Wiring Among Batteries

JCTex · July 8, 2015

My bank is about to be 3 pair of Lifeline 6CT's wired in series. These are 300Ah. I will connect the entire bank to the charge controller using 4/0. I'm going to make the parallel connections using the "equal distance" method. That is, I will put a bus bolt at the end of each of the Pos and Neg main 4/0 cables and attach a cable from each of the 3 remaining Pos poles to this bus (likewise with the Neg side). Each connecting cable will be the same length.

I can save a bunch of money if I can do all the inner-bank lines with 2/0 or 1/0 cable. For clarity, the bridges between each 6V battery pair and the lines from each combined pair to the 4/0 bus would be less than 4/0.

My question is whether this is advisable or must I run 4/0 throughout the entire bank?

Jerry

Yarome · July 8, 2015

You don't have to use 4/0 throughout. You can make your connections as you've outlined, but I'm curious why you would want to. It depends a little on which controller you are using and how large your array is, but 2/0 throughout would never be a bad thing and probably more than adequate.

I'm also curious why you are thinking of using a bus/terminal block to make independent connections for each paired cells... and how are you going to keep equal distance between your series connections compared to your parallels if they have to take a trip to the block? Are portions of your bank going to be situated in different locales? I don't know your layout, but that would, in 'most' cases increase the run lengths and the cost of your cabling.

It's certainly doable as you've outlined, I'm just curious why some of the above would be necessary.

Had a brain fart and had to edit. :blink:

oldjohnt · July 8, 2015

Pebble, I'm having a hard time envisioning and accurately computing the Amp Hrs, Volts and possible maximum Amperage in your particular series or series/parallel combinations. A drawing or diagram would help but don't go to the trouble on my account. That being said, if the amperage in one certain path is X amps, and the wires ampacity for that particular current path is sufficient with low enough voltage drop, I don't see different wire sizes IN DIFFERENT CURRENT PATHS as a problem PROVIDED for balancing purposes you use equal sizes and equal lengths as I think you are "where necessary".

If one path may be conducting X amps but another is conducting far less Y amps, the wire in the Y circuit DOES NOT HAVE TO BE AS BIG AS IN THE X CIRCUIT. Of course, the X or Y circuits if in parallel paths should be the same size and length as I think you understand and are doing correctly.

LISTEN, NOTE: Sure bigger wire equals less voltage drop,,,,,,,,,,,, and bigger is better,,,,,,,,,,,,, and it wont hurt if bigger then necessary wires are used. I'm ONLY saying just because one current path may conduct 200 amps DOES NOT MEAN if there's another path that only conducts 100 amps, you need to use 200 amp wire where only 100 amps flows PROVIDED YOU MAINTAIN THE LENGTH AND BALANCE YOU DISCUSSED IS ADHERED TO "WHERE REQUIRED".

You would NOT use different wire sizes where there are parallel current paths WELL DUH you know that, but provided the wires ampacity is sufficient and voltage drop isn't a problem YOU DONT HAVE TO USE 4/0 WIRE IN A PATH WHERE 2/0 SUFFICES JUST BECAUSE 4/0 IS USED IN ANOTHER LOCATION

NOTE for those (like me often lol) that believe in overkill and over design and are (Iike me) ultra conservative designers, sure use 4/0 or 500MCM or whatever you please, I'm NOT here to stop or argue against you, I'm sort of like you in many ways lol. I'm ONLY trying to answer Pebbles question electrically accurate as I see it.

For a good explanation of how to wire series and parallel batteries, see this:

http://www.smartgauge.co.uk/batt_con.html

That's my story n Ima stickin to it

John T

JCTex · July 10, 2015

Yes, John T, that's it. For those electric gurus wanting to help, go to that link and look at Method 3. In fact, that site is one of my sources for doing this.

I'm not sure of the amperage that will be going thru these cables. Shore power and gen power is a maximum of 50A. The charger built into my Magnum Hybrid 3012 is about 100A, I think. The charge controller is, I suspect, the source,of the largest current into the batteries. That will be either a Midnight Solar Classic 150 or an Outback, I haven't decided. I looked under Lifeline and couldn't find any number saying this is the most amps the 6CT's can receive at a time.

Country Coach wired my existing two 8D's with 4/0. So, using that as a clue from engineers who knew, I'm staying with 4/0 to and from the total bank to the main bus bar (which includes the charge controller, inverter, and engine alternator).

After confirming what I want to do for parallel connections in Method 3 of the above link, I repeat my question. Can I use 2/0 for the parallel wires and the wires between the 6V's making them in series? I think both of you who helped so far say Yes, but please revisit now you can see the actual wiring diagram. Caveat, the drawing in the link is for 3 12V batteries; I'll be using 3 paired 6V's). Thanks for your help.

