There is something odd here - you've gone from overcharging to not charging at all.
I presume that you have a wire that goes from your alt master (Cessna switch) directly to the two wires on your alternator (or through about a 5 amp breaker), otherwise you would have a regulator in there. My previous post assumed a separate regulator.
Does the battery hold a charge and start the airplane?
Your 30 amp breaker would most likely be connected to a third wire off your alternator - a fat wire, size 10, at least. That would go directly to the battery after the breaker.
Assuming the above is now correct (and only if that is correct - if not email me off line, and I'll give you a call), here's how I'd tackle it:
1. Assume that you don't know whether the alternator is putting out or not - with the breaker popped, the battery won't charge. Remove the fat wire from the alternator and check for voltage between the fat wire and ground at the engine with the master on. You should have battery voltage there. This proves continuity through the breaker, wire, master, and connection to the battery.
2. Connect a charger there, negative to the alternator cae or engine block, and charge the battery, still with the master on. Charging the battery from the alternator location gives a good indication of any bad connections. If the battery is very low, or bad, you very easily could pop a 30A breaker. When the battery is charged, you'll have over 13.5 volts on the battery, and low current from the charger.
3. You should check the sticker on the alternator. If you got a 60 amp alternator, and a 30 amp breaker, you've got a problem. But, a 60 amp alternator requires #8 wire - about the size of a pencil, after the insulation is removed. The wire should be sized for the alternator. The breaker should be sized for the wire.
4. Remove the belt from the alternator, and with the field wires hot, spin it (either way) by hand while reading voltage from where the fat wire would be connected to the firewall ground. You should see something DC. Not much, 2-3-4 volts perhaps, but something.
5. There should (theoretically) be a wire from the case of the alternator to the engine block, and absolutely a solidly connected braided ground strap from the engine block to the firewall. Make sure they are there. Charge current goes from the alternator to the pos battery, out the neg battery, to ground, through ground back to the alternator case. Any bad connections will cause trouble. Normally not enough current to start the plane, but nonetheless. . .
6. Once your battery is charged, connect everything back up, turn off the master, and let it sit overnight. When you return, your battery voltage should still be approx 12.5 volts.
7. Start the plane with the avionics, alternator, and lights off. Voltage should be about 12 before start, 9 or less while cranking, and return to about 12 volts when running.
8. After the plane is running, turn on the alternator switch. You should see the voltage increase over 1 volt, and the ammeter (if you have one) show no more than half scale, and decrease to about zero within 3 minutes. If the voltage is over 15, shut down, and throw the alternator through at auto-parts store window.
Hope this helps. . .
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I followed the check list and found..