Quote:
Bill, Et Al -
Correct me if I'm wrong here, but technically, Amps are the unit of measure for electrical current in a particular circuit at a given voltage through certain Ohms resistance in the wire. [remainder snipped to fit within posting requirements] ...
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Gregg -
Electrical stuff is really pretty simple - but the terminology is confusing. (Keeps us electrical engineers in a job!) But for most purposes, a good analogy can be drawn between a solar electric system and a water system, where the terminology is easier to understand. Let me try this.
A water tank is the same as a battery. You can put water (or electric energy) into it - and then later, you can take that water (or electric energy) out of it. In each case, you need to know HOW FAST you are filling (or emptying) the tank, and HOW LONG you fill (or empty) it at that rate, because these things tell you HOW MUCH you put in, how much you are taking out, and how much is left at any given time.
In other words, you need to know the RATE at which you fill (or empty), the TIME which you run that rate, and the QUANTITY that you move.
The RATE at which water flows in a pipe is measured in "gallons per hour". The QUANTITY of water that moves is measured in gallons. Similarly, the RATE at which electric energy flows in a wire is measured in "amps". The QUANTITY of electrical energy that moves is measured in amp-hours.
So, for example, if you pump water into a tank at the RATE of 4 gallons per hour, and you let it flow into the tank for 6 hours, then the QUANTITY of water that you put into the tank is 24 gallons. Right? Four gallons per hour X 6 hours = 24 gallons.
Similarly, if you pump electricity into a battery at the RATE of 4 amps, and you let it flow into the battery for 6 hours, then the QUANTITY of electrical energy that you put into the battery is 24 amp-hours.
Once you have put 24 gallons of water into the tank, then you can withdraw it at any rate you choose, until it is gone. For example, you could draw 1 gallon per hour for 24 hours - or 8 gallons per hour for 3 hours - or 48 gallons per hour for 1/2 hour. Or on-and-off at varying rates, until you have used up the entire 24 gallons.
Similarly, once you have put 24 amphours of electricity into the battery, then you can withdraw it at any rate you choose, until it is gone. For example, you could draw 1 amphour per hour for 24 hours - or 8 amphours per hour for 3 hours - or 48 amphours per hour for 1/2 hour. Or on and off at varying rates, until you have used up the entire 24 amphours.
Sound tricky? Yes, certainly, until you realize that "1 amphour per hour" is the same thing as "1 amp"! So to rephrase the paragraph above, "once you have put 24 amphours of electrical energy into the battery, then you can withdraw it at any rate you choose, until it is gone. For example, you could draw 1 amp for 24 hours - or 8 amps for 3 hours - or 48 amps for 1/2 hour." In each case, you take 24 amphours out of the battery.
Did that make any sense? I hope so. In your post, you have the right picture, though the terminology (again) is confusing. What you are quite correctly saying is that if your solar panel charges your battery at 4 amps, and it does so for 6 hours of daylight, then it puts 24 amphours of energy into your battery. Later that night, you can withdraw that energy at the rate you choose. You can run a small light (2 amps) all night long (12 hours), or you can run a TV/VCR (3 amps) for 8 hours, or you can run your furnace blower (6 amps) for 4 hours. Or you can run all three (11 amps) for a bit more than 2 hours.
So in a practical sense, you need to know two things - the amount of time that the battery is being charged or discharged (this is easy, just look at your watch), and the rate at which it is being charged or discharged. To determine this, you need an ammeter. Without an ammeter, you don't know what is happening with your battery.
So your post is correct - good for you - with one minor exception. The whole system is running at 12 volts, and you can't get a shock from 12 volts. So your caution "Don't grab both wires when you're doing this..." isn't quite correct. Grab all the wires you want, you won't feel a thing.
This explanation is gaggingly long, I know, and perhaps isn't wonderfully clear, so feel free to ask more questions. I haven't done this in a long time ...
By the way, purists may take exception to certain points in the analogy. Like most analogies, it is instructive but not perfect. If you object, and would like to contact me off-list, please do so.
Bill
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