Electrical Musings

[goboatingnow]

Originally Posted by chala

If a single bank consists of two or more battery in parallel then this configuration will be one of the less efficient. It is known that to charge a battery more energy must be provided to the battery than the battery will return. Up to 20% more energy as been quoted. If for example a 14 amps current was drawn from a bank of 3 batteries it will be pure luck if the load was equally shared. It is possible to observe for similar batteries a discharge ratio of 8A for the closest battery and 2A for the furthest. When the discharge current is interrupted the batteries will equalize and in doing so up to 20% of the energy transferred will be wasted. This wastage will also occur each time that the chemistry of each battery differs. In a 2 battery bank this wastage can be minimized by the use of a blocking diode. It is also interesting to note that when some one start to connect two battery in parallel they, most of the time ad more and it can also be said that when the configuration reach 5 battery, the 5th battery do no more than compensate for the wastage. Unless each battery is equipped with a way of monitoring the circulating current this wastage will remain unnoticed. This may explain the serious discrepancy that occurs between the energy supplied to the bank and the energy returned from the bank.

This is simply not the case. There are no " circulating currents". Each battery shoulders the load more or less evenly ( in essence pro rata to their discharge equivalent series impedance ) as required, a simple circuit analysis shows that. Blocking diodes serve no purpose.

Larger banks are more efficient, suffer less cycles and last longer.

Dave

[chala]

Originally Posted by noelex 77

If the batteries are correctly wired the resistance to all the batteries in the bank will be equal so the discharge will be even.

Correctly wired would mean that every ”spur” from each battery would have the same exact resistance. I have never see that and it will be very time consuming to achieve and difficult to maintain mostly in a boat. Even if you were able to tune the circuit it would be near impossible to tune the batteries therefore the discharge is unlikely to be even.

Originally Posted by noelex 77

A larger bank charges more efficiently ( efficiency goes down with higher charging voltages). It also discharges more efficiently due to Pukets equation.

I doubt that the capacity of a battery changes according to the rate of discharge (Peukert Equation) will be much different between a single battery and a (larger bank) of the same capacity.

Originally Posted by noelex 77

Discharging one battery bank while charging another brings about the charging efficiencies you are quoting.

It is no question of discharging one battery bank while charging another it is the question of equalizing the battery, (toped up) which involve charging the battery in some case at a voltage between 14.8 to 15.2V for a 12V system. Process which is much safer for the on board electronics and faster if done with the battery disconnected from the load.

Originally Posted by chala

And the best way to achieve this when using solar is to have two banks one in use and the other being toped up.

Originally Posted by noelex 77

I am not sure I am following your argument.

Due to the popularity of connecting batteries in parallel in boats, I can understand that the argument may be hard to grasp. Now I have yet to see in the electrical traction industry or in battery back up installation, batteries connected in parallel.

[s/v Jedi]

chala, you will just have to swallow it: you're wrong, got it mixed up

cheers,
Nick.

[chala]

Originally Posted by goboatingnow

This is simply not the case. There are no " circulating currents". Each battery shoulders the load more or less evenly ( in essence pro rata to their discharge equivalent series impedance ) as required, a simple circuit analysis shows that. Blocking diodes serve no purpose.

Larger banks are more efficient, suffer less cycles and last longer.

Dave

Have you tested it?

Originally Posted by goboatingnow

Blocking diodes serve no purpose.

If you are so fare off I may not even try to convince you.

[chala]

Originally Posted by s/v Jedi

chala, you will just have to swallow it: you're wrong, got it mixed up

cheers,
Nick.

Not at all.

[hummingway]

Any chance the discussion can be made with facts instead of hyperbole? It's an interesting subject but not improved by statements suggesting one or another person is "mixed up" or unable to understand. If you have a citation or logical argument by all means put it forward. If you wish to state your opinion do so as well but understand that it carries no more weight then any other member's opinion.

[Dockhead]

Indeed. This has turned into food fight. Besides that we are light years away from the original topic.

As the OP, I can say that I have been convinced of the 'one big bank is better' theory, based on quite a lot of facts, and don't really want to reargue that question.

We were talking about other electrical things.

[noelex 77]

Originally Posted by chala

Correctly wired would mean that every ”spur” from each battery would have the same exact resistance. I have never see that and it will be very time consuming to achieve and difficult to maintain mostly in a boat. Even if you were able to tune the circuit it would be near impossible to tune the batteries therefore the discharge is unlikely to be even.

There was a tread on this quite recently.
http://www.cruisersforum.com/forums/...ank-82854.html
It is quite easy to achieve equal resistance, for a two battery system it just means leading the positive feed from one battery and the negative from the other. There is nothing extra to maintain and the batteries remain at the same voltage so no "tuning"is needed.

Originally Posted by chala

It is no question of discharging one battery bank while charging another it is the question of equalizing the battery, (toped up) which involve charging the battery in some case at a voltage between 14.8 to 15.2V for a 12V system. Process which is much safer for the on board electronics and faster if done with the battery disconnected from the load.

Equalisation is different to regular charging. There is some advantage to doing this when disconnected from sensitive electronics. Your original post suggests you are in favor of isolating the battery during a regular charge cycle.
Did you just mean during equalisation?

[chala]

Originally Posted by hummingway

Any chance the discussion can be made with facts instead of hyperbole? It's an interesting subject but not improved by statements suggesting one or another person is "mixed up" or unable to understand. If you have a citation or logical argument by all means put it forward. If you wish to state your opinion do so as well but understand that it carries no more weight then any other member's opinion.

