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couple of FWF wiring questions

Desert Rat

Well Known Member
Hey All-

I've reviewed previous threads etc but have a couple of questions;

1.

Van says remove the starter jumper, Sky-tec says leave it. I understand the reasoning behind both philosophies. The starter that came on my engine is a 149-12XLT. The only thread I could find on this is a few years old and I'm not sure which model starter it was talking about.

Is there really a run on issue with this particular starter such that I would see any real benefit to ditching the jumper and going with a wire from the I terminal on the relay? If so, can anybody comment on what gauge that wire should be? I really have no idea how many amps that thing can pull.

2.

Is there any problem with routing the big starter wire, alternator B-lead and field wire all together?

It would certainly make life easier to just bundle them, but in the back of my mind I have this fuzzy recollection that you shouldn't route the field wire with anything else. I don't know if that's true or if I am mis-remembering. I can't find anything on Vans drawings that says one way or the other.
 
1. My IO360 delivered last year came with a Skytech lightweight starter. Don’t have the model number. I do hear the starter stay engaged on some starts. I’m going to install the input from the ignition terminal when I get a chance. Vans drawing OP-10 specifies 16 gauge for that wire.

2. There should be no problem running those wires together.

Mike
 
Terry, I'm not sure I would route them together. By that I mean in the same bundle with the wires laying next to each other. When the starter is engaged there obviously is quite a bit of current flowing through the starter wire that could result in some coupling to the Blead which would intern result in the output of the alternator being adjusted. I'm not sure of the exact magnitude of this effect, but I would think it would be safer to provide some air gap to reduce any coupling effects. The amount of coupling is dependent on the spacing and the length of the area where the wires run parallel to each other. So reducing parallel lengths and/or increasing the air gap helps to reduce any coupling.
 
Terry, I'm not sure I would route them together. By that I mean in the same bundle with the wires laying next to each other. When the starter is engaged there obviously is quite a bit of current flowing through the starter wire that could result in some coupling to the Blead which would intern result in the output of the alternator being adjusted. I'm not sure of the exact magnitude of this effect, but I would think it would be safer to provide some air gap to reduce any coupling effects. The amount of coupling is dependent on the spacing and the length of the area where the wires run parallel to each other. So reducing parallel lengths and/or increasing the air gap helps to reduce any coupling.

Interesting hypothesis…never heard it before! But I can say that I have run these wires together in bundles for thousands of hours on more than a few airplanes with no problems…. Maybe I’m just lucky! ;)
 
Thanks guys- My concern was just what Ray described, except I was thinking field wire, not B-lead. One of Vans OP drawings for engine electrical shows the start wire running down one side of the sump and everything else on the other side of the engine, which strikes me as odd unless theres a potential issue here. i.e. when you hit the go button, you have several hundred amps zooming down that big wire, and then immediately collapsing.

I didn't get to the point where I needed this info after I posted it yesterday, so I'll go to the source and get a definitive answer.

I'm driving up to Newton today and picking up my alternator, so I'll ask B&C directly. I used to work with Dave Swartzendruber at brand C and he'll know off the top of his head.
 
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Field wire

Thanks guys- My concern was just what Ray described, except I was thinking field wire, not B-lead. One of Vans OP drawings for engine electrical shows the start wire running down one side of the sump and everything else on the other side of the engine, which strikes me as odd unless theres a potential issue here. i.e. when you hit the go button, you have several hundred amps zooming down that big wire, and then immediately collapsing.

I didn't get to the point where I needed this info after I posted it yesterday, so I'll go to the source and get a definitive answer.

I'm driving up to Newton today and picking up my alternator, so I'll ask B&C directly. I used to work with Dave Swartzendruber at brand C and he'll know off the top of his head.

Keep us posted Terry. I need to install that Field wire and planned to route it in the "B" lead fire sleeve.
My Starter wire and Start wire are in a separate fire sleeve. Both sleeves run along the Starboard side of the sump about 1" apart. The other route adds quite a bit of length.
 
Hey Guys-

This afternoon I had a good conversation with Dave up at B&C. Off the top of his head, he said there wouldn't be any reason related to magnetic fields and whatnot that you couldn't run all that stuff together.

