Question about Contactors

I'm just getting started designing my electrical system and I have a lot to learn. I have 'lectric Bob's book and have been reading through it.

My question is on Contactors. I know I need to connect the pos lead from my battery to a battery Contactor (using 4AWB welding cable) - and then run a 6AWB (or other appropriate sized) cable to my main bus from the pos terminal of the contactor (of course, I need to connect the neg from the batter contactor to the neg bus on the firewall).

Where does the 4AWG cable go from the contactor? Do I need a Starter Contactor, or does the solenoid on the starter serve this purpose?

I'm still figuring out the difference between a schematic and the actual implementation, which may combine several "schematic devices" into a single device (such as a regulator and an alternator together like the PlanePower alternator).

Any suggesions, beyond those in the aeroelectric book, that would streamline my design and reduc weight and cost?

Jeff
Building an RV-10

Contactor wiring

First, I suggest you subscribe to the AeroElectric Matronics list and do some searching there, and on Bob's website (http://www.aeroelectric.com/)

An 'architcture' shows what components are in your electrical system (battery, alternator, fuseblocks, circuit breakers, radios, lights ...), and how they are connected. Your implementation defines wire lengths and sizes (which depends on the length and current it's expected to carry).

For a typical system:
The 4AWG wire goes from Battery '+' terminal to one side of the contactor. The other side of the contactor goes to your main bus (probably 6 or 8AWG) and to the starter contactor (probably 4AWG) , and to the alternator (probably 6 or 8AWG).
The Battery '-' terminal goes to your ground block (forrest of tabs) which is also connected to your engine ground straps (bolt through the firewall).

Bob has an article on his website (http://www.aeroelectric.com/articles/strtctr.pdf) that explains why he recommends a starter contactor. You get to decide whether to do it or not.

The subject of internally regulated alternators (like the PlanePower) vs. Externally regulated borders on religion - like 'primer wars'. If you research that subject on the Matronics list, it will take you a week (full time) to read everything. There are no absolute answers - you get to decide what works for you

Thanks Dennis - We're neighbors!

THanks Dennis,

I appreciate your reply. I noticed you're in Rochester Hills. We're in Waterford - fly out of PTK. You keep a plane here also?

Jeff

With respect to implementation from the schematic, what helped me was to thoroughly review the schematic while standing next to the plane. As a starting point, label each component in the schematic with respect to which side of the firewall it will be on. This will help you to start getting a grasp on the size, number, and location of firewall penetrations that will be needed. Then, try to identify a specific location on the plane that makes sense for each component. Some are fairly standard, and Vans plans as well as various builder web sites can help you establish these. For others, there is a fair amount of variability and you will need to make some decisions based on what is possible,the degree of access you desire, and what you will have on your instrument panel.


I initially tried to make wiring diagrams at home (away from the plane) but quickly gave up. At least for me, it just wasnt possible without the plane to look at so you can see all the potential difficulties with various wire routes. The best advice I can offer is to get your components located, then do the job one wire at a time, starting with the more straight forward obvious routes, and building from there. You will undoubtedly make a few goofs and have to redo some wires, but there is no shame in that. My wiring diagrams were completed AFTER installation of each circuit, as I often changed the route during wire installation.

I didnt know a volt from an amp when I started, but worked through it all by reading and re-reading the the AeroElectric Connection and an occasional query to the AeroElectric List. I am now confident my electrical system is superior to the one offered in Vans' plans. Better yet, I actually understand my system and have a reasonable chance of succesfully trouble shooting it in the event I do have a problem.

Go get um!

erich weaver

Hey neighbor!

jrdalton said:

THanks Dennis,

I appreciate your reply. I noticed you're in Rochester Hills. We're in Waterford - fly out of PTK. You keep a plane here also?

Jeff

Click to expand...

My 7A is in the garage at the moment I plan to base it at Ray Airport (57D).
I'm in the middle of wiring right now - so if you want to see electrical stuff just let me know.