Re: [Amel Yacht Owners] First Impressions: Firefly Batteries.
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:
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
Amel 54 #099
From: amelyachtowners@... [mailto:amelyachtowners@...]
Sent: Friday, December 15, 2017 10:02 AM
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.
SM 240 Aletes
Falmouth Harbour, Antigua