Battery Voltage in the Morning

[ramblinrod]

Originally Posted by Maine Sail

But a "charge voltage" can only be applied when you have charge current flowing INTO the battery. If the battery is seeing a -1A load it is still a discharge voltage reading.

The terminology charge or charging does not apply to a discharging battery. The solar system is only applying current to offset the load the battery sees but the battery is still physically discharging not charging. There is no "charge voltage" in a discharging battery. A charge voltage increases terminal voltage it does not allow it to decrease...




With a discharging battery there is no charging happening. The PV just throws current onto the bus and so does the battery. The PV and battery are sharing powering the load. For the PV this is not a charge current or charge voltage it is simply supplying load current. It will not become charge current or charge voltage until it can drive current into the battery and begin increasing terminal voltage.



Precisely, this is because the battery is not charging and is physically discharging. Using the term "charging voltage" to a battery being discharged is the disconnect folks are having with your description.

A battery with a -1A load is not charging it is discharging. The current supplied by the PV is only feeding the loads and reducing the load on the battery but the battery is still not being "charged". We need current flowing into the battery, not out of it, before we can technically describe it as being "charged"..

Still 12.6V on a 460Ah bank under a -1A load -30Ah's down is a perfectly reasonable loaded voltage reading...

Just for fun, consider the following:

1. A simple charger, battery, and load, all in parallel.
2. The charger outputting a voltage to the charging circuit, to induce a charge current. (Actual amount doesn't matter.)
3. The load drawing current through the load circuit. (Actual amount doesn't matter.)

Where is the charge current going?"

Now lets conduct a proper circuit analysis and consider cable resistance.

Is some of the charge current going into the battery?

The answer is "YES".

Is the battery being "Charged".

If the definition of battery charging is, "A supplied voltage, inducing a current, creating a chemical reaction to increase the charge present on the battery plates, the answer is "Absolutey" (as I posted earlier).

Now lets consider the rate of charge current vs load current.

If the load current exceeds the charge current, is the net result that the battery is being discharged?

The answer is "YES".

Does this prove that a battery can be "charged" and "discharged", at the same time?

"YES".

[Maine Sail]

Originally Posted by ramblinrod

Here we go.

The very first question was, "Can the voltage be believed".

If this means, "Is the voltmeter reading the terminal voltage properly", my answer is "maybe". (I can't say "Yes" because the voltmeter could be out of calibration, have a high impedance issue with a test lead, a weak battery, be affected by a source of EMI, or any number of issues that would make it inaccurate, ie "can't be believed".

If the original question means, "Does the voltmeter reading accurately represent the battery state of charge, when the solar panel charger is connected", (which was my interpretation) my answer is "NO" (assuming there is substantial current flow in the charging circuit, as described by the original poster). Even if it is lower, than the load current, the current flowing through the charging circuit (I have called this "charge current") induced by the voltage produced by the charger (I have called this "charge voltage") is increasing the battery terminal voltage, so the battery terminal voltage "does not" accurately represent the battery state of charge.

That is the science. This post (and any terminology I have used) can be refuted by anyone, but it is absolutely correct (in my opinion), and can be easily confirmed by controlled scientific experiment.

He simply asked if the voltage reading under a -1A load could be believed. I never saw him ask about the voltage reading being correlated to SOC.

Originally Posted by sailorboy1

The other morning my solar panel was supplying about 2 amps into the system, the battery was discharging about 1 amp, the batteries were 30 AH out of a 460 AH bank, the voltage was reading 12.6V.

Can the voltage be believed?

The answer is still absolutely. He did not ask if this 12.6V reading represented any SOC just if it could be believed. At -30Ah down on a 460Ah bank with a -1A load. The answer to that is yes it can be the actual terminal voltage and it would not be odd. In reality it could have likely been slightly higher but he did not present us with any hundredths of a volt data.

It does not tell you SOC and I did not see the OP ask about SOC.. 12.6V is a perfectly acceptable loaded terminal voltage for a 460Ah "rated" bank with a -1A load even -30Ah's down from 100% SOC.

