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1. 02:20 PM - Re: Re: Dual Battery Dual Alternator Power Distribution System (Bill Watson)
2. 05:15 PM - Re: Dual Battery Dual Alternator Power Distribution System (lwesterlund)
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Subject: | Re: Dual Battery Dual Alternator Power Distribution |
System
I do actually use the redundant feeds on my GRT screens but each unit is
redundantly connected to 1 bus. One feed goes through a power
stabilizer and the other directly to the bus.
One of the things I wanted to be able to do was to run parts of avionics
bus with engine off, without endangering a start by running down my
battery. I knew from my previous IFR flying experience that being able
to run the panel without killing the starter battery was useful in
fllight planning and waitiing out local weather.
I have (3) GRT HX MFDs. They do not have integral on/off switches and I
chose not to add any. They are all on 1 bus along with the the G430.
When that bus is switched on, one battery starts to drain pretty
quickly. When I first installed them I connected them to only 1 bus and
things worked as desired. During some upgrades and load rebalancing I
decided to connect them to both buses without really thinking it
through. I mean, belts and suspenders must be better, right?
That was a mistake because now I could not control where the load from
the (3) MFDs went unless I turned off 1 bus (and during flight planning
and clearance receptions I ideally want the whole panel with dual comms
up and running). But I did add a power stabilizer to avoid brownouts
during tough starts. With that added, I did use the redundant feeds to
connect to the power stabilizer and the bus directly, with both
connections fed from the same bus. That now works as desired.
As as been discussed elsewhere here, the proliferation of backup
batteries can be a problem. Each of those batteries should be
maintained as carefully as the main battery in a single battery system.
What's the use of the backup if it doesn't perform in a predictable way
when needed? So I will soon be running with zero backup batteries and
depending entirely on the robustness of the Z-14. Even my backup EFIS
will depend entirely on the Z-14 for power.
It seems that one key thing I had to understand about the bus
architectures and the Z-14 in particular is that they are designed and
built in a manner as robust as say the control system. There are a few
fat wire connections at a few points with only a few very reliable
components that could possibly fail. The failure of an alternator or
controller is signaled and bypassed while the battery keeps everything
running, etc. With dual buses, batts and alts, having redundant power
feeds on individual components is redundant. One relies on the
redundant bus architecture to handle power failures.
On 11/5/2018 2:03 PM, lwesterlund wrote:
>
> Mauledriver,
>
> Thanks for the quick and detailed response.
>
> I completely agree that Z-14 is an amazingly robust architecture. The one limitation,
as I see it, is that it doesnt take advantage of the dual power feeds
for capable equipment. You wrote:
>
> But I initially had my dual input gear (the 3 GRTs and the G430) connected to
> both buses but over time came to understand that it was unnecessary
> redundancy with the cross feed capability and sometimes it was a
> liability. Maybe we can discuss the experiences that led me there later.
>
> Please help me to understand why using the redundant feeds might be a bad idea.
Thanks.
>
> Lance
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=484447#484447
>
>
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Subject: | Re: Dual Battery Dual Alternator Power Distribution |
System
Again, thanks for the detailed reply. Your approach certainly makes sense when
using a conventional power bus. Afterall, what could possibly go wrong with a
solid brass bus bar? Its darn near bullet-proof.
As I asked in my reply to Bobs response, what if you are using the VPX system?
As robust as it is, its still not as failure proof as a solid hunk of metal. Even
with dual power feeds, it becomes a single point of failure. Hence my proposed
design.
If theres a better way that leverages that technology, Im all ears. But I dont
think you can just plop the VPX into the Z-14 architecture without modifying it
to resolve the new SPOF.
I appreciate that the more conservative approach from a power system risk management
perspective is to simply use Z-14 as published. Im interested in the VPX
because, IMO, it helps to reduce other elements of risk. For instance, it prevents
deploying the flaps above Vfe, will detect and alert an open circuit (like
the pitot heater), and will control wig-wag lights.
Any thoughts or suggestions or insights on how to include a VPX in a dual bat dual
alt system would be much appreciated.
Lance
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=484638#484638
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