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Old 02-08-2020, 15:11   #91
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Re: Battery Cable Parallel Sizing

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Better fire production.
Depends if the batteries are installed on the port or starboard side.
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Old 02-08-2020, 15:21   #92
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Re: Battery Cable Parallel Sizing

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Agreed, I donít think many can charge at .4c.
But we donít know about FF yet, they havenít 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?
Our 450 AH firefly 24 volt system is solar charged daily but seldom to full. I run the generator once or twice weekly, 60 amps, 28 volts. We have completed two seven month seasons in the Caribbean on anchor with the FF. I also have a similar sized Lifeline bank in reserve that is 12 years old, still good.
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Old 03-08-2020, 08:50   #93
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Re: Battery Cable Parallel Sizing

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So your saying that you canít get the same ampacity of a single wire with multiple wires?
No, not doubling up two that have the same no. of strands verses one wire with the same no. of equal sized strands.
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Old 03-08-2020, 09:00   #94
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Re: Battery Cable Parallel Sizing

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Our 450 AH firefly 24 volt system is solar charged daily but seldom to full. I run the generator once or twice weekly, 60 amps, 28 volts. We have completed two seven month seasons in the Caribbean on anchor with the FF. I also have a similar sized Lifeline bank in reserve that is 12 years old, still good.
Are they are doing good and living up to claims regarding psoc conditions?
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Old 03-08-2020, 09:11   #95
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Re: Battery Cable Parallel Sizing

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Our 450 AH firefly 24 volt system is solar charged daily but seldom to full. I run the generator once or twice weekly, 60 amps, 28 volts. We have completed two seven month seasons in the Caribbean on anchor with the FF. I also have a similar sized Lifeline bank in reserve that is 12 years old, still good.
A nice neat looking installation. It tells a lot about the owner.
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Old 03-08-2020, 09:24   #96
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Re: Battery Cable Parallel Sizing

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Our 450 AH firefly 24 volt system is solar charged daily but seldom to full. I run the generator once or twice weekly, 60 amps, 28 volts. We have completed two seven month seasons in the Caribbean on anchor with the FF. I also have a similar sized Lifeline bank in reserve that is 12 years old, still good.

Have you actually capacity checked the Lifeline bank?

I’m keeping 440 AH of Lifeline as a secondary bank too, partially as if I lose one of the Fireflies, I lose the whole bank, but also they are still good, just lost significant capacity.

Interestingly they have lost capacity when I sit in a marina on 13.3 V float 24/7, not when we are cruising and cycling them, equalizing hasn’t recovered any significant capacity.
I have not done an actual correct cap check, I go by the Smart Gauge, which also tracks exactly with Lifelines voltage under load SOC chart.

Except for the loss in capacity, my Lifeline bank is fine, it still fully charges in the same time it always has, and gets me through the night easily. If I wasn’t tracking capacity, I don’t think I would have noticed a capacity loss.

The other way I track capacity is that I have to set my amp counting battery monitors to a lower capacity for them to match the SOC the smart gauge computes, I trust the Smart Gauge because it matches Lifelines chart.

Point is I think many, many cruisers have banks that are “dead” but they are large enough so that even meeting the definition of dead, they still get by.
I’d bet your Lifelines at 12 yrs old are “dead” but still had enough capacity for you so they are fine.


On edit, I notice that you have no air gap between individual batteries, do they get warm with no air circulation? Firefly specs 1” space all around each battery I think.
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Old 03-08-2020, 09:31   #97
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Re: Battery Cable Parallel Sizing

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No, not doubling up two that have the same no. of strands verses one wire with the same no. of equal sized strands.
Iím trying to wrap my head around what your saying unsuccessfully, excepting for derating for multiple wires in a bundle, two identical wires will carry roughly twice the load of a single wire.
There are many reasons to run multiple wires, one is if a large wire is simply too stiff, another is to stream line manufacturing stock, if you can stock one size wire as opposed to several, itís a lot easier and more efficient.
It may however take more time to run several wires as opposed to just one, itís a balancing act.

But a very short section of small wire can carry quite a lot of amps, itís when you add length you get into voltage drop. Take a fuse for example, a fuse is nothing but a very small wire, yes there is voltage drop, itís not excessive due to the short length of the fuse.
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Old 07-08-2020, 06:58   #98
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Re: Battery Cable Parallel Sizing

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Originally Posted by a64pilot View Post
Iím trying to wrap my head around what your saying unsuccessfully, excepting for derating for multiple wires in a bundle, two identical wires will carry roughly twice the load of a single wire.
There are many reasons to run multiple wires, one is if a large wire is simply too stiff, another is to stream line manufacturing stock, if you can stock one size wire as opposed to several, itís a lot easier and more efficient.
It may however take more time to run several wires as opposed to just one, itís a balancing act.

But a very short section of small wire can carry quite a lot of amps, itís when you add length you get into voltage drop. Take a fuse for example, a fuse is nothing but a very small wire, yes there is voltage drop, itís not excessive due to the short length of the fuse.
From my understanding, the two parallel wires amounting to the same crosssectional area are actually a bit better. Larger surface area makes the thermal issue a bit better, and there is a tiny advantage in that charges like to run on the surface of the wire as opposed to the middle (remember that like charges repel so they want to get as far from each other as possible, so there is a bit more charge density close to the surface where there are not charges in the insulation pushing them back).

