Originally Posted by Ed-White
Stu after reading a bunch of your posts and links I am beginning to understand a bit more..takes time right. I have a couple of questions I couldn't find the answers for maybe you can help here. I bought the boat last year, it came with the 3 agm batteries in two banks, a 90 on one and two 75's on the other through a 1-2-b switch. 51amp delco alt. internal reg. The PO had the A\O wired to the ignition switch!, the tach wired to the alternator output nut. There is a xantrex 10amp shorepower unit, 3 stage wired to both batteries. There is also a west marine
combiner disconnected in the battery compartment. Here is my question: (I plan to get an external regulator and a higher output alternator) If I combine the 3 agm batteries in one bank and run everything off of that bank, buy one more reserve wet cell battery and run that to the second bank as a reserve, reconnect the combiner and attach the a\o to the big bank, do you think that I can keep the agm's alive with a moderately sized alternator(100amp), and will the wet cell battery have any downside to that system? Thanks.
A few thoughs here:
1. You shouldnt mix battery chemistries unless you have a charging system that can differentiate. Depending on what sort of combiner you have you may be able to get the set up to work but wet cells and AGMs have different charging requirements.
2. "keeping the agms alive" will have more to do with how often and how far down you discharge them and how long you are able to run your engine. In theory you should be able to keep them alive with the 50 amp alt you have if you have it converted to an external reg., add a smart reg, and run the engine long enough.
3. I would first determine if the AGM's you have are in fact still good by enlisiting the services of a good marine electrician with the proper meters or through tests found in Calder's book.
4. Once you know the answer to #3 then you can decide if it makes sense to pursue the path of all AGMs or switching to wet cells. For the majority of cruisers wet cells offer the best value and make the most sense because unless you have a really big charging system you will never be able to take advantage of the high CAR (charge acceptance rates) of AGMs and realize the shorter recharge times, and unless you are able to float them regularly they will die an early death and at these are not cheap
5. A 100 amp alternator is generally speaking more than adequate for the majority of cruisers out there unless you are talking about a really big battery bank. You mentioned I believe looking to get to a 400ah bank. Assuming you keep your depth
of discharge to 50% you are talking about needing to replace 200ah. With a 100amp alt and a smart regulator you are probably looking at a few hours of engine running, say maybe 3-4hrs.
6. You really should consider performing an energy analysis and first determine what your needs are then build a balanced electrical system
that can meet those needs. What sort of cruising do you do? Are you live aboard full time on the hook or are you a weekender with an occasional 1-2 week summer cruise
who can regularly plug
into shore power
? I sailed my ericson
38 as the later and found a 200ah bank to be just fine. We pulled about 70-90ah out every 24hrs and with a few hours of engine per day and regular plug
ins to shore power
we did just fine. OUr biggest draw was the fridge at 50-60ah. I got 9 years out of a pair of gel cells that to my knowledge are still going strong. You need to know how many amps you are going to pull out every 24hrs then add a fudge factor, then double that number. Now you have your battery bank size. Once you know the battery bank then you can built the appropriate charging system.
7. The one item I havent seen mentioned is a battery monitor
. Thats probably the most important piece of gear
in the equation. It will allow you to tell a lot more about what you are doing to your batteries.