Quote:
Originally Posted by tommyd
I disconnected them from the converter a few hours ago and plan on checking them in the morning. Does the converter continue to send 13.8 volts to the batteries even after they are fully charged but at a reduced amperage? The batteries aren't warm like an overcharge. Thanks for the help .
|
You've just pointed to something that is often not well understood about charging batteries.
Back to basics may help to understand what happens better.
Why current flows? It flows due to the difference in voltage of two spots. It is not something seperate that any power source changes to change the amps moving but simply as the voltage difference in two spots changes, the current changes.
We often speak of voltages in our RV as the difference in the voltage of the battery as compared to the ground connections. The difference is often 12 volts. So if we accidentally connect the 12 volts at the positive post to ground, we get a really big rush of current. Big flash, big trouble as too much current flows!
But if we connect the 12 volts at the start battery to some other point like the
coach battery when it is maybe 10 volts, we get a lot less current flowing as the DIFFERENCE in potential (voltage?) is not 12 volts but 2 volts!
Current flow is directly changed by the DIFFERENCE and it works the same if we are speaking of a 24 volt source into an item that is at 22 volts. The difference is only 2 volts and the current is determined by that difference.
All that is spelled out by Ohm's Law but that tends to confuse lots of folks who are not used to the formulas, etc. used there.
The big take away is that when we have an alternator that can put out a whole bunch of amps (125??) what controls how much it actually puts out is the difference between that point and the point where it is being stored or used, like the battery.
Rather than trying to control the output amps as well as the voltage, we use the theory and just control the voltage.
When the alternator starts and finds a weak battery at some low voltage like 10 volts, the difference in the 14-14.5 from the alternator creates high amp flow as the difference in potential is pretty high (4-4.5 volts?) but as that flow reaches the battery and has to start reversing the chemical reaction that has been making the battery voltage go down, it soon runs into the area right at the positive post being a higher voltage than the first 10 volts and that automatically slows the current flow.
But we also don't want to drive six hours with an alternator putting out 14.5 into a battery which is ideally only going to charge to 12.8 as that just boils off water, gets hot and all kinds of things we don't want.
So we have different stages of charge with different things like alternators and converters. We want them to put out higher voltage to get a low battery brought up quicker but then we don't want to over charge it, so as a really good charger gets closer to the correct final level, it begins to back the output voltage down in stages. But if we turn on a bunch of stuff, it can also boost the voltage back up and put out lots more if needed to keep the batteries from going back down.
Different chargers have different levels and ways to do it but there are often bulk charge at higher voltage, some mid level voltage and a final float voltage as the battery reaches the ideal level to maintain it best.
One of the nice things about just controlling the voltage and letting the current go with what fits is that we don't have to figure in so many variables.
If you leave a site and the coach batteries are all way down, the alternator just stays in bulk or higher voltage mode a bit longer and if we turn on several things as we drive, that just keeps the voltage difference a bit lower, longer and the alternator still just works on getting all the batteries connected back up to some preset level where it senses that it is nearing the point where it lowers the output voltage to keep from overcharging any of the connected batteries.
At one point you asked about the converter taking over from the batteries. That is not done but it is more like they are all on the same connectionand if you are using the battery to run a vent fan, it is not so much that the power is coming from the battery but more that the power is taken out of the whole circuit connected together, so saying it is coming from the batteries or from the alternator is not really possible without watching a speciifc electron.
Kind of like having several buckets all connected and a pump putting water in at the same time. Kind of like asking if the water came out of bucket one or two or from the pump? The batteries are just storage for what the alternator is putting out and we never expect to need more than it can handle as it is so oversized to cover the worst load we should ever have.
Or kind of like you and the wife having a shared account? You and her put in, the money comes out and is it your money or her money doesn't really count as long as the input is more than what's taken out??? I sahould never mention that idea!!!