Re: [Amel Yacht Owners] First Impressions: Firefly Batteries.

Ryan Meador

You are correct and incorrect :)  Modern chargers typically operate in three different modes: bulk, absorption, and float.  In bulk mode, the charger determines the current (it is operating as a constant-current source), and that current is usually the maximum rating of the charger.  In this mode, it adjusts the output voltage to maintain the desired current.  The voltage steadily rises as the battery charges until it reaches a certain point, then the charger switches to absorption mode.  In this mode, it operates as a constant-voltage source, and the current is determined by how much the batteries will soak up (it steadily decreases).  Eventually the current drops below a certain threshold (or a timer expires) and it switches to float mode, which is similar to absorption mode but a lower voltage, and the intent is to not have any significant current flowing into the batteries at all -- just offsetting their self-discharge.  Most chargers can provide up to their full current in float mode if necessary, so if you turn on an appliance it is actually the charger providing the power and not the battery (or only a tiny bit from the battery).

SM 233 Iteration
Boston, MA, USA

On Fri, Dec 15, 2017 at 1:01 PM, Thomas Peacock peacock8491@... [amelyachtowners] <amelyachtowners@...> wrote:

I never thought I would need to learn so much about batteries, when my original intention was just to sail.

We have relatively new AGM’s, and notice that they charge (generator running, Heart Interface) at 40 to 50 amps for an hour or two, and then drop down to about 15 amps. The Heart charger is set for wet cell charging, at the recommendations of the Heart people. As it’s an older model, the only other setting was for gels; there is no setting for AGM.

I had been under the impression that the charger determined how many amps were sent to the batteries. A lot at first, and then tapering to acceptance, then float. With your comment about the Fireflys accepting a lot more amperage than AGM, I now question my understanding. Does the battery also determine how many amps flow in? I had thought that if the charger sent more amps than the battery could handle, the result would be toasted battery or worse. Is there some sort of interplay between the batteries and the charger?

Thanks a always to all those who continue to educate me.

Tom Peacock
SM 240 Aletes
Falmouth Harbour, Antigua

On Dec 14, 2017, at 12:06 AM, greatketch@... [amelyachtowners] <> wrote:

In a previous post I explained my rational for purchasing Firefly batteries in this battery replacement cycle.  They arrived a few days ago (finally!) and here are my initial impressions.

Physical fit:  They are Group 31 batteries, which is nothing but a specification on the physical size of the battery case, so they should be drop in replacements, right?  Wrong!  They are a little bit higher than our old Lifeline batteries, so I needed to trim a bit off the wood brace on the bottom of the compartment lid.  Also, the terminals are high enough that the battery terminal fuses I had been using no longer fit under the lid, so I swapped four 125 amp terminal fuses for a single 500 amp ANL fuse.  Neither was a big deal, but both were annoying.

It is very not fair to evaluate batteries when first installed.  Batteries take at least 10 charge/discharge cycles to settle in to their long term groove.  That said...  

One of the reasons I went with these was their higher charge acceptance rate.  Wow.  What a difference.  Our Lifeline AGMs (which are very good at rapid charging) would taper down to 18 amps charge rate by the time they got to 85% charge.  The Fireflys were still accepting over 50 amps at 85% charge...  Once they have settled in and I have a bit more experience with them I'll post more hard data, but so far, they look like they will at least match my expectations.

Again, these are not for everybody. They are expensive, hard to get, and need proper charge voltage control (especially on float) that not every charging system can do. The benefits of the extra cost really depend on how you use your boat.

Bill Kinney

SM160, Harmonie

Fort Lauderdale, FL

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