Now you get me confused.

Originally Posted by Dockhead

Indeed. This has turned into food fight. Besides that we are light years away from the original topic.

As the OP, I can say that I have been convinced of the 'one big bank is better' theory, based on quite a lot of facts, and don't really want to reargue that question.

We were talking about other electrical things.

I thought that you were asking for assistance and I mentioned to you the inefficient configuration of your system. A bit like if you tell me that you have problem walking and I point out to you that you have the right shoes on the left foot now, if you are happy with this configuration it is fine by me. Sorry hummingway.

Originally Posted by noelex 77

There was a tread on this quite recently.

I have noted the following.

Originally Posted by Andina

battery to battery flow will equalize the charges.

Originally Posted by Andina

Even with identical batteries that internal resistance will vary

Originally Posted by goboatingnow

internal battery resistance differences.

Originally Posted by Andina

(Although the series resistance may not necessarily be a constant value. There is also a high resistance in parallel to represent the self discharge rate.)

All the above, point to circulating current.

Originally Posted by Andina

1. The battery with the faulty cell will get hot, even start to steam on a big bank. You can easily determine which cell is bad, the battery will be hotter at that spot.

2. All the charger output will be going into the bad cell trying to bring the voltage up. Since the voltage is not rising no current is going into the good batteries so you will notice the low voltage the first time you try to use power or a low voltage alarm will go off in one of your instruments..

Once you remove the bad battery the good ones will recharge with no damage other than being discharged quite deeply by dumping current into the dead cell.

Even with matched batteries, sooner or later this can happen. The only difference with matched batteries is they all die about the same time so you're without the battery bank until they are all replaced.

What is much harder to detect is a battery that has gone Open Circuit in one cell. Now the only symptom is reduced capacity and you need to separate them to test which it is. Fortunately batteries going open circuit is rare in comparison to a shorted cell.

Imagine the above at sea with a one big bank.

[Dockhead]

Originally Posted by chala

I thought that you were asking for assistance and I mentioned to you the inefficient configuration of your system. A bit like if you tell me that you have problem walking and I point out to you that you have the right shoes on the left foot now.

I was asking for assistance, and I am grateful to all attempts to help by you, and by everyone else.

But I don't have a problem with my battery bank, and wasn't asking how to configure it. My batteries are working really well, in fact, despite my stupid attempt to kill them recently. I get nearly 24 hours of living on board out of them, including inverter running 24/7 charging multiple phones and laptops, cooking dinner in a microwave, using a coffee machine, toaster, etc., etc.. They work fine despite their no doubt diminished capacity.

My problem is how to charge them, especially now that my genset is broken I have started another thread on that, at the risk of boring everyone (http://www.cruisersforum.com/forums/...tml#post972333) . . . .

[hummingway]

Originally Posted by chala

Now you get me confused.

I will simplify. Statements like, "If you are so fare off I may not even try to convince you.", do nothing to further the conversation. Not trying to convince someone is always a valid option. We ask members to be respectful of others opinions.

[goboatingnow]

Originally Posted by chala

Have you tested it?

If you are so fare off I may not even try to convince you.

Batteries contribute current as an imperfect voltage source. Hence as each battery is loaded its SOC falls , of the bank is made up of similar chemistry and capacity, each battery discharged more of less together. A simple test with a hydrometer will confirm this. Yes there may be minor difference but it's minor.

Blocking diodes used in the context you mentioned serve no purpose.

The issue about circulating currents is a myth. Of course if you introduce a charged battery in parallel with a discharged one then current will flow until the battery internal EMF reaches the good battery. But charged batteries paralleled more or less discharge together. If you don't believe me look at the thevenin equivalent circuit of two batteries paralleled.

A larger bank lasts longer because for the same AH consumed the bank is discharged to a smaller degree. Equally charging efficiency can be improved since the acceptance current is multiplied by the number of batteries making better use of the charge source.

Yes of course in an ideal world using series only strings produces a better result. But then again traction suits series as the voltages are higher. Parallel banks of similar chemistry, age and capacity work well enough to do the vast majority of us.

There is no need to attempt to exactly equalise the series resistance in any battery leads. It's simply a futile undertaking.

Dave

[chala]

Originally Posted by hummingway

I will simplify. Statements like, "If you are so fare off I may not even try to convince you.", do nothing to further the conversation. Not trying to convince someone is always a valid option. We ask members to be respectful of others opinions.

You are absolutely right. I give any one the right to deny. I also give myself the right to no further the conversation when faced with some absurdity. I find it honest to let it know and do not support the burning of heretics. Coming from someone with so many posts, and supposedly so knowledgeable, I take that opinion as an insult. Sadly some CF members do welcome opinions like a bunch of Balinese dogs welcome strangers.

[ShaunJ]

To Chala.... OK
Why can't we all just get along?
We are talking about charging batteries right?

[Dockhead]

Originally Posted by ShaunJ

To Chala.... OK
Why can't we all just get along?
We are talking about charging batteries right?

+1

No one is burning any heretics. In fact it's definitely good to challenge the accepted wisdom, even if you're ultimately wrong.

Note that Hummingway's comment was not directed to one person only. He simply meant that this form of argument: "you're wrong!" "am not!" "are too, and your mother wears army boots!" is useless and adds nothing to anyone's knowledge. Hummingway was only criticisizing the FORM of the argument, not the argument itself. So no need for anyone to be offended.