Jerry

Yarome · July 10, 2015

Country Coach wired my existing two 8D's with 4/0. So, using that as a clue from engineers who knew, I'm staying with 4/0 to and from the total bank to the main bus bar (which includes the charge controller, inverter, and engine alternator).

After confirming what I want to do for parallel connections in Method 3 of the above link, I repeat my question. Can I use 2/0 for the parallel wires and the wires between the 6V's making them in series? I think both of you who helped so far say Yes, but please revisit now you can see the actual wiring diagram. Caveat, the drawing in the link is for 3 12V batteries; I'll be using 3 paired 6V's). Thanks for your help.

Jerry

Really? Did they? "using that as a clue from engineers who knew". Are they calculating distances or just slapping in the biggest they can find and passing on the cost to you? I don't know. Give me a dime and I can find 20 other installers that would swear 10 gauge is more than adequate. They would be wrong, but hey.. they are "professionals", right? :P I don't know your distances and such, so I really shouldn't comment, but 4/0 is MASSIVE!!!!

I'm certainly no solar guru. Ask Jack or John who hooks me up with a 2 amp plug from his rig to run my portable ice maker. (I really only need 1.78amps to run it, but don't tell John.) :huh:

As you have asked again, I'll ask again... what is your reasoning for using "method 3" and running your paired banks to a terminal post instead of paralleling your 6v's in series directly? There might be extenuating circumstances where that might be a viable option, but it's pretty darn rare unless those circumstances exist. I can't see how building in longer runs and building an additional resistance factor can be of benefit unless it is absolutely necessary.

Not to be disparaging... if it's something you feel confident in, then I would go for it. I just don't personally understand it from the information that has been provided thus far.

Again, you are more than able to run different gauged lines. As long as the inter battery connections are of the same length and gauge, you can run those to a terminal block and run the accumulative voltage/amps with a different gauge wire connection to your rigs systems. That IS workable.

oldjohnt · July 10, 2015

Pebbledropper, You're a man near my heart, I like, within reason, a conservative or overkill design over the long haul, especially when its done to protect a fairly hefty battery bank investment and can better balance ALL the batteries in the system. Id hate for only 1 or 2 batteries to fail prematurely when that could have been prevented had I invested more time and money in my initial system wiring (such as SmartGuage recommends)

4/0 Copper THWN 75 Degrees has an ampacity of 230 amps (80%of which is 184 Amps)

2/0 Copper THWN 75 Degrees has an ampacity of 175 Amps (80% of which is 140 Amps)

Its my opinion being both an Electrical Engineer and an Attorney, is that when the manufacturer recommends or a dealer installs X wire gauge, its likely a conservative rating and perhaps/possibly MORE then needed, but they are covering their you know what against possible liability and negligence lawsuits. If engineering specified say X gauge, after the legal department reviewed the specs, I can see it being increased lol. That's just how attorneys operate !!!!

HOWEVER, you wont see me saying go ahead use lighter gauge wire then the manufacturer suggested. I guess what I'm saying is just because someone wired some "portion" of the system with 4/0, don't necessarily mean smaller wouldn't have still satisfied the NEC and voltage drop considerations OR THAT YOU NEED ALL 4/0 in certain places. Also, the ratings I cite have to do with the max current such that heat is sufficiently dissipated and the insulation does not degrade ITS STILL TRUE BIGGER WIRE EQUALS LESS VOLTAGE DROP which is why as distance increases bigger then what the NEC specifies may be what the manufacturer recommends.

Now to your question: NOTE those parallel wire runs DO NOT have to carry the current of the runs where your total battery bank wires to say an Inverter or a DC buss or distribution system. That's one reason where 2/0 might suffice in one location, while 4/0 is required FROM the total battery bank TO say your biggest load like an Inverter.

YOU ASK "Can I use 2/0 for the parallel wires and the wires between the 6V's making them in series?"

a) If you're talking those Method 3 connection wires off each batteries + or - , and the max CONTINUOUS load in those individual cables is 80% of 175 amps = 140 amps,,,,,,,,,, and the length is reasonably short (say mess then 3 feet) ITS MY OPINION SURE 2/0 WILL WORK FINE.

As far as the series connection of two sixes to make up the 12 volts, SAME ANSWER BUT SEE ABOVE the parallel wiring doesn't carry the current of the total entire battery bank to a big load like an inverter!!!!!!!!!!!!!!!!!!!!!!!!!! That's where you may need bigger wire, say perhaps 2/0 in the Method 3 parallel wiring, but 4/0 FROM total battery bank TO inverter.

You see I just cant give any exact or spoon fed answer unless I have all the exact load figures in front of me and sure, given the type of data and reasonable assumptions the fine gents above I could make an engineering approximation, but it looks they have that pretty well covered.

