New Battery Bank (is this wired correctly?)

[SV Bacchus]

It's been said several times already but I really don't like laying a +/- over each other. Long term that is just asking for trouble. An earlier poster suggested turning 3 of the batteries so the cables can connect without crossing over each other. If you can do that, I would..

[epiic]

Originally Posted by svmobert

Will try to address several of the points made in a single reply..

1.) There is no inherent issue with odd number of batteries in Parallel, it only matters in Series wiring.
2.) In Parallel wiring you can daisy chain or use a star configuration. With 2-4 batteries, Daisy chaining is "ok", but with 3+ batteries you will find that the middle batteries receive a bit less charge compared to the end batteries. This is what star wiring will solve.
3.) If you are daisy chaining between batteries, you take + from the battery at one end of the bank, and - from the battery at the other end of the bank for your loads. (In your photo, based on the two wires leaving and presumably connecting to the 7th battery, your current wiring breaks the proper daisy chain)
Note: The way it's wired in the photo, where the 7th battery is sort of fronting the other 6, your charging and loads will stress the 7th battery significantly (and also your charge level will be measured on the 7th battery. This will leave the other 6 batteries undercharged over time.
4.) If you are using star wiring, the ideal scenario is that the cables from the central bus bars to the batteries are all the same length. This ensures that the wire resistance is the same for each battery, and means that charging, discharging, voltages will all be essentially equal across all the batteries. Star wiring also makes it relatively easy to remove a bad battery from the bank if needed. since your 7th battery is in a different cabin, maintaining the same cable length for it as for the other 6 batteries *might* be difficult. A little difference isn't that big of a deal though.
5.) The Firefly Oasis batteries are VRLA (roughly equivalent to AGM) so gassing and wood enclosures it not really an issue. Just make sure that the cables are protected from chafe where they meet the wood sides, etc.

All that said, let's address your specific situation..

The 6 batteries pictures ARE wired correctly for a daisy-chain parallel bank. However with the addition of the 7th battery, as you described, the bank is incorrectly wired.

This is no ordinary AGM battery. The Firefly Oasis is essentially an AGM battery with Lithium Battery benefits - They can be charged very quickly, not harmed by sitting partially discharged, can handle PSOC (Partial State Of Charge) conditions for long periods of time without being damaged, and can be deeply discharged (down to 10-20%) without long term damage. What this means is that 6 batteries provide >600ah of USABLE capacity. A 660ah lead-acid, agm, or gel bank would only provide about 300ah of Usable capacity.

My personal recommendation is to dump the 7th battery from the bank, in part because it's probably not necessary, and because it complicates the wiring and charging of the battery bank. If you want to use the 7th battery, I'd consider making it an isolated electronics battery, for SSB radio or other sensitive electronics. Put all your normal house loads, chargers, inverters, etc on the main bank, connect the 7th battery to the bank via an Echo-charger unit or DC-DC converter so that the 7th battery gets charged by the house bank as needed, and then connect your sensitive loads to the isolated battery.

Hopefully that all helps. And by the way, I'm jealous of your Firefly's... Those are on my list if my cruising budget allows, but for now I have a 4x150ah AGM bank that works fine.

This all makes perfect sense to me. Thank-you so much for your advice.

So 7 batteries can be wired in parallel but only if they are wired in "spoke" or "bus bar" configuration with equal length cables.

So I shouldn't wire the 7th battery (technically the 1st battery since its directly connected to the charge controller) in parallel normally...? I can connect the positive wire from the 1st battery and the negative wire to the 2nd battery and extend the negative from the charge controller all the way to the last battery...

I will definitely reverse the position of the batteries so the positive and negative wires do not cross.

[savoir]

I suggest getting rid of battery #7. With an odd number of batteries you won't be able to avoid that battery doing either too much or too little work. Dedicating the battery to a non house purpose isn't a bad idea - maybe electronics, maybe windlass.

[smac999]

the number of batteries doesn't matter but ideally you want the bank wired end to end which you don't currently have. (those 6 are but the 7th won't be based on only 2 wires leaving that bank) you'd need a 3rd wire leaving. you'd probably only need to change / add one wire. but it's hard to tell without seeing the rest of it.

if you move the batterie's you'll end up with 2 different lengh wires. right they are they are exact matches for lengh. just cover them in plastic loom where they cross. no sense in redoing them all.

by adding the 7th you're throwing the wire lenghs off a bit but if its' end to end I woudn't worry about it.

[epiic]

This is how it is currently wired.

[epiic]

This is how it should be wired.

[soerencarlsen]

(Wood is not a good surface material for batteries.???)

wood boxes have been used for battery boxes ever since wood was discovered ;-)

[epiic]

My final question: If I wire it correctly, would this cause me any problems?

The 1st battery in the starboard aft cabin is about 6ft away from the battery bank in the port aft cabin. That is quite a distance compared to the others.

