Any EXP Bus II experts?
I've got a "legacy" RV-8 that we are upgrading the panel from round dials to Dynon. This requires a new shunt installation and, as a result, new leads from the shunt, to our EXP Bus II. I do have the EXP installation manual and have studied it.
*please note - I don't intend to start a discussion of how I should just change the EXP out for breakers. The EXP has worked perfectly, I'm 70 years old and already grumpy as h#$&, sore from climbing in and out of the RV-8 eight hundred and forty nine times yesterday and already have my hands full with removing and replacing the entire panel. Thank you now back to our regular program.
It appears that the b-lead from the shunt, the battery lead from the master contactor and a line to a hot battery buss all meet and are connected at the BATT connector on the EXP II. Is that correct or should the b-lead go to the ALT connector. I must note that the airplane has been flying and charging perfectly. I am going to take the switch panel apart from the side rail so I can get a closer look but it sure appears that the three lines all connect at the BATT connector.
Lastly, are ANL fuses used before the EXP? This plane doesn't seem to have one. I'm still looking though. Part of the challenge of being a downstream owner and doing an upgrade is finding things that, while intuitive to the builder, are not obvious to a later owner. There could still be a hidden breaker that I just haven't found yet.
BTW, this aircraft is rear battery with master and starter relay located aft. The new Dynon shunt is firewall located versus the old Westach shunt which was located behind the panel.
Not gonna be of much help here… nevertheless, installed a EXP on a previous aircraft, quite a few moons ago. Didn’t have to play with shunts nor ANLs, went direct feed from the battery which was in close proximity. Since your battery is located rear and the EXP front, yes, I would use a suitable ANL, assuming you feed direct from the battery solenoid.
Mine was wired 15 years ago. So after a quick check of the manual + from memory what I did on my -7 was to use a separate master relay and I wired the alternator via a ANL fuse firewall forward to the switched side of the master relay.
(Firewall Fwd battery, master and starter relay’s)
This means the alternator circuit is protected however if it blows in flight you can’t reset it. (My thinking is that if it blows, it does it for a reason and you shouldn’t be resetting high amp circuits in flight)
Also it reduces the length of the heavy high amp wire needed and the need for another pass through in the firewall.
The control circuit for the Alt comes off the 5A spade connector on the EXP bus, which allows for switching the alt on/off.
According to the installation manual if you wire the alternator to the input peg on the EXP bus you need to use a circuit breaker or fuse.
Also looking at the wiring diagram for the EXP bus the battery and Alt are effectively connected anyway so putting the Alternator on the same post would make no difference. (This would only be an issue if you were using the master relay built onto the board itself)
The hot battery bus wire needs to be connected either to the live side of the master relay or directly to the battery. If you have a master relay in the back once it’s turned off there will be no power coming into the EXP bus.
I feel your pain I recently had to replace a shunt in a friends Rv-6 and working upside down one handed behind the panel wasn’t my idea of fun!!!
Thanks everyone. After a night's rest, lots of reading and conversations with my VAF friends (thanks, Brian, Walt, Peter, Dan and others), I was able to get everything sorted out and back together and I learned a bunch in the process. Thanks, Rob
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