What size cable to use battery to Inverter?

westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
I did some pricing of welding cable today and found some new ‘old’ stock OO at a great price, $12.15 / meter ($3.68/ft). It’s 20% less than elsewhere and only 5% more than the O size.
Got me thinking about just what size I really will need between the 24V BB and the 1500W Inverter. The load will be ~62.5 A (50A @ 30V to 71.5A @21V). Surge is 3000W 125A. (the manual calls for #4 ga wire and a 100A) fuse.
Using the No Outage voltage drop calculator, for 24V, 72A, 75*C, 8 feet one way, Copper wire,
I get with:
4 ga. 1.5 % drop
2 ga. .9 % drop
1 ga. .7 % drop
O ga. .6 % drop
OO ga. .5 % drop

All of these are ‘acceptable losses’, as the total line losses from PV to inverter remain below 3.75% @ 4 ga, 2.75% @ OO ga., but how does one do a cost/benefit analysis on these numbers?:confused::confused:

From what I read, 2 ga. is borderline for Amps,(72), thus I need to use O ga, minimum for a 30% ampacity buffer. Then, considering I might want to eventually go to a larger 2000W inverter, (manual calls for #O wire with 125A fuse) I am leaning towards using OO ga. BB to inverter.

Do I have this figured out correctly?
Am I being too cautious/overestimated?
KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada


  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: What size cable to use battery to Inverter?

    the figures are pretty close to what you figure them to be. the 2/0 may be overkill, but it will take out a large problem area for v drops even with an expansion to your proposed 2kw. wire won't ever be cheap and will no doubt go up in years to come so i'd take advantage of it.
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