Battery and cable cutoff question...

[galladanb]

I always get such great answers from you guys in here...

Today's question concerns a what if...
Like, for instance, what if I use the same connections for the battery cutoff switch
and for the 12v power to the distribution panel?

I have a charger / inverter that has 2/0 cables to the batteries (2 6v EGC2's)
and I will have run cables from the inverter / charger to the cutoff switch
to the fuse to the batteries.

Can I simply tie the power for the distribution onto the same bolt?
also would it be OK if the power cable to the distribution panel be only 2AWG and not 2/0?
Would that make any difference? The Dist panel only has an input for the 2AWG sized cable.

And also for an additional question, another what if...
Will it be OK if the ground from the distribution panel is only 4AWG?
Again, that is all the panel has provision for...

In addition, in case anyone has been following our build, and has also been seeing my extra
side posts about various electrical install issues...

I did a kinda major screw up the other day. I agonized over ordering the cables from the GenuineDealz guys
and finally dropped the order this last Monday, and on Tuesday I realized I made this screw up...
I thought I had 3/8 terminals on everything.

NOPE! Only on the Cutoff switches. All the other connections are 5/16ths....

So when the cables got here yesterday, ( I KNOW RIGHT? SUPER FAST SERVICE!!!!!!!!!)
I felt that gut kick in knowing I had messed up really bad. I called them and they said I really had a couple of choices.

1.) Do a return and pay a 30% restock fee, which since it was my fault, I thought was very reasonable!
2.) Send them all back and they could replace the /38 ends with 5/16th ends where ever I need them. Also reasonable!
3.) Use them as is with big and or lock washers...

So there is my 3rd question of the day, should I go ahead and just use washers and press on?

I mean there is not a lot of slop there, so would it be a big deal????

 

[BradKW]

They will be fine on 5/16" studs...SS washer and nuts.

I suggest using a bus bar after shut off for distribution. If I weren't on the phone I'd link the one I used, it's a Blue Sea

 

[John61CT]

The higher the amps more critical getting the right matching studs & rings.

Great resource here, see "Pick You Lugs" : http://www.pbase.com/mainecruising/battery_cables

 

[BradKW]

I've read tons of stuff by Maine Sail over the past year and he's incredibly knowledgable.

It's worth saying though that I also learned to take him with a grain of salt so to speak. That linked article was one example of when I became confident I didn't need to actually follow all his advice and still things would work out fine. I'm referring specifically to his views on crimping and crimpers... his bashing of the Harbor Freight crimper was where I learned that there were cheaper option than his mega-bux tool kit. I went on to buy a hydraulic crimper off Amazon for under $40 and have since posted a review here, including cut open lugs to show cold weld.

Also fair to say, I wouldn't have known what was important and been able to make informed choices without reading Maine Sail's article.

But I guess my point is that he writing about standards he believes important when dealing with off shore boating and huge engines and generators. I am quite sure he is right. I am also quite sure that my 3/8" lugs are perfectly fine on my 5/16' studs. I didn't even order the cables wrong, I just ran outta 5/16" and didn't feel like running to West Marine

 

[John61CT]

Well I'm being super-conservative cautious for now with stuff like electrics, brakes, propane. Maybe down the road I'll relax a bit. . .

And I did put in the caveat about level of current, 300A flow vs 50 would make a difference.

 

[Weight]

The stud only serves to hold the cable lug against the battery flat or bus bar flat. I have some of the same problem. I use stainless washer, lock washer, nut. Torqued to 110 inch pounds.

 

[galladanb]

So, in general... I'm good to go?

 

[SternWake]

Make sure there is no washer between ring terminal and the surface it is to rest on. Stainless steel is not a great electrical conductor. The threaded studs are not intended to carry any of the current, merely to hold the ring terminal tight to conductive surface. Diameter of the ring terminal mating to the stud is for maximum surface area for the conduction of electricity, and minimal resistance and heating and voltage drop at that point, at high currents. It will also keep the ring terminal fram squeezing to the side when tightneing the nut, and from further reducing surface area between ring terminal and buss bar .

MaineSail does take things to extreme lengths of precision and quality above and Beyond ABYC standards, that are usually overkill for what RV'ers are doing. But nobody should be promoting halfassery 101 either and ringng the just fine bell after patting themselves on the back.

How to do something right so that it does not become a problem all too quickly, and 'good enough for now and the near future' can be quite far apart.

The more amperage which flows the more important it is to minimize resistance on electrical connectors, and to keep it low as they age and this is achieved by doing it right the first time, not waiting until it becomes an issue later possibly causing failure or perhaps a lengthy diagnosis of the issue, which stemmed from a poor crimp initally executed.

I own and use the HF crimper too, and while adequate, perhaps, it is far from Ideal, and nobody who makes serious cables for marine systems would proudly display it. And while one can rotate the dies to attempt to get 'earless crimps' this is no where near as good as a hexagonal crimper with The proper size dies that required no rotation to achieve a pretty result. Mashing a crimp back and forth when rotating the crimp within the dies weakens the copper lug and the wire stranding and will increase electrical resistance while reducing mechanical strength. Will this matter? Likely not unless it is asked to pass ~70+ amps for a long time.

