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Old 24-06-2012, 08:27   #121
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Re: Electrical Musings

A battery with an internal short... yes I had that once when the plates bent and touched. This is a zero Ohms hard short and the internal heat build-up was so big that the battery housing cracked open and all the acid ran out with just some splatters onto me. This opened the short well enough :S

Another thing that happens is shedding from plates building up on the bottom and creating a short. This is often not a hard zero Ohm short, so it becomes a drain for the bank.

Case #1 is normally with thin plate flooded lead acid batteries, i.e. starter batteries and in my case a non-maintenance type. These plates can bent from heavy usage (long starting) and after that only a light nudge might make plates touch. The reaction is violent and will melt the plates where they touch, which disconnects the short again. So, in case of a parallel bank, you keep power.

Case #2 is normally with thick plate deep cycle batteries. In a parallel bank you see voltage down like at 10V. The solution is to check batteries for temperature and disconnect the one that is overheating or hotter than the others. In a series bank you loose power due to low voltage.

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Old 24-06-2012, 09:56   #122
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Re: Electrical Musings

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Your Britain example is ludicrous
You may see it that way. I find that accident tragic. Had these sailors been better advised they may still be enjoying a good sail.

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cruising boats have more than 1 battery bank
Very wise, the precept that you do not parallel batteries was accepted in the fifties in the seventies paralleling dry cells was recognised as a waste of energy.

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You extol how safe your design
I have many designs. I would think that you are mentioning the one in this forum. It is the description of a 12/24V system. The design as limitations that any competent person will understand. Adequate warnings are displayed. I do not remember ever having extolled how safe this design is.

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Everything in life is a risk, electrical fires can happen connected to the grid, no batteries involved!
I support strongly the view that accidents are made.

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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.
I am advocating that it can be that good management of a boat electrical system can make the boat safer and possibly without the intervention of a watchman.
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Old 24-06-2012, 10:05   #123
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Re: Electrical Musings

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Originally Posted by s/v Jedi View Post
A battery with an internal short... yes I had that once when the plates bent and touched. This is a zero Ohms hard short and the internal heat build-up was so big that the battery housing cracked open and all the acid ran out with just some splatters onto me. This opened the short well enough :S

Another thing that happens is shedding from plates building up on the bottom and creating a short. This is often not a hard zero Ohm short, so it becomes a drain for the bank.

Case #1 is normally with thin plate flooded lead acid batteries, i.e. starter batteries and in my case a non-maintenance type. These plates can bent from heavy usage (long starting) and after that only a light nudge might make plates touch. The reaction is violent and will melt the plates where they touch, which disconnects the short again. So, in case of a parallel bank, you keep power.

Case #2 is normally with thick plate deep cycle batteries. In a parallel bank you see voltage down like at 10V. The solution is to check batteries for temperature and disconnect the one that is overheating or hotter than the others. In a series bank you loose power due to low voltage.

cheers,
Nick.
I had a shorted out cell in a battery. It was my old batteries which were well knackered by that time. I left the boat in Cowes on shore power for several weeks during the winter, came back to the smell of boiling electrolyte.

I presume the plates fell apart in that cell. What would have happened if I had not come back at that very moment (the electrolyte had not boiled out) I don't know, but I suppose the risk of fire is relatively low, since boats don't burn up all that often, and knackered battery banks are a common phenomenon.

More boats spend more time unsupervised on shore power than they do unsupervised without shore power, and any danger from shorted cells will not be reduced by pure series wiring, if the boat is on shore power.
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Old 24-06-2012, 10:07   #124
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Re: Electrical Musings

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Very wise, the precept that you do not parallel batteries was accepted in the fifties in the seventies paralleling dry cells was recognised as a waste of energy.
More than 1 battery bank does not mean that batteries are not conected in parallel.

