Electrical Musings

[chala]

Originally Posted by noelex 77

Most crusing boats have battery banks consisting of batteries wired in parallel. So you better elaborate on your safety concerns.

What happen when 1 battery short circuit?

[s/v Jedi]

Originally Posted by chala

What happen when 1 battery short circuit?

If you don't know what happens, then you should not judge the parallel connection as unsafe.

cheers,
Nick.

[DotDun]

Originally Posted by chala

What happen when 1 battery short circuit?

Before I care about this happening, please cite what is the percentage of batteries produced that exhibit this type of failure?

You are debating the virtues of paralleling multiples batteries to make a bank vs deploying multiple banks. IMO, it comes down to the human intervention involved in managing multiple banks or the ease and efficiency afforded by having just one large bank.

Given that lead acid battery technology is pretty well known, including frequency of failures and failure modes, I opt to have one large bank. I would venture to guess that 99+% of all paralleled batteries that have been serviced properly will last ~5 years. I budget to change batteries at this interval, it's worked so far.

You can do as you like.

[noelex 77]

Originally Posted by chala

What happen when 1 battery short circuit?

Batteries can be protected by a fuse directly on the battery post, but most people feel this overkill. Conventional wiring practices provide a good level of protection. I always secure the battery leads so there is no chance of them providing a short circuit path even if they become detached from the batteries. The batteries themseves also need a strong tie down system
Series connected batteries and a single battery can short circuit. These sort of accidents are fortunately rare, but you obviosly feel paralleled battery banks are much more at risk why?
.

[Maine Sail]

A direct quote from the Enersys/Odyssey Battery Technical Manual:

"Parallel Connections

It is common to have batteries connected in parallel to achieve a desired amp-hour capacity. This is done by connecting all the positives to each other and all the negatives to each other.

Typically the positive and negative leads to the load are taken from the same battery; usually the leads from the first battery are used. This is not a good practice.

Instead, a better technique to connect the load is to take the positive lead from one end of the pack (the first or last battery) and the negative lead from the other end of the pack.

The two methods are illustrated above. Solid lines and arrows indicate positive terminals and leads; broken lines and arrows indicate negative terminals and leads. In both illustrations, the positive leads are connected to each other; similarly the negative leads are connected to
each other. The only difference is that in the first illustration the positive and negative leads to the load come from the first and last batteries. In the second case, both leads to the load are tapped from the same battery.

The first schematic is recommended whenever batteries are hooked up in parallel to increase battery capacity. With this wiring, all batteries are forced to share both charge and discharge currents."

[chala]

Originally Posted by DotDun

Before I care about this happening, please cite what is the percentage of batteries produced that exhibit this type of failure?

Not so long ago, in Britain, the extract of a coroners report published in a British boating magazine in regard of “two” casualties, made the mention that due to a fault developing in a new battery, the crew of the vessel where unable to start the engine or radio for help.
One casualty is one too many and there is no need for percentages.

Originally Posted by DotDun

You are debating the virtues of paralleling multiples batteries to make a bank vs deploying multiple banks. IMO, it comes down to the human intervention involved in managing multiple banks or the ease and efficiency afforded by having just one large bank.

By one large bank I understand that you mean one large bank made of batteries in parallel and not one large bank made of large cells connected in series.
To compare the two configurations: The one large bank made of large cells connected in series is safer and more efficient than the one large bank made of batteries in parallel. As for ease of installation, the one large bank made of large cells connected in series is safer to install than the one large bank made of batteries in parallel.
As for ease of operation, if it does not already exist, an automatic system that minimizes the possibility of human error would be easy to construct. In any case a boat operator should be conversant with managing the boat electrical installation.
When it comes to choosing between safety and ease I choose safety.
[/QUOTE]

[noelex 77]

Originally Posted by chala

Not so long ago, in Britain, the extract of a coroners report published in a British boating magazine in regard of “two” casualties, made the mention that due to a fault developing in a new battery, the crew of the vessel where unable to start the engine or radio for help.
One casualty is one too many and there is no need for percentages.

