Paralleling Batteries - Page 4 - SailNet Community
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post #31 of 80 Old 09-07-2006
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Actually, you would probably just yank the wires from the bad you want to have separate house and starting banks, unless your engine is small enough to start by hand, which is not the case for most in-board diesels.

For the most part, I'm not talking about paralleling the house and starting banks, but having several 12V batteries in parallel to create a larger 12V bank.

Your point is still quite valid though. If a single 2V cell in the large battery banks that hellosailor is advocating, you're basically screwed. Apparently, that thought has not occurred to him.

Personally, I'd rather have a half or two-thirds my battery capacity at the right voltage, than almost 83% of my capacity at too low a voltage to run anything safely.


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post #32 of 80 Old 09-07-2006
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"let's get real world."
By all means. Just bear in mind that every time we go over one set of criteria or options--that's only one set, not dogma, not one size fits all.

"Quite apart from cost (2-3 times at least)"
Cost based on what? If you haven't shopped for industrial cells locally, you don't know the costs. I can buy a 12V 80AH deep cycle from WallyWorld for moaybe $55. Or $85 from the battery store. Or $129.95 from the auto parts store. And they're all rated "the same". Prices vary widely and the only prices that anyone has posted for cells here--are the ones that I said represent the HIGHEST END. Now consider these are industrial cells (like Rolls uses) and the users expect 10-15 years of life out of them. Still want to compare them, at any price, to the WallyWorld battery that will last 4-5 years tops?

"and size (where the hell do I put these tall batteries) "
Again, look at the options, don't get stuck on what I said were first hits from the web. These are not tall batteries or tall cells. You can buy them tall--OR SHORT. Remember, Rolls is using these cells in conventional boxes that are sold in conventional sizes and shapes. This is an OPTION not a RESTRICTION.

"and maintenance (12 cable connections to inspect and maintain instead of 2), what happens when you lose a cell during a passage?"
Maintenance? What maintenance? My "cousin" drove a main battle tank and his daily maintenance including using a mirror on a stick to observe electrolyte levels in the battery cells, because they were located where heads couldn't get. You don't need cable connections for these cells. Depending on the options you have chosen, you can bolt them directly together (again, as Rolls does internally) or bolt them with buss bars, or use cables. I'd use cables only if they were the right solution to get more cells into a more restricted space. And if you know how to use bolts, they don't just let go. Like any critical bolt, you need to at least come close to the right torque setting. You'll see Dave's pictures above of battery labels actually tell you what torque to use on them. And you use nylocks, or thread lock, or locking (double) bolts, as apropriate. Yes, it is possible to use bolts reliably.

But more important, how do you think the six cells in each of your parallel batteries were assembled? Ooops, no bolts, they are welded and sealed, no access possible. If a weld was bad in that cheap battery--you lost it. So maybe bolts aren't so bad after all...somehow, they hold most of the boat together.

"You're two days out of LA headed for Hawaii, and one of the cells on your ONLY 12V house battery develops a short. "
OK, so what? If that happens in a "12v" battery, you're screwed, you've got no battery. If it happens in your ONLY battery, you're still screwed, no matter what kind it is. The debate over series/parallel should not be confused with the debate over whether to put all your eggs in one battery. I'd suggest that a second battery, whether it was an SLI battery or a second house bank, would still be prudent. But again--that's a totally separate issue!

"Do you think the sailor with the paralleled battery bank gives a damn that he/she may be losing a tiny percentage of efficiency by paralleling the house battery banks???"

Nope. Most boat owners (and remember, most are not global cruisers and most have boats under, what is it, 32' OAL?) are also satisfied with automotive charging systems and replacing their batteries every 3-4 years.

And those are also the folks who run "A+B" all the time, and call TOW_BOATS_R_US around 4PM Saturday when the stereo has killed both batteries.

Does that mean they're doing things the best possible way? No. But that's a pretty good thing, if you run a tow boat for a living.
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post #33 of 80 Old 09-07-2006
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Pictures! / Stats! / Sources!

Of all the posters in this thread, you seem to be the most familiar with single cells. While I realize that every battery is just 'bank in a box' it is still a sort of wierd and foriegn notion to most folks to build your own battery. Can you provide links to web pages that show pics and stats and prices of individual cells?