Again, if I were the designer and assuming the runs are short so voltage drop is NOT a problem, Id specify 2/0 MINIMUM if the Max "CONTINUOUS" load was no greater then 80% of 175 or 140 Amps, and specify 4/0 MINIMUM if the Max "CONTINUOUS" load was no greater then 80% of 230 or 184 amps BUT THEN IF I PUT ON MY ATTORNEY HAT AND WORKED FOR THE MANUFACTURER OR INSTALLER ID BUMP THEM UP A GAUGE LOL Also, the NEC specifies certain MINIMUM standards but that don't mean bigger cant be used PLUS it does reduce voltage drop.

FINALLY my opinion regarding those those SmartGuage wiring methods. Sure some may consider their methods overkill and that's fine, they can wire as they please. HOWEVER if you study and understand their engineering theory and logic, I believe it to be correct. The thing is if you factor in battery investment and wish to maximize their longevity ITS AGAIN MY OPINION the battery balance achieved using their wiring methods improves overall longevity of the "entire" battery bank IE will reduce the chance of one battery in the bank failing prematurely. THEIR METHOD ACHIEVES BETTER BATTERY BALANCE

Sure any person can testify """"by golly he didn't wire his like Smart Gauge and he never had a problem in 40 years BLAH BLAH BLAH""""" BUT THAT DONT DISPROVE THE SMARTGAUGE METHOD ISNT SUPERIOR. If all the batteries aren't balanced one can fail while another has remaining life.

Summary Opinion: The 2/0 and 4/0 wire you asked about will likely suffice (Provided your actual loads are within specs!!!!!!!!!!!!!!!!!) and be fine, but I especially like your using the Smart Gauge method even if some don't like it, or believe in it, or think its overkill, or swear they did otherwise and it worked fine and you don't need to do it that way. Anyone is welcome to wire as they please, its their RV, their money, their choice but likewise, this is your RV and you should do the same and NOT what I or others might think.

Best wishes

John T

Jack Mayer · July 10, 2015

Not to prolong the agony here, but:

You wire for the heaviest current. Bill has it knocked.....the inverter load is almost always the heaviest current draw in a "normal" system. And in this case you would wire for the inverter load. 4/0 main feeds is NOT overkill. FOLLOW the inverter manuf. instructions. In this case Magnum will specify 4/0 wire.
NEVER, EVER assume an RV manufacturer did something "correctly", and make other judgements based on that. I have consistently seen bad wiring - ESPECIALLY in more advanced electrical systems - from RV manufacturers.
The SmartGauge wiring methods are correct and tested. But notice the very small "improvement" as you move from the "obvious" methods, that yield a big reward, to the "nuanced" methods that yield little to no improvement. Where you draw the line is up to the installer. The biggest improvements are diagonal loads/charge and equal length wires. The buss is an improvement but actually it is often more justified as an installation convenience. I always use a single stud to bring together the +/- load lines and use that as the battery attachment point. I rarely put in a true buss for the batteries, but if you can swing it in your installation it is helpful. Your choice.
In this particular scenario you can use 2/0 inter-battery without an issue. Most people find it easier to wire with all the same wire, because you don't have to order multiple sizes. But it is not necessary from an electrical perspective for either load or charge. You just have to do it right.

oldjohnt · July 10, 2015

Jack, "Not to prolong the agony here, but" I LOVE IT, great comment

Pebble, For the most part, 3 or 4 people agree and arrived at basically the same, your 2/0 and 4/0 proposal should work, PROVIDED your actual once all is installed and operating "Continuous" loads do not exceed 140 and 184 Amps. If that's so and your lengths aren't excessive, Id not hesitate to use 2/0 and 4/0 cables UNLESS for added safety and warranty issues the manufacturer suggests larger cables, and even if your cables (based on ACTUAL loads) are overkill, I wouldn't let that worry me, better safe then sorry plus reduced voltage drop.

Now go for it and wire as you please, we report you decide.

John T

JCTex · July 11, 2015

Thanks very much, everyone. I hope all this helps someone else who also needs to upgrade battery and inverter systems.

I called Magnum Techs. Very helpful. Said my MS hybrid 3012 has a maximum current draw of 400A. They want 4/0 between the bank and the inverter; but in an "equal length" parallel connection, inner-bank connections can be 2/0 without problem. She said she's know of others who did it. Like all above, she cautioned to make all parallel wires the same type, lugs, and length.

For reasons stated in their Manual, Magnum wants the main 4/0 cables banded together as soon as possible once they leave the joining terminal lug to the parallels. They want them together tightly by nylon ties or tape. I can do this but probably only if I do all these connections along the long center axis of the bank.

This will be fun. Now, I have to integrate as much of the existing Country Coach disconnect switches, breakers, and cat fuses as I think prudent. I'm still not sure where the engine alternator charging line attaches or to what.

