Firefly batteries and the rest of the charging system

Discussion in 'Musings With Maine Sail' started by tfox2069, Apr 21, 2019. Add this thread to a FAQ

  1. tfox2069

    tfox2069

    Joined Apr 8, 2011
    51 posts, 11 likes
    Hunter 36
    Intrepid US Deale, MD
    So I’m looking at replacing my house batteries on my 2009 H36 within a year and doing some research. I’ve read the AGM thread and done some reading in MarineHowTo.com as well. I’ve installed a Victron BMV-712 monitor, and am nearly done installing 160 watts of solar run thru a Victron 100/20 MPPT. Currently have PO installed 2 4D Deka (WM branded) 198 Ah AGMs and a ProMariner ProTech i 1230i Plus shore charger, and a stock 60 amp internally regulated alternator and (new) belts on the 3YM30. The reason I’m considering replacing is the batteries are original (I’m fairly certain), and capacity loss is substantial, though I’m still working on a test as MaineSail prescribed to get a tighter figure on capacity remaining. My usage is mostly day/weekend overnight sails, with occasional 7-10 day trips away from the slip. Otherwise the boat is plugged in and the charger engaged. My energy consumption is 130Ah/24 hrs away from the dock. I sail on the Chesapeake bay.

    I’m leaning toward 3 paralleled Group 31 110Ah Firefly batteries. I’m primarily interested in thoughts on what I may need to do with regard to my alternator and/or shore charger, if anything. I would like to maximize the life on the Firefly batteries. Other suggestions welcome.
     


  2. Stu Jackson

    Stu Jackson

    Joined Feb 26, 2004
    20,528 posts, 946 likes
    Catalina 34
    224 CA Maple Bay, BC, Canada
    Why bother? With your use, non-WM brand fla wet cell deep cycle batteries will do just fine.
     


  3. Johann

    Johann

    Joined Jun 3, 2004
    232 posts, 39 likes
    Hunter 336
    US Pensacola
    Since you will have to run the engine about every other day to charge the batteries when you’re out on the hook, I’d look into upgrading the alternator to reduce engine run time and make more efficient use of the diesel. Maybe a CMI-80 with external regulation.

    As far as the shore charger, Firefly recommends charging at .4C about once a week if you’re deep cycling. So that’s 132 amps for 3 firefly G31s.
     


    Last edited: Apr 21, 2019
  4. Johann

    Johann

    Joined Jun 3, 2004
    232 posts, 39 likes
    Hunter 336
    US Pensacola
    After thinking about it, how about going for a 150 amp Balmar with a serpentine belt, and leaving the shore charger alone? You will typically be deep cycling on the hook, so why upgrade both the shore charger and alternator when I think it would be about the same cost to just go big on the alternator.
     


  5. dlochner

    dlochner

    Joined Jan 11, 2014
    3,742 posts, 1,728 likes
    Sabre 362
    113 US Fair Haven, NY
    I'm with @Stu Jackson on this. Why spend the extra money on Fireflys? True deep cycle FLA batteries will do just fine. Think about 6v golf cart batteries, 4 of them will give you ~440 amp hours. It will need a new charger, one that can support about 50 amps, like a Sterling 1250. A larger externally regulated alternator will be helpful too, but no need to go with a 150 amp Balmar for your usage. The CMI 90 amp should be sufficient for your plans. 4 new GC batteries, a new charger, and a new alternator and regulator will set you back about the same as 3 Fireflys alone.
     


  6. IStream

    IStream

    Joined Nov 14, 2013
    174 posts, 8 likes
    Catalina 50
    US Seattle
    I'm with Stu and dlochner on this. With your use case, FLA isn't just fine, it's appropriate. If you upgrade your batteries, you'll need to upgrade your charging to take full advantage and also to prevent damage.
     


  7. Maine Sail

    Maine Sail Moderator

    Joined Feb 6, 1998
    10,950 posts, 747 likes
    Canadian Sailcraft 36T
    US Casco Bay, ME
    If you go Firefly you will want at the very least a new charger and at a bare minimum external regulation. This makes the whole cost a rather big pill to swallow, about 3.2K to 4K in total and that is if you DIY the entire thing....

    One big mistake I see many Firefly owners doing is not discharging to 80% DOD.. The value in these batteries is that you can use 80% of the capacity and still exceed the cycle life of a typical deep-cycle AGM (the WM AGM's are not a true deep-cycle AGM) that is discharged to only 50%. Because of the PSOC tolerance it often means a smaller bank than you previously had by at least one battery. With only three Firefly batteries you'll actually have more usable capacity, about 264Ah usable, than you had with the Deka 4D's, 198Ah. Heck just two Firefly batteries will yield 176Ah usable compared to 198Ah for your WM/Deka's..

