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fionatr
fionatr

Posted: Fri Dec 30, 2016 4:26pm

Post Subject: Batteries

Hi, I was talking to my mechanic at my marina about putting new batteries in my boat and he was saying that I should not have more than 5 batteries and I was wondering why. Also what are the important things to know about the different types of battery that are available? Thank you, Fiona

Tony-B
Tony-B

Posted: Fri Dec 30, 2016 6:09pm

Post Subject: Batteries

This is going to end up as a long technical reply. As the forum software does not allow paragraphs and also messes up Word control characters I think you would read and understand it more easily if I emails the reply direct to you, possibly as a Word attachment so please send your email address to Tony@TB-Training.co.uk. I will put a reply on here but it will be a very long block of text and not easy to read.

Tony-B
Tony-B

Posted: Sat Dec 31, 2016 8:14am

Post Subject: Batteries

FIRST PART OF REPLY Subject: Batteries 1. I was talking to my mechanic at my marina about putting new batteries in my boat and he was saying that I should not have more than 5 batteries and I was wondering why? 2. Also what are the important things to know about the different types of battery that are available? Answers This is difficult because there is much you have not told me but I will do my best to give some sort of answer. Please come back to clarify anything I have got wrong about your boat or that you do not understand. This might to and throw for weeks. I am going to assume this is a 12 volt system with a number of batteries connected in parallel. That is with all the positive posts joined together and all the negative posts joined together. I am also going to assume that you only have engine driven alternator charging perhaps plus some solar. Solar charging will be contributing very little for the next couple of months so I will ignore that as well. I am going to deal with the second question first because it is marginally less involved. I am also gong to ignore very expensive battery types like spiral plates deigns. Any figures given are indicative and not factual. Check with the battery manufacturer, they do vary. Question 2: The battery types are listed below plus their characteristics. 1. WET OPEN CELL TYPES These tend fall into two categories, Leisure/duel purpose batteries and Traction/semi-traction batteries. In all cases they have removable cell caps that allow topping up and the easy removal of acid for diagnostic purposes. They can be topped up with distilled/de-mineralised water to replace the liquid lost to gassing when high charging voltages are used – say above 14.5 volts They are a good type if you have an advanced alternator controller fitted, an alternator set to deliver more than about 14.5 volts, or a battery charger that allows equalisation charging. Equalisation is done at infrequent intervals at 15 volts or more for a short period of time. Charging at more than about 14.5 volts may well convert some of the electrolyte in the battery to gas so the ability to top up is very important. Leisure batteries will be at the cheaper end of the price range and may well use calcium in their construction. This increases the voltage at which they start to make gas BUT they can only stand a fairly limited number of charge – discharge cycles. Typically about 150 at the lower end and up to 400 at the upper. Traction (expensive) and semi-traction batteries may not use calcium so may gas more at higher voltages but they will have more or many more charge discharge cycles. These may be the best buy IF and only if you really know how to look after batteries. You could destroy a £1000+ set as easily as you can a £200 set of leisure batteries if you do not keep then fully charged and well looked after. This type of battery or in some cases sets of individual 2V cells may have a 1500 or more cyclic life but you pay for it. If a battery label gives both an Amp hour (Ah) and Cold Cranking Amps (CCA) it is likely to be a leisure type. If no CCA is mentioned it is likely to be a traction or semi-traction type. The latter type is likely to take regular equalising better than the former. People who know tend to refer to leisure batteries as starting batteries with handles on. This refers to their internal construction of many thin plates rather than few