The only time I have been 'up close and personal' with individual cells is in the emergeny power room of a Nuc. Plant where the cells were in glass containers about a foot square and 3 feet high. Other than that I remember seeing pictures of batteries being repaired back when the cells were set in tar in the box and one used a hot knife to melt out the bad cell and insert a new one. Anyway I understand that SHORT cells must be available because that is what is used to make Rolls 8D's etc etc, but how to find them. I looked around a bit on google and found US Battery and Trojan but they only had 6V, 8V, 12V batteries that I saw. I did find 4V on the surrette site but the shortest was 16" tall.

May personal preferance so far is to have two twelve volt banks that can be paralleled if desired and I would leave them paralleled most of the time. I would prefer to build my own bank out of 2V or 4V cells.
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"it is still a sort of wierd and foriegn notion to most folks to build your own battery.' Consider that most of us, myself included, talk about buying AA batteries or D batteries for a flashlight. Ain't no such thing, a "D" cell is a cell. A 9-volt battery is indeed a battery of six smaller cells. A watch again a cell, not a battery. So yes, we all have some foreign notions. After all, the grade schools don't teach you 'A boat is a hole in the water that you throw money into' either, do they?

I haven't seen much about them on the web. has a list of their standard products. East Penn/Deka doesn't seem to have any list, or even indicate they make them on their web site. Considering that lead cells are, after all, LEAD and shipping costs can be killer on them, I think it is more effective to look in your local Yellow Pages for a local distributer. They're usually located in some grimy industrial corner but a few phone calls should track them down. And a call to any major manufacturer (JCI, Interstate, East Penn, etc.) should be able to wring some kind of industrial contact number out of them. Just tell 'em you have a fork lift, or a nuclear reactor, and you need a local source of battery cells.

And of course, if you're under 36' and you're not running a reefer and AC, a pair of Group31's might be all you need. I still like the concept of separate and redundant supplies, unless there's a good reason to match a big charger to "one big bank". And even then, I'd want an isolated "spare". Maybe an SLI for the starter, or a separate deep cycle forward on the winch, or even a relatively small 12v17Ah AGM battery, 1/3 the size of a shoebox, which makes a good emergency starter even for a small diesel engine. (I'm sure the current draw violates proper usage, but "emergency" is the trump card.)
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Preventive Maintenance

Oh, oh, Hellosailor, No thread lock. It does not guarantee a good connection or a connection that won’t corrode. As I stated before, preventive maintenance must be performed on battery systems, series or parallel. One of the most important chores is inspection of the connections for tightness and corrosion. There are literally hundreds of connections in a typical battery installation for telecom and each one must be checked to insure good contact, no corrosion and correct torque. You can be sure that during maintenance of that tank that one of the routine chores was to clean and tighten those connections.

These connections “settle” during thermal cycling and vibration and you will be able to tighten them even though they have not backed off or turned.

All connections, bus bar or crimped, must be regularly checked.

Connections on a boat should be inspected at least once a month. I actually just got back from a sail this afternoon and installing additional batteries to my bank and even though I regularly inspect my connections, I found two loose and one starting to corrode.

Preventive maintenance MUST include inspection and retorquing battery connections, no excuses.

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post #36 of 80 Old 09-07-2006
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"I still like the concept of separate and redundant supplies, unless there's a good reason to match a big charger to "one big bank". And even then, I'd want an isolated "spare". Maybe an SLI for the starter, or a separate deep cycle forward on the winch, or even..."

Well, now you're talking! This is exactly what we "parallelists" have been talking about all along, although it seems like we're trying to nail jelly to the wall to get this concept through.

- Yes, two or more house banks to provide redundancy.
- Yes, combine them for efficient charging with a large alternator and smart marine regulator.
- Yes, combine them for convenience and for "shallow cycling" rather than "deep cycling", without having to switch between battery banks.
- Yes, a completely separate battery for the engine.
- Yes, redundancy....I have that bank forward you mentioned (two golf-carts) dedicated to the windless. There's also the separate engine battery.

Where we differ is with regard to your conviction that a reasonably-priced battery bank -- or two of them for redundancy -- can on most modest cruising boats be built up from readily available, not-too-costly, and not too tall 2V cells.