    Another area folks don't account for is the usable capacity that can be stored quickly when cycling to 80% DOD. This means your charging system is working as efficiently as it can and you can restore about 60% of your capacity (80% DOD to 80% SOC, at charge efficiencies pushing 98% where with flooded or standard AGM your looking at only 30% of your energy being returned at a high efficiency. This also means that your alternator & regulator had better be ready to handle a long bulk charge duration.

    That being said, your described use does not really warrant a dire need for Firefly or even AGM batteries for that matter. For a few hundred dollars some 12V Golf Car batteries (T1275 or J150 Trojan's), or 6V Golf Car batteries in series/parallel, will allow you to dial in your charging system so that when or if you decide to go Firefly, your system is ready for it..
     


    tfox2069 likes this.
  8. Hello Below

    Hello Below

    Joined May 7, 2012
    589 posts, 61 likes
    Hunter e33
    CA Maple Bay, BC
    Friday, I replaced 4 x 6V US Battery Golf Car batteries with Trojan T125s FLA. I had seriously considered, in fact was on a wait list for 4 x Firefly Oasis AGM G31 batteries. But in the end I could not justify the total additional expense when the FLAs had given me 7 full years of 100+ days per year away from our marina. Quality control issues, as stated by Nigel Calder in Sail Magazine (September 2018), was also a factor in my decision.
     


    tfox2069 likes this.
  9. tfox2069

    tfox2069

    Joined Apr 8, 2011
    51 posts, 11 likes
    Hunter 36
    Intrepid US Deale, MD
    Great input. Really appreciate it. Lots to think about.
     


  10. Garbonzo

    Garbonzo

    Joined Dec 4, 2018
    16 posts, 5 likes
    Balboa 27
    NA US Denver
    Glib response and I think you might consider ventilation concerns with wet cell replacement for arm.
     


  11. tfox2069

    tfox2069

    Joined Apr 8, 2011
    51 posts, 11 likes
    Hunter 36
    Intrepid US Deale, MD
    I genuinely appreciate the thinking and depth of responses from highly experienced forum members. Between their prolific - and incredibly informative - postings, I'm weighing my options for this battery replacement/system upgrade. Since I'm thinking the comments through and haven't made a decision I thought it only polite to acknowledge the comments and say thank you. So I'll have to disagree with you that my comment was in any way insincere. But hey, YMMV.

    Fair point about ventilation with wet cells. They'd go into a fiberglass battery box whose top is screwed down, in a huge cockpit locker which is otherwise mostly empty. There don't appear to be any penetrations thru the box (e.g. its not screwed DOWN, which Maine Sail points out could risk leaking battery acid out of the compartment in the event of fluid loss in the box). Not entirely sure it vents outside significantly; if anyone has ideas on whether I should take overt steps to vent the battery compartment I'm certainly interested in thoughts.

    Can you clarify what you mean by 'replacement for arm'?
     


  12. Garbonzo

    Garbonzo

    Joined Dec 4, 2018
    16 posts, 5 likes
    Balboa 27
    NA US Denver
    Whoops. Mean AGM
     


  13. dlochner

    dlochner

    Joined Jan 11, 2014
    3,742 posts, 1,728 likes
    Sabre 362
    113 US Fair Haven, NY
    Battery boxes should have some ventilation. One common worry is hydrogen off gassing from the charging process. When an electric current is passed through water, the water molecules break down in to their constituent parts, Oxygen and Hydrogen gas. While hydrogen is explosive there is very little hydrogen stored in a battery and hydrogen being the lightest element quickly dissipates given half a chance.

    The other concern is sulfur compounds that off gas. These are not explosive but they are corrosive. When they escape and condense on moist metal they form acids and they can be corrosive. That's why you don't put batteries directly underneath expensive chargers and electronic devices. Again allowing these to dissipate slowly is helpful.

    So, the battery box needs some ventilation and the area the battery box is in needs ventilation. The vents don't need to be big and they are not nearly as troublesome as heavier than air explosive gases such as propane and gasoline.
     


  14. Maine Sail

    Maine Sail Moderator

    Joined Feb 6, 1998
    10,950 posts, 747 likes
    Canadian Sailcraft 36T
    US Casco Bay, ME
    Guys,

    Please understand that the ABYC does not differentiate battery ventilation between standard open flooded batteries and valve regulated lead acid batteries such as GEL, AGM, TPPL AGM or Carbon Foam AGM, they all require ventilation. The only thing that differs between AGM and flooded, in regards to standards compliance, is the need for acid containment with batteries that could leak electrolyte.
     


    tfox2069 likes this.


Teak companionway doors
Amazing artisan quality, custom made to fit your boat.
Winch covers
Any brand, every size, any color!
Ready-made sheets and halyards
Now faster than ever, our calculator tells you what sizes you need.
20% OFF innovative boat clips!
FixClip holds laundry, tools, anything to rails and life lines even in strong winds.