The E-bus alt feed: a different idea

[kentlik]

Originally Posted by jcarne

All good points as well Carl. I like your double avionics master idea. Another way to skin the cat. I like how you pointed out conserving battery capacity as a nice feature of the quick load shedding method should the backup alternator not work/ not come online for some rare reason.

I like cats...dogs too.

[jcarne]

Originally Posted by kentlik

I like cats...dogs too.

Me too but I really try and avoid skinning those...

[rapid_ascent]

As I plan out my ebus items most of my avionics is able to be on that bus. So you effectively have two paths to power most of the avionics. My GNS430W is a power hog so for now it?s on the main bus. I?m not sure I really like that idea but it seems like it consumes a lot compared to everything else.

[N546RV]

Originally Posted by Mich48041

Bob N's diagrams have two current paths supplying power to the E-Bus, one
through a diode and one through a relay (or switch). Eliminating one of those
paths greatly reduces the reliability of the E-Bus. Relays are much more likely
to fail than a diode.

I don't think this idea qualifies as "eliminating one of those paths." It still provides two possible paths to power the E-bus, just like Bob's diagrams. The primary difference is that the alt feed switch in Bob's diagram is additive - closing that switch connects the second feed to the E-bus but does not disconnect the feed from the main bus.

The comment on failure probability for a relay vs diode is good info, thank you - and it fits with my gut feeling, if for no other reason than just comparing solid state vs mechanical parts.

Lots of good discussion here.

[emsvitil]

Originally Posted by lr172

changing poles on that switch/relay will create a momentary open to your e bus feed. That will cause a reset/brown out for any circuitry, requiring a reboot/restart for advanced equipment.

creative wiring of a triple throw switch could avoid that, but it would combine the two busses for a brief moment.

Larry

Add a large(ish) capacitor to the E-bus to supply power during the brief switch-over.

[jcarne]

Originally Posted by emsvitil

Add a large(ish) capacitor to the E-bus to supply power during the brief switch-over.

That would solve the brown out problem but I will say that from my HVAC days capacitors were without question the part with the highest failure rate. Perhaps they sell better grade ones with good records but my experience doesn't show it.

[Foghorn]

Dennis,

You should post this question on Matronics list under Aeroelectric. Then you?ll get Bob himself to give you the pros and cons. With your permission I can post it for you.

Jeff

[emsvitil]

What do you expect the amp load to be on the E-bus?

[Mich48041]

the alt feed switch in Bob's diagram is additive - closing that switch connects the
second feed to the E-bus but does not disconnect the feed from the main bus.

I consider that an advantage. Why would you want the E-bus disconnected from the main bus?

[walkman]

Originally Posted by emsvitil

Add a large(ish) capacitor to the E-bus to supply power during the brief switch-over.

I simply check the battery buss works correctly by engaging the ebuss before engaging the master/alt prior to start, then leave the ebuss enabled all the time. I don't see any need to turn the ebuss back off.

If the alt fails then all I need to do is open the alt/master and not two actions.