I wish I could take credit for having learned all I know about Solar
from having experimented and read and tried this and that, but I can't. I have read tons and sifted a lot of BS. I have read many peoples "opinions" and I do trust one source. He may not know it all, but he's got me convinced that he knows more than most folks. He's DONE all the trial and error stuff.
The following is from his blog. You should take a week or two and read it (his blog). Really, it might take that long. I've read it several times (it took that many to begin to understand it) and I've tweaked my system like he recommends and darn if it doesn't work just like he said it would. As with most advice, one may take it or leave it, but for what it's worth, here's his:
VOLTAGE: For the sake of simplicity, I am only going to talk about the requirements of standard flooded wet cell lead acid batteries, which is what most of us use. The major points apply to all types of batteries, but the actual numbers will vary. It is very important for you to research the charging requirements of your batteries if you are using any other type and make sure that your charging system provides what they need, or you could end up damaging them by over charging or never getting them fully charged, which will also damage them. Battery
manufacturer’s specifications say that a standard 12 volt wet cell battery
needs to be charged to between 14.4 to 14.8V and then held there for some time before it will be fully charged. The Trojan Battery company says 14.8V daily charge (at 77 degrees F) and Interstate will tell you over 15V. Trojan’s 2010 Users Guide has a new chart that shows you should actually vary the voltage depending on the amps you supply for charging and even higher voltages are recommended. Of course they recommend temperature regulation. So all of those out there who are telling you 14.8V is too high do not know what they are talking about. How long it takes to get the charge in depends on how far it was discharged. Trojan says to keep charging until a hydrometer test shows that the battery is charged and not one charger available today can do this. The best chargers can do a reasonable guess at state of charge by providing constant voltage and watching the amps taper as the battery fills to tell them when the battery is full. However, they rely on whatever the designer or programmer gives them for guidelines and are only as good as that data. Many do no work worth a hoot. A fully charged battery can be maintained at a full state by applying a 13.2 – 13.6 volts “float” charge. All of the talk about how many amps a charger puts out means nothing. It is the volts (pressure) that you need to push the amps (volume) into a battery. VOLTS, VOLTS, VOLTS!! Also, the amps pushed into a battery at a higher voltage contain more power than those at a lower voltage. Remember, volts times amps equals watts, so amps pushed at 10% higher volts give you 10% more watts. Therefore, the power stored in the upper range of a battery’s charge is greater, so it is very important to get a full charge. Low voltage DC is not easy to get through wire without losing power due to voltage drop or resistance. It is huge problem in an RV. Use big wires and short wiring runs to get around this. It is good practice to use one or even two sizes bigger wire than recommended to limit voltage drop. This charge voltage has to actually reach the battery, not just the output terminals on a charger. If you cannot get your batteries up to 14.4 volts (14.8 is better & faster) with whatever charging system you have and then keep them there while pushing amps in for more than an hour or two, your batteries will never be full.
JUST WHAT IS A FULL BATTERY?? The general consensus on this issue is not correct and this is the primary reason that most RV electrical
systems do not work very well. The batteries in my rig show 12.8 volts after the sun goes down and will usually show 12.5-12.7 after watching TV & running lights
all evening. I typically see 12.5-12.6 on the meter if I manage to get up before the sun rises, but the truth is that I had to look at it as I wrote this because we never look at the voltage, using the percent of charge on our meter instead. These same batteries used to work like everybody else’s before I figured this out, so this is fact, not opinion. My charger works so well because it is set to get the batteries up to 14.8 volts (temperature compensated) and hold them there until charged and since it is solar
, it runs all day. We often see well over 15V on cold days; that is what it takes to charge a cold battery. It is so important to get your batteries full because a 95% charged battery has 10% less usable power in it than a 100% charged one, since you are trying to keep it in the top 50% of its operating range (5% of full = 10% of 50%.)
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