Let's move out of the general to the specific. Could you please recommend -- with specificity -- brands, sizes, and costs for a 12V house bank (say, 450-700AH at the 20-hour rate) which will fit into a battery space with a height of not more than 11-12"?

No waffling about look at local dealers, search the Internet, etc. Let's have your specific recommendations.

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I'm done with the theortical BS that hellosailor puts out, gimme real world prices and shipping,(hasn't been done) tell me how you did it on yours, post a jpg of them on your boat, or off with your head! (ok, just kidding about the last part)

I don't mind "options" hey, throwing a 454 big block in the stern is an option too, just not very practical. or real world

first, rolls doesn't ship just the cells, they want the whole battery and will ship you a whole battery... have you EVER SHIPPED 200 lbs via Parcel Post?
If I need a new battery, I don't want to spend a week or more in port waiting for UPS or FED EX Ground, and just for grins, the bahamas aren't all that out of the way for many sailors here. AND I've seen enough of the grimy industrial portions of the bahamas to last a lifetime, thanks. I'm not saying that parallel must be better, but, damn, buddy, the whacked out "options" you give are... whacked out.

I did notice that you rebutted none of the points I've made, nor, told us about the fashionable cells in your boat.

and while I'm at at it,just gander at the number of distributors in the bahamas...from rolls...its DC Battery in Miami. sorry.

Now, suppose you come up with local distribs and prices for those 2 volt cells for me in oh, say the Bahamas? or hell, LA an Houston, Baltimore, and Bangor and, Miami. Surf theory boy, surf!

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post #38 of 80 Old 09-07-2006
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A little lite reading !

A little light reading. Don't have any ties to these folks but the info seems resonabley complete, clear and good.
For a good compromise on size and weight and until the "buy a small 2Volt cell issue" gets sorted out the 6V golf cart batteries seem a good choice. I have L-16's and a place to put them, however at 124lbs and 16+" tall but I would not wish them on anyone that did not require very high capacity. I will keep looking for 2V cells but so far I have found 4V cells (24" tall) at several 'off the grid' places on the web. Any of those folks that specialized in 'OFF THE GRID' solar/wind etc are a wealth of info on things battery.

Excerpted from:

Lifespan of Batteries

The lifespan of a battery will vary considerably with how it is used, how it is maintained and charged, temperature, and other factors. In extreme cases, it can vary to extremes - we have seen L-16's killed in less than a year by severe overcharging, and we have a large set of surplus telephone batteries that sees only occasional (5-10 times per year) heavy service that are now over 25 years old. We have seen gelled cells destroyed in one day when overcharged with a large automotive charger. We have seen golf cart batteries destroyed without ever being used in less than a year because they were left sitting in a hot garage without being charged. Even the so-called "dry charged" (where you add acid when you need them) have a shelf life of at most 18 months, as they are not totally dry (actually, a few are, but hard to find, the vast majority are shipped with damp plates).

These are some general (minimum - maximum) typical expectations for batteries if used in deep cycle service:
Starting: 3-12 months
Marine: 1-6 years
Golf cart: 2-6 years
AGM deep cycle: 4-7 years
Gelled deep cycle: 2-5 years
Deep cycle (L-16 type etc): 4-8 years
Rolls-Surrette premium deep cycle: 7-15 years
Industrial deep cycle (Crown and Rolls 4KS series): 10-20+ years
Telephone (float): 1-20 years. These are usually special purpose "float service", but often appear on the surplus market as "deep cycle". They can vary considerably, depending on age, usage, care, and type.
NiFe (alkaline): 3-25 years
NiCad: 1-20 years

Battery Size Codes

Batteries come in all different sizes. Many have "group" sizes, which is based upon the physical size and terminal placement. It is NOT a measure of battery capacity. Typical BCI codes are group U1, 24, 27, and 31. Industrial batteries are usually designated by a part number such as "FS" for floor sweeper, or "GC" for golf cart. Many batteries follow no particular code, and are just manufacturers part numbers. Other standard size codes are 4D & 8D, large industrial batteries, commonly used in solar electric systems.

