What size battery interconnect cables

System

Hi everyone

Newbie here again to ask another question...

I'm building an 8 battery bank inverter system which will be placed in a truck bed tool box in my Ford F250. It will be charged during the day as I drive from client to client ( I'm a mobile dog groomer) by my truck's alternator and plugged in at night to my house (charged by an 80amp IntelliPower 9180 charger with Charge Wizard ) to top off the batteries. I will have my trailer's shoreline able to plug into this inverter system to power up my tools.

The batteries are ( 8 )6v 220ah Concorde AGMs connected to a 5000 watt Aimes Inverter... connected in series/parallel... inverter cable 4/0... 400 amp fuse block to the chassis of the truck...

My question is - what size battery interconnect cables do I use? I was going to use 2/0, soldered welding cable custom cut, but should I be using the  3/0 or 4/0 size interconnect cable instead?

Thank you for your advice in advance if you have any suggestions.

rplarry

Re: What size battery interconnect cables

Pez
Obviously if you used 4/0 you would not have any problems with too much current since you are useing 4/0 for the inverter connects. If your power needs are not maxing out the inverter then you can use smaller interconnects. Another possibility is to use solid bar stock as your interconnects. If your battery bank is mounted solidly and will not move then you might consider solid connects. It will save you some money. If your bank is not solidly mounted then don't consider solid and go with stranded copper at least 2/0.
Larry

mike95490

Re: What size battery interconnect cables

pez wrote:

It will be charged during the day as I drive from client to client ( I'm a mobile dog groomer) by my truck's alternator and plugged in at night to my house (charged by an 80amp IntelliPower 9180 charger with Charge Wizard )

I'm not sure your truck's alternator will do much for you. They are set often to 13.8V, and will provide a bulk charge, but I don't know how you are going to charge a series - parallel setup with only 13.8V Most are only 100Amp, at 4,000 RPM
Also, when you battery bank gets low, it may BBQ your alternator. You may want to consider an aftermarket super-duper-heavy-duty alternator to install, just for charging the battery pack.
here's some: http://www.balmar.net/Page13-98seriesalts.html >300A

niel

Re: What size battery interconnect cables

the alternator won't do much for your battery's charge needs, but it would stop them from being depleted too far. now as to whether those gauges will work does depend on the current drawn and the total resistance presented by the wire. that resistance depends on what gauge of copper wire you use, the distance of both the plus and minus wires, and the temperature of the wires. the pv voltage drop calculator works for calculating the voltage drop from your batteries to the inverter. just pretend the batteries are the pvs. the link to the calculator is here: http://www.wind-sun.com/smf/index.php?topic=1477.30  so what good is knowing the voltage drop you might ask? this is wasted power and it wastes it in the form of heat. you didn't specify if you inverter is 12v or not, but i'll assume for example's sake that it is. if the voltage drop is for example 1.2v this represents 10% of the voltage, but in another way of looking at this, this represents up to 1.2v x 400amps = 480watts lost.
now buss bar is a good way to do the battery interconnects. please do pay attention to the equivalent gauge # the buss would have, but going with the wire is fine too. just watch those connectors either aren't bad or don't go bad on you if you use the wire. also watch for possible shorts and prevent battery movement because that will weaken the connections.
i'd offer to run the program for you, but in getting the new operating system vista, i find i can only use certain programs that are approved for the os and so far that excel equivilent program i used is not listed as approved. for the record, i do not like vista and had i known it was like this i would've bought xp. my xp was put into the pc by somebody else like a preinstalled system, but too many quarks in it due to attacks by viruses rendered the program useless after time and it crashed recently. my advice is stay away from vista if you are serious of having your pc do things for you. i view it as a step backwards from what xp's abilities were and you need lots of memory and high processing speed with vista as it bogs down your system making it slow. there are also major sound and video card issues going on right now too.

crewzer

Re: What size battery interconnect cables

Pez,

Your 5,000 W MSW inverter is rated at 90% efficiency at full power, and the low voltage cut-off is 10 V. Accordingly, the rated input current will be (5,000 W / 10 V) / 90% = 556 A. The NEC requirement for the battery-to-inverter cables is 125% of rated current, so that’ll be 695 A.

See: http://aimspowerinverters.com/_wsn/page9.html

I think you’ll need a bigger fuse, and you may well need 500 MCM cable. I’d recommend that you use the same cable for the battery interconnects.

See: http://www.cobrawire.com/x-flex/

Note that your battery bank will be rated for 12 V x 880 Ah. Assuming it's fully charged and healthy, the bank will probably not last longer than one hour under full inverter load. If the batteries are fully discharged, which, BTW, is not a good thing to do to batteries on a regular basis, I’d estimate that it’ll take the 80 A charger about 14 hours to fully recharge the battery bank.

I also like the idea of a bigger alternator with a three-stage charger/regulator.

HTH,
Jim / crewzer

System2

Re: What size battery interconnect cables

Thanks everyone for all of your input  8-)

I won't be using the full 5000 watt inverter load, normally only 2500-3000 watts maximum for roughly 15 minutes per dog for large dogs, small dogs will only take up 1200-1500 watts for 15 minutes. So I groom 6 dogs per day - which makes my maximum usage approximately 4500 watts per day. I definitely will never discharge the batteries more than 50% ... (doesn't the inverter automatically turn off if batteries dip below 50%?). I can just turn my generator on if batteries discharge too much. Battery bank will be mounted solidly.

I will soon also have a second inverter system (Magnum 4024) in my trailer that I tow ( the mobile dog salon ) which will be charged by (4) 130 watt Kyocera Solar panels mounted on the trailer roof in case I need a little extra power. ( This will just be a 4 battery bank of the 6v 220ah AGMs.)



I will look into the after market alternator and bigger cable and fuses and maybe buss bar.

Thanks niel for the thought of running that program for me ... fortunately I have a Mac so Vista can't mess with me :-P, hope it stops messing with you ASAP

Grateful for your suggestions   8-) :-)
Pez

niel

Re: What size battery interconnect cables

thanks and good luck with your setup. btw, do not rely on the 10v kickout from the inverter. most batteries are dead by the time that point is reached. i, for the life of me, don't know why they put the low voltage disconnect so low as it is useless in my opinion.

crewzer

Re: What size battery interconnect cables

...maximum usage approximately 4500 watts per day. I definitely will never discharge the batteries more than 50% ... (doesn't the inverter automatically turn off if batteries dip below 50%?).

4/0 wire should be OK for a 12 V inverter running at 3,000 W. 4,500 Wh is ~400 Ah from your battery bank, or ~50%, as you indicated. There's a difference between a "resting" battery's voltage at 50% SOC, and that of a battery under load, which is always lower. The inverter won't disconnect at 50% SOC, but the spec's imply that it will when the battery voltage drops to 10 V. As niel indicated, this a very low set-point, as 12 V batteries are considered to be 100% discharged when they drop to 10.5 V under load.

HTH,
Jim / crewzer