Sounds like an alternator problem. I don't know anything about the 200g, but 15.6V could be hurting your battery, and there really should be a voltage regulator between the alternator and battery. I thought most alternators actually had a voltage regulator built in, so yours may have a problem (if you have one???). If your alternator doesn't have a voltage regulator, then it sounds like a good idea to install one.
the SA-200 had a voltage regulator attached to the frame under the alternator. but if it's been replaced with a car alternator, chances are the original regulator was cut out of the loop.
Thanks, I believe my alternator has an internal voltage reg. I haven't had any battery problems . I think I'll disconnect invertor and see what voltage I get then. Mabey the alternator senses the extra load and tries to compensate. Usually when your alternator shows more than 14v you either have a bad battery or bad connection and I have nether.
On an alternator the voltage regulator controlls the power going to the rotor, which is actually the field current. If You inadverdantly hook the brush lead to the battery on an externally regulated alternator the voltage will go high as it is uncontrolled. The other posibility is that the regulator is faulty and is feeding full power to the rotor. On the old fashoned regulator with a coil and contact points the contacts may be burned together.