thicker ones. The construction tends to govern their cyclic life so for most boaters the construction is not very important although cyclic life is. 2. SEALED FLOODED CELL Basically the same as the above except you can not get into the cells for diagnostics or topping up. With this type it is VITAL that you never exceed their maximum charging voltage (say 14.4 volts but it varies with their construction and materials). No access to the acid makes them hard for a boater to diagnose. Note:- The lead plates in a battery may be held apart by porous plastic separators on their own or they may also have the plates inside glass fibre pockets as well as using separators. Pocketed plate batteries will be more expensive but are likely to last longer. 3. AGM Absorbed Glass Mat. These have all the gaps inside the cells filled with glass fibre wadding impregnated with the acid. They are also sealed batteries so it is vital that you never exceed their maximum charging voltage. This can vary from below 14 volts to 14.5 or more so CHECK to make sure you do not dry the acid out. This type of battery can charge faster than wet types and give a better discharge. The wadding acts like the pocket so they tend to have a longer life WHEN LOOKED AFTER. No access to the acid makes them hard for a boater to diagnose. They are more expensive that the above type but in some circumstances the extra cost is worth it if you ignore the diagnosis problem. 4. GEL BATTERIES These do not contain liquid acid but an acid gel. They are expensive and despite their advantages I feel they are not likely to be cost effective for inland boaters. Some expensive batteries have their plates made in a spiral form. This gives them strength and potentially a longer life. They are usually gel batteries. Battery Designation. Batteries are “measured” by:- Case dimensions/size Terminal layout In some cases these together give a numerical designation like 644 Cold Cranking Capacity (CCA) This shows how many amps the battery can supply when new and fully charged to start the engine. This is not relevant for domestic batteries. Most boats have start batteries that are have a far higher CCA than one for the same engine in a van/car/digger so it hardly matters for start batteries unless you are gong to fit a much smaller one. Amp hour capacity (Ah) This shows how many amps a new and fully charged battery can supply over a 20 hour discharge period. Forget the 20 hour bit but grasp that a 100 Ah can be assumed capable of supplying 100 amps for one hour, 50 amps for two hours, 25 amps for four hours and 1 amp for 100 hours. In reality high currents will give a little less time and low currents a little more. Do not worry about this. Just grasp the basic Ah thing. Cyclic life This shows how many times you can charge and discharge a battery until it is likely to fail. The deeper the discharge and the more times you do it the more cyclic life you use up. This is why it is considered best practice to never discharge domestic batteries below about 50% of fully charged before recharging. If you only discharge to 50% you in effect double the cyclic life. Battery life When a battery discharges the negative late changes from lead oxide to lead sulphate and when charge the action is reversed. Unfortunately the longer the lead sulphate is left before recharging the harder it becomes and requires ever higher voltages to re-convert it to lead oxide. Before very long the voltage required would be high enough to destroy the battery so in effect a safe charging voltage is used BUT the Ah capacity of a battery gradually decreases as the sulphate builds up. When it gets to 50% of its original capacity the battery is considered failed. This is what “kills” most boat batteries but many new live-aboards destroy then by also continually deeply discharging the batteries and never properly recharging them so they both run out of cyclic life AND suffer bad sulphation. In some cases they destroy new batteries in a very few weeks. To maximise battery life keep them as fully charged as practical for as long as possible. This probably means charging for two to four hours every day with a long weekly charge of maybe eight hours or more. You can consider a battery is fully charged when the charging current has fallen to one or two percent of the bank capacity and it has failed to drop over about an hour.

