My second letter to the Editors
Written in the fall of 1999. Later corrections and clarifications have been added in [blue].
To the editors,
In the latest copy of Ocean Navigator, only half of my letter to the editor was printed. I am somewhat distressed that the second point was left out instead of editing/tightening. This is very poor editing judgment indeed. At the very least, Chuck Husick could have replied to the second point privately, namely my assertion that his energy household exercise was terrible. I expect a full, professional response to the following comments:
First of all, let me apologize for not researching more battery literature prior to writing my letter to the editor. Chuck Husick is right, the literature indicates that deep discharge wet cells can last 3x longer than AGMs. For example, here is some manufacturer life cycle data at a 50% depth of discharge:
Life cycles at 50% Depth of Discharge
|Rolls (CS-plate)[500 series]||3,000 cycles||Chart @ DC Battery|
|Rolls (CH-plate) [400 series]||1,020 cycles||Table @ Windsun|
|Lifeline AGM||1,000 cycles||Chart @ Lifeline|
However, this comes at a price that the average boat owner is unwilling to pay. As Nigel Calder states "the very steps taken to reduce damage from cycling... increase the chances of damage from sulphation" (p10). Equalizing batteries is hazardous as flooded cells may begin to boil, venting corrosive gases, etc. As Mr. Calder continues "With proper charging and maintenance, a top quality wet-cell deep-cycle battery will have a longer service life in a cycling application than any gel cell. However and this is a big however, these batteries are rarely charged and maintained properly, with the result that very few live up their potential." (p11)
Lastly, how many CH vs. CS plate cell systems are in use today, since even under ideal circumstances CH cell-plates (.15" thick) are about life-cycle and amp-hour equivalent to Lifeline AGM batteries?
2) Failure modes of flooded vs. AGM cells
Will a shorted AGM spew potentially blinding electrolyte? Can the wet cell withstand an inversion w/o damage or loss of electrolyte? Will a submersion K/O the battery? Etc. The answer is that AGM batteries are used in mission critical environments for a reason: They are inherently safer than other lead-acid battery types and ANY battery can be disabled by improper charging.
However, AGMs can tolerate conditions that would many batteries to fail. For example, even under the conditions of the MIL-SPEC B-8565J (Section 4.6.22) test (overcharging a AGM to 16V @ 130deg F cell temperature) the batteries did not produce more than 1% hydrogen, and functioned normally after the test! Modern charging systems have failsafes against overcharging and woe to the boatowner who updates his batteries and not the charging system!
3) Re: Price premium of AGM vs. Wet Cell
Since we are comparing premium-priced Rolls batteries to AGMs for life-cycles, the comparison should extend to the cost per Amp-hour as well. Using Chuck Husicks claimed 3 to 1 $/Ah premium ratio, I should be able to find a Rolls group 30H CS-cell battery for about $57-72 (GRP 30H Lifeline AGMs go for $172 at windsun.com, $216 at West Marine). Please let your readers know where they can find such good deals on Rolls batteries!
4) The toxicity of flooded cells.
Chuck Husick's 50 years of experience with flooded cells w/o incident is more a testimony to his skill/caution/luck than anything else. Not "to consider [my] flooded cells a toxic hazard" indicates he is a lucky man indeed! Any battery guide for flooded cells points to the dangers of the electrolyte, venting, etc. Provisions can be made to minimize risks... proper gear for servicing flooded batteries include a face shield, a acid-proof apron and arm length gloves for good reason. However, I think the average boatowner may take comfort in an inherently safer system consisting of AGM batteries that don't require the kind of tender-loving care that relatively dangerous wet cells insist on.
5) Individually switching batteries on and off
While it is important to test battery run-time on a annual basis, I would like to point to Nigel Calder, Ample Power on paralelling batteries, and Surrette Batteries tech bulletin 502, among others who advocate single large battery house banks to minimize discharge levels, minimize sulphation, and maximize load efficiency.
As Mr. Calder put it on p26-27:
"1. For a given total battery capacity, wiring the batteries into a single high capacity bank, rather than having them divided into two alternating banks, will result in a longer overall life expectancy.
2. All other things being equal, any increase in the overall capacity of a battery bank will produce a disproportionate increase in its life expectancy (through reducing the depth of discharge at each cycle)...For a given load over a given period of time, a single large bank will at all times maintain a higher terminal voltage than a divided bank with each half used alternatively."
Any boat will appreciate the inherent "idiot-proofness" of a large bank and its higher voltage and ampere capacity instead of relying on a operator to switch batteries on and off at the right interval before recharging them. Furthermore, a single deep-cycle wet cell battery may very well be brought to its knees trying to supply a high-ampere load, such as a windlass. Especially within the context of an emergency, the boat owner should not be distracted by having to switch on multiple batteries to operate critical equipment.
6) Battery bank sizing
Chuck Husick missed some basic suggestions made by several well respected sources in the community. To paraphrase Ample Power: "battery capacity should be 4x daily needs or 4x highest current load, whichever is greater (p 82). Nigel Calder comes to the same conclusion (p14). Cruising Equipment uses a smaller 3x factor. Surrette also has a minimum capacity guide based on boat length.
Chuck Husick arbitrarily designed a battery system that was to recharge 8 hours per day. No one in the sailing industry advocates this type of diesel or battery abuse. His battery bank would go through multiple 50% discharge cycles on a given day, severely limiting it's lifetime, even if it was a perfectly maintained Rolls CS unit. However, my guess is that the diesel would fail first.
Utilizing Chuck Husicks proposed constant 20A load, I arrive at 480Ah consumed per day. Using the conservative 4x battery capacity factor, that calls for a 1,920Ah battery bank (!!!). To recharge, a gen-set would be best, given that a flooded 1,920Ah bank could bulk absorb as much as 480 Amps. Gen-sets can be quiet (see fisher-panda) and don't consume as much fuel as a oversized engine driving an undersized load.
7) Re: using a Isolator Eliminator
The eliminator is used in conjunction with the above, well accepted battery set-up: One large house bank, and a small, dedicated starter bank. The eliminator is only meant to recharge the starter bank. Charging efficiency is thus not paramount, as starter banks only need to be topped off within the context of a properly maintained electrical and mechanical system. See Ample Power for more info on this.
8) Since Mr. Calder is also a contributor to your magazine, perhaps he could proof-read Chuck Husicks work?
Constantin von Wentzel