The example you quote supports the connection of batteries in parallel, not series.
The failure of a single battery in a series battery bank will mean there is no hope of starting the engine from that bank. Disconecting the defective battery does not help. The voltage will be too low.

In a parallel bank the failure of a single battery still gives the opportunity to start the engine using the remaining battery, or batteries, which will have the correct voltage to turn the starter motor

Most crusing boats have multiple banks that will start the engine anyway, but you seem to advocating series conection but using examples that support parallel connection!

[chala]

Originally Posted by noelex 77

Batteries can be protected by a fuse directly on the battery post,

Yes but it must be remembered that batteries can produce explosives gases and all electrical apparatus in proximity must be of an approved type that suit the location including temporary recirculating fan.

Originally Posted by ebaugh

I've read this thread and thought about posting before...but did not. You don't need an EE degree to understand the issues involved. E = I x R and P = I x E pretty much is as far as you need to go.

As quoted a simple representation and calculation of the circuit involved may demonstrate to you that the current is not excessive but will require the rapid and safe disconnection of the faulty battery to prevent total discharge of the other paralleled batteries. If a rapid disconnection is not effectuated it is possible that the heat generated by the current flowing into the short circuit may damage nearby cells with further damaging result.

Originally Posted by noelex 77

Series connected batteries and a single battery can short circuit. These sort of accidents are fortunately rare, but you obviosly feel paralleled battery banks are much more at risk why?

The risk is the same it is the consequence of the event that differ.
A short circuit in paralleled batteries will dissipate all the energy that the paralleled batteries can provide.
The short circuit failure of one cell in a series configuration will affect the potential of that configuration. The energy dissipated in that short circuit can also be calculated. The simple interruption of the current flow to the load will stop the current flow in the faulty cell. If a spare bank is available a simple Break Before Make or a more complex Make Before Break (hot switching) will resume supply of the power to the load with the flick of a switch.

[Dockhead]

Originally Posted by chala

Not so long ago, in Britain, the extract of a coroners report published in a British boating magazine in regard of “two” casualties, made the mention that due to a fault developing in a new battery, the crew of the vessel where unable to start the engine or radio for help.
One casualty is one too many and there is no need for percentages.



By one large bank I understand that you mean one large bank made of batteries in parallel and not one large bank made of large cells connected in series.
To compare the two configurations: The one large bank made of large cells connected in series is safer and more efficient than the one large bank made of batteries in parallel. As for ease of installation, the one large bank made of large cells connected in series is safer to install than the one large bank made of batteries in parallel.
As for ease of operation, if it does not already exist, an automatic system that minimizes the possibility of human error would be easy to construct. In any case a boat operator should be conversant with managing the boat electrical installation.
When it comes to choosing between safety and ease I choose safety.

[/QUOTE]

Well, I have already admitted to being an electro-ignoramus. But I am firmly convinced of one thing about battery bank architecture -- service bank for deep discharge loads should be a single big one. If possible made up of a bunch of large 2.2v cells in series with nothing in parallel. And completely separate banks of purpose-built starting batteries for starting engines and gensets.

Since large 2.2v cells are a different shape and cost a fortune, it would require gigantic modifications to most boats to realize this kind of service bank. So most of us make do with what we can fit in the spaces provided for that purpose, which means for most of us a good bit of parallelling. In my concrete experience it works pretty well and have not experienced or heard of people experiencing problems as a result of paralleling batteries, but while admitting that non-parallel banks will be more efficient.

As to safety, I am not happy with the way my boat is set up. With cheap electronics, I can't see why we couldn't have some kind of practical battery management system which would work at the individual battery level. Which would disconnect a battery in microseconds which experienced a shorted cell, and set off alarms. Which would disconnect the whole bank once it falls below say 30% charge in order to prevent killing the bank, just like any $99 cell phone does. Surely our battery banks are primitive and stupid for not having this obvious and logical function.

