marigold said:
Can someone elaborate a bit on what the initial charging amps ratings mean? It sounds like some batteries require more amps to charge than others, which could be an issue if only charging off solar (maybe too low?)
Also, I'm wondering if most people have their batteries hooked up to both solar and the alternator to charge, or if it's common to just use solar. Thanks
A depleted battery can accept very large charging currents from a high amp plug in charging source, or an alternator. Battery manufacturers tend to assume these will be the charging sources used, and their recommended charge profiles are for the plug in charger.
Trojan battery recommends that their depleted battery be charged from depleted at a 10 to 13% rate. 10 to 13% of the battery capacity, or a minimum of 22 amps for their golf cart batteries in series that are rated at 220 AH.
At the other end, Odyssey recommends a minimum of 40% be applied to their depleted battery, and this is 40 amps for a 100AH battery
I do not know how much an Odyssey's cycle life would be shortened by recharging at a much slower rate, but with the rather extreme price paid for their batteries, I would not want to find out.
As the battery charges, its voltage rises toward the Absorption voltage. As the voltage rises to this maximum allowed voltage of the charging sources regulator/controller, the amps will taper. The higher the state of charge of the battery, the less amps are needed to hold it at these absorption voltages. When the amps taper to very low levels the battery can be considered fully charged and automatic charging sources drop to float voltages, which require much less amperages to maintain.
Different battery manufacturers have different recommended absorption voltages, and these are listed for when the batteries are 77F degrees. Higher ABSV's are needed at lower temps and lower ABSV's at higher temps.
Meeting this ABSV for a certain amount of time is important, not just for maximizing battery life, but for preventing premature failure. If a battery never gets high enough, for long enough, premature failure will happen. How premature it fails is the unknown variable with many contributing factors.
Since Solar is not an instant type of charging source when the sun rises, but ramps up slowly, peaks and then lowers throughout the afternoon, the recommended charge profiles cannot be matched. However it is wise to at least have the minimum recommended rate be approached at Noon in the summer. This is closer to a 2 to 1 ratio than the usually recommended 1 to 1 ratio. 1 solar watt per 1 AH of storage.
The higher the ratio the happier the battery when deeply cycled day after day. When not deeply cycled, but shallowly cycled to say 85% then this ratio becomes less important.
Lower$ AGMs tend to recommend charging rates not exceed 30% or so. These AGMs are likely much more suited for a Solar recharge regimen.
The recommended rates by battery manufacturers are quite helpful when deciding what Amperage plug in charger to buy for the battery capacity, but they are not so helpful when the charging source is to be solar.
My personal experience has shown that for best battery longevity, it is not merely about replacing the amp hours used plus a little more, but having a higher charge rate available by the sun to get the batteries up higher quicker in the day. While My underbody battery box is capable of holding two group 27 batteries for 230AH of capacity, and did so for 3 sets of batteries, after the last set of 27s failed, I replaced them with a single group31.
While I am cycling this single 31 battery deeper than two 27's in parallel, it is being recharged at a higher rate via my solar, which is my primary charging source, and I am already ahead on the $/cycle ratio, and I have never come close to not having enough battery capacity.
My previous 27s likely could have benefitted from higher absorption voltages, and more frequent equalization cycles, but they were a PITA to access the cells to check specific gravity, and electrolyte level, and the level was a contributor to their earlier demise as I let it get low on two sets.
One can surely set up a house battery system so it need not ever hook to the alternator, but then it is more important to have a higher solar wattage to battery capacity ratio. On a cloudy day, an alternator can replace in 15 minutes what would take the solar all day to do.
Wiring up a solenoid to charge the house batteries I know seems quite complicated to 12v newbies and i know not needing to do this is quite desirable, but I recommend against it, as the alternator is very capable of returning a battery to 80% charged quite quickly when properly cabled to the house bank, and can and will greatly extend its longevity and can be much more a reliable system.
One can always add a solenoid and cabling at a later date. If one wires up their own solar system, then they will see that pulling power from the alternator is no more complicated than that.
Again, one need not strive for absolute battery charging perfection, but achieving acceptable battery longevity also require that some minimums are met. Reaching Absorption voltage and maintaining it for long enough for the battery to get to the 95% range, as often as possible, need not be complex or complicated. Just get as much solar you can afford and fit on your roof, and do not get too much battery capacity for this amount of solar. If other charging sources are also to be incorporated, and regularly applied, then the solar wattage to battery capacity can be lowered.
It is quite difficult to have too much solar when one is deep cycling their batteries daily, but it is quite easy to have too much battery capacity for ones amount of solar.
