Al,

Yes, wiring is done (airplane is flying).  Although if there is a serious flaw in my design, I'm willing to modify things.  I understand your philosophy of putting the essential bus next to the battery, but I followed Ed's argument and went with circuit breakers for all flight critical equipment.  So, if I locate the circuit breakers next to the battery, I can't reach them to reset them in flight, which is the big benefit of using circuit breakers in the first place.  The routing of the big feed wire to the essential bus is pretty safe from shorting on any ground sources, so I should probably remove the 60 amp fuse and hook it direct to the battery.  Sounds like the best option. 

 

Mark S.

 

On 12/4/07, Al Gietzen <ALVentures@cox.net> wrote:

 

So, what's the most reliable method of getting the big fat wire from the battery (in the tail) to the essential bus at the panel?  I had initially connected this wire directly to the battery (unfused), but later added the big 60 amp fuse.  Being a fiberglass plane, would a carefully run unfused wire be preferrable to a fused wire?  Is a relay more reliable than a big fuse?  Would a solid-state relay be even better? 

Fuses are very reliable, certainly more than a relay.  I didn't put my engine critical "bus" (actually a 6 place fuse holder) at the panel.  I preferred to put that 'bus' near the batteries, and then ran the smaller wires (each now protected) to the switches on the panel, and on to the engine. Things are then fault tolerant because blowing any one fuse doesn't keep the engine from running.  Also avoids a large noisy wire at the panel; which can be more of an RF issue than the distributed smaller wires.

 

Depending on where your large wire (10 or 12 AWG?) has to run, with no risk of abrasion or shorting to other wires it can be fine unprotected.  Every case is different.

 

I have a #2 wire running from the contactor near the battery in front to the starter on the engine in the rear.  No fuse or breaker is appropriate for that.

 

I assume you wiring is all in place, and not a work in progress.

 

Al G

 

Mark S.

 

On 12/4/07, Al Gietzen < ALVentures@cox.net> wrote:

 

That's what I did... Flight Critical bus is always hot, although I did add a 60 amp fuse back near the battery. 
 Mark S.

Is that fuse in the only power path to the engine critical bus?  I think fuses are a very reliable way to go; but for this application they are synonymous with "fault tolerance".  IOW, blowing one fuse does not shut you down.  Actually, I would also apply the fault tolerance idea to the use of breakers for critical items.

One of the nice things about our setup is we have dual plugs, dual injectors, dual controllers, and dual fuel pump. That gives you the potential for very high reliability - a failure of any one of the pair does not put you on the ground.  I chose to use a separate circuit to each to gain failure tolerance. Each circuit is protected with a fuse, and the fuse holder is powered directly from both batteries with isolation diodes so even a battery failure doesn't stop the engine.

Wires are cheap and light and very reliable. Fuses cost only pennies, so change them out and check the contacts every annual, or every 6 months if you feel like it. I like that better than a breaker that has been in the panel for 10 years. Fault tolerance = high reliability. (I almost said – fuses and fault tolerance, but I don't want to start that fuses vs breakers discussion again J )

FWIW,

Al