Tony-B
Tony-B

Posted: Sat Dec 31, 2016 12:18pm

Post Subject: Batteries

PART TWO OF REPLY:- Can more that five batteries be used? Based on the facts given the answer would seem to be this is nonsense but with more information it just might be correct. How are the batteries in the bank connected? Each cable connecting a battery to the next causes a tiny bit of voltdrop so the more of these cable you have (interlinks) the less charging voltage is available for some batteries so some cells may never get fully recharged. To combat this effect all positive and negative charging and take off leads should be at opposite ends of the bank. That is positives on one end and all the negatives on the other, if this is not done the more batteries in a bank the greater the effect of voltage loss will be. In fact the more batteries in a bank the less effective wiring as described becomes so a more complex wiring system is required to minimise the loss of charging voltage. Perhaps the engineer could see there was something sub-optimal in the way the batteries are wired so did not want to add more and have to explain why you needed some extra wiring work. You say 5 batteries but this may mean four domestic batteries and one start battery. We must ignore the start battery for this question. If fitting more domestic batteries means they will have to go on both sides of the boat then two interlinks will be much longer that the rest and make the problem I described above more likely. It also means that to improve the situation would be far more costly with a lot of very thick cables involved. You could however move the engine battery to the other side and fit a new domestic battery in its place as long as the wiring rules above are employed. Why do you want more batteries? So often boaters think that just adding another battery will solve their electricity problems and it turns out the problem has nothing to do with battery Ah capacity and all to do with excess use and/or insufficient charging. Perhaps the engineer assessed your use, size of alternator and charging regime and concluded that battery capacity is not the problem in your case so was unwilling to spend your money when he new the problem would not be solved. When looking at batteries and charging system or any time you have problems you should start by doing a power audit where you list all the electrical items on the boat and how long you use each on (usually) every day. Then you take the amps drawn by each one and multiply it by the hours used. This will give you the Amp hours you need to store. It also provides the information upon which you can calculate your charging needs. Sample calculations here http://www.tb-training.co.uk/16elect.htm#bmn68 I have already discussed the 50% discharge “rule” so whatever the Ah figure you come up with must be doubles. We have also discussed the loss of capacity caused by sulphation so you really need even more capacity. A rule of thumb is that your power audit figure is about 25% of the bank capacity you need to install. Recharging the batteries From the power audit you know how much electricity you have taken out of the batteries but it is far from clear how much you need to put back in because batteries can be anything between about 50% and 90% efficient at charging. This means you may have to put back in anything between 10% and 50% more than you took out (figures from web searches). The truth will be somewhere in the middle but it will alter with temperature, age, and battery construction/type. I like to take 30% as the figure but it is a personal choice. From now on all calculations should not be viewed as much more than informed guesses. Lets say your power audit showed 80Ah per day. 130% of 80 Ah = 104Ah. This looks simple, lets just run a 70 amp alternator for 1.5 hours – Nothing could be further from the truth, this will lead to chronic undercharging and sulphation. Alternator output is only at its rated maximum for maybe 20 minutes on a well set-up and properly used system. From then on it gradually drops over many hours to a very low figure around the 1 to 2% of battery capacity so the alternator’s maximum output is a useless figure to use. Experience shows that over a two to four hour period the average alternator output on a well designed and used system would be about 50% of the maximum. As soon as the time is extended that figure drops more and more. So using the figures above 50% of 70 amps = 35 amps Putting back 104Ah will tale 104/35 = 2.9 hours – nearly twice the time most people would think. If the time needed to fully charge the battery was longer then that average of 50% of alternator output would get less and less the longer it took. This all gets all but impossible to work out so the rule is to charge at around 14.2 to 14.5 volts until the current has fallen to 1 or 3% of battery capacity and/or the charging current has stopped falling for an hour (I know I have repeated this). Conclusions Possibilities for saying you can have no more than 5 batteries:- No physical space Wiring sub optimal and the work required to make it optimal not wanted. The problem is not battery capacity as such but a lack of charging or excess consumption so he would get a bad name through no fault of his own. Lack of knowledge leading to poor advice. Further reading that may help: http://thunderboat.boards.net/thread/81 7/battery-charging-primer http://thunderboat. boards.net/thread/867/battery-state-charge-meter s-tell?page=1 Only read the first item, don’t confuse yourself with the rest.

Tony-B
Tony-B

Posted: Sat Dec 31, 2016 12:20pm

Post Subject: Batteries

If anyone wants the replies in Word format please email me Tony@TB-Trining.co.uk

Tony-B
Tony-B

Posted: Sat Dec 31, 2016 12:21pm

Post Subject: Batteries

Idiot - Tony@TB-Training.co.uk

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