HOWEVER- He pointed out that at all costs, do whatever it takes to eliminate even the smallest potential for the B-lead and field wire to chafe and short together.

We discussed how "whatever it takes". Might mean extra anti-chafe, standing off the field wire from the rest of the bundle, whatever solution gives 100% certainty that those wires will never chafe together to a point that they would short.

The reason seemed obvious once he pointed it out. Since the B&C alternator is externally regulated, If the field wire and B lead short together, it will completely bypass the voltage regulator and the alternator will bootstrap right up to its max voltage. The only way to keep it from grenading the rest of the electrical system would be to shut off the battery master.

I don't think this is necessarily a deal breaker, but under the cowl where things are vibrating and flopping around, I'll likely run everything except the field wire in one bundle up the right side of the sump, but the field wire will be separated from the rest via standoffs from the main bundle, or maybe run up the left side. I'll decide what makes the most sense in a day or two.

so now we know.
 
Field wire

Sounds like I need to heat shrink the Field wire before snaking it through the firesleeve. Thanks for the update.
 
If you support the alternator field wire with the starter cable and they chafe and short you only get the overvoltage condition when the starter motor is running. On my installation it was worth the risk and easy to inspect.
 
Pathway

If you support the alternator field wire with the starter cable and they chafe and short you only get the overvoltage condition when the starter motor is running. On my installation it was worth the risk and easy to inspect.

Good idea.
 
Starter wires

Following up and asking a new question. Sorry about the thread stealing.
I understand running the Alternator Field wire with the big Starter cable.
What about the smaller Starter wire? Can that run in the same bundle?
 
Yeah
The starter and starter solenoid wiring are examples of wires that should be run together. They can’t interfere with each other and are at the same potential at the same time.
 
Larry- after giving this quite a bit of thought, here's what I did;

I routed all the starter/alt wires together down the r/h side of the sump. I sleeved the B lead in nomex and the field wire in fiberglass anti-chafe just because thats what I had in my stash. For good measure, I sleeved the small wire to the starter in fiberglass as well just because I had enough sleeve to do that one too.

The field wire is run separately from the B lead under the sump with about 1/2" gap between. The one place where they would have come together was at a stand off from the sump so there I used 2 adels butterflied together.

Electrically, the only place they have a chance to get together is where the field wire is routed up the firewall and through the passthrough with the rest of the power wires. Since that isn't a vibration prone area I chose to route it outside the Nomex sheath everything else resides in, but run them all together. I figure that the chances of it shorting to a power wire through all that insulation areas remote as to be almost non-existent.

it the first picture, the two wires hanging down are the B-lead and the field wire.

hope that's helpful!
 

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Just a little advice, use bolts instead of screws. And use steel lock nuts forward of the firewall. Fiber lock nuts are a definite no go. In high heat arias. They tend to loose their locking abilities when heated. And if you need to remove the clamp for whatever screws tend to get there slots stripped.

Hope this helps
RD
 
yeah, I suppose I should have added the disclaimer that any fiber lock nuts in my FWF pictures are temporary. I was out of the appropriate all metal lock nuts when I was fitting this up.
 
Thread drift in a way but
Note the AN365 nylon locking nuts on the fuel injector lines on the engine as delivered from Lycoming. They are rated to 250F. If the wiring to your starter is above that you have much bigger problems.

We keep adding requirements based on misconceptions and hearsay. It’s a wonder anyone finishes these things
 

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Thread drift in a way but
Note the AN365 nylon locking nuts on the fuel injector lines on the engine as delivered from Lycoming. They are rated to 250F. If the wiring to your starter is above that you have much bigger problems.

We keep adding requirements based on misconceptions and hearsay. It’s a wonder anyone finishes these things

Yep. I wondered that too. I replaced them on mine.
I also used bolts instead of the Vans recommended screws. Hard enough to install an Adel with a bolt. Screws are an exercise in frustration.

Thanks Terry
Where did you get yhat red fiberglass and Nomex?
 
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I'm afraid I don't have a current source. I got it at one of the aircraft surplus stores here in Wichita a few years back. Don't remember if it was The Yard or Boeing Surplus.

I've seen the Nomex used on helicopters and military stuff. The fiberglass is on a lot of the wires up in the gear wells of Bonanzas and the like.
 
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