---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 03/05/10: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 08:31 AM - Z8 scrapped . . . (Robert L. Nuckolls, III) 2. 08:46 AM - Z8 scrapped . . . (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 08:31:33 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Z8 scrapped . . . I've been wrestling with the design goals for tying two alternators to their own dedicated battery busses and then tying one or both to a main bus. Alternators using B&C alternator controllers are not suited to this idea at all. They're marginally okay if one of the alternators is the SD-20 with an SB-1 regulator set to "relax" the SD-20 when the main alternator is functional (al la Z-12). But managing the input terminals to the alternator controllers from an always hot battery bus adds more poles to a DC MASTER switch or adds complexity to the system when handled with multiple switches . . . with an attendant risk of mis-positioned switches causing mis-behaviors. There's also the issue of compliance with the legacy "switches-off, max-cold" philosophy for fat wires. The design demands either b-lead disconnect contactors or fat diodes on heat sinks. The design looks better with internally regulated alternators because they don't have the LV warning systems and they do regulated voltage sensing internally at the b-lead. But this demands b-lead contactors as opposed to b-lead diodes because the voltage drop across the diode cannot be compensated for by sensing bus volts downstream of the diode. So one COULD do some Z24-like implementations of two alternators driving dedicated batteries . . . but we still have paralleling issues and increased pilot workload to properly position switches. The system was looking like we needed 5 contactors total. 2 battery, 2 b-lead, 1 starter. Finally, with the Z-8 dual-battery/dual-alternator configuration, you can't have both alternators driving the main bus at the same time . . . because of load sharing issues. So this means that while you can have both alternators running to support their respective flying loads, only one can be connected to the main bus at a time. If one wants two, capable alternators and two batteries, then Z-14 is still the architecture of choice offering totally independent systems with cross-tie capabilities. Z-13/8 is still the elegant choice for low-cost, light-weight, simple-operation. This has been a useful exercise in that it validates the work already published and illuminated the messiness of what was initially perceived as another recipe for success. My recommendations for optimizing Noah's adaptation of an SD-20 into his project is replace the SB-1 regulator with a generic "ford" style regulator, add a b-lead contactor to implement fat-wire disconnection when parked. Take field power/ voltage sensing directly from the battery bus through a fusible link then to 5A breaker, crowbar ovm and then to contactor+regulator bus connection. Placard the system against simultaneous operation of both alternators. Bob . . . ________________________________ Message 2 _____________________________________ Time: 08:46:34 AM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Z8 scrapped . . . My recommendations for optimizing Noah's adaptation of an SD-20 into his project is replace the SB-1 regulator with a generic "ford" style regulator, add a b-lead contactor to implement fat-wire disconnection when parked. Take field power/ voltage sensing directly from the battery bus through a fusible link then to 5A breaker, crowbar ovm and then to contactor+regulator bus connection. Placard the system against simultaneous operation of both alternators. ALTERNATIVELY Consider going to Z-14. Use aux battery consistent with experimentation to deduce smallest satisfactory performance. Set the SB-1 up to 14.4 volts. 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