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Reader charges battery piece missed key points

Jan 1, 2003

To the editor:I am new reader to your magazine and have enjoyed most of the articles so far. However, Chuck Husick's article in the 1999 annual issue warranted some closer attention to detail from your editing staff ("Ensuring reliable electrical power," Issue No. 97, Ocean Voyager). I have two objections to the content of the article: the absence of gel-cell/absorbed glass mat (AGM) batteries and some of the advice given for the flooded cells. Husick disregarded non-flooded cell batteries. These alternative battery types deserve attention. The weaknesses of flooded cells should have led Husick to examine alternatives. Below are what I think are some of the pros and cons of non-flooded batteries (gel and AGM in particular). Pro:· Minimal maintenance (if properly charged)· Much safer· Very high charge acceptance· Orientation freedom·

Con: 15% less amp-hour capacity for a given group size· Twice as expensive as inexpensive flooded counterparts· Require sophisticated regulators not found on every boat· Some custom adjustment to lower set points required· Less use/familiarity worldwide· Fewer shapes/sizes to choose from For example, Mr. Husick goes to great lengths describing how long an engine must be run each day to recharge depleted banks. Gel and AGM batteries allow higher charging rates, resulting in less engine running time and motor wear. They are also much less toxic on a day-to-day basis than their flooded counterparts. And, multihulls aside, the extra battery weight is not a problem. The higher initial cost is not objectionable either, given that some flooded batteries cost even more. The biggest stumbling block is the smaller distribution network/availability of/familiarity with non-flooded batteries around the world. Properly maintained, gel cells and AGM batteries last longer than their flooded counterparts. Most after-market regulators now come with preset charging patterns for many kinds of batteries, and more marinas are familiarizing themselves with alternatives to flooded cells. Furthermore, it is possible to have different types of battery banks, even with only one alternator and regulator, by using the isolator-eliminator manufactured by Ample Power. So much for omitting other battery types. If that was not enough, the writing in the article on flooded cells is vague enough to cause some headaches. Discharging individual batteries from a bank, as he describes it, is possibly the best way to shorten battery life. Discharging batteries as a bank (in parallel) leads to less internal resistance (and heat losses), lower loads on individual batteries, and a lower average discharge level prior to charging. Ideally, a boat should only have two banks: one for the engine, another for the house loads. Large banks allow the alternator to run at a very high output, minimizing engine/genset running time. Constantin von Wentzel is a technical consultant who enjoys sailing and working on his boat The Cats Pyjamas, a Prout Escale catamaran. Chuck Husick replies: My discussion of batteries was limited to flooded-cell types in recognition of the fact that the majority of boats use this type of battery, not because of any prejudice against the various non-flooded battery types (also called Valve Regulated Lead Acid batteries, or VRLAs), which include both those with gelled electrolyte and those using absorbed electrolyte construction. Both of these alternative battery types were discussed in my 1998 Ocean Voyager battery article ("Battery systems for the voyager," Issue No. 89, Ocean Voyager). There are points raised by Constantin von Wentzel with which I agree and some which I believe to be incorrect. He comments that the AGM and gel-cell types are much safer than the conventional flooded types. This is true in one sense and quite untrue in another. An inverted AGM or gel-cell battery will not leak electrolyte. However, overcharge a VRLA and the internal pressure may exceed the pressure-relief setting of the safety valves, resulting in discharge of electrolyte and ruin of the battery. Overcharge of the flooded-cell battery may cause harm, but it's not likely to render the battery useless. The orientation freedom of the VRLA types can be of advantage in some installations; however, the manufacturers generally do not recommend that they be used in other than a valve-up or valve-down position. I agree with the negative points for the VRLAs mentioned by von Wentzel, except that the price premium for equal energy storage capacity may approach 3:1 rather than the 2:1 ratio he mentions. It is true that the VRLAs can accept a higher, in some cases much higher, charge current than the flooded-cell types. In fact, it is this capability that led to the development of the AGM as a substitute for the NiCad batteries used in starting aircraft jet engines. This characteristic can be useful for those boat owners who must limit engine running time to the minimum and who are willing to install the very large alternators and regulators needed to do a recharge in the minimum possible time. According to von Wentzel, VRLAs are less toxic than the flooded-cell batteries. Perhaps I have missed something in working with flooded cell batteries for more than 50 years, or perhaps my tolerance for toxicity is unusually high. I do not consider my various flooded cell batteries a toxic hazard. Another claim by von Wentzel is that, properly maintained, VRLAs last longer than flooded-cell batteries. This statement is not supported by the facts. There are many grades of both types of batteries. Battery life depends more on initial quality, intelligent use, and proper maintenance than on battery chemistry. One of the largest battery back-up systems I have ever seen, with more than two megawatts of storage capacity, uses flooded-cell batteries. The designers of this system considered all types of batteries before choosing to use the flooded-cell batteries. Another claim by von Wentzel is that it is possible to charge two types of battery banks from a single alternator by using an isolator eliminator. Since the VRLAs typically require a lower charging voltage than the flooded cells, while accepting a higher charge current, it would appear that a significant amount of alternator-derived energy would have to be wasted as heat in order to simultaneously charge two dissimilar battery banks. It is possible to construct a suitable power system, but I don't believe it would be practical, cost-effective solution. My advice is to use whatever type of battery you feel is best and not mix battery types on one boat. The point in von Wentzel's letter that I most strongly disagree with is his claim that it is best to discharge an entire bank, made of parallel connected batteries. He cites the advantage of lower internal resistance offered by the paralleled battery arrangement. This is true; however, it is significant only when really high current loads are to be supported. Paralleling batteries is an accepted and recommended practice when very high current loads are present, such as when starting a very cold diesel engine. Using von Wentzel's approach, paralleling batteries in a single bank will deprive the user of any advance notice of deterioration of a single battery. This is especially poor practice when using VRLA batteries, where it is impossible to determine the condition of a single cell. With a flooded-cell battery this is easily done using a $10 battery hydrometer.


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