We all know we need backups on any circuit needed for comfortable completion of a flight. I aim for that. I have several circuits that fit that need, things like transfer pumps, injection pumps, ECU's and Ignition Coils. I am Installing Nuckolls' Z-14 (IFR and Electrically Dependant Engine) and SDS’ EFII. I would like your review and criticisms of the schemes offered, and any alternatives you can offer too.
I have two of each important device (pumps, coil power, ECU's, injector power) and two always hot buses. I suspect we benefit from being able to connect either pump to either bus, and have two independant switches/circuits to do so too. For take-off and landing, many of us will want both pumps (or other paired devices) running, so I am looking to that as well.
The clever way seemed to be two 700-2-10's (a progressive DPDT switch with On-On-On functionality) for each device pair, in parallel, with one connected to the Main Battery Bus, the other to the Aux Battery Bus. I KNEW that gave me an error state that we would not do deliberately but which was likely to occur: both buses running one pump. Upon first review with both buses hot, this is a "so what?" with the only loss being only one pump on when we were trying for both. But when one bus has gone cold, we are then trying to power everything left On on that cold bus through the fuse and switch for the Hot bus. Sure, if we REMEMBER to close the Bus-Tie first and/or turn off everything on the cold bus and both buses do go hot, no problem, but if one bus is still cold, we lose access to pump as both fuses pop. One more out of order switch throw and we are out both pumps or coils or .... BAAAD.
Yes, I have run Fault Tree Analysis and then Failure Modes and Effects Analysis for my base scheme the way I was taught by duPont using order of magnitude estimates with detectability, severity, and failure probability. I plan to run the exercises on the alternatives too. FTA and FMEA are very useful tools for estimating if one scheme is significantly better or worse in total.
So, what are the alternatives?
Two SPST switches in parallel for each function, each connecting one bus to one pump. That costs me half of the bus-pump possibilities, which sounds detrimental.
Series switch set that uses a 2-10 sequenced to a 2-1 that let's me select bus to either pump and to run both pumps, while precluding one pump on both buses simultaneously. This looks worse with two switches in series - instead of having a SPOF, I have doubled it - UGH.
The scheme I like is paired 700-2-1's for each function with one switch per pump. This allows either bus to power each pump. No cross bus connection is possible, each pump (or other device) is separately powered by either bus, and there is always the other pump.
Thoughts please on all of these schemes and my judgment here... If you have a better scheme to be replicated several times in my panel to allow running both devices from either bus, I am all ears.
Bill
I have two of each important device (pumps, coil power, ECU's, injector power) and two always hot buses. I suspect we benefit from being able to connect either pump to either bus, and have two independant switches/circuits to do so too. For take-off and landing, many of us will want both pumps (or other paired devices) running, so I am looking to that as well.
The clever way seemed to be two 700-2-10's (a progressive DPDT switch with On-On-On functionality) for each device pair, in parallel, with one connected to the Main Battery Bus, the other to the Aux Battery Bus. I KNEW that gave me an error state that we would not do deliberately but which was likely to occur: both buses running one pump. Upon first review with both buses hot, this is a "so what?" with the only loss being only one pump on when we were trying for both. But when one bus has gone cold, we are then trying to power everything left On on that cold bus through the fuse and switch for the Hot bus. Sure, if we REMEMBER to close the Bus-Tie first and/or turn off everything on the cold bus and both buses do go hot, no problem, but if one bus is still cold, we lose access to pump as both fuses pop. One more out of order switch throw and we are out both pumps or coils or .... BAAAD.
Yes, I have run Fault Tree Analysis and then Failure Modes and Effects Analysis for my base scheme the way I was taught by duPont using order of magnitude estimates with detectability, severity, and failure probability. I plan to run the exercises on the alternatives too. FTA and FMEA are very useful tools for estimating if one scheme is significantly better or worse in total.
So, what are the alternatives?
Two SPST switches in parallel for each function, each connecting one bus to one pump. That costs me half of the bus-pump possibilities, which sounds detrimental.
Series switch set that uses a 2-10 sequenced to a 2-1 that let's me select bus to either pump and to run both pumps, while precluding one pump on both buses simultaneously. This looks worse with two switches in series - instead of having a SPOF, I have doubled it - UGH.
The scheme I like is paired 700-2-1's for each function with one switch per pump. This allows either bus to power each pump. No cross bus connection is possible, each pump (or other device) is separately powered by either bus, and there is always the other pump.
Thoughts please on all of these schemes and my judgment here... If you have a better scheme to be replicated several times in my panel to allow running both devices from either bus, I am all ears.
Bill
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