Rotating batteries

[DeepBass9]

My batteries are approaching 1 year old, so I would like to rotate them. I know that the first battery in the string does the most work, so presumably that holds all the way through to the last battery which does the least work (this is one string of 6v batteries). So how to rotate them? If I number them 1,2,3,4,5,6,7,8 from the positive to the negative, how should they be rotated?

23456781 ?

81234567 ?

56781234 ?

Something else?

[phil.g00]

2 hours ago, DeepBass9 said:

I know that the first battery in the string does the most work

How do you know that?

[Wilfred]

Same with the top and bottom bricks in lithium ion battery banks.

2 hours ago, DeepBass9 said:

56781234

I would do this, but it might be my slight OCD kicking in

[phil.g00]

51 minutes ago, Wilfred said:

Same with the top and bottom bricks in lithium ion battery banks.

No, not the same thing at all, lithium bricks are in parallel, his are in series.

[phil.g00]

@DeepBass9, Are you having a laugh?

[Wilfred]

1 hour ago, phil.g00 said:

@DeepBass9, Are you having a laugh?

I laugh at myself plenty times a day, if I made you laugh, I have completed my daily task for the day LOL.

At least I am learning something new everyday

 

[DeepBass9]

3 hours ago, phil.g00 said:

How do you know that?

Because if you have flooded lead acids, as they age you find you pour way more water into the first batt than the others, and when they eventually die it will be that battery, if left unrotated like my first bank. Hence the question if anyone has some advise.

I should get 8 years from my bank, so if I rotate them one a year, I can cycle through the lot.

I think the 23456781 rotation will work best actually, as the batt that has done the heavy lifting first, will now be at the end of the string.

Edited December 17, 2019 by DeepBass9

[DeepBass9]

2 hours ago, phil.g00 said:

@DeepBass9, Are you having a laugh?

Now I am....

[phil.g00]

@DeepBass9,

Sorry,  at first I did wonder what you were considering with your sealed batteries, then I genuinely thought you maybe indulging in a bit of leg-pulling.

OK,  I'll give you a serious response:

There are reasons that batteries age at a different rate,  that stem from the fact that the batteries are not perfectly identical so inherently they will age at different rates.

Electrically, considering these inherent differences, it makes not a jot of difference what sequence the batteries are in series, because electrically each battery experiences the perfectly identical current regardless of its sequential position in the circuit.

That said environmental factors, not electrical factors can be different between different batteries in the bank. 

Your experience with the first battery in a bank of FLA's taking more water was:

a) purely coincidental, as it was inherently the weaker battery, but if you did rotate and found the same to be true, then:

b) The first battery has a different temperature profile to other batteries, through either being more exposed to the ambient temperature/ breeze/sunlight etc by being on the outside, or because of a poor connection (or a different type of connection) causing more heat.

Lets say it is some environmental factor akin to this, then you would want each battery to serve its duty equally on the outside of the bank, as you say.

Although it wouldn't matter where a battery was sequentially once it wasn't on the outside of the bank.

 

[DeepBass9]

Hmmm, not so sure about the batteries being all electrically identical. Midpoint voltage of a bank is measured to monitor battery health. I am not the only person who has reported first battery in a string problems, although the  internet has little to say on the topic. The batteries are creating the current, not just merely part of a circuit. So if all 8 batteries are producing 1 Coulomb, 8C passes through the first batt, 7C through the second etc.

 

Edited December 18, 2019 by DeepBass9

[phil.g00]

25 minutes ago, DeepBass9 said:

Hmmm, not so sure about the batteries being all electrically identical.

The batteries aren't electrically identical, I never said they were.

 What I said, or at least mean't to say if I wasn't clear, was that the electrical current every single component passes in a series circuit is identical, regardless of its sequence in the series circuit. 

In other words, the resultant electrical the wear and tear on each battery might be different because some batteries might be tougher, but what each battery has to endure is electrically identical.

