Battery Cable Parallel Sizing

[a64pilot]

Originally Posted by kmacdonald

If you chose to connect the batteries the traditional way where the batteries are set side by side with the positive terminal oriented the same way and you connect the load positive and negative to opposite ends of the battery bank it will still be balanced but the interconnects will carry the full load current and require larger cables.

So what’s the downside to needing full size cables?
Always, always oversize wiring, you’ll never wish you hadn’t.
Weight may matter on a super light carbon fiber racing yacht, but wiring weight on a cruising boat is just insignificant.
Besides want to save wiring weight? Go to a 24 or better yet a 48V system, or even better go all high voltage AC.

[Cadence]

If there is enough voltage drop in any cable to worry about battery balancing there is a problem.

[sailorboy1]

Originally Posted by Cadence

If there is enough voltage drop in any cable to worry about battery balancing there is a problem.

Well you wouldn't know that unless you did the cals and decided how much of "enough voltage drop" to be concerned about. Otherwise you would just be guessing

I did it all and am good. I need at least 00, otherwise every time I flush the head the voltage drop makes the TV turn off. THAT is totally unacceptable

[jharding]

when I set up my battery bank and inverter/charger the length of wires dictated that I use 4/0 wire so we did all connections with 4/0 I have never regretted it and it is not that hard to work with, getting the length right and the lugs oriented right is very helpful may take a little trial and error. I'm probably not as balanced as I could be, hopefully the large wires make up for it.

[Cadence]

Originally Posted by sailorboy1

Well you wouldn't know that unless you did the cals and decided how much of "enough voltage drop" to be concerned about. Otherwise you would just be guessing

I did it all and am good. I need at least 00, otherwise every time I flush the head the voltage drop makes the TV turn off. THAT is totally unacceptable

It sounds to me like you need to wire your battery bank to a buss with a short run and then distribute to various needs from there with the appropriate wire gauges and fusing. Frankly it sounds like an accident looking for a place to happen with what you have.

[a64pilot]

Originally Posted by Cadence

It sounds to me like you need to wire your battery bank to a buss with a short run and then distribute to various needs from there with the appropriate wire gauges and fusing. Frankly it sounds like an accident looking for a place to happen with what you have.

How do you incorporate a battery switch in that scenario?
I’m sure what he has is what most all of us have, big fat wire to battery switch, big fat wire to engine, smaller wire from battery switch to buss bar in CB panel that all the DC loads come off of.

My 0000 wire will only be 0000 to the inverter, the rest of my DC system, being the wire to the battery switch, then to the engine and then the ground to the engine is 00.
I know, I’m not talking about him, but those of us with big inverters, ought to follow the inverter manufacturers recommendations as to wire sizing, and of course thats ground and power wire.

But finally wire can only be too small, it can’t be too big. I was having voltage problems with my fridge, old 10 ga wire and when the bank was low it was causing starting issues once in a blue moon. So I replaced the wire with 6ga to a terminal block one foot away from the controller and ran 10 ga for that last foot, because you can’t use spade terminals on 6 ga wire, it’s too stiff. But since then I don’t have any issues, is 6ga excessive? Yes I’m sure it is, but can I have too little voltage drop? No. Is it likely that electronics last longer with less voltage drop and less fluctuations in voltage? Probably.

[sailorboy1]

Originally Posted by Cadence

Frankly it sounds like an accident looking for a place to happen with what you have.

FRANKLY I have no idea how you could jump to such a conclusion. You know NOTHING about my setup other than that it is going to have 4 batteries, of which 3 are next to each other and the other is going to be about 1 foot away. Of course you only know this it you read the written info. Otherwise all you are doing is waging a dog.

[NorthCoastJoe]

It has been a fun read, seems to me that the normal corrosion that happens between cleanings would be more of an issue than anything else. For all my electrical work I go to a table and use one size larger than recomended.

[Cadence]

Originally Posted by sailorboy1

FRANKLY I have no idea how you could jump to such a conclusion. You know NOTHING about my setup other than that it is going to have 4 batteries, of which 3 are next to each other and the other is going to be about 1 foot away. Of course you only know this it you read the written info. Otherwise all you are doing is waging a dog.

I'm not truing to be contrary. If you have enough line lose when you flush the head to drop your TV your wiring has a problem or your batteries are reaching end of life. Take it for what it is or isn't worth.

[kmacdonald]

Originally Posted by a64pilot

How do you incorporate a battery switch in that scenario?
I’m sure what he has is what most all of us have, big fat wire to battery switch, big fat wire to engine, smaller wire from battery switch to buss bar in CB panel that all the DC loads come off of.

That's right. The location of the switch matters. The closer to the batteries the better but the switch is often located where convenient.

Reasoning: When the switch is a long way from the batteries there is a voltage drop at the starter AND the DC panel when cranking the engine due to drop in the long big fat cable. The voltage drop is often large enough to disrupt electronics. Like getting scalded showering when someone flushes the toilet. The simple solution to that is obvious.

[kmacdonald]

Originally Posted by NorthCoastJoe

It has been a fun read, seems to me that the normal corrosion that happens between cleanings would be more of an issue than anything else. For all my electrical work I go to a table and use one size larger than recomended.

Quite reasonable.

[Q Xopa]

Originally Posted by sailorboy1

the question is the cable SIZE BETWEEN each 12V battery. Not the positive on one end of the bank and the negative on the other.

Pos at one end, and Neg at the other, is a start, better than most but still not the complete answer.

Essentially you need EQUAL flow into and out of all batts. Generally best done using same length leads from all Negs and all Poss.

Ok of course this wont always be practical.

Thats a creative solution you are proposing using different diameter cables.

Im sure someone will breaze along here that knows more than me, but sounds reasonable, you could get atleast pretty close to properly balanced this way.

I think with DC current, cable cross sectional area and length calculations should be possible. Blue Seas calculator? I would guess that different gauge cables only coming in disreate sizes, you could adjust with some length variations.

Lets face it, most parallel instalations arent balanced to some degree and the owners are usually oblivious and often not overly effected. Yes as you obviously know, some life is lost.

Good luck.

[Bycrick]

If one has to have a "long" battery cable run just to locate the switch in a "convenient" location, consider using one of the Blue Sea Remote Battery Switches. Locate the switch close to the batteries and the remote control wherever is convenient. The difference in cost is about the same as 8 feet of 2/0 cable.

[sailorboy1]

Originally Posted by Cadence

I'm not truing to be contrary. If you have enough line lose when you flush the head to drop your TV your wiring has a problem or your batteries are reaching end of life. Take it for what it is or isn't worth.

Well YES the batteries are near their end of life. That's the reason for this whole thing!

[kmacdonald]

Originally Posted by Bycrick

If one has to have a "long" battery cable run just to locate the switch in a "convenient" location, consider using one of the Blue Sea Remote Battery Switches. Locate the switch close to the batteries and the remote control wherever is convenient. The difference in cost is about the same as 8 feet of 2/0 cable.

Now that's good advice!