Power Consumption Question.

Joe A · Feb 7, 2008

What a great explanation, Stu...

Now I wish I had purchased two batteries last season for my Mac 26S instead of just one. I have taken very good care of the one I bought, do you think it's too late to parallel a second of the same type.

Don S/V ILLusion · Feb 7, 2008

Corollary to what Stu quoted

I often wondered which is better - one large bank or two smaller ones. Each theory has it's arguments both pro and con. In the example Stu cited, one large bank arguably can last longer as it will be discharged proportionally less than a smaller one for a given load. This theory has at least one major drawback I can see - being the inevitable failure of one or more cells in the bank. When that failure does eventually occur, the entire bank is jeopardized and if it is a shorted cell, the jeopardy is compounded.I certainly defer to Calder but his theory, albeit true in my opinion, ignores the consequence of the eventual failure of a cell so I am left wondering whether Rob is better off with separate, isolated banks.No declarative answer from me - just wanted to see if anyone else has an opinion

ruedi ross · Feb 7, 2008

It's been my experience

that if you buy quality batteries and treat them right that one cell going bad is a relatively rare occurrance. That usually happens to cheaper batteries and batteries that are abused. I work with remote solar installations and FWIW,in 15 years I have NEVER seen an AGM with a bad cell.

Rob Hessenius · Feb 7, 2008

2 Isolated Batteries

The reason why I went with 2 isolated batteries was a simple one. I already had two group 27 deep cycle batteries and a Guest two bank, 10 amp charger. I thought about putting them together to gain amp hours, but never thought about the "health factors" of a larger bank. After reading Stu's post, I might not have the best system for my usage, but I have to live with my past decision.What started this whole thought was when I bought the charging system for my outboard. I wanted to get away from hauling a generater on my trips (7 days) when I trailer my boat over to Lake Michigan or Superior. I was hoping to have a way to see the state of charge in my batteries. After looking into the Link 20, which I think is the bees knees, it does much more than what my initial need was.

Stu Jackson · Feb 7, 2008

the inevitable failure of one or more cells

may happen regardless of how the bank is set up.If a failure occurs, you are going to simply remove the individual battery from the bank anyway (right?!?), doesn't matter how it's wired.I have difficulty understanding why anyone would set up two separate banks given the basic physical FACT that the same batteries last longer wired together.The ONLY situation I've come across in the last ten years that I've been actively engaged in boat electrical system design and installation where two equal banks make sense was for one of our members who has four golf carts in two banks. He's a racer, and wanted the lightest possible situation with backup. Our C34s (Mark I) come with a battery box that fits four Trojans or American battery six volts PERFECTLY. He rarely, if ever, goes cruising away from shorepower for more than a day.Otherwise, any big house bank (rgeardless of the type of batteries) with a small separate start bank is the preferred design that lengthens the life of whatever batteries you choose to buy.

Rob Hessenius · Feb 7, 2008

Change

I can easily turn my two battery system into a dual parallel bank. Visually I would have to deal with a battery on/off switch. Make a jumper and move a couple of wires over to the other on/off switch.Would this be better for the health of my batteries?

Paul Akers · Feb 7, 2008

Wow *yks, Stu Makes Sense!

I really don't mean to sound sarcastic, Stu. But all of your logic makes a lot of sense (Boy, do I love HOW). I've learned so much over the years. I'm glad that I have 1 , 3-battery bank and 1 starting battery (Isolated)!

Stu Jackson · Feb 7, 2008

Would this be better

Perhaps we need to go back to the original question on this post, since my latest posts have been regarding battery life.Basically, folks, each of you needs to determine how YOU use YOUR boat, there just is NO ONE BEST way to do anything, it all is based on use.A skipper who wants to anchor out a lot with minimal engine or other charging sources has a different "BEST" way to do battery design, sizing and setups than a marina hopper.The self sufficiency requirements of anchoring and cruising require the largest house bank with a separate start bank, with a healthy sized properly regulated alternator, perhaps other sources like solar, wind or a generator. Could even get away without (HA!) a battery charger completely.A marina hopper can actually use the pitiful battery arrangements that come with stock boats, a wimpy alternator and nothing more than a good quality shorepower charger (many of the ones that come with stock boats are also pitiful).Many of us fall somewhere in between, so you need to think the SYSTEM out. The post I linked to about system design (http://www.c34.org/projects/projects-electrical-system-upgrade-2.html) describes the issues facing many of us, and suggests one of many ways to do an upgrade.I installed a Freedom 15 I/C when we bought our boat back in 1998, have upgraded to a large 360 AH house bank with a separate start bank with a combiner, installed a higher output alternator and Max Charge regulator and just finished installing a Link 2000. I ran the boat for 8 of those 10 years with an old (1986) alternator with an Auto Mac without the Link because I did an ENERGY BUDGET and knew the draw on our system.Which is exactly what the original question was: what is my consumption? How you choose to meet that consumption is based on how you use your boat, how you may want to use it in the future, and what equipment you choose to install to meet those demands.Your boat, your choice.

