E-Bus Current Needs

I've been working on my wiring requirements for my 7A and was wondering what kind of loads people were coming up with for the E-Bus. Mine is getting kind of high (30 amps). Granted many of the loads are intermittent (Flaps, trim, etc.). I want to make sure I wire and fuse it correctly from the Battery Bus. Any input would be greatly appreciated!

Aeroelectric Bob

Paul,

Aeroelectric Bob has some documents here that may help you do a full load analysis by phase of flight...

http://www.aeroelectric.com/PPS/Load_Analysis

gil in Tucson

pwhaley6347 said:

Granted many of the loads are intermittent (Flaps, trim, etc.).

Click to expand...

Items such as flaps do not need to be on the endurance bus, as they are not required for the enroute portion of a flight following a (presumed) alternator failure. When the airport is made, you flip the battery master back on and run your flaps or whatever. Since most electrical items can be turned off or simply not used, the primary rationales for the e-bus are to not have the master contactor sucking up any of the remaining battery power. and to have quick, convenient load shedding.

I forgot about those! Thanks!

Here's a spreadsheet that may be useful.

Third link on the page at http://www3.telus.net/aviation/flying/RV-9A/photos/Electrical/Electrical_photos.html

Vern Little

William Slaughter said:

Items such as flaps do not need to be on the endurance bus, as they are not required for the enroute portion of a flight following a (presumed) alternator failure. When the airport is made, you flip the battery master back on and run your flaps or whatever. Since most electrical items can be turned off or simply not used, the primary rationales for the e-bus are to not have the master contactor sucking up any of the remaining battery power. and to have quick, convenient load shedding.

Click to expand...

William,

Allow me to pose a counterpoint.

One big benefit to having an e-bus, that is alternately fed, is that if your master contactor fails, you have options. This is in addition to the obvious advantage of "pre-calculated" load shedding. But anyway, go with me on this one for a minute...

Flaps. Certainly don't need them to land my RV-7, but I'd definitely prefer to land with flaps down if I have a choice.

So what happens if the master contactor fails? All of those extra items you might think to place on your MAIN bus because they're non-essential...well, they're now INOP since the main bus is offline. It's not like you even have the option of flipping the master back on when the airport is made. With a dead contactor, you're SOL.

When I set up my RV-7's electrical system, I put several more items on my E-bus than ordinarily would be there. Fuel pump, flaps, trim, etc. Stuff that is normally OFF and momentary loads. My feeling is that by putting them on the E-bus, I've built better reliability into the system. Not only do I NOT have to "flip the master on" (assuming the main contactor is still alive), possibly letting more smoke out of the wires if that's the case, but I provided these "nice to haves" an alternate source of power than the contactor.

For what it's worth, my Main bus is only a 10-circuit fuse block. My E-bus, on the other hand, is a 20-circuit fuse block.

Food for thought...

Dan,

I saw your list of equipment sorted by bus type on another post. What size fuse did you use on the battery bus terminal that feeds the E-bus?

Thanks.

It's a 15-amp fuse.

Nomenclature and Design Goals

Dan, "E-buss" has perhaps become something of a vaguely defined term, meaning different things to different people. As defined and promoted by Bob Nuckolls (and referenced by me), it's mission is primarily to allow a low stress continuation of the flight following an alternator failure, via predictable load shedding, including the current needed for the master contactor. Your combination places more design emphasis on dealing with a master contactor failure. Perhaps it should be called the MCF buss. The ultimate in ensuring that nothing is rendered INOP by a contactor or switch failure would be to have everything on a battery bus, but then you lose the ability to render the plane electrically "cold" before that crash landing. Choices, choices. I encourage anyone wiring their own plane to first buy and read The Aeroelectric Connection, then use their knowledge and well considered design goals to make their own system design choices. There's no one architecture that is the "magic bullet" for all cases. I shudder to think how many hours I've got invested in my electrical system design (mostly finalized), but at least it gives me a break from de-burring!

Failure of the E-buss

I am still getting all the kinks out of my plane. I was supprised when testing my E-buss switch that it work a very short time and then failed. I went back to the Normal buss right away.

The failure point was the fuse from the battery buss to the E-Buss. As per Bobs' plans I had put a 7.5 amp fuse here.
I wanted a lot of options for continued flight and so had a lot of stuff on the E-buss, (guess that it must have been more then 7.5 amps worth ).
I have change to a 10 amp fuse, but have not tested this yet.

How much (amps) stuff are people putting on there E-Buss?
How big of fuse is being used?
Maybe I should change this to a curcuit breaker so that I can shut off some things and then reset the breaker?

Kent

Kent:

You seem to be approaching fuse/breaker selection from the wrong direction. Don't cut and try to find a rating that doesn't blow. Instead, calculate your load, ensure your wire sizes are correct and then select the rating that is appropriate for your system. "Cut and try" may cause a chain of unforeseen problems as you progressively identify the next weakest link in your electrical system possibly via smoke and flames.

Each aircraft will be different. Just remember that you will have a continuous load on the e-bus and you will also have some transients. Your continuous load should be met by your secondary alternator, if equipped, (or you will be depleting your battery some) but the fuse or breaker must be sized to include the transients.

I have 10 fuses on my e-bus plus and another 5 on my B-bus (I have an E-mag and P-mag). My continuous load on the e-bus (includes the b-bus load) is 9.9. This includes 1.5 for panel lights which I can turn off if my battery starts getting too low. The total load is 13.4 counting all the transient loads (trim servos, SL-30 transmit, windscreen fan, stick isolator relay). I'm using Z-13/8 so I'll be able to fly well past the fuel endurance with this load.

The 9.9 gives me an IFR bird with 1 GRT EFIS, EIS 4000, 2 servo A/P, trim, com/nav and panel lights.

I have a 15 amp fuse for the e-bus.

Jekyll