Just beware that 'just fine', is an opinion, and could be a very uninformed opinion by someone looking for reassurance from others who share that uninformed opinion.




The professional quality crimpers are quite expensive though. I've filed out my HF crimper's dies for thick wall ring terminals bigger than 4awg, and take extra care to align the dies before beginning the crimp as they otherwise will be misaligned and possibly kink or puncture the crimp.

Just because one can cover an ugly crimp with nice adhesive lined heat shrink does not mean the crimp is a good one which will safely handle 100+ amps for an hour without heating excessively.

On high current wire terminations, A IR temp gun can easily reveal a poorly executed termination, before it causes a failure.

https://www.amazon.com/Thermometer-...F8&qid=1492883948&sr=1-5&keywords=IR+temp+gun

It can be useful on all electrical connections to find high resistance. I found my Napa grade fuse block was worthy of a proper sledgehammering and then the trash bin after hunting for high temps with my IR gun, and none of the circuits were anywhere near the max rating of the individual circuit or the block as a whole.

I highly regret most of my 'good enough' electrical terminations and the tools purchased to make them and the budget friendlier components.

But they have proven to be 'good enough' so far, but I would be embarressed if Mainsail were to ever look at some of them.

 

[John61CT]

I have been purchasing top-notch crimping tools on eBay for a small fraction of their value, e.g. $65 delivered for a $3,000+ tool.

Maine Sail's tool prices are currently a lot lower than much cr^ppier stuff out there.

Proper connectors, terminators, fuses etc are not at all worth skimping on IMO, so much stuff looks just like known-good products is actually dangerously cheap Chinese junk.

Not to say all Chinese made is junk, depends who's spec'ing and testing QC, just means buyer beware, squared.

 

[galladanb]

Regrettably, the last two comments here are???

I'm sorry, I don't get their point in relation to my question.
Is it OK to use the 3/8 terminals on the 5/16 posts?

And FYI, the posts on the batteries come up out of the plastic case, and there really is no metal around them, as far as I can see...

I was planning on placing a larger washer first, then the cables, then a smaller washer, then the nut.

Sound good?

 

[SternWake]

NO!

do not place a washer down first, unless it is pure copper and the samne or bigger surface area as would be without it.

http://www.pbase.com/mainecruising/battery_meltdown_averted

 

[BradKW]

Regrettably, the last two comments here are???

I'm sorry, I don't get their point in relation to my question.
Is it OK to use the 3/8 terminals on the 5/16 posts?

And FYI, the posts on the batteries come up out of the plastic case, and there really is no metal around them, as far as I can see...

I was planning on placing a larger washer first, then the cables, then a smaller washer, then the nut.

Sound good?

Are you saying that there is not a metal base at bottom of the threaded stud? I have not seen that if so, and it definitely changes things...

 

[Michael4104]

Do as SternWake says. No washer first. Wire lugs go straight to battery terminals/studs.

 

[John61CT]

Yes very strange if no metal base for the nut to clamp the ring to horizontally.

Pics?

If you end up with ring protruding outside the nut, in no contact with any metal, plus the gap on the inside, to me that means even less likely the larger ring size is OK.

Unless the current amps is very low.

 

[galladanb]

OK, revision and apology here...
Yes the battery posts DO have some surface to put the connection onto.
They are the same freakin color as the case, so I just missed them.... Sorry for the panic!

Now, Can I place several cables on the same posts?
Bare in mind, I'm asking about the huge 2/0 connectors...

I need one for the charger / inverter and one for the 12v distribution panel, also, the same for grounding side...???

And is it OK to mix sizes? The Charger ones are 2/0 and the distribution will only accept 4AWG max...

SO can I run what I need and not have any issues???

 

[Optimistic Paranoid]

I believe that you are not supposed to put more than 4 lugs on any post.  That's code on boats, enforced by the Coast Guard, and if it's not code elsewhere, it's certainly "best practice".

The other thing is that you are not supposed to put a large, heavy lug over a small, thin lug. 

Say you've got a 2/0 wire and a 10 gauge wire.  If you put the 10 gauge wire down first, and add the 2/0 gauge wire over it,  all of the current from/to the 2/0 gauge wire has to pass through the thin lug for the 10 gauge wire, which probably can't handle that kind of amperage.  So the correct way to do it is to put the 2/0 gauge wire down first and put the 10 gauge wire on top of it.

 

[John61CT]

And make sure of clearances, rotation etc so all the surfaces are clear and flat-parallel on their own, not relying on the nut snugging stuff together.

 

[SternWake]

three 2/0 gauge thick wall ring terminals/lugs might not stack with enough threads on the stud left over to get the nut on enough threads


Either a Buss stud or this dual terminal fuse block could be a solution to that:

https://www.amazon.com/Blue-Sea-Systems-Terminal-Block/dp/B002INJXO6

https://www.amazon.com/Blue-Sea-Sys...1493161742&sr=8-7&keywords=blue+seas+bus+stud

Don't let weight of battery cables or their stiffness exert too much force on the threaded battery stud/post, and do not overtighten.