I am using 2/0 cable for everything.

[Delancey]

Originally Posted by epiic

My final question: If I wire it correctly, would this cause me any problems?

The 1st battery in the starboard aft cabin is about 6ft away from the battery bank in the port aft cabin. That is quite a distance compared to the others.

I am using 2/0 cable for everything.

Per Nigel Calder - "It is not acceptable to expand battery banks by wiring in additional batteries in a different physical location, the reason is the batteries will be at different ambient temperatures, which will cause them to discharge and recharge unequally, which will further exacerbate the temperature differences. Aside from the fact this will prematurely age the batteries, in a worst case scenario of high-load discharges and fast recharges, the batteries can be driven to a dangerous condition known as thermal runaway, which can lead to an explosion. "

[epiic]

Originally Posted by Delancey

Per Nigel Calder - "It is not acceptable to expand battery banks by wiring in additional batteries in a different physical location, the reason is the batteries will be at different ambient temperatures, which will cause them to discharge and recharge unequally, which will further exacerbate the temperature differences. Aside from the fact this will prematurely age the batteries, in a worst case scenario of high-load discharges and fast recharges, the batteries can be driven to a dangerous condition known as thermal runaway, which can lead to an explosion. "

In theory yes... but in reality, highly unlikely.

My BMK has a battery temp sensor. If the batteries get too hot, my inverter/charger backs off.

[epiic]

Ok, I officially have it wired up correctly this time.

My only worry is the length go cable from the 1st battery to the other 6 batteries. Its about 6ft.

Obviously, there will be a voltage difference due to the length of 2/0 cable. Couldn't I just double up another pair of 2/0 cables to make the voltage drop less?

[admiralslater]

I installed fireflys last year on our Outremer .so far so good .We run a off the shelf Isotherm fridge, frigaboat deepfreeze and an engle cooler in the cockpit (yes for drinks) most but not all the lighting is led and we have electric winches and cabin fans. we have never seen the batteries go under 80 %. Charging is done with stock alternators which external regulation, 600 watts of solar through mppt controllers and a sterling 40 amp smart charger . you will have plenty of power . I am thinking about putting fireflys on the boat up here so if you decide to get rid of the 7th battery let me know
David

[rwidman]

1) One would think that common sense would have someone seeking advice before purchasing and installing seven expensive batteries.

2) Anyone who believes you cannot connect an odd number of batteries in parallel needs to step away from the keyboard and just read.

The object here is to keep the battery leads as short as practical and ensure that current is delivered from and returned to the batteries as equally as possible. Putting one battery in a different box with different length cables makes that impossible to do. Drawn on paper, battery leads have no resistance but in real life they do and this needs to be accounted for.

So, based on the need for even power distribution, the seventh battery is a problem and should probably be repurposed.

There are multiple ways to connect the remaining six batteries to end up with even distribution and charging.

[hellosailor]

Ignoring the larger cabling issues, which are real, and if each battery sees a slightly different voltage from cable losses, it will charge differently and eventually, that will be a problem. Bare wood anyplace on a boat is bad. If there's a diesel spill, or anything else, it gets into anything, even marine plywood or teak, and the stink lives forever. Or it rots. With wet acid batteries, the acid or acid vapors will chew into bare wood. So, a couple of coats of good white marine bilge paint are a good idea even if the batteries are sealed and acid won't be an issue. Similarly on ventilation, sealed batteries don't need it, except they are always "valve regulated" and during charging or overheating they may blow out hydrogen (boom) or acid fumes, so they really should be sealed off and ventilated overboard. While you're recabling would be a good time to paint the battery box (easier to pull them out one at a time, right?) and then recable them when the paint is dry. Followed by a sealed cover and ventilation.

[Sandero]

Originally Posted by hellosailor

Ignoring the larger cabling issues, which are real, and if each battery sees a slightly different voltage from cable losses, it will charge differently and eventually, that will be a problem. Bare wood anyplace on a boat is bad. If there's a diesel spill, or anything else, it gets into anything, even marine plywood or teak, and the stink lives forever. Or it rots. With wet acid batteries, the acid or acid vapors will chew into bare wood. So, a couple of coats of good white marine bilge paint are a good idea even if the batteries are sealed and acid won't be an issue. Similarly on ventilation, sealed batteries don't need it, except they are always "valve regulated" and during charging or overheating they may blow out hydrogen (boom) or acid fumes, so they really should be sealed off and ventilated overboard. While you're recabling would be a good time to paint the battery box (easier to pull them out one at a time, right?) and then recable them when the paint is dry. Followed by a sealed cover and ventilation.

Unfinished wood? My diesel stays in the tank... if there is a leak it is in the engine *room* and goes down into the deepest part of the bilge. I have some *unfinished* wood on the boat for years... or even decades... and it's fine... teak, oak, marine ply. But I have lots of finished wood as well and have sealed batteries. No problem mon...