Rod,
If the amp meter is zero with the engine stopped and airframe loads turned on, that means the amp meter is indicating the total output of “alternator B”, not just the amps of charge or discharge of the battery. So what this tells me is that at the time you took the photo (that you posted), alternator B was providing 8 amps in total to the airframe electrical loads. I would think that’s a couple of amps shy of the total electrical load at the time. So the battery is probably discharging slowly as it picks up the difference. Or possibly it’s at equilibrium, but it’s surely not charging the battery as it should. Alternator B should be able to provide up to 30 amps depending on RPM. Something is wrong.
There are some common problems with the 912iS “B” charging system. Start out by looking at the three yellow wires running from the stator to regulator B. It’s somewhat common for these wires to overheat at the connector located at the regulator leads. I’ve seen two of these wires melted together, which shorts out a portion of the stator. Or, the heat can cause the connector to go bad and you end up with low or zero alternator output. There is a new connector that can be installed to help with this problem (see SI-912i-024).
There have also been some regulator failures, but that’s typically all or nothing. I have also seen one phase of the alternator B stator burn out and go to ground, leaving the alternator working at partial output just as you are describing. You can test the stator with a volt-ohm meter. This procedure is described in the heavy maintenance manual, but you can start by unplugging the connector between the stator and regulator and testing the resistance between the three stator leads (in pairs) and each lead to ground. None of the leads should be grounded.