I am just waiting for lithium-ion batts to be fully developed for this use and mass produced. Surely this is just around the corner, with so much development going on for electric vehicles and so forth. 400Ah's of lithium ion batts with full BMS system -- ah, that's a dream. All of these problems we have been arguing about would be a thing of the past. No more fiddling with Dr. Frankenstein style, medieval concoctions of lead and sulphuric acid. No more obsessing about depth of charge, no more fussing. No more equalization, no more specific gravity readings. Just use the power, and top up when it gets low -- just like we do with our cell phones. Christ, I can't wait.

[chala]

Originally Posted by noelex 77

The example you quote supports the connection of batteries in parallel, not series.

Lets go back to the basic. If for example someone buys two 12V batteries he will have the choice to parallel them or to create two banks each consisting of one 12V battery. If one battery develops a short circuit fault in a parallel configuration as per the tragic example you loose both batteries. In the other configuration you only loose the faulty battery. One good 12V battery still remain operational.

[noelex 77]

Originally Posted by chala

Lets go back to the basic. If for example someone buys two 12V batteries he will have the choice to parallel them or to create two banks each consisting of one 12V battery. If one battery develops a short circuit fault in a parallel configuration as per the tragic example you loose both batteries. In the other configuration you only loose the faulty battery. One good 12V battery still remain operational.

Multiple banks are always better (I have advocated the advantages of 2 house banks as well a separate start bank for a long time) but most crusing boats have more batteries than would be practical to separate into different banks, so we are left with the problem of how to connect these batteries.
Separate banks will need to connected together most (or all) of the time for maximum effecency anyway.

[Wotname]

While Chala is correct in maintaining that a battery that fails due to an internal short becomes potentially dangerous when connected in a parallel bank, I have let to see a battery fail due to an internal short.

I know it is possible and therefore it has probably happened but I wonder if any of the posters here have personal experience (or even second hand accounts) of batteries failing due to internal shorts.

I have had many batteries fail due to either open circuit or high internal resistance.

[DotDun]

Originally Posted by chala

Lets go back to the basic. If for example someone buys two 12V batteries he will have the choice to parallel them or to create two banks each consisting of one 12V battery. If one battery develops a short circuit fault in a parallel configuration as per the tragic example you loose both batteries. In the other configuration you only loose the faulty battery. One good 12V battery still remain operational.

Your Britain example is ludicrous, cruising boats have more than 1 battery bank and the norm is to have a crossover switch to connect the house to the start battery or the engine to the house bank. This "normal" configuration covers a single event of battery failure. If you are so inclined, a tertiary battery can be added to cover more than one failure. Maybe if the vessel in the report had a redundant battery, they could have started the engine and/or called for help.

You extol how safe your design, but refuse to cite any numbers to corroborate your thesis. Everything in life is a risk, electrical fires can happen connected to the grid, no batteries involved! The British example does not count, that is an example of a design with no redundancy.

What you are advocating is that a boat with requirements for 1000ah of house batteries to have 5 banks, 1 engine start battery and 4 house banks (assuming the largest single 12v battery is 250ah). If you would like to switch between the 4 house banks every 125ah, that's your choice, I would rather sleep all night.

So again, what is the percentage of batteries in service that exhibit the failure you are worried about?

When a battery fails as you describe, what percentage result in a fire due to a fused paralleled battery?

[chala]

Originally Posted by Wotname

I know it is possible and therefore it has probably happened but I wonder if any of the posters here have personal experience (or even second hand accounts) of batteries failing due to internal shorts.

Boats do burn mysteriously. A forensic examination normally does follow. I do not know if the investigators do check for a parallel configuration after all it is not a crime to have such configuration. But I know that insurers are far more fussy. It would be silly to broadcast that a fire may have been started on a boat due to a parallel connection.

[noelex 77]

Originally Posted by chala

. But I know that insurers are far more fussy.

The vast majority of crusing boats have batteries connected in parallel. Many of them are insured.