E Buss Power

apatti · #1 03-18-2009, 07:52 PM

All,
I have been researching the archieves concerning E-busses. Typically, E-busses are powered via a diode off the main buss. This electrically isolates the busses. Most people also have a SPST switch which, when closed, provides direct power (bypassing the diode and the associated .7V drop) to the E-buss from the battery side of the master contactor.

A while back someone (Dan C., I think) posted that he always flies with the this "E-buss Direct" switch always closed. I was thinking of doing this also. So, why would I need the diode??? If there is a failure on the master buss or the alternator goes tango uniform, I just turn off the master buss. Am I missing something?

Thanks,

SMO · #2 03-18-2009, 08:17 PM

As you mentioned, in the normal mode (ebuss switch open) the ebuss gets its power from the main buss, passing through the diode. If you fly with the ebuss switch closed then there are two sources of power for the ebuss, one from the main buss and one direct from the battery.

When you turn your master off, and close the ebuss switch, the ebuss only has one source of power which is direct from the battery. However without the diode the main buss will also get powered up from the battery, through the ebuss, and out to the main buss. The diode is the mechanism that stops this flow to the main buss.

The only drawback I can see to flying with the ebuss switch closed is that if you forget to open it when you shut down, you will still be powering the ebuss. This is only a concern if the items drawing power from the ebuss are not switched off independently.

apatti · #3 03-18-2009, 09:10 PM

Quote:

Originally Posted by SMO

...
When you turn your master off, and close the ebuss switch, the ebuss only has one source of power which is direct from the battery. However without the diode the main buss will also get powered up from the battery, through the ebuss, and out to the main buss. The diode is the mechanism that stops this flow to the main buss.

...

Mark,
Thanks for the reply. I am not sure if this is the norm or not, but I have my E-buss Direct switch coming off of the battery side of the Master Contactor. Therefore, if the master is off (contactor open) there is no electrical path from the E-buss to the the main buss. So I don't see how the main buss will be powered by the battery. However, everyone seems to be using the diode, so I worry that I am missing something basic.

To try and keep me from leaving any of my busses powered, I plan to have panel light indicators (LED's) to remind me the busses are on.

SMO · #4 03-18-2009, 09:33 PM

Ok, you have a switch between your battery and your ebuss. Do you have a wire between the ebuss and the main buss? If the answer is "no" then you will have to have turn this switch on to power the ebuss equipment each time you fly, and you have to turn your master on which powers your main buss. No diode required.

Most folks seem to follow Bob Nuckolls method which is to have the switch between the battery buss, which is always powered unless the battery is disconnected (dont know if you have this), and the Ebuss. The switch is normally open and the ebuss is fed from the main buss. Therefore the operation 99.9% of the time is to only turn the master on and off to get power everywhere.

Wired up this way, the only time you need to operate the ebuss switch is in the event of a electrical failure and you shut the main buss off with the master. The only purpose of the diode is to prevent ebuss power from back feeding to the main buss in this situation.

If you want to see this PM me your email address, I can email you the wiring diagram for my -4.

Bob Brown · #5 03-18-2009, 09:57 PM

That's exactly right Mark. That's the way most of us Nuckollheads are wired and it meets the intent of the (z-11?) drawing from Aeroelectric Connection. Think of the diode as a valve, that lets power go one way, but not the other. To do so, it burns a little power...but that's typically not a worry. So if you have a runaway alternator or other terminal electrical glitch, which should be indicated SOMEWHERE on your panel, you can turn off the master, turn on the E-Bus (which is running straight off the battery and isolating everything else, will typically give you your minimal functionality that you need to easily land soon) and land. The design of the system is your own, but read Aeroelectric for a few ideas for what is appropriate on your Essential Buss...and remember that you might have a few high amperage items, but they might only be used at the last minute (flaps, lights).

apatti · #6 03-19-2009, 08:19 AM

Quote:

Originally Posted by SMO

Ok, you have a switch between your battery and your ebuss. Do you have a wire between the ebuss and the main buss? If the answer is "no" then you will have to have turn this switch on to power the ebuss equipment each time you fly, and you have to turn your master on which powers your main buss. No diode required.

The only wire between my main buss and my E-buss runs through the master contactor. Thus, I can easily isolate the E-buss by opening the master contactor.

So if I understand correctly, the downside of not having the diode is you have to power up the E-buss separately each time you fly. And, there is a chance you will forget to power it down at the end of each flight and thus drain your battery. In my case the E-buss will be connected to the GRT B power inputs, the main buss will be connected to the GRT A power inputs, and the Aux Battery buss will be connected to the C power inputs. If I forget to power down any of these busses, the GRT's will remain on and should serve as a reminder.

I own and have read Nuckolls book. And, I know it is the bible. So, I don't take deviating from it lightly. That is why I asked this question. But, if the only reason for the diode is so I don't have to turn on/off the E-buss direct switch each time I fly, I think I will go without it.

Thanks to all.