Don S/V ILLusion · Feb 7, 2008

still not convinced but I agree regardless

Running a battery bank in parallel is certainly a controversial topic on sailboat e-mail lists. I do it myself (4 - 6V Trojans in parallel/series) so no one gets an argument from me. I do, however think it's somewhat of a crap shoot, both from a technical, as well as a strategic point of view for the following reason(s). As Stu implies, let the user make an informed judgement. Two brand new batteries of identical type and capacity can be operated in parallel, and the nominal capacity of the 'bank' will indeed be twice the capacity of each battery. For some period of time, they will continue to operate in this fashion; during recharge, each battery will draw the same current, and their electrochemical conditions will be identical. However, as the batteries age due to manufacturing tolerances and so forth, their electrochemical condition may differ.At some point, the weaker battery will begin to draw measurable current from the stronger one, and the total capacity will diminish. There is a possibility that one of the batteries will develop a shorted cell, and the result will be that the other battery will be dumping a huge amount of current into the damaged one Granted, it rarely happens and probably won’t in the first few years of battery life, but why take a chance? Is there anyone here who has never had a battery in their boat, car, tractor, etc fail? I think so! There's another problem with running batteries in parallel. As in the original poster's message, let's assume you've got a pair of identical batteries, which you are using sequentially. When one of them becomes depleted, you start your engine, and the alternator attempts to recharge the battery. Chances are good that the alternator will be working fairly hard, in the first hour or two, to supply the amount of current that the battery will accept. Eventually, the terminal voltage rises, the current reduces, and you reach a fully charged condition. Now let's assume that you've got the same two batteries, in parallel and you deplete them to the same level as in the previous example. The problem now is that you need twice the current to recharge the 'bank' in the same time period, but alternators are not linear devices, and you won't get twice the current, because heating will lower the maximum output, and you're asking the alternator to do twice the work as in the previous example.

Maine Sail · Feb 7, 2008

Don..

I've heard this argument before but......Consider what a 12V battery is made up of? Individual cells or "2.1 or "2" volt batteries"! Each 12v battery is already made up of six individual 2.1v batteries, put together in series, inside one case. Your simply talking about these individual batteries in separate cases..12 volt lead acid batteries used in the RV, automotive and Marine Industries usually consist of, and are made up of, six 2.1 volt cells in series to form a single 12-volt battery! Your already combining separate cells and essentially two six volt "banks", if you will, or 6 2.1 volt banks to create a 12V battery!! 12V Batteries are constructed of several single cells connected in series. Each of these cells in a 12v or 6v battery produces approximately 2.1 volts. A six-volt battery has three single cells, which when fully charged produce an output voltage of 6.3 volts. A twelve-volt battery has six single cells in series producing a fully charged output voltage of 12.6 volts.A battery cell consists of two lead plates a positive plate covered with a paste of lead dioxide and a negative made of sponge lead, with an insulating material or separator in between. The plates are then enclosed in a plastic battery case and then submersed in an electrolyte consisting of water and sulfuric acid. Yes there can be manufacturing irregularities between cells but you still have six separate batteries in ONE 12V battery any way so adding another six in a separate case is not going to make any difference...This argument on these "sailboat e-mail lists" are obviously by folks who don't know or fully understand battery construction. There is NO such thing as a wet 12 volt battery cell in the Marine, RV or Automotive industry and each 12 volt or 6 volt battery is already made up of smaller 2.1 volt or "2" volts batteries. Separating them into smaller cases, like two group 31's vs 1 4D and then paralleling them or in the case of a 6v putting them in series then parallel is no different than what is already going on inside your 12v or 6v battery.Each and every 2.1 volt cell could possibly go bad as each cell is a 2 volt battery...... Quote:"Now let's assume that you've got the same two batteries, in parallel and you deplete them to the same level as in the previous example. The problem now is that you need twice the current to recharge the 'bank' in the same time period, but alternators are not linear devices, and you won't get twice the current, because heating will lower the maximum output, and you're asking the alternator to do twice the work as in the previous example."This is why it's important to size an alternator to your bank! You don't want a 55 amp stock alternator charging a 450ah bank....I used to run a 90 amp alternator on my 4-T105 450ah bank and even at 50% discharge I never saw it put out much more than 60 amps and after about twenty minutes it would tail back to about 30-40 amps until it got closer to 80% of charge then it tapered again to about 15 amps and by the time it was at 90% of charge it was accepting about 6-7 amps per hour.........Are you suggesting a 4D or an 8D is ample battery???