-30Ah's down from a "full" 460Ah bank means approx 6.5% of the Ah capacity has been used. A -1A load on that bank is a discharge rate of .002C. This is really quite minuscule and should not affect downward terminal voltage very dramatically..

Here is a 96Ah (actual tested capacity/105Ah "rated") Lifeline battery with -6.7% of actual measured & tested Ah capacity removed. The image shows the battery under a 5.25A constant load (0.05C load) after 1:14 minutes at this discharge rate of 0.05C showing a loaded voltage reading of 12.574V or essentially 12.6V.

Now AGM and FLA do perform slightly differently as they discharge, in regards to voltage due to varying Peukert, but the load on this Lifeline was massively higher than the load on the OP's bank, a .05C load vs .002C load. To see the equivalent load on his 460Ah bank would mean discharge load of 23A.

So yes the terminal voltage can be believed and if anything is a bit low for the -1A load it was seeing. This means the battery bank is possibly sulfated, not the capacity the OP thinks it is or it was not technically charged to 100% SOC.







The real question should not even revolve around what teh solar was doing. All that matters is that the battery was discharging at -1A with -30Ah's removed from an assumed 100% charge...

The question could have been:

"My 460Ah bank was seeing a -1A load with -30Ah's removed, after a full charge, is 12.6V a reasonable voltage reading with a -1A load?"

The answer is yes it is reasonable.

[Maine Sail]

Originally Posted by ramblinrod

Just for fun, consider the following:

1. A simple charger, battery, and load, all in parallel.
2. The charger outputting a voltage to the charging circuit, to induce a charge current. (Actual amount doesn't matter.)
3. The load drawing current through the load circuit. (Actual amount doesn't matter.)

Where is the charge current going?"

Now lets conduct a proper circuit analysis and consider cable resistance.

Is some of the charge current going into the battery?

The answer is "YES".

Is the battery being "Charged".

If the definition of battery charging is, "A supplied voltage, inducing a current, creating a chemical reaction to increase the charge present on the battery plates, the answer is "Absolutey" (as I posted earlier).

Now lets consider the rate of charge current vs load current.

If the load current exceeds the charge current, is the net result that the battery is being discharged?

The answer is "YES".

Does this prove that a battery can be "charged" and "discharged", at the same time?

"YES".

No it does not.. A battery is either charging or discharging it is not doing both at the same time.

CC/CV charger, controllers & regulators do two things constant-current (bulk to their max ability) and constant-voltage (limit voltage / absorption, float or EQ).

In bulk they put as much current onto the bus as they can. If they have been successful in actually charging the battery, when the terminal voltage rises to the voltage limit, they hold voltage steady and current begins to taper off as the SOC rises.

They are simple. They essentially supply constant-current then limit-voltage. They can only limit voltage when they have charged the battery by supplying enough current to overcome system loads and raise the SOC to the bulk/absorption transition point voltage..

CC/CV charge sources put current onto the bus and this current, if high enough, is what raises the terminal voltage. If there is not enough current to raise voltage (requires more current into the bus than system loads being take off the bus) the battery is just discharging at a rate offset by the chargers max current capability.

A battery contributing any energy/current onto the DC bus is discharging regardless of what the charger is contributing. The charger would simply be acting as a constant-current power supply if the system load exceeds its current capability.

Test question:

The vessels DC system is consuming 41A and the vessels charging system is contributing its maximum rated current of 30A. Is the battery charging or is it discharging?

A) Discharging
B) Charging

[Cadence]

Boy!This has gotten long winded. A battery is no more than a capacitor treat it as such.

[sailorboy1]

This reminds why I try not to ask any "technical" questions on forums anymore. There is always an "expert" who just isn't going to stop till EVERYONE believes their answer.

BTW - both my wife and I were Navy Nuclear power operators. I always find it a little funny how complex people can make a little sailboat be.

[ramblinrod]

Originally Posted by Cadence

Boy!This has gotten long winded. A battery is no more than a capacitor treat it as such.

Be careful how definitive your statements are.

https://www.bing.com/images/search?q...2o0&ajaxhist=0

[ramblinrod]

Originally Posted by Maine Sail

Test question:

The vessels DC system is consuming 41A and the vessels charging system is contributing its maximum rated current of 30A. Is the battery charging or is it discharging?

