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Author Topic: Battery bank cables, what size to use?  (Read 3430 times)
scanzel
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« on: May 28, 2008, 07:21:25 AM »

What size of battery interconnect cable are you using? I have 8/ 100 amp hour AGM batteries that will probably be in series/parallel for 24 volts to a 24 volt Magnum 4024 inverter. Huh
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« Reply #1 on: May 28, 2008, 07:26:49 AM »

Bigger is generally better.  For DC power, length is almost as important as gauge.

I used as short a lengths as I could plan for, and went 4 ought.  Thats about as big as is easily available and is also flexible enough to use.

Why use your precious and expensive power just to heat up wires? supersize it.
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Jim Stewart
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« Reply #2 on: May 28, 2008, 08:07:14 AM »

I'm getting ready to set up the same type system and power my 2500 watt xantrex inverter.  The inverter book told me not to use anything less than 4/0 wire to power anything from 0-10' and didn;t recommend having the inverter more than 10' away from battery bank.  I'm using flag style battery terminals to reduce the work of connecting the wire to the battery terminals.  I can solder or crimp the terminals to the 4/0 wire.  The 4/0 wire is going to run you anywhere from $7-$9 per foot.  I got 10' of red and 10' of black and plan on wiring all 8 of my batteries together and then hanging my inverter right at the end of the battery run.  The you'll need a little 4/0 for the ground wire.  It really depends on the wattage of your inverter....but as H3Jim said, bigger is better.  Good welding fine strand wire is the best.  Flexible and you that will lower the amount of amps lost in the run of wire.  Terminals cost me about $5 a piece.  Here is where i got my stuff.  Don;t know if it was the cheapest, but they were easy to talk to and i could get everything in one place.  http://shop.genuinedealz.com/
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« Reply #3 on: May 28, 2008, 08:17:54 AM »

Because I bought my generator, inverter and my batteries from Wrico, he sold me wire and connctors at his cost  if I went to his shop and did the  work.  While several years ago now, and copper has jumped in price, I paid $3 a foot plus about $1.50 each for the crimp connectors.  He has a crimper that I used to make the cables. 
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Jim Stewart
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« Reply #4 on: May 28, 2008, 09:28:17 AM »

...and don't forget when you wire your banks up, to come in from opposite sides of the bank with your plus and minus wires.  This keeps the batteries completely balanced during heavy loads no matter what the size/resistance of your wires....
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1962 Crown
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« Reply #5 on: May 28, 2008, 11:11:34 AM »

I am brand spanking new to this, but, I remember reading somewhere that you didn't want your inverter in the same space as your battery bank.  The idea was the vent gases from the battery could harm the inverter. 

Some of the smart guys will jump in now and tell us what the real deal is.

Frank
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« Reply #6 on: May 28, 2008, 11:39:38 AM »

Some random thoughts on this subject.

As noted above, you must think about mounting the inverter in the same compartment as the batteries.  They need to be mounted very close together.  In my case, I built a tight battery box with vents in the bottom (out the floor) and mounted them in the same compartment.

I think you will find that the inverter manual will ask you to mount the two cables together (parallel) for as long a distance as possible to cut down on electrical "noise"

Be sure to put a fuse in the system along with a battery disconnect.  I can give you a fairly good vendor for the fuse later (rushing and can't find it right now).  For the battery shut off switch look at this thread:
http://www.busconversions.com/bbs/index.php?topic=6174.msg62054#msg62054

Jim
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Jim Shepherd
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« Reply #7 on: May 28, 2008, 12:34:37 PM »

The gas that escapes batteries is very corrosive. Corrosive gasses & expensive electronics (let's say an inverter) don't play well together.  Shocked

If it were me, I'd have a bulkhead between the properly vented battery compartment & the inverter.  Cool
When planing the venting for the battery compartment, I'd be sure to give consideration to where the corrosive gasses are directed. I wouldn't want them getting sucked in with the cooling air for the inverter.
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« Reply #8 on: May 28, 2008, 01:08:56 PM »

My 6 golf cart batteries are in one bay next to the bulkhead seperating another bay which has my inverter. I mouinted my inverter up higher than the batteries as they are directly on the bay floor but will soon put them in a vented box as well. My inverter directions said to keep them seperate for obvious reasons stated!
BS
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HB of CJ
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« Reply #9 on: May 28, 2008, 02:06:28 PM »

Yeah, same answers based upon hard experience.  The closer your $expensive$ invertor is to your also $expensive$ battery bank, the better both will like it.....if the connecting cables are of the proper size.  Using the properly sized cables doesn't add that much $$$.

If you feel the need to have the invertor separate from the batts, then it is super more important that the connective cables are sized to MIMIMUMIZE (sp?) the voltage drop.  Double up the 0000 cables if you have to.  Yes again, wire the batts to equalize the current paths.

Some (most?) instructions may be happy if you run cables based upon about a 2% voltage loss at an average load.  No.  What you should try to do is to run cable that will only see about a 1% voltage loss at maximum load.  See the difference?  Costs you a little more.

