Hi Don,
I am not arguing with your experience. Nor am I saying that I am an more correct than you are. My experiences with a variety of different battery technologies have lead me to different conclusions. I do agree with you that gel cells are not a good answer for our type of projects, though they are still being made for certain applications.
Much like the fact that electric drives are not the best solution for every boats, I don't think that any one battery technology is the "best" answer for every situation. In selecting batteries, I try to balance cost, volume, weight and effective capacity. Each type of battey represents a different combination of attributes. Because EVs and eBoats have high current demands, the Peukert Effect of each battery type is an additional factor for the decisions here. If cost is the primary concern and volume and weight are not as important, then FLA is a great solution. If battery volume or weight are more important than cost, then Lithium represents a better value. If effective capacity for a given weight or space is important but Lithium is too expensive, then AGM offers a reasonable alternative.
I appreciate your experience and value your contributions to our discussions, but you'll have to forgive me if I don't take your word as gospel. This whole internet experience adds another wrinkle to our conversations, you don't know me, and I don't know you. We're all here to share our experiences and learn from people that we may never meet. But beyond all that, this is a place where we can express different opinions, and as long as each of us can keep an open mind, applying critical thought, there is an opportunity to learn. Perhaps someday, I'll think back and say "You know, Don said the same thing all those years ago". Time will tell...
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "desulfator" <desulfator@...> wrote:
>
> Hi Eric,
>
> I don't think it is an opinion after conducting about 10 years research into AGM and flooded cell recovery methods. :)
>
> Although many applications use AGM for convenience. AGM still has a long way to go to match the longevity of flooded cell.
>
> The drive to provide a sealed battery started with gel cells. It had electrolyte in a geled state which would not spill unless the case cracked. It was the only lead-acid battery that could function in a zero-g environment and had relaxed shipping requirements.
>
> It was quickly discovered that if the battery was brought into the gaseous state, a bubble would form in the gel.
>
> This effectively removed that plate area from contact with a severe capacity penalty. It is one of the reasons all gelled cells had limited voltage charging requirement. To my knowledge, I don't believe anyone manufactures them any more.
>
> The next step in attempts to provide sealed batteries is the AGM. In this battery the separators are wetted to 97% capacity with liquid electrolyte. They were still limited to a reduced charging voltage. Unfortunately, the pressure relief valves tend to leak, resulting in cell dehydration and cell death.
>
> So while some folks will use AGM for the reasons you cite, it has to be remembered that the advantage is offset by AGM's limited lifespan.
>
> If cost is a factor in battery bank management flooded cell appears to be the winner.
>
> If cost is not object, then AGM or lithium chemistry can be considered.
>
> Don
>
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