Hey Rswalm, what determines how much power is "available" to charge your battery is the panel, or the array of panels. The charge controller has 2 jobs, keep the battery from being overcharged from the panels, and keep the battery from back feeding into the panel at night. When a controller has a 30 amp rating, that means the array cannot deliver more than 30 amps or it might burn out the controller. Most people always use a controller that is rated at least 1.25 times the array maximum amperage, a 30 amp controller can safely control a 24 amp array for many years.
Panels are rated in watts. To get this they take the panels "maximum power point" amps and volts and multiply them together. What is more realistic is to take the panels amp rating, Imax on the data plate on the panel, and multiply it by the "nominal" voltage of your battery bank. We have 120 watt panels here, they have an amp rating of 7.5 amps. They are designed for 12 volt battery charging, and as such have a max voltage of 18 volts. 7.5 X 18 = 135 watts, but at 12 volts, 7.5 amps X 12 volts = only 90 watts. In reality this is what is being delivered to your battery bank. The point is you need a controller that can handle at least as many amps as your total solar array can deliver in perfect conditions. Three of my 120 watt panels can deliver 22.5 amps, which is fine for a 30 amp controller, but the battery will only receive 22.5 amps at the most, less once the battery begins to reach full charge, then the controller will taper off what is coming from the panels to protect the battery from boiling off all it's fluid. So in the end it will take longer to put the power you need back in the battery. A lead acid battery that is discharged 50 % will probably take at least 6 hours to fully recharge, no matter how big the solar array is. Battery capacity is measured in amp hours (AH). Cold cranking amps are a measure of a battery's ability to start a car, not power a light bulb. If you had a completely dead 200 AH battery and you could charge it with 200 amps, in theory it would be full in an hour, but in reality the battery would be destroyed in minutes with that amount of power.
There is a great book at the library, "The Complete Battery Book," by Richard Perez that explains all this in detail. Richard is also the founding editor of Home Power Magazine, the only periodical that gets into the nuts and bolts of renewable energy. We subscribed 18 years ago, and today our home is completely powered by the wind and sun. We use golf cart batteries here, Trojan T-105 to be specific, they hold 220 AH each, at 6 volts. Four of them give us a 220 AH 24 volt pack. My array max amps is 32 amps, about all the batteries can handle when discharged 50 %. You never want to completely drain a lead acid battery, it does permanent damage to the cells. They will recharge again, but only a portion of the battery will hold power after that. Check out Home Power if you really want to get into renewable energy. Our home was actually featured in a couple articles years ago. Take care R, Rudydoo
