Half a battery bank

[capta]

I've been messing about with 'electrickery' for a number of years, but this one leaves me wondering.
For 5 years I've had 4 Trojan T-145 deep cycle batteries connected as below, series/parallel.
To the best of my knowledge the bank performed just fine, but as of late things were not going well. A stint at the dock with shore power and a Xantrex charger has left me with half the bank.
Batteries A & B are completely trashed, yet C & D seem just fine and quite able to run the boat's systems. I don't understand why just two went so very bad.
All connections were tight and there has ALWAYS been plenty of water in all the batteries. No corrosion on any of the terminals. All the cables are soft and flexible and the crimps seem good.
It's almost like the boat has been running on only A & B all this time and C & D are like new.
So now I need two new batteries and 'they' say, "never mix old batteries with new". Am I supposed to chuck what seem to be good batteries and spend an extra $450.00 for four new batteries, instead of two? OUCH!

 

[JamesG161]

Isolated, what do bats A & B read in VDC? My config has a isolator between the banks to prevent A&B from draining C&D.

When full charged and isolated, what do bats C & D read in VDC?

Those reading will give you most info about each.

The 6VDC crowd rely on matched pairs. No two are identical twins.
Jim...

PS: If your batteries are not zero VDC the they are not dead.

 

[centerline]

I've been messing about with 'electrickery' for a number of years, but this one leaves me wondering.
For 5 years I've had 4 Trojan T-145 deep cycle batteries connected as below, series/parallel.
To the best of my knowledge the bank performed just fine, but as of late things were not going well. A stint at the dock with shore power and a Xantrex charger has left me with half the bank.
Batteries A & B are completely trashed, yet C & D seem just fine and quite able to run the boat's systems. I don't understand why just two went so very bad.
All connections were tight and there has ALWAYS been plenty of water in all the batteries. No corrosion on any of the terminals. All the cables are soft and flexible and the crimps seem good.
It's almost like the boat has been running on only A & B all this time and C & D are like new.
So now I need two new batteries and 'they' say, "never mix old batteries with new". Am I supposed to chuck what seem to be good batteries and spend an extra $450.00 for four new batteries, instead of two? OUCH!

one thing about the diagram you have posted... you need to remember that electricity will ALWAYS take the path of least resistance, so amps out will always be drawn from the closest batteries.
this means that the first to two batteries in your diagram will be the "working" batteries in the system (except in cases of very deep discharge cycles)....

with batteries having a limited number of charge/discharge cycles in their lifespan, and with the first 2 batteries in the system being cycled, the wiring is letting the other 2 batteries just set dormant, but they are still aging.
and as you are learning thru experience here, it would almost be better to not even have them in the system if they arent connected into the system correctly.

the pos and neg wires coming from the boat to the bank will need to connect to the "bank" at opposite corners so the protons all have to flow thru the wires and all the batteries an equal distance so the bank is drawn from and charged equally all the time.
this will allow all the batteries to all be cycled together and age equally...

 

[Johnb]

If those were mine I would check the specific gravity (S.G.) in each of the cells and if one or more is significantly different then after 5 years that battery is kaput. If they are all equally low I would dig deeper.

One cell that has developed high internal leakage will not charge properly and then not contribute to the voltage produced by the bank. (the bank voltage is the sum of all the individual cell voltages). It will also behave like a high resistance so the cells that are good cannot deliver their energy. In addition because that bank has a low voltage it will drain the bank in parallel with, though not necessarily very fast but it will get there.

 

[capta]

If those were mine I would check the specific gravity (S.G.) in each of the cells and if one or more is significantly different then after 5 years that battery is kaput. If they are all equally low I would dig deeper.

One cell that has developed high internal leakage will not charge properly and then not contribute to the voltage produced by the bank. (the bank voltage is the sum of all the individual cell voltages). It will also behave like a high resistance so the cells that are good cannot deliver their energy. In addition because that bank has a low voltage it will drain the bank in parallel with, though not necessarily very fast but it will get there.

The SG is fine on C & D. No appreciable difference and about 1270, temp compensated. But it's not like I can just disconnect them as one can do in a vehicle.

 

[Johnb]

The SG is fine on C & D. No appreciable difference and about 1270, temp compensated. But it's not like I can just disconnect them as one can do in a vehicle.

What about the S.G. on A and B?

 

[capta]

Isolated, what do bats A & B read in VDC? My config has a isolator between the banks to prevent A&B from draining C&D.

When full charged and isolated, what do bats C & D read in VDC?

Those reading will give you most info about each.

The 6VDC crowd rely on matched pairs. No two are identical twins.
Jim...

PS: If your batteries are not zero VDC the they are not dead.

This arrangement is supposed to give me one, 12 volt battery bank, with one positive and one negative connection to the system.

 

[capta]

one thing about the diagram you have posted... you need to remember that electricity will ALWAYS take the path of least resistance, so amps out will always be drawn from the closest batteries.
this means that the first to two batteries in your diagram will be the "working" batteries in the system (except in cases of very deep discharge cycles)....

with batteries having a limited number of charge/discharge cycles in their lifespan, and with the first 2 batteries in the system being cycled, the wiring is letting the other 2 batteries just set dormant, but they are still aging.
and as you are learning thru experience here, it would almost be better to not even have them in the system if they arent connected into the system correctly.

the pos and neg wires coming from the boat to the bank will need to connect to the "bank" at opposite corners so the protons all have to flow thru the wires and all the batteries an equal distance so the bank is drawn from and charged equally all the time.
this will allow all the batteries to all be cycled together and age equally...

