DC wire and fuse sizing

Yoshi_TAB

Hi,

While doing my lithium battery and inverter install in my 2021 320.  I've done extensive looking around for how to size wire and fuses for a system.  I've come upon a few sites that keep getting referenced a lot (there are many out there).  I thought I would pass them along for those who may need this info and are not aware.  I also  found a few things most confusing and often debated in the community. I'm not passing these on to debate them, just what I've learned.  Also when using wire length in these calculations, round trip is always used (although not always highligted  to do so)

1.  To use continous or peak power of inverter. Seems like continous is most often used, but some will say to use peak to "add a degree of safety".  Obviously this increases wire and fusing size.

2.  To upsize wire to the next AWG size. Many will do this to add "a degree of safety"

3.  What type of fuse is "best".  For lithium batteries and high amp circuits, you often see Class T used vs. ANL or  mega fuses.  It has to do with how fast they blow and its ability to  interupt the circuit and not arc when the fuse blows.  Class T fuses are more expensive and larger.


Wire Sizing Calculator – EXPLORIST.life

Fuse Sizing Calculator – EXPLORIST.life

Calculating Inverter DC Wire & Fuse Size | DIY Solar Power Forum (diysolarforum.com)

Circuit Wizard - Blue Sea Systems

MuttonChops

Yoshi_TAB said:
. . . not passing these on to debate them, just what I've learned.  . . .

HaHa 

A_boondock_owner

Yoshi_TAB said:

While doing my lithium battery and inverter install in my 2021 320 ...

Wanted to mention (from my limited experience working with solar) that an easy mistake to use when working with DC and AC breakers, they are not interchangeable. Make sure if you're using breakers on the 12VDC side to use *DC* breakers, they have different "trip profiles."

Yoshi_TAB

A_boondock_owner said:

Wanted to mention (from my limited experience working with solar) that an easy mistake to use when working with DC and AC breakers, they are not interchangeable. Make sure if you're using breakers on the 12VDC side to use *DC* breakers, they have different "trip profiles."

Hi, Thank you for pointing that out.  That is important to keep track of when buying componets. 

Breakers vs. fuse is another area I found that seems to get discussed a lot when designing a 12V system.  Folks like to use breakers in order to have a way to turn the power off the circuit (like an on/off switch).  Breakers also eliminate the need and cost to have spare fuses when the circuit blows.  But I found concensus that using fuses is prefered because 1.  Breakers can wear out (especially when using it as a switch..since it's mechanical nature); 2.  They tend to have a wider range of when they blow; (a 100 amp breaker may blow between 95-105 amps) which may or may not matter in a system.  3.  You have to be more worried about cheap knockoffs (like from Amazon).  Stay with name brands.  4.  Generally more expensive on higher amp circuits.