Jerry

oldjohnt · July 11, 2015

CONGRATULATIONS Jerry, Id love to see your system once all wired up. Hey, if 3 or 4 of the gang here PLUS the manufacturer agree 2/0 and 4/0 suffices (subject to actual max continuous load in my advise) IT MUST BE OKAY LOL The same length thing is to insure, of course, one conductor doesn't carry a lot more current then its mate. The one time I perhaps/might/maybe vary from manufacturers recommendations is if the wire size they specify IS SMALLER THEN WHAT THE NEC ALLOWS. Although its rare, their tech department may or may not be the sharpest tool in the box nor familiar and experienced with the NEC, as their rules and tables and graphs and all their cites back to other sections is even more confusing then reading law cases or statutes lol The NEC cant get through a sentence without referencing back to 2 or 3 other sections each of which references back to 2 or 3 more IT USED TO DRIVE ME TO DRINK LOL

You mentioned: "I'm still not sure where the engine alternator charging line attaches or to what."

FWIW and there can be several different methods, the circuit which charges my house battery bank via the engines alternator when running, consists of a mechanical isolation relay which has a time delay that doesn't latch in until a set period AFTER the engine starts and the engine battery and alternator and its regulation system has time to somewhat stabilize. So perhaps look for an isolation relay (may be solid state or mechanical) and some cables located from your house battery bank up to your engine battery area. The cables on mine (engine system back to house battery bank) are No 2 or 4 as I recall, NOT any thin wimpy 6 gauge or so. The only thing is my alternator may not do near as good a job of properly and fully charging my deep cycle house batteries as either my Smart Solar or Smart Charger can, plus there could be issues with the alternators charging amps capacity SO IM NOT SAYING IF OR HOW YOUR ALTERNATOR SHOULD OR SHOULD NOT BE USED TO CHARGE YOUR HOUSE BANK WHILE DRIVING. Maybe it does maybe it doesn't at all???? Maybe your alternator could have issues if coupled to that many and different type of batteries??? It depends on your system and alternator etc NOT HOW MINE OR OTHERS WORKS. Do your homework. PS I was talking about a Motorhome if a trailer its a completely different animal PS I also have an emergency push switch which closes the isolation relay to "jump" my engine battery from the house batteries should it be discharged.

Ya know, if you have plenty of Solar you could not even fool with your engine alternator perhaps laboring or over working to charge all your house batteries, just allow the sun and a smart solar charge controller to charge them while driving!!!!!!!!!!!!!! Besides those Lifelines may not like nor your alternator like trying to charge them !!!! If your Smart Solar Charge Controller is suitable for and set to charge the Lifelines properly, I'm not sure I would even mess trying to let your alternator charge them as it may do more harm then good to BOTH your Batteries and Alternator. Maybe there IS NO CONNECTION HOUSE BATTERIES TO ALTERNATOR AT THE TIME AND FOR GOOD REASON?????????

Job well done

John T

oldjohnt · July 11, 2015

Thanks a lot Bill,

Good info. I still utilize the NEC for the most part as far as current rating is concerned, even if the voltage is 12 or 120, as current flow is what determines the amount of heat and how much can be dissipated without degrading the insulation, regardless if there's 12 or 120 line to line. BUT HEY IM OLD FASHIONED AND CONSERVATIVE LOL and my code book is soooooooooooooo outdated grrrrrrrrrrrrrrrrrrrrr. If there were any minor differences in the NEC concerning a wires ampacity if 12 or 120 volts wiring is concerned, YOU KNOW ME, ID OPT FOR THE BIGGER WIRE !!!!!!!!!!!!!!!!!

While I currently have my house battery bank connected to the engine battery while driving (AFTER the time delay) I've never measured how much actual charging current actually flows back, but I do know there's enough current flow to raise my house battery bank voltage to around 14.2 volts while driving, so its getting some current at least. HOWEVER, its my belief the Alternator on its own is never going to do as good of a quality job to completely charge my deep cycle battery bank like either of my Smart 4 stage chargers. I AGREE CHARGING FROM A CHARGER/INVERTER LIKE YOU MENTIONED IS BEST plus it makes for less alternator work.

PS I have a motorhome, NOT pulling a fifth wheel, and my house battery bank is less then 10 feet from my engine battery connected with 2 or 4 gauge copper wire, SO THATS A DIFFERENT ANIMAL then if you're talkin 5fifth wheel

NO I haven't followed how they modified the NEC for trailer manufacturers, since retired I don't keep up on that stuff like I used to when I was practicing BUT THANKS FOR THE INFO I will have to educate myself.

THANKS AGAIN BILL, I really enjoy this sparky chat

John T Old, and out dated lol