[DrDave]

I believe the C system is the same as the A and B and D. There is no paralleling function of those regulators. Please refer to the charging system diagram. There are two separate regulators that operate one at a time. You can easily confirm this by identifying the regulator 1,2 switch. Just because they screwed two regulators to the firewall doesn't mean it uses both of them at the same time.

In this system it has two alternators charging one battery. The two alternators are controlled by one regulator. As an aside, there are two-and-a-half ways to run this system; regulator 1, regulator 2, run/standby switch with each regulator. I give half-credit for that since in the standby mode it bypasses the contactor, alt field breaker, and master switch. The standby circuit goes to the battery terminal of the OVR. Cool system. I see no reason to change the architecture of the system.

Now back to your original question, I would put in one Zeftronics R25102A. This will charge the system around 28.4V with a healthy field circuit. This model is approved for your airplane. You don't have to live with that low 27.4V system. Your battery will thank you.

Report your results. As always I would be glad to help.

Dave