A) Discharging
B) Charging

Test Answer:

1) If the definition of "charging" is that "the battery state of charge must be increasing", the correct answer is that the battery is "discharging".

2) If the definition of "charging" is that "the battery is accepting charge current", the correct answer is "C, All of the above".

Some of the battery stored energy is being accepted by the load. Some of the charge current is being accepted by the load.

But here's the biggy, wait for it...some of the charge current is being accepted by the battery.

Therefore, the battery is both discharging and charging at the same time, but because the discharge current is greater than the charge current, the net result is the battery state of charge is declining.

In my opinion, answer 2 is more correct.

[boatbod]

Jeez... how frigging complicated do you want to make it?

If there is a net reduction in the state of charge of a battery in a circuit it is by definition DISCHARGING. Doesn't matter whether there is a 10,000A load on the circuit and 9,999A are being supplied by a nuclear reactor. The battery is supplying that last 1A and it is therefore being DISCHARGED. Energy is flowing OUT of the battery, not into it.

[StuM]

Simple question. In the OPs situation, in how many directions are electrons flowing through the battery?

Two possible answers:

1. According to RamblingRod - two directions simultaneously.
2. According to most other posters - one direction.

(Please correct me if I have misinterpreted anyone's stance)

[Cadence]

Originally Posted by StuM

Simple question. In the OPs situation, in how many directions are electrons flowing through the battery?

Two possible answers:

1. According to RamblingRod - two directions simultaneously.
2. According to most other posters - one direction.

(Please correct me if I have misinterpreted anyone's stance)

I think I recall that. If electrons are flowing in one direction something is flowing in the other direction.
Albert may have been able to tell us? Have no idea what it has to do with the battery charging in real life?

[sailorboy1]

How many experts does it take to screw in a light bulb. And as long as it is sticking into the socket are you screwing it in no matter which direction you turn it?

[StuM]

Originally Posted by Cadence

I think I recall that. If electrons are flowing in one direction something is flowing in the other direction.
Albert may have been able to tell us? Have no idea what it has to do with the battery charging in real life?

A battery is either:
charging, - converting lead sulphate and water to lead and sulphuric acid, in which case electrons are flowing in one direction
or
discharging - converting sulphuric acid and lead to lead sulphate and water, in which case electrons are flowing in the other direction.

You don't get both happening at the same time. The closest you can get to that is to have no electron flow i.e. neither charging or discharging.

[ramblinrod]

Originally Posted by Cadence

I think I recall that. If electrons are flowing in one direction something is flowing in the other direction.
Albert may have been able to tell us? Have no idea what it has to do with the battery charging in real life?

You could be referring to "minority hole current" but that isn't what we are dealing with here.

[Cadence]

Originally Posted by StuM

A battery is either:
charging, - converting lead sulphate and water to lead and sulphuric acid, in which case electrons are flowing in one direction
or
discharging - converting sulphuric acid and lead to lead sulphate and water, in which case electrons are flowing in the other direction.

You don't get both happening at the same time. The closest you can get to that is to have no electron flow i.e. neither charging or discharging.

Stu,

It sounded like someone brought up theoretical physics about electron flow and assuming if they flow in one direction something is flowing in the other, protons? If that was the case I could not see it having anything to do with battery charging. I is possible I read them wrong? If so, bad me.

[Mike OReilly]

Originally Posted by Cadence

It sounded like someone brought up theoretical physics about electron flow and assuming if they flow in one direction something is flowing in the other, protons? If that was the case I could not see it having anything to do with battery charging. I is possible I read them wrong? If so, bad me.

I recall some electronics courses from my ancient past taught electrical current in terms of electrons and holes. Never made an physical sense ... protons do not flow in electric circuits (although they certainly do in a plasma).

I've been reading this thread with fascination. No wonder us mere electrical mortals get confused. I understand basic physics here. A battery cannot be both charging and discharging. It may be receiving multiple inputs and outputs, but it has a cumulative state. It's like solving a vector problem. There may be multiple forces acting on a body, but there is a single cumulative vector which results in a single specific state.