Some common battery size codes used are: (ratings are approximate)

U1..................34 to 40 Amp hours......12 volts
Group 24..........70-85 Amp hours.........12 volts
Group 27..........85-105 Amp hours.......12 volts
Group 31..........95-125 Amp hours.......12 volts
4-D................180-215 Amp hours.......12 volts
8-D................225-255 Amp hours.......12 volts
Golf cart & T-105.......180 to 220 Amp hours.........6 volts
L-16.........................340 to 415 Amp hours........6 volts

Cycles vs Life

A battery "cycle" is one complete discharge and recharge cycle. It is usually considered to be discharging from 100% to 20%, and then back to 100%. However, there are often ratings for other depth of discharge cycles, the most common ones are 10%, 20%, and 50%. You have to be careful when looking at ratings that list how many cycles a battery is rated for unless it also states how far down it is being discharged. For example, one of the widely advertised telephone type (float service) batteries have been advertised as having a 20-year life. If you look at the fine print, it has that rating only at 5% DOD - it is much less when used in an application where they are cycled deeper on a regular basis. Those same batteries are rated at less than 5 years if cycled to 50%. For example, most golf cart batteries are rated for about 550 cycles to 50% discharge - which equates to about 2 years.

How depth of discharge affects cycle life on batteriesBattery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%. Obviously, there are some practical limitations on this - you don't usually want to have a 5 ton pile of batteries sitting there just to reduce the DOD. The most practical number to use is 50% DOD on a regular basis. This does NOT mean you cannot go to 80% once in a while. It's just that when designing a system when you have some idea of the loads, you should figure on an average DOD of around 50% for the best storage vs cost factor. Also, there is an upper limit - a battery that is continually cycled 5% or less will usually not last as long as one cycled down 10%. This happens because at very shallow cycles, the Lead Dioxide tends to build up in clumps on the the positive plates rather in an even film.

The graph above shows how lifespan is affected by depth of discharge. The chart is for a Concorde Lifeline battery, but all lead-acid batteries will be similar in the shape of the curve, although the number of cycles will vary.

Amp-Hour Capacity

All deep cycle batteries are rated in amp-hours. An amp-hour is one amp for one hour, or 10 amps for 1/10 of an hour and so forth. It is amps x hours. If you have something that pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) x .333 (hours), or 6.67 AH. The accepted AH rating time period for batteries used in solar electric and backup power systems (and for nearly all deep cycle batteries) is the "20 hour rate". This means that it is discharged down to 10.5 volts over a 20 hour period while the total actual amp-hours it supplies is measured. Sometimes ratings at the 6 hour rate and 100 hour rate are also given for comparison and for different applications. The 6-hour rate is often used for industrial batteries, as that is a typical daily duty cycle. Sometimes the 100 hour rate is given just to make the battery look better than it really is, but it is also useful for figuring battery capacity for long-term backup amp-hour requirements.
Why amp-hours are specified at a particular rate:

Because of something called the Peukert Effect. The Peukert value is directly related to the internal resistance of the battery. The higher the internal resistance, the higher the losses while charging and discharging, especially at higher currents. This means that the faster a battery is used (discharged), the LOWER the AH capacity. Conversely, if it is drained slower, the AH capacity is higher. This is important because some folks have chosen to rate their batteries at the 100 hour rate - which makes them look a lot better than they really are. Here are some typical battery capacities from the manufacturers data sheets:
Battery Type.............100 hour rate..........20 hour rate.......8
Trojan T-105................250 AH...................225 AH.........n/a
US Battery 2200..............n/a......................225 AH........181 AH
Concorde PVX-6220.......255 AH...................221 AH.........183 AH
Surrette S-460 (L-16)....429 AH...................344 AH.........282 AH
Trojan L-16..................400 AH...................360 AH...........n/a
Surrette CS-25-PS........974 AH...................779 AH..........639 AH