Most crusing boats have a house bank or banks consisting of batteries connected in parallel.
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Old 24-06-2012, 13:00   #125
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Re: Electrical Musings

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The vast majority of crusing boats have batteries connected in parallel. Many of them are insured.
EVERY boat I work on has parallel banks, my buddy who does UPS system for the pharmaceutical, telecom and banking industries also parallels MASSIVE & massively EXPENSIVE banks, as do solar installers, Vendee globe racers, the aeronautical industry etc. etc.....

The problems Chala extols just DO NOT happen the way he "presumes" they do. Have I seen shorted cells? Yep, plenty just had an Odyssey battery dated C-10 with a cell short that I warrantied last Friday. The other batteries it is paralleled with are perfectly fine. Had another cell short eight weeks ago and the bank was dead. Owner used the other bank for three weeks before even calling me. The shorted battery identified and replaced. The other batty it was paralleled with was charged, tested, equalized and placed back into service as the "new" start battery as it was still in better health than the "starting battery". Two new house batteries were installed. Those batteries had lasted him 7 years.

I probably see about 2-3 cases per year of "shorts", that's it. In most of these cases, except for AGM's, the batteries were WELL BEYOND their useful life span. I installed over 40 batteries in just the last six weeks so do get to see LOTS of boats with parallel banks, which is most all of them. Only the small fishing boats lack a parallel bank but they do use the BOTH feature and also parallel.....

I just came from a boat (installing a new plotter) with a 9 year old parallel bank (3 12V batteries). They still test pretty well and are surprisingly well balanced. I have advised the owner to replace them as there are some sulfation issues, but at 9 years that is to be expected. The vast majority of fires are cause by dead shorts in wiring not the batteries.

Seeing as every battery manufacturer I deal with, Exide, Deka/East Penn, US Battery, Crown, Superior, Concorde/Lifeline, Odyssey, Trojan, Full River etc. etc. all say parallel banks are perfectly fine and accepted I would love for Chala to step up to the plate and provide this "data" form the 50's & 70's, where it was "accepted" that parallel batteries are not "safe"...

Also those deaths were not the fault of a parallel bank they were the fault of an IMPROPER battery installation. We also do not even know whether the bank was "parallel" or a single battery.

A link to this "data" would be nice... That boat should have had a second bank and those boaters would likely be alive today. They simply did not follow good industry accepted practice of two battery banks. To blame it on parallel batteries is a stretch. If they had a single bank of series batteries, and a cell shorted, guess what, they'd still be dead.... Safer?


I think the millions, upon millions, of parallel banks, and the sheer lack of the doomsday predictions coming true are enough proof that parallel batteries are quite safe.......
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Old 24-06-2012, 13:41   #126
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Re: Electrical Musings

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You may see it that way. I find that accident tragic. Had these sailors been better advised they may still be enjoying a good sail.
And you believe that knowledge of the dangers of paralleling batteries would have saved their lives?

Please provide evidence to support your claim.

I agree, this was a tragic accident. But using it to bolster your argument is ludicrous.
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Old 24-06-2012, 15:51   #127
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Re: Electrical Musings

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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.



You did say a fault in "a" new battery. You said nothing of that battery being in parallel with another one and I have not seen what the article said.. If in fact it was "a" battery, as in single, then it is really 6 2V series cells. Seems this could have just as easily been a problem of a single battery, which in reality is series.... Do you have this "article"?

They clearly should have had a back up bank, hand held VHF, EPIRB or any one of the myriad of other devices well prepared boaters use... They chose not to have those devices, or level of preparedness, and as such they perished... I see no evidence of paralleling batteries causing the incident unless you can present us the article.

In many years of doing this I have never seen paralleling of batteries be deemed as the cause of a catastrophic episode.
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Old 26-06-2012, 07:17   #128
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Re: Electrical Musings

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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.
hard to grasp or accept.
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Old 26-06-2012, 08:34   #129
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Re: Electrical Musings

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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.
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hard to grasp or accept.
Concept grasped! Acceptance is easy when accompanied by evidence, something that is missing in this thread.