Stu Jackson · Feb 7, 2008

Not trying to convince anyone

but presenting different points of view.Rudi's reply #44 is also one of them.I've had more troubles with alternators than batteries on cars, for instance. Yes, automobile batteries have a rated life, just like batteries used on boats. Point is, a well maintained boat battery should last much longer than a car battery, because car batteries are openly being charged incorrectly at 13.8V which is essentially and inherently crippling.Keeping the boat banks charged properly with proper three stage charging by both shorepower and alternator and other input systems, going down only to approximately 50% of capacity, and watching what you are doing related to cleanliness, temperature compensation, etc., will result in long life of batteries.Does stuff happen? You bet, because who knows what lurks in the hearts of batteries?

The chance of getting a lemon are slight but it does happen. Do batteries "age" differently? Sure, but not enough to matter nor to "worry" about.Once again, your boat, your choice. I just continue to recomend that you learn all you can, and then make your own choices, intelligently, not based on voodoo electricity theory

but real world how-it-works technology.One "argument" for not (or never) paralleling batteries would result in nothing BUT single individual batteries for battery banks. Ever try to haul a 4D?

Bob V · Feb 7, 2008

Don, I think you are mistaken

At least on your last point about charging two batteries seperately vs the same two hooked in parallel. What your charger "sees" is either one large "bucket" or two "small buckets". The amount that it takes to replace what has been used goes in at a rate that is dependant on your alternator's (or whatever charging source) capacity. If you have a smart voltage regulator, it will sense when the "bucket" is getting full and slowly turn down the "volume" as the level reaches the top of the bucket(s).I find the bucket and pump analogy helpfull here. I used the same analogy when my wife asked me why if we had just spent all of the money on a bigger alternator and voltage regulator we still ran out of electricity at the same time if we stayed put in an anchorage. I explained the we had just purchased a bigger "pump" to fill our bucket and since that bucket was always full when we got to the anchorage after a night in a marina it would last the same amount of time. The next step is to buy a bigger bucket.So if you invest in a really large bucket and you are still filling it with a small hose it will take a very long time to get a full charge. If you have a really big hose to fill your bucket and only a small bucket it won't last you any longer than it did before.I do agree with your point that as batteries age, it is likely that cell deterioration will not be uniform. The thing that makes it worth it is that when you're talking about batteries 1 + 1 > 2. I do not know how it works but I have seen the graphs that prove it. Two batteries that are hooked up in parallel have more that twice the capacity of those same two batteries used one at a time.Bob V

Maine Sail · Feb 7, 2008

I think Don meant..

I think Don meant have two batteries not paralleled and charge them at different times? While it would reduce load on the alternator it would drastically increase engine run times....!!!

Don S/V ILLusion · Feb 7, 2008

All great arguments

and all of which serve to provide excellent info to anyone interested.One point - I am aware any battery is a combination of cells...and I suspect so does everyone else.

It is, however, still a valid consideration when combining multiple batteries as the statistical probability of cascade failure expands with additional cells/batteries being combined, irrespective of quality or charging systems, each with their own falabilities.As I said, I too combine batteries but believe it worth the few minuites to air the other side as this was getting to sound like a group hug.PS - I thought that was what I said (about two batteries being charged separately)Bob V - I'd like to know how two combined batteries have more amps than they do separately. Are you referring to a parallel pair having the combined total of both?

Bob V · Feb 7, 2008

First off Don

Allow me to list my credentials. I have none that are relevent to this discussion. Although I was trained in marine electronics back in the late sixties while I was a GMM3 (missile technician) in the USN. I don't remember much of the sixties and I doubt the veracity of what I do remember but it was a good time. ;-)I used to use my two 4D's one at a time saving one for starting the boat. I got into a disusssion of electrical upgrades with someone more knowledgable on the docks one day when I was out cruising. He brought over an article complete with a graph showing two batteries in parallel vs two batteries used seperately. The article claimed that you would have more useable AH in the parallel configuration. I believe the effect was due to greater efficency in the batteries when they were close to full charge and keeping them closer to full charge by using both at once. Bob V

Steve Dion · Feb 7, 2008

Group 27's but what about height?

You mentioned that you only have room for group 27's. Do you have any additional height in your battery compartment? I have recently seen 400AH VDC batteries for sale. This is about the same footprint with more than 2 times the capacity!