 

26 minutes ago, DeepBass9 said:

The batteries are creating the current, not just merely part of a circuit. So if all 8 batteries are producing 1 Coulomb, 8C passes through the first batt, 7C through the second etc.

OK, you are misunderstanding an electrical fundamental,  so hopefully we can bring on a gestalt.

Here goes:

If an electron goes in one side of the bank, one comes out the other end simultaneously.

 I could use the term "Coulomb" interchangeably as a coulomb is just a collective noun for a number of electrons.

Think of a pipe full of water, put a drop in this end and a drop must exit the other end. Now, join both ends of the pipe together, and apply some energy to cause circulation. Nowhere along the pipe does the water pile up in a heap.

Or, alternatively as people like to often restate Kirchoff's law:  " You can't get a bucket of Amps".

Batteries are not a store of electrons, they are not a bucket of Amps. Electrons don't wait in the batteries until called on.

Batteries are a store of energy. Electrical energy is converted to chemical energy,( and back again).

Electrical current (or Amps) is a term that describes the flow rate of electrons, and the  flow of electrons is the medium that allows the transfer of energy.

No flow, no transfer.

This is the basis of Ohm's law.

Exactly the same number of electrons pass through every battery ( and every other component) simultaneously in a series circuit. 

The energy transferred by the current (Or Power which is equal to "I" squared "R")  will be different based on the internal resistance "R" the battery presents at the time.

The internal resistance of a battery changes based on its state of charge, and as I said the batteries are not perfectly identical.

The difference in internal resistances can and does result in some batteries being out of balance voltage-wise, but the "I" , current through each battery is perfectly identical to the last electron. (Because V= IR)

This is regardless of its position in a series circuit.

1 hour ago, DeepBass9 said:

I am not the only person who has reported first battery in a string problems

I would look at the different environmental circumstances that arise because of the first battery's physical position, its not because of its electrical position in the circuit.

 

[NigelL]

Another possible explanation is that the first battery operates at the highest voltage relative to ground (assuming 0V ground reference). This high voltage, relative to the surroundings, creates an increased opportunity for an unwanted low-level conductive path to ground. This could be from accumulated deposits from vapour released during charging etc.

One can observe a related effect in electronic circuitry that is installed near the coast - i.e exposed to humidity/salty atmosphere. The corrosion and degradation of electronic parts increases significantly as the operating voltage increases (unless protected with conformal coating).

 

[phil.g00]

15 minutes ago, NigelL said:

Another possible explanation is that the first battery operates at the highest voltage relative to ground (assuming 0V ground reference). This high voltage, relative to the surroundings, creates an increased opportunity for an unwanted low-level conductive path to ground. This could be from accumulated deposits from vapour released during charging etc.

One can observe a related effect in electronic circuitry that is installed near the coast - i.e exposed to humidity/salty atmosphere. The corrosion and degradation of electronic parts increases significantly as the operating voltage increases (unless protected with conformal coating).

I am not sure if you understand the concept or not.

So a quick test:

If I took a 50mm2 cable direct from my most positive terminal of my unearthed battery bank and bolted it direct to earth, would I get fireworks?

 

[NigelL]

5 minutes ago, phil.g00 said:

If I took a 50mm2 cable direct from my most positive terminal of my unearthed battery bank and bolted it direct to earth, would I get fireworks?

Hi Phil, of course you would not get fireworks in your situation - due to your battery being "unearthed". I do understand and agree with your explanation - my post was aimed at DeepBass9.

53 minutes ago, NigelL said:

Another possible explanation is that the first battery operates at the highest voltage relative to ground (assuming 0V ground reference).

Given the assumption of a ground reference (as stated in my previous post), this is a reasonable explanation for a (very) small electrical difference between batteries, dependent on their position within the string.

[phil.g00]

37 minutes ago, NigelL said:

Hi Phil, of course you would not get fireworks in your situation - due to your battery being "unearthed". I do understand and agree with your explanation - my post was aimed at DeepBass9.