State of Charge

Here are no-load typical voltages vs state of charge

(figured at 10.5 volts = fully discharged, and 77 degrees F). Voltages are for a 12 volt battery system. For 24 volt systems multiply by 2, for 48 volt system, multiply by 4. VPC is the volts per individual cell - if you measure more than a .2 volt difference between each cell, you need to equalize, or your batteries are going bad, or they may be sulfated. These voltages are for batteries that have been at rest for 3 hours or more. Batteries that are being charged will be higher - the voltages while under charge will not tell you anything, you have to let the battery sit for a while. For longest life, batteries should stay in the green zone. Occasional dips into the yellow are not harmful, but continual discharges to those levels will shorten battery life considerably. It is important to realize that voltage measurements are only approximate. The best determination is to measure the specific gravity, but in many batteries this is difficult or impossible. Note the large voltage drop in the last 10%.
State of Charge........12 Volt battery............Volts per Cell
100%.............................12.7............. ............2.12
90%...............................12.5............ .............2.08
80%...............................12.42........... ............2.07
70%...............................12.32........... ............2.05
60%...............................12.20........... ............2.03
50%...............................12.06........... ............2.01
40%...............................11.9............ .............1.98
30%...............................11.75........... ............1.96
20%...............................11.58........... ............1.93
10%...............................11.31........... ............1.89
0...................................10.5.......... .............. 1.75

********* end of excerpt ********

Last edited by sailandoar; 09-07-2006 at 10:52 PM.
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Cardiac? "gimme".
Sorry, Santa says you'll have to get them yourself. I'm not going to find your local yellow pages and chase down your local industrial suppliers.
What I'm sailing on right now requires a lot less power, I go A/B and alternate two Group31's and that's enough for my modest needs. No reefer, no stereo, and no big budget to be invested. Now, seize on that and proclaim that means I'm unable to do the math and planning for a larger installation, by all means. That would be like saying the design team for the International Space Station are unqualified, because they've never been in orbit before.

"6V golf cart batteries seem a good choice." Yes. And yes again, height can be a problem. AGM would allow you to lay those down--but AGM is a whole other set of considerations and price increases too. two good points: No acid leaks and 25% faster charging rates. Two bad points: Can't replace electrolyte, and a 20-40% price difference. Ooopsie.

From your web quote:
"Deep cycle (L-16 type etc): 4-8 years
Rolls-Surrette premium deep cycle: 7-15 years
Industrial deep cycle (Crown and Rolls 4KS series): 10-20+ years"

And that's something else I'm afraid totally eludes CardiacPaul. The 2V cells are industrial cells, with a typical lifetime 2x-3x longer than the "marine" 12V batteries from WallyWorld. If, IF, they cost a bit more...that's still a different price for different goods. But some folks think all batteries are the same. No skin off my back.

Windsun's range of useful charge from 10.5 to 12.7 volts is a bit generous, the old scale from Practical Sailor that I have on my hydrometer case runs from 12.6 to 11.6 and from experience I can say that at 11.8 volts they're still useful--soetimes--but in my book, well overdue for replacement.

I did some homework, check me out on this, will you? Using Thevenin's equation the current flowing between two batteries should be equal to the voltage difference between the two batteries and the total of the two battery resistances, yes?

So let's rashly and randomly pick two of the common "one man can easily lug these" Group27 batteries, rated at 12.6V 88AH nominal capacity, off the same production group with a difference of 0.1V in their "fully charged brand new" state. The mfr's data I've seen claim these can put out 3300A into a dead short and that's close to the internal resistance claimed of roughly 0.004 ohms, cited at 60Hz not at DC.

With some rough numbers, that tells me the current flow between the two batteries will be 12.5 amps when they are initially connected. ( 0.1v divided by 0.008 ohms) Once the battery voltages equalize--which should be, what, five or ten minutes? that current flow should drop to near zero. So the 12-amp flow is not a concern IF it only lasts once for a few minutes.

And if the two batteries were finely matched and only differed by 0.01 volts, the flow would be a piffling 1.25 amps initially.

Do those numbers sound right (ballpark) to you? Indicating that the internal impedance of the battery, and the match of battery voltages, will be a major factor for those first minutes?

But then, what happens in the real world, as both batteries self-discharge and the acid in them equalizes charge, at different rates?

I guess that's what your experiment will tell us, I'm not sure how to model things past that.
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Sounds correct, however as you mentioned, things sometimes happen differently in the real world.

BTW, that current represents energy going from one battery to the other. The total energy of the system (discounting self discharge, which is really a chemical reaction, and resistive heating which will be negligible) remains constant. So even with the current flow you won’t be loosing any capacity. Once you put a load on the system BOTH batteries will discharge into the load.

There are two types of fools...

One says this is old, and therefore good..

The other says this is new, and therefore better...
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