Is it plausible that other industries don't parallel batteries as they enjoy the freedom to design their system end to end?

Or is there evidence that safety issues when paralleling batteries drove them not to?

"Hmm, 12v & 675ah or 36v & 225ah, both 8100wh. Hmm, when using 12v the wire has to be bigger and voltage drop is more detrimental. Since I get to spec the motor also, let's go with 36v!"

No such luxury in the consumer marine appliance market.
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Old 26-06-2012, 08:54   #130
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Re: Electrical Musings

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wire has to be bigger and voltage drop is more detrimental. Since I get to spec the motor also, let's go with 36v![/I]"
No such luxury in the consumer marine appliance market.
What about smaller banks sharing the load, smaller the wire the more efficient it is at dissipating the heat.
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Old 26-06-2012, 16:33   #131
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Re: Electrical Musings

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What about smaller banks sharing the load, smaller the wire the more efficient it is at dissipating the heat.
Err... the wire size remains constant regardless of number of banks as it voltage dependant. Big wire for 12V, not so big for 36V.

Also surprised to think that heat is primary consideration in determining what wire gauge to use.
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Old 26-06-2012, 18:03   #132
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Re: Electrical Musings

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What about smaller banks sharing the load, smaller the wire the more efficient it is at dissipating the heat.
Can I ask Chala where you are either formulating or reading the nonsense you put into electrical comments on this forum. Its rare that one meets such an ill-informed perspective, that I wonder where its coming from. I ask it in all seriousness.

Dave
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Old 26-06-2012, 21:28   #133
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pirate Re: Electrical Musings

Probably based on reality, the most dangerous battery bank is a series bank that is being charged.

Especially if we are talking about a large charge capability, when it isn't temp compensated, whether from an alternator, comby, or straight shore charger.

Why...because as soon as as you take one of the series cells away from the bank. It becomes a nominal bank voltage minus that cell. All chargers are designed to charge a bank to 2.5 volts per cell bulk/absorption for FLA's, and 2.4 volts per cell AGM, & 2.4 Gell.

Now if we take one, two, three, or six cells from the bank, it can never reach nominal voltage of the charger.

So lets say we have 2 FLA's, 6-volt to make 12 volt.

Scenario one we have one cell go, so now we have a 11 volt nominal bat bank connected to a charger. The chargers job is to charge the bank to 12 volt nominal, which is 14.8 bulk/absorption....this can never happen because the remaining cells will overheat long before the charger can bring an 11 volt nominal bank to 14.8 volts.

Scenario two: We have 2, 6-volts bats in series to make 12 volts, then we have a high resistance connection to one of the 6 volt bats, now we have some where between a 6 volt nominal, and a 12 volt nominal, with a charge source attempting to bring the cells to 2,5 volts each.

Under any of these scenarios, the series string can never come to 2.5 volts per cell.

Lacking temp compensation, the charger will continue to poor the amps to the bank... and eventually the bats will hit 130 F, and either spilt their case and spill acid or worst case develop a dead short and casue a spark that ignites the the sulfuric gas, which will cause an explosion.

Worst case scenario, the battery cables are woeful undersized and the heat starts a fire.

What happens if the bats are not in spill proof boxes, the sulfuric acid, then drains into the bilges and mixes with sea(salt)water to make Chlorine gas.

LLoyd
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Old 26-06-2012, 21:42   #134
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OK, your turn now, explain why or if Ike gave the Russians a shot at Berlin and muzzled Patton, in terms of economics and the economics of war (both) and somehow, make that relevant to cruising and especially to electrical self-sustainence.
Could it hae something to do with Patton's likely "charge" on Berlin would outpace his artillery "batteries"?

Rimshot...
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Old 26-06-2012, 21:54   #135
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Re: Electrical Musings

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What happen when 1 battery short circuit?
A properly fitted fuse will disconnect the bank, from the bus.

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