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

Mohammad Shirloo

Hi Tom;
The theory of battery charging is fairly complex. However, if we were to look at it in very simplistic terms, the charger has set charging algorithms designed by the manufacturer of the charger to adjust voltage and hence current output, based on specific battery chemistry that has been set on the charger. This algorithm is designed for safe charging of the battery. How much current the charger will put out is based on how much current the battery will accept, which is mainly determined by the voltage of the battery while being charged.
In most cases like our cruising vessels, the charger will work in three stages:
  1. Bulk charge. The charger will put out the maximum rated current (minus the current being used by the systems that are being utilized on board) until the voltage of the battery reaches a set voltage. This voltage is determined by the battery chemistry, type and manufacturer.
  2. Absorption. The charger will keep the voltage constant and will reduce current output to maintain a set voltage.
  3. Float. The charger will reduce the voltage to the float voltage, again provided by the manufacturer and set on the charger, and only provide a trickle charge to maintain the float voltage.
The voltage that the charger "sees", is determined by many different factors, but the main ones are chemistry, age, internal resistance, resistance of wires going from the charger to the batteries, heat etc.
So you are correct that the charger determines how much current is put out, but the algorithm within the charger that decides how much voltage and current to put out is based on how it sees the battery reacting. Therefore as the batteries get older, have more internal resistance and are able to accept less current, the charger reduces the amount of current quicker so the maximum voltages are never exceeded.
This is a very simplistic explanation of what is going on. You can find volumes of theoretical information online about batteries.
Mohammad and Aty
B&B Kokomo
Amel 54 #099

From: amelyachtowners@... [mailto:amelyachtowners@...]
Sent: Friday, December 15, 2017 10:02 AM
To: amelyachtowners@...
Subject: Re: [Amel Yacht Owners] First Impressions: Firefly Batteries.


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] <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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