Battery Cable Parallel Sizing

[GILow]

Originally Posted by sailorboy1

Is it worth it to try to "balance" the cable size of a 4 battery bank in effort to try to get equal amps out of each battery?

I think it is.

I simply made all three of my cable sets the same length. Yes, this meant two of them were longer than needed, but it seemed the simplest way to ensure the best chance of equal draw.

I think the size differences in cables approach would be difficult as the jump between sizes is just too great. (unless there is a huge difference in cable runs.) And I'm bothered by the maths on this one, I suspect the difference in draw would be non linear based on current, even though V=IR is linear. I suspect it is a little more subtle than that.

[GILow]

Originally Posted by sailorboy1

I need at least 00, otherwise every time I flush the head the voltage drop makes the TV turn off.

That's a safety feature to ensure you are dealing with only one load of sh-t at once.

[kmacdonald]

Close to four years on T105's cruising full time seems good to me. A lot better than 2 years on a set of lifelines some people claim. I know, that's a head scratcher for sure but it's only money and thankfully not mine. Talk about a hole in your pocket.

[a64pilot]

You can kill any battery, and do it in a short time too. My Lifeline bank is going on 6 years old, has lost capacity and I simply don’t trust them to go off where batteries aren’t available .
Reading the manual for the Firefly batteries is different from what I hear on here. It seems you need a big charger and to hit them with a .4C charge rate until they are full, and follow that with a 24 hour float.
For my modest size 450 AH bank, that’s a 180 amp charger, most can’t do that, and many have larger than 450 AH.

I can do the 180 amp charging, I suspect they won’t take that much current for long anyway, but the 24 hour float is going to take shorepower, because I’m not running a generator for 30 hours once a month.

[sailorboy1]

I have a cruiser friend who has FF and I bet can't charge any faster than .1C and hasn't had a problem.

[sailorboy1]

I had some wine last and am now thinking straighter.

Looking at voltage drop of 3’ of 4/0 and 2/0 at 150 amps it is so little difference that i think i will get the smaller ones. 2/0 is the recommended size for my inverter and there is 4/0 from the batteries to the switch.

In theory i could do smaller, but that jst seems silly to play around with.

[kmacdonald]

Does anyone know why a lot of lithium drop in manufacturers use 10 AWG wire to connect the cells to the battery post? Different manufacturers use differing numbers of wires but usually all 10 AWG wires.

[a64pilot]

Originally Posted by kmacdonald

Does anyone know why a lot of lithium drop in manufacturers use 10 AWG wire to connect the cells to the battery post? Different manufacturers use differing numbers of wires but usually all 10 AWG wires.

Length of wire, and capacity of the battery in amps doesn’t exceed what 10 ga can carry.
Multiple wires is of course the same as one larger wire.

[Cadence]

Originally Posted by a64pilot

Length of wire, and capacity of the battery in amps doesn’t exceed what 10 ga can carry.
Multiple wires is of course the same as one larger wire.

I don't believe that is true. The circular mil. area is a function of the sq. of the radius.

[sailorboy1]

Originally Posted by kmacdonald

Does anyone know why a lot of lithium drop in manufacturers use 10 AWG wire to connect the cells to the battery post? Different manufacturers use differing numbers of wires but usually all 10 AWG wires.

Better fire production.

[a64pilot]

Originally Posted by Cadence

I don't believe that is true. The circular mil. area is a function of the sq. of the radius.

So your saying that you can’t get the same ampacity of a single wire with multiple wires?

[kmacdonald]

FYI: The standard 10% and 3% voltage drop wire size selector guides is not what you should be using to size your battery interconnects.

[a64pilot]

Originally Posted by sailorboy1

I have a cruiser friend who has FF and I bet can't charge any faster than .1C and hasn't had a problem.

Agreed, I don’t think many can charge at .4c.
But we don’t know about FF yet, they haven’t been out there long enough and or in large enough numbers.
Even the testing I keep seeing is over 30 cycles etc extrapolating the future based on one will recover after 30 cycles, well what about 300 cycles?
How often can I do a restoration charge? When should I do a restoration charge? How much capacity loss before a restoration charge is necessary? How many back to back deep discharges with corresponding full charges to include the 24 hr float are necessary to recover capacity?
The 24 hour float is unrealistic for cruisers, if iDeep discharge regularly I need to fully recharge and float for 24 hours every week?
What is the definition of a deep discharge?

[kmacdonald]

Originally Posted by a64pilot

So your saying that you can’t get the same ampacity of a single wire with multiple wires?

I think he misunderstood what you were saying. He mistakenly thought you meant that two 10 AWG wires cant carry more current than one 10 AWG wire.

[kmacdonald]

It's becoming apparent why there is such a discrepancy between peoples experience with the same batteries. Not only the use scenarios vary but also the details of installation. Anecdotal reports need to be given all the credibility they deserve---------- very little.