Crimping is also important.  We learned that the best low voltage, high amperage connections are crimped WITHOUT using sodder.  We had access to the special, big, heavy, ($expensive$ again) hand crimper which looked kinda like the mother of all bolt cutters.

Dont feel shy about using recycled heavy welding cable.  We found a super deal on 0000 and 000000 cable that was in an actual gold mine and was decommissioned simply because it had reached a certain age.  Multi strand copper inside a very flexible rubber jacket.

Pay the extra money to use the proper cable size, along with having the connections crimped properly using the proper equipment.  This is not a place to try to save $$$$, it may come back to bite you in the end.  Shrink wrapping the connections. Good luck.  Smiley Smiley Smiley
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« Reply #10 on: May 28, 2008, 02:52:47 PM »

Concerning the crimping.  I use Del City as a supplier for a lot of my bus and business parts.  Their copper terminals are reasonable:
http://www.delcity.net/delcity/servlet/catalog?parentid=1015&page=1

The hammer type criming tool is ideal for making good connections and is cheap:
http://www.delcity.net/delcity/servlet/catalog?parentid=1027&page=1

Jim
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Jim Shepherd
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H3Jim
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« Reply #11 on: May 28, 2008, 03:02:07 PM »

Good comment aobuthte battery outgassing.  I used AGM's so thats not an issue.  Althogh they can still outgas, they are much less likely.  and I mounted the inverter high up in the compartment, and the batteries covered, are at the bottom and vented down.
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Jim Stewart
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« Reply #12 on: May 28, 2008, 03:11:38 PM »

Good comment aobuthte battery outgassing.  I used AGM's so thats not an issue.  Althogh they can still outgas, they are much less likely.  and I mounted the inverter high up in the compartment, and the batteries covered, are at the bottom and vented down.

Curious. Is the gas heavier than air and if the box is vented out the bottom, where does the fresh air come into the box to let the gas out?

Richard.
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« Reply #13 on: May 28, 2008, 07:21:38 PM »

Good question.  If its just hydrogen, that's lighter than air and would rise.  I have no answer, but I have not had any issues, although that's not a guarantee I'm not doing damage that will surface later.
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Jim Stewart
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Nick Badame Refrig/ACC
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« Reply #14 on: May 28, 2008, 08:03:23 PM »

Hi Scanzel,

Here is a DC wire calculator.

http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html

Nick-
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« Reply #15 on: May 28, 2008, 08:19:16 PM »

Whatever wire you use, it would be prudent to make sure the insulation is rated for your intended use.

I don't want to even think about the consequences if the insulation fails when you have that many batteries connected together.
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« Reply #16 on: May 29, 2008, 04:49:39 AM »

Whatever wire you use, it would be prudent to make sure the insulation is rated for your intended use.

I don't want to even think about the consequences if the insulation fails when you have that many batteries connected together.


Kyle brings up a good point!

Make sure you also consider your routing and attachment points to eliminate potential wear through points.

I deal with a lot of high voltage dc plant issues(another hat I wear) and we probably spend more time on securing and isolating than any other part of an installation.

Be Safe!

Cliff

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« Reply #17 on: May 29, 2008, 06:54:11 AM »

and when you are using wrenches to tighten the cables, do all the positives first, then the ground.  That way if the wrench is on the positive, and it touches the frame, you won't weld the wrench.  With hundreds of amp hours in these batteries, they can heat something up to red hot really fast.

Don't ask me how I know this.....
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Jim Stewart
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« Reply #18 on: May 29, 2008, 07:15:11 AM »

I would strongly recommend that you not use the hammer type crimper.  I have many years experience with heavy power installation and suggest you find someone who has the proper hydraulic crimper to make up your connections.

There is more to it than just a good mechanical connection.  When done properly, the wire and connector are fused together under tons of pressure, essentially becoming one unit.

In addition, the compression tool and dies must be properly matched to the connector you are using. In other words you cannot properly crimp a Burndy connector with a T&B tool. Both are very good brands. Also, be sure to use a light coating of anti-oxide on the wire before making the crimp.

Len
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« Reply #19 on: May 29, 2008, 07:27:45 AM »

When you are working around batteries please remove all your rings  I had a accident several years ago where my wedding band was shorted out with a wrench and melted on my finger and did that hurt for a long time
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TomC
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« Reply #20 on: May 29, 2008, 08:07:52 AM »

All the talk of venting can be eliminated by just using AGM batteries.  They don't vent, plus they can be mounted in any position, except upside down.  Good Luck, TomC
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« Reply #21 on: May 29, 2008, 09:26:39 AM »

While AGM's don't normally  vent, they do have vents on them, and can under extreme situations, vent.  They are the best choice however.
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Jim Stewart
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« Reply #22 on: May 29, 2008, 02:30:17 PM »

I guess I'm just in a funny mood.  Sorry.  H3Jim....hydrogen gas goes up, soosss should'nt the batts vent to the top with a dedicated explosion-proof fan located and pulling air in from the bottom?  Damage can occure...and with your setup....BOOM!  Hate to nitpic, but stuff happens.

