 91.911764706 fault amps

Use pure copper 4 awg with 105c insulation and 150 amp fuse for each battery and for each inverter/charger
The batteries should be fused with class-t fuses as close as possible to the battery positive terminal
The inverter/chargers get fused on the lynx distributor with mega fuses.

The high level topo is...

lynx_power_in<->lynx_shunt<->lynx_distributor

You will have 2 free port pairs on the lynx_distributor for future expansion.

DC Distribution systems & Fuses - Victron Energy

Victron Energy's DC distribution systems monitor the state of charge of your battery and the state of each fuse. View products now.

www.victronenergy.com

 

[John Frum]

Those batteries are not LFP.
What is an appropriate low voltage disconnect for them?

 

[Hedges]

48V is "Safe Extra Low Voltage", doesn't have the same requirement for preventing contact by the Great Unwashed.
(Exact voltage threshold for SELV definition may vary with location and time.)

Extra-low voltage - Wikipedia

en.wikipedia.org

https://www.edn.com/what-does-selv-mean-for-power-supplies/

Switches "rated" for 48V would hold off somewhat higher voltage, but aren't approved/listed for higher voltages.
Most switches would get burned if switched "hot", with current flowing. Switched "cold" not so much of an issue.

Lots of cheap switches that overheat at "rated" current. Often for starter battery, very brief use. Blue Sea sells quality switches.

Midnight has DC breakers for 175A and 250A, with 50kA interrupt rating. Those would be good for batteries.

 

[Rhombeus]

Those batteries are not LFP.
What is an appropriate low voltage disconnect for them?

High voltage disconnect = 4.05 v per cell group x 16 = 64.8 v
Low voltage disconnect = 3.5 v per cell group x 16 = 56 v

 

[Rhombeus]

Is it a bad idea to upsize the wiring for when I add a second inverter (total 6000w), and use fuses sized for the lesser load = 3000w?

ie. Use 1/0 wiring and 100 amp fuses in the lynx distributor?

3000 ac watts / .85 inverter efficiency / 56 volts low cutoff = 63.0252101 service amps
63.0252101 service amps / .8 fuse headroom = 78.7815126 fault amps

 

[John Frum]

Is it a bad idea to upsize the wiring for when I add a second inverter (total 6000w), and use fuses sized for the lesser load = 3000w?

ie. Use 1/0 wiring and 100 amp fuses in the lynx distributor?

3000 ac watts / .85 inverter efficiency / 56 volts low cutoff = 63.0252101 service amps
63.0252101 service amps / .8 fuse headroom = 78.7815126 fault amps

If you use 1/0 awg you can use 250 amp fuses.
The fuse protects the wire.
Typically higher ampacity fuses have lower resistance.