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Originally Posted by Motor31
I could be all wet about it but IIRC charging voltages much above 15 volts start to get into the equalization range for batteries and are not intended for maintenance charging purposes. That means excessive boiling of the electrolyte in the batteries and shortened life span as well.
I would think that voltages above 14 volts isn't very good for 12 volt applications. I haven't seen any "appliances" indicating a volt range over 14 volts on the specs.
Does anyone have the installation manual and spec sheet for the inverter in question to look what the factory indicates is normal operation?
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Battery Charging is a tricky thing. There are comprimises that must be understood. Two of the things we need to consider are: Overcharging and Undercharging. Both can prematurely destroy the battery.
Overcharge the batteries and risk damage from excessive heat, gassing of electolyte and depletion of the positive grid. Gassing is not the most serious for a flooded cell battery. Within reason that is a maintenance issue. Plate buckling due to heat and depletion of the grid is another matter and can prematurely shorten the life of the battery.
Undercharge the batteries and risk sulfation of the battery plates which reduces capacity, incomplete charging and consequently a lot less battery capacity available -- capacity that you paid for and are lugging around. Sulfated plates will shorten the useable battery life.
RVers probably break down into two camps when it comes to battery charging philosophy:
Those who most always use FHU and need only concern themselves with battery maintenance. Their batteries are most always connected to a charger (converter) when under heaviest use.
Those who regularly dry camp for long terms and rely heavily on the deep cycle capabilities of their battery set while disconnected from the grid. They need to be able to
fully charge their batteries quickly and not deplete them below 50% of their AH capacity to preserve battery life. Staying at least 70% of full charge is even better.
Charging Voltage and Current parameters for the two scenarios are aptly discussed at
BatteryUniversity.com. This site ofers a great deal of practical information about batteries of all types.
Installation and User manuals for the Xantrex RS3000 Inverter/Charger are available on the
Xantrex web site. Refer to Appendix B of the User Manual for the Battery Charging Reference including the charge algorithm for this device.
Complications arise when we compare those values to the requirements stated for the
Interstate U2200 battery. Decisions must be made - it is a bit of a tightrope walk. Who do we believe: the inverter/charger supplier or the battery manufacturer?.
I have quoted charge values earlier so no need to do it again. They were the manufacturers values - not mine.
I will leave you with this to ponder. If 13.8 Volts will charge a battery to 75% capacity how could we utilize that battery in a system that needs to work on the top 30 to 50% of the battery capacity? It would be seriously impaired. The need to increase charge voltage and duration to complete the last 25% of charge and do it quickly becomes paramount. It requires higher charger voltage to do that.
Mike, I agree with you that 15.5 volts sounds too high for an absorption charge rate. That value is what the battery mfr states but it is only 0.1V below their equalize rate. It is puzzling and I have avoided it. My absorption voltage is set at 14.8V on my solar charger. That is what Trojan specs are and is about half way between the Xantrex and Interstate specs. It is at the high end of the Battery University rate for aggressive charging of
sealed lead-acid batteries.
When equalizing it is important to isolate the batteries from their loads so I have no problem with the 15+Volts there.
Lest anyone think the difference between 14.4V and 14.8V is trivial - it is not. At the micro-ohm battery resistances involved there is a great deal of change in current flow between these values.
Can't say if my appliances are at risk because of this but every off-grid user that uses batteries to store energy is faced with the same scenario. I would think the subject would be widely discussed if it was a problem. I have not seen that discussion.