In short, two parallel wires having the same or greater cross section should be better than a single wire.
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Old 07-08-2020, 07:04   #99
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Re: Battery Cable Parallel Sizing

Usually not a good thing to connect 12 volt batteries in parallel to make a house bank. If one of the batteries developes a bad cell, other batterie(s) connected in parallel will discharge into the bad battery, trying to equal the voltage. Much better to use two 6 volt batteries in series. For extremely large house banks, use six 2 volt cells in series. For example, the Surrette Battery Company makes 6 volt marine batteries in the 250 - 930 Amp Hour range and 2 volt cells in the 1,000 - 5,000 Amp Hour range.
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Old 07-08-2020, 07:40   #100
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Re: Battery Cable Parallel Sizing

Statistically, if two sets of batteries of batteries were otherwise IDENTICAL, using fewer larger cells will always be more reliable than more smaller cells. The problem in the real world is that combining six 2-volt cells of 100 AH probably will not have the same physical/electrical characteristics as combining a bunch of 12-volt batteries together.

Multiple 2-volt cells in a single bank theoretically yield greater reliability, but less redundancy when a cell fails.

You pay your money and takes your chances.

Multiple parallel wires increase the overall current capacity. But each must be separately fused at its ampacity. So using multiple wires is usually only worthwhile in very special cases.

Skin effect only applies to alternating currents, and even then only at higher frequencies unless youíre talking about very big wires or very high current (as in AC utilities).
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Old 07-08-2020, 07:41   #101
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Re: Battery Cable Parallel Sizing

that is silly in lots of ways
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Old 07-08-2020, 07:44   #102
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Re: Battery Cable Parallel Sizing

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Statistically, if two sets of batteries of batteries were otherwise IDENTICAL, using fewer larger cells will always be more reliable than more smaller cells. The problem in the real world is that combining six 2-volt cells of 100 AH probably will not have the same physical/electrical characteristics as combining a bunch of 12-volt batteries together.
A 12 volt lead acid battery IS six 2-volt cells just six cells in a single "box". There is not much difference with six cells in one box and six boxes each with one cell.

Then again I agree with you that the prior statements was way to absolute. The idea that you could never put cells in parallel is just silly.

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Multiple parallel wires increase the overall current capacity. But each must be separately fused at its ampacity. So using multiple wires is usually only worthwhile in very special cases.

Skin effect only applies to alternating currents, and even then only at higher frequencies unless you’re talking about very big wires or very high current (as in AC utilities).
Agreed on these. Half assing it and using multiple connectors not separately fused which is likely what someone would do is a safety risk.
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Old 07-08-2020, 08:15   #103
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Re: Battery Cable Parallel Sizing

Lead-acid cells are ALWAYS 2-volts. For more than 2 volts, you combine them in series. For more energy/current, you combine them in parallel. The question then becomes: what combination of serial and parallel provides the "best" results.

Assuming all the 2-volt cells in a bank are identical, regardless of how theyíre packaged, the more cells you have, the lower the overall reliability.

So, a pair of T-105s, rated at about 220AH at 6v each, will yield 12v at 220 AH. Using the Trojan 12-volt battery in the same case size, which has twice the voltage per battery, but half the AH capacity, yields the same overall capacity. The two series-connected 6-volt batteries will have six cells. The parallel-connected 12-volt batteries will have 12 cells. So the parallel bank will have half the overall reliability of the series bank.

That in no way is a statement that one should never hook batteries in parallel. Itís simply a statement that the more of something that one has, the more likely that that one of them will fail.
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Old 07-08-2020, 08:16   #104
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Re: Battery Cable Parallel Sizing

Not sure if this is allowed on CF. If not the mods can remove it.

We had a domestic (3 x 95AH) battery bank failure in Oct 2019. We bought 3 x 100ah replacement batteries and then started researching why the original 15 month old batteries collapsed. There were many contributing factors and one of those was the sizing and length of the cables between the batteries.


In the linked video we show 4 options of linking 4 domestic batteries together for balanced discharge and recharge. We chose option 3.


https://youtu.be/Wf5ijiVV93c
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Old 07-08-2020, 08:19   #105
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Re: Battery Cable Parallel Sizing

1. "A 12 volt lead acid battery IS six 2-volt cells just six cells in a single "box". There is not much difference with six cells in one box and six boxes each with one cell." - True, but you are missing the point, individual 2 volt cells are only used in extremely large house banks, ~1,000 Amp Hours and up. 2 volt cells in this Amp-Hr range weight several hundred pounds and up, so batteries in this Amp-Hr range are assembled on the boat from individual 2 volt cells.

2. "The idea that you could never put cells in parallel is just silly." Please be respectful !! 12 volt batteries should NEVER be wired permanently in Parallel, but only connected in parallel for emergency use using individual switches on each battery. When permanently connected in parallel, a bad cell in one battery can discharge the whole bank.
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