Nick....sorry again....the chart provided (I believe) is sized for a 3% voltage drop, which over time may adversly affect the invertor?  Less then 1% is better. We found this out the hard way with our solar homestead years ago.  $$$.  Upsizing the gage of cable saved us a lot of energy.  Smiley Smiley Smiley
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« Reply #23 on: July 02, 2008, 05:47:59 PM »

I thought I would update this thread. 

It got a bit off subject, but the replies confirmed that I had a wire gauge issue.  I had used 6 gauge for my 30 foot run and the 12V alternator was rated at around 130 amps.  I was getting very low amperage to the battery as measured by my Bogart Tri-metric battery "state-of-charge" meter.

I bought some welding cable off of Ebay.  It was stated as being 1/0, but my 1/0 ends were almost impossible to install, so it may have been 2/0.  I installed the cable with 200 amp fuses at both ends and it sure made a difference.  I now get a net of over 70 amps (probably 20 amp draw most of the time for a gross of 90 amps) when the batteries are down to about 50%. 

It sure seemed strange to put such large cable on such a small alternator (22SI size) with equally small terminals, but the wire tables do not lie.

Jim
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Jim Shepherd
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« Reply #24 on: July 03, 2008, 04:43:06 PM »

the studs at the ends are only a small part. had you only been going 2 or 3 feet you could run a small cable. the 30 feet is killing you and the small wire has too much loss through it. I just replaced all my battery cables as the insulation was coming apart. took about 25 feet to go 8 by the time it went up and over and around so I had to run 4/0 cable. hated the price but I know that it will handle the load.
steve
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« Reply #25 on: July 04, 2008, 07:04:23 AM »

Steve, your wire size agrees with the recommendations of Prestolite/Leese Neville (http://www.prestolite.com/literature/tech/alts/TSB-1001_wire_size.pdf). According to that table you are good for 250 amps.  In my case, I was not able to easily run anything over 1/0.  That gives me a capacity of about 125 amps for my 30 foot run.  Given my alternator, that is probably OK
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Jim Shepherd
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« Reply #26 on: July 04, 2008, 12:03:08 PM »

If I may give an informed endorsement, try these guys.  Give them your specs, they cut, crimp and wrap your cables and they look as professional as anything.  Quick turnaround too!

Mike Nediano
Genuinedealz.com, LLC
866-970-3325 toll free
http://shop.genuinedealz.com

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« Reply #27 on: July 04, 2008, 02:55:12 PM »

When I first went to school we had to solder everything.  Crimp wasn't on the menu.  Later when it was discussed it was determined to be less of a quality connection that soldering/silversoldering.  It was just way cheaper in terms of man hours and also a crimp is better from a QA point cause soldering takes skill.  Just remember and NEVER forget....no acid flux or acid core....only rosin.  Don't forget that.

About that welding cable.  You may want to rethink that a little.  Fine stranded copper is a real plus if you have to bend the wire/cable like maybe ever.  It has a serious drawback and that involves batteries.  Battery acid dissolves copper and the rate at which it dissolves copper is kind of a constant according to the acid concentration.  Now if you have a solid copper wire... lets say it will be eaten through in 100 units of time.  If you have 2 strands and same gauge....it will take half as long.  If you have 100 strands, same gauge, it will take 1 unit of time or one one hundredth the time.  If acid environment is not an issue....go stranded.  All bats eventually start out gassing acid and the terminals start to grow white stuff.  I use it but I seal it in shrink tubing after a liberal coating of silicone grease to the wire part under the shrink.

HTH

John
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« Reply #28 on: July 04, 2008, 03:53:44 PM »

Good comment aobuthte battery outgassing.  I used AGM's so thats not an issue.  Althogh they can still outgas, they are much less likely.  and I mounted the inverter high up in the compartment, and the batteries covered, are at the bottom and vented down.

Ahh..Yes... But AGM's can go into TNM ( Thermo Nuclear Meltdown ) and explode after
swelling up casually and making a hissing noise.

My preference is to separate the battery compartment from where the inverter is mounted. You MUST cool these inverters when they are running and a closed up
compartment is a bad idea. They can get really hot whether charging or inverting.
Keeping that extra heat away of the vicinity of the batteries is just a good idea.

The other reason is that a $1k to $4k inverter is too easily destroyed by a $50 battery that takes a dump or starts venting.
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« Reply #29 on: July 04, 2008, 04:45:34 PM »

The size is clearly described in the installation manual of your inverter. I chose to go with 4 aught big boy cable. This stuff is hugh but worth every penny as you consider a fire in the bay with all the electrical and it makes sense. The biggest challenge was finding good quality ends and then a crimper. I would buy my cable on the e place ($4 a foot) both black and red and then take it to an industrial battery supplier and have the professionally crimp the ends. I was very happy with the end result. It did cost be about $250.00 for the entire cable set up from bank to switches to inverter. I like the comfort knowing that my system is safer because I spent the money up front.

Good luck!

Grant
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