Ok, you have 4 @ 15 Watt panels, each of which will put out about an Amp of current and 2 @ 5 Watt panels, each putting out a little bit less than a half an Amp. You can connect all of your panels positive leads together, and all of your panels negative leads together, and connect them to your controller as you will still be under 7 Amps. That will take care of the panels.
The thing that you were thinking of with reducing the total output to that of the weakest panel only applies when connecting them in series, for higher voltage, where you have to force all of the current from one panel through the other. In that case the smallest panel forms a bottle neck. For your case, at 12V, you will be connecting them in parallel, so this does not apply.
As for the Tape mill, most commonly, you would rectify the output and connect it directly to the battery. The rectifier will prevent the battery from backfeeding into the mill, and spinning the tape drive as a motor. Without a dump load you will have to monitor the mill and disconnect it (by shorting on the mill side of the rectifier) when the batteries are full to prevent over charging the battery. For flooded batteries, you can usually get away with a little over an amp for every hundred amp hours without having to worry about that too much, but a tape drive mill could put out 15 Amps or more depending upon the motor in a sustained windy period, so you would have to either have a dump controller, or disconnect the mill in high wind unless you have about a 2000 Amp hour or larger Flooded type battery.
A dump load which turns on a load of some type when the voltage is too high, or in some, too high for too long, to use up the extra power and protect the battery. There are commercial versions available, or if you are proficient and confident in your abilities, plans to build your own posted in stories on this discussion board and elswhere on the Web.
You should have a way to shut down the mill even if you have a dump load controller. If your batteries are disconnected for some reason, there will be no load placed on the mill when it spins up, and this high speed free wheeling is generally bad for wind turbines. The forces created can cause self destruction of the mill in some cases, and excessive or accelerated wear on the bearing and brushes in most.
For a tape drive mill you can place a heavy duty switch, such as an old knife type switch if you can find or make one on the mill side of the rectifiers. Shorting this switch will then short the output of the mill, which may shut it completely down or at least create enough of a load to prevent it from overspinning for most winds. The rectifier prevents current from being fed from the battery across the switch.
Have fun with this, I suspect it is the start of something you will tinker with and improve for years. It is a lot of fun, Rich Hagen