If you would be so kind as to draw me a diagram of what you are trying to explain, I would very much appreciate it.

 

[Finally Free]

If you would be so kind as to draw me a diagram of what you are trying to explain, I would very much appreciate it.

Sorry but my drawing on a tablet sucks. But here is basically the way it should be wired.

 

[Ron20324]

Sorry but my drawing on a tablet sucks. But here is basically the way it should be wired.

Not to worry. I think we understood the original drawing was a wiring scematic, not a cable run diagram.

 

[Don Lucas]

The battery voltage and specific gravity of batteries C&D being good don't really tell you anything about their life remaining or capacity. All it tells you is that they are charged for their current capacity.

Wired the way in the original post, batteries A&B would carry more load than C&D. But I don't see why that would result in A&B being trashed and C&D being fine. If A&B discharged C&D should have supplied them and died the same death.

There must be something other than this different, or it could be that C&D really aren't far behind A&B far as remaining life.

 

[JamesG161]

In a bank, if A is good and B is bad, A+B is trashed. Thats why you need SG and VDC ( on each individual battery), in a supposed charged state, to see if you have a BAD battery.

Trashed mean to me, CAN'T HOLD A CHARGE!

Weak means you have reduced capacity.

Since you eliminated wiring, it suggests a bad battery.
Jim...

 

[centerline]

Sorry but my drawing on a tablet sucks. But here is basically the way it should be wired.

Yes... if we take the scribbles out of the picture, thats correct.
It will allow for a more evenly balanced electron flow thru all the batteries, rather just the first two in the bank..

 

[capta]

Sorry but my drawing on a tablet sucks. But here is basically the way it should be wired.

Thinking about it, I certainly did not have any splices or joints in the wiring, so the actual configuration was as you drew it. All cabling ran to and from lugs.
I guess that is why I don't see how A & B could be totally trashed and yet C & D seem fine. I've been running the boat on C & D without any problems for a week now.

 

[All U Get]

Just thinking through this, where does your solar or wind tie in? Do they primarily charge the C&D batts? That reminds me I have to change my cables like Finally Free.

All U Get

 

[capta]

Just thinking through this, where does your solar or wind tie in? Do they primarily charge the C&D batts? That reminds me I have to change my cables like Finally Free.

All U Get

All positive charging leads (solar, eng alt, 40 amp electric charger, 80 amp electric charger) go directly to positive battery terminal. All negatives go through a busbar to a single cable to the negative terminal, so power in and out runs through the same terminals. A, B, C, and D are supposed to be one bank of 12 volts, not two banks.

 

[JamesG161]

you need to remember that electricity will ALWAYS take the path of least resistance, so amps out will always be drawn from the closest batteries.

So true!

But how we can nearly eliminate that difference is WIRE SIZE!

Check your wire sizing tables.

If bigger diameter cable is expensive or no space, then double up on the longer runs.

To TRASH a battery... ( means no more 6/12 VDC after charging )

1) crack a cell ( in heavy seas, lose batteries can bounce )
2) Sulfonate the cells (drawing them completely empty can coat the lead plates/mesh with thick lead sulfate)
3) Overheat the battery. ( This can melt/destroy the internal cell separation )
4) Dry out the battery ( no more water in wet or AGM cells. It takes water to work them)
5) Too much water. (sulfate white/yellow dried powder all around battery or low SG )

Have you tried a "super charge" to recover them? Take the trashed ones to Auto Zone or who ever and they can try that to recover them.

Are you sure they are trashed?

Put a selector switch in your system.

AB or CD or BOTH. Then you can use the older battery set without the "boogie man rule of thumb" ruling your battery life.

Charge both together. Consume the oldest bank first and when near 11VDC switch to your new bank. When the oldest bank is about 4x faster to give up capacity then buy new ones for the weak bank.

All this battery info can be web searched.

Jim....

 

[JamesG161]

I forgot a possible damage to trash.

6) Freeze a battery (during a very cold winter the solution can freeze and break a cell )

Jim

 

[capta]

Take the trashed ones to Auto Zone or who ever and they can try that to recover them. Are you sure they are trashed?
Jim....

Yes, Jim, I'm absolutely positive that they are trashed, but if you'll loan me your Lear jet, I'll be glad to take them to Auto Zone in case I'm wrong. Just have your pilot call me when he gets to Grenada, OK?

 

[JamesG161]

Oh my a poor country boy! I was born in Magnum OK, down Altus way.

Heck everyone drives to the "City" for the cheapest barbed wire, best boots and Sunday hats. Do it then! Surely OK City has a one type of AutoZone maybe even 2.

I am lucky, my inverter/charger(IC) has a "balance mode" or boost charger built in.

My bet is one of A+B was the "snake in the barn" and bit the other.

Buying just one bank is ok if you have a bank to bank isolator or Combo switch.

I use this neat/cheap volt meter at the helm to see my battery state. Cheap and color coded LED display to tell you when to recharge.

http://www.amazon.com/gp/product/B00962CQNC?psc=1&redirect=true&ref_=oh_aui_detailpage_o06_s00

I used to have to go below to see a less informative battery state display.

That would also head off a snake problem.
Jim...

PS: Go Sooners!