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Battery cable guage
By Dave B, Section Controls Posted on Fri Oct 30, 2009 at 08:48:21 AM MST
8 6 volt L-16s for 24 volt-vague search results

Searching for suggested battery jumper size is resulting in vague answers. I'll be running 8 6 volt l-16s for 24 volt with a DR3624 inverter / charger. The Xantrex manual states 4/0 for the controller cables and battery run which will not be more than 10' to my disconnect. I guess I would assume no less for the connecting cables between batteries. I'm not looking for a cheap way out but just a little confirmation which seeems tough to find. Any suggestions with this and possibly a good source for the cable and ring connectors would be much appreciated. I'd like to make my cables. Thank you, Dave B.

Battery cable guage | 10 comments (10 topical)

Re: Battery cable guage (3.00 / 0) (#1)
by hydrosun on Fri Oct 30, 2009 at 09:05:08 AM MST

Since you are doing 2 strings of 4 batteries, each string is only providing 1/2 the amperage. So you should be able to use 2/0 wire for the interconnects. Be sure to connect the wires to the inverter at opposite corners of the battery bank to keep the current pathways even through the two battery strings.
Chris

Re: Battery cable guage (3.00 / 0) (#2)
by DanG on Fri Oct 30, 2009 at 12:54:19 PM MST

Whoa - I just checked my favorite vendor that I've done local pickup from, and heavy wall plated 4/0 lugs are $2.10 a pop (small pain) and 4/0 cabling has gone into nose bleed large pain territory. (waytekwire) Watch eBay and Craigslist for bulk wire buys, I snagged 25' of used four-conductor 4/0 (2000v with three 0awg grounds) delivered for $1.50 a foot (100+ feet) ... Just had to get the wife to hold the heat gun to soften the armored sheath so I could razor it apart to get the wire out. Welding cable is an option but you need to find lugs rated for fine-stranded cable, and choosing used welding cable means flaws in the sheathing. Finding copper bar stock from battery interconnects is a option. In anyway you accomplish this would be a good idea to have fuse (Doomsday prevention) as near to the battery as possible...

Re: Battery cable guage (3.00 / 0) (#3)
by FishbonzWV on Fri Oct 30, 2009 at 02:51:35 PM MST

Hi Dave,
I have 11 feet of 2/0 4 conductor fine strand copper that I don't need.
I used it on my battery bank (8-6V Group 27 AGMs).
If you would like to have it for the shipping cost shoot me an email.
It's an SO type cable so I'll have to strip off the outside coating.
I'm trying to clean out stuff I don't need anymore.
Bonz

Re: Battery cable guage (3.00 / 0) (#4)
by Volvo farmer on Fri Oct 30, 2009 at 03:53:44 PM MST

I have the exact same battery setup and voltage. We went 2/0 on the interconnects and 4/0 on the inverter run. I'm pretty sure that is the correct sizing.

Volvo Farmer

Re: Battery cable guage (3.00 / 0) (#5)
by richhagen on Fri Oct 30, 2009 at 03:56:30 PM MST

I think it was Stephen Fahey (Sparweb) who posted a link to the NEC guidelines for solar installations. I printed it out and have it at home, but don't have it handy at the moment. If you were to use 2/0 wire for the battery interconnects, then I think you would be required to fuse them accordingly as well. I would likely opt for 4/0 all the way even though it is a pain to work with and the costs are significantly more. That way I could just fuse the positive ends of cables from the bank to the inverter with a fuse rated for up to 4/0, about 250 Amps which should be fine for exposed THHN copper cable, and have a breaker at the DR3624 of about a 175 to 200 amps at the inverter, although I would definitely double check all of this before I did so. I would also fuse any other cables from the battery bank at a rating appropriate for the cables size. Rich
'A Joule saved is a Joule made'

Re: Battery cable guage (3.00 / 0) (#6)
by Volvo farmer on Fri Oct 30, 2009 at 05:21:03 PM MST

My system was installed by a professional, to 2006 NEC code, and passed local inspection. There are no fuses other than a 250A breaker before the inverter in the DC distribution box, and of course all the charging sources and controllers have appropriate sized breakers.

Either something has changed in three years, or my installer and inspector missed something, or there are no fuse requirements in the battery box itself.

I'd be interested to see that link to the NEC code if anyone finds it.

Volvo Farmer

[ Parent ]

Re: Battery cable guage (3.00 / 0) (#7)
by FishbonzWV on Fri Oct 30, 2009 at 05:57:25 PM MST

http://photovoltaics.sandia.gov/docs/PDF/checkcdcrnr.pdf

[ Parent ]

Re: Battery cable guage (3.00 / 0) (#8)
by dnix71 on Fri Oct 30, 2009 at 06:49:12 PM MST

There were changes in the 2008 NEC relating to solar. If you did your install earlier, then they didn't apply then.

Send me an email. dnix71 yahoo. I have the current NEC in pdf form if you want it.

[ Parent ]

Re: Battery cable guage (3.00 / 0) (#9)
by Dave B on Fri Oct 30, 2009 at 11:46:42 PM MST

Wow,

What a great response, thank you. More searching seems to prove out that 2/0 is fine for the interconnects but 4/0 is required for the battery to inverter and disconnect. I'm going to check with local suppliers just to get an idea on costs. Who knows, maybe pre-made will be the best. Anyone who has purchased battery supplies from a particular company with good service and reasonable pricing I would sure appreciate the contact information. Thank you again to all, Bonz (you've got mail) Dave B.

[ Parent ]

Re: Battery cable guage (3.00 / 0) (#10)
by hydrosun on Sat Oct 31, 2009 at 11:34:46 AM MST

I know in the past people would use welding wire and make ends with copper pipe crimped and soldered and flattened and drilled. I've got a big crimping tool and get cast copper lugs. The soldered lugs are probably better.
Chris

[ Parent ]

Battery cable guage | 10 comments (10 topical)

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