mariasman said:
However, the rate of charge must be slowed as the state of charge reaches around 80% full or higher. Hence, charge controllers will taper off the charge rate at this point.
I have to take exception only with the wording on this, and then will stray. Semantics. forgive me.
Charge controllers do in fact taper the charge rate when absorption voltage has been attained, but they do this by not allowing voltage to exceed a preset limit. The battery then accepts what it needs at the voltage allowed by the charging source, so it is the battery which is really limiting the rate at which it is being charged, the controller is limiting the voltage.
Battery voltage in regular usages, should not be allowed to exceed a certain level. Lets say 14.8v at 77F
So the solar controller/charging source allows upto 14.8v, and then says no more, and enters the constant voltage stage. The absorption stage. It basically starts throttling amperage to limit and hold this voltage.
It only allows enough amperage to pass to maintain that 14.8v. Any more amps and voltage would have to rise. Any less amperage and it could not maintain that voltage. The absorption stage cannot be sped up, except with higher voltages, and safely one should not allow higher voltages (electrical pressure)
The amperage required to hold battery at absorption voltage, tapers downwards as time goes on.
how quickly this tapers is determined by the battery(s) themselves. the controller is simply throttling amperage to ensure voltage does not keep rising.
The battery itself dictates how much amperage it requires to be brought upto or held at and absorption of 14.X volts.
Yes there is some solar excess wattage going to waste in the later parts of the time consuming Absorption stage. 80% charged to 100% charged cannot be safely accomplished in less than 3.5 hours, and usually this is longer.
This freaks some people out. Such people can turn on other loads, or turn up the compressor fridge, charge laptops other devices, divert some solar wattage/ excess amperage available, to the engine battery, or just not worry about it, as long as the sun is high enough to maintain absorption voltage for a as long as the battery requires to reach 100% all is well.
Those turning on loads need to ensure the solar can still maintian absorption voltage. If the additional load drops voltage to 14.2 from 14.8v, then the load is too high. Wait a little longer. Let the battery stay at 14.8v.
Any Charging source, whether it be a solar or an alternator or a smart charger, is basically controlled by a voltage regulator, not an amperage regulator. These will have a maximum available amperage they can employ to get a battery to the preprogrammed voltage limit. With solar this amperage limit is the amount of solar wattage and Sunlight intensity at that moment. With an Alternator it is dependent on how fast it is spinning. With a plug in charging source it is limited by the maximum output of the charger and if a variable charge rate charger, by the rate chosen.
The battery accepts what it wants, what it can at the voltage allowed. In the bulk phase the charging source is allowing everything it can to pass, as it wants to get the battery to the absorption voltage. Voltage limitations generally only begin in the mid 14v range. Too many charging sources are timid, and do not allow absorption voltage to be held for long enough. Good charging sources allow the user to program how high absorption voltage is, AND how long absorption voltage is to be held. Good users determine how long absorption voltage should be held in their usage pattern. Ideal absorption voltage is also dependent on battery temperature. The best charge controllers have battery temperature sensors.
The difference in battery longevity/ total cycles accumulated before battery failure, on a battery that reaches 100% daily, and one that reaches 95% daily, is about 50%.
Any charging source. whether it is Solar, plug in charger, or alternator, has a voltage limiter on it, and almost all of these will drop that voltage prematurely, leading to a premature demise of the battery.
As one cannot easily see the premature degradation happening without tools and experience and the interest to do so, most have no idea that absorption voltage is not being held long enough.
The charging source flashing a green light and dropping to "float' mode/stage does not mean the battery is full. It only means the charging source held absorption voltage as long as it was programmed to do so. Whether this time was long enough, can only be determined by a human with the tools and desires and knowledge to verify it.
Unless absorption voltage and its duration can be changed and adjusted by the end user, 95% of the time the charging source will get it wrong, and undercharge the battery. This is more and more true on deeply cycled batteries. The deeper the discharge the longer the absorption voltage should be held.
As the batteries age the time it should be held increases too.
It is not as if the batteries will instantly die if 'IDEAL" absorption voltage is not achieved and held long enough. They will simply degrade faster. One need not obsess over Ideal, but one should be aware of what Ideal would be if one wanted to achieve it.
Achieving it requires time and effort expended occasionally, with the right measuring tools and knowledge.
Is it worth it, or is it simply easier to replace the batteries more often?
That is where the variables lie.
But unless one has the tools temperment and knowledge to know for sure, one does not know that their voltage controllers are properly doing their job, and should not make claims of my batteries are full by 12:30 every sunny day. Verify it before making that claim.
An overwhelming percentage of users would find their claim to be false, and to a huge degree if they employed a hydrometer, or an Ammeter in addition to theat voltmeter.
But there is certainly bliss in ignorance, or simply not caring.
And of course having the money to simply replace batteries more often.