Good answer, I did note your reference to ground, I just wanted to make sure that it wasn't another common mistake of giving ground the tag of 0V without there being an electrical connection.

But, supposing the batteries were tracking down to earth, it wouldn't be the highest voltage battery that would bear the brunt, it would be the earthed battery. The earthed battery would have to pass the accumulative current of all the upstream batteries' parallel leakage circuits. The highest voltage battery relative to earth would be the least affected, with only its own tracking current to deal with.

Incidentally, larger battery systems of higher voltages are often centre-tap earthed through a high resistance. This has the advantage of  earth fault detection, when the P-E voltage is different to the N-E voltage.

There isn't really much current flow because of the high resistance on the centre-tap, the idea is to get an alarm and solve the issue before a second earth fault develops  on the opposite battery leg and blows the fuses.

 

 

 

Edited December 18, 2019 by phil.g00

[NigelL]

5 minutes ago, phil.g00 said:

But, supposing the batteries were tracking down to earth, it wouldn't be the highest voltage battery that would bear the brunt, it would be the earthed battery. The earthed battery would have to pass to accumulative current of all the upstream batteries parallel leakage circuits.

Yes - that makes sense. Maybe the "first" battery, that DeepBass9 mentioned, was the one connected to ground?

[phil.g00]

18 minutes ago, NigelL said:

Yes - that makes sense. Maybe the "first" battery, that DeepBass9 mentioned, was the one connected to ground?

Maybe, again if you are going to earth your batteries, it is another argument favouring a centre-tapped earth instead of the bank's positive or negative.

In my sub-60V DC system, I haven't earthed the batteries.

[bizwig]

Something I have noticed in many lead acid batteries connected to inverters and in vehicles is that the cell closest to the positive pole goes dead. I don't know why this is.

[DeepBass9]

So I am busy pondering this, and the theory sounds nice, everything is all equal in a circuit. But my experience is that with flooded lead acid batteries, you put more water in the first one in the string, and less and less up to the last one in the the string. That happened over and over until that bank failed, and when I tested the batteries and found four not so  bad ones to make a plan until I could replace the bank, guess where they came  from? The negative end of both strings. So for whatever reason,  the first  batteries in a string work harder than the last.  

So this is a real phenomenon. Which is why I am going to rotate my batteries. There is no downside to this and only upside.

 

 

Edited December 19, 2019 by DeepBass9

[DeepBass9]

It may be convenient for calculations to assume that current is all equal in a circuit, maybe that is not actually the case. The water analogy aluded to above  does not hold water, as there is a pressure drop through  the system, analogous to electrical resistance which means that the flow rate is not identical everywhere.

 

[phil.g00]

8 hours ago, DeepBass9 said:

It may be convenient for calculations to assume that current is all equal in a circuit, maybe that is not actually the case. The water analogy aluded to above  does not hold water, as there is a pressure drop through  the system, analogous to electrical resistance

True

8 hours ago, DeepBass9 said:

analogous to electrical resistance which means that the flow rate is not identical everywhere.

 

False

[DeepBass9]

That water analogy only works in the simplest of cases. 

[phil.g00]

Kirchoff's current Law states that total current entering ( a junction) equals the total current leaving.

This isn't a debate.

This is a fundamental electrical law, it applies in every case, to every circuit, everywhere at anytime, always. No exceptions ever, since the dawn of time.

Flat earths, Egyptian sun gods, witches, Y2K they have all been and gone.

The difference between water theory and electricity is that there are records of parting  the waters, walking on water and other such miracles, but nobody (including Him) has managed to defy the laws of nature with electricity yet.

A miracle isn't happening round at your house either. 

It is so fundamental to electrical theory, it is the reason I initially thought you were jesting.

 

 

 

 

 

 

[DeepBass9]

That's all very nice, but it still doesn't explain the observation.

[phil.g00]

Maybe not, but having ruled something out, you are left with less options.

"When you have excluded the impossible whatever remains, however improbable must be the truth."  -- S.Holmes