Join Date: Apr 2006
Thanked 168 Times in 165 Posts
Rep Power: 12
"If that is true then why is the "DOD" not to be considered? "
Because, the DOD argument has nothing to do with how the batteries are ganged up. You can run your batteries to any DOD regardless of the series/parallel/alternating configuration. Bozo had red hair and big shoes, Bozo was a clown. Therefore everyone with red hair and big shoes is a clown? No, that's invalid logic. Same thing with the DOD argument. Invalid and fallacious since how deeply you cycle your batteries is a decision that can be made independent of how you configure (gang) them.
OK, let me address why I disagree, one more time:
1. lower "depth of discharge" in real world usage (far from a fallacious argument);
A: Yes, fallacious and invalid. As above, you can cycle the batteries to any depth, regardless of configuration. That's not debatable, that's fact.
2. lower acquisition cost;
A: Still unproven. As I've said, yes, you an easily get cheap batteries from a bulk store. That doens't mean buying industrial batteries from an industrial source is any more expensive.
3. smaller size...will fit where other options won't;
A: False again. Watt-hour for watt-hour, the battery bank size will not differ at all. And I can fit six 2.2v cells into a wide variety of spaces where your pair of 12V cells simply can't go. If anything, the advantage here is for 2.2v cells in series.
4. easier on your back, assuming it's you who have to schlep the batteries;
A: False again, same as #3. The 2.2v cells are available in a much wider range of sizes/weights.
5. better availability worldwide...a key factor for cruising sailors;
A: False again. Anywhere there is shipping and freight, there are industrial battery suppliers supplying the 2.2v cells for fork lifts. You may not see them on the main shopping street or by the upscale marinas--but they are there until you get way off in the boonies, at which point you are looking at "emergency repairs" not scheduled battery replacement. Since these batteries can be expected to have a 10-15 year life, there's no reason to worry about "Oh wow, I need 500AH of batteries RIGHT NOW!" for any purpose besides emergency repairs.
6. faster charging, lower run times for engine and/or generator;
A: Totally false. Charging speed will depend on the system chemistry (AGM versus wet) and the alternator capacity, and the battery capacity. Given the same battery capacity, chemistry, and a sufficient alternator output to match that, the charging time will be the same for either configuration.
7. endorsement by experienced sailor-engineers such as Calder and Verry.
A: Specious logic. Yes, it is pleasing to say that "someone said it is good" but we're looking for facts not opinions here. What Dave and Calder have said is that you can, under some circumstances, get away with it. They have not, to my knowledge, made any point that parallel battery installations are in any way BETTER. Again, aside from the fact that you can build them with WalMart batteries.
So out of your seven points we have:
And your only point made is the one I've conceded all along, that you can certainly use cheap stuff from WalMart real easily in parallel banks.
"A single point of failure for a connection will render the single bank as you advocate useless. A parrelled bank has a greater chance of being at lease partially usable, if at a lower capacity." I think you've got that backwards.
A connection failure can be remedied with a wrench. A CELL FAILURE is the only thing that would take down the series battery bank. The odds of that same cell failure taking down your parallel bank are double or higher. IF you catch the failure in time, sure, you can split the bank and run on half of it. But you can also do that by using two banks. Unless your bank sizing and alternator are matched/mismatched in certain ranges, that's going to be a questionable point anyway. If you have a 500AH parallel battery bank, you'll need a 100AH continuous rated alternator to charge it in minimal time. Vary the alternator size, vary the bank size...and you may find that running two alternate banks provides a better answer--plus that redundancy.
Regarding the loop between the two batteries "The current will be very small and eventually stop. " This is the first and only time I've ever heard that. Have you measured this? With wet or AGM cells? What were the specifics?