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Originally Posted by mburch
Rick,
I think the reason you need 2x 0.063" strips (or 1x 0.125" strip) between the master and starter relays is to handle the zillions of amps of starting current. But the next connection downstream that you're talking about only has to handle the operating loads of the rest of the aircraft, not starting current, so it doesn't have to be as beefy. Seems like you ought to be able to determine what gauge of wire you'd need for the relay-to-current-limiter connection (based on your load analysis) then check the cross sectional area of that wire vs the area of a 0.063" copper strip, and be good to go.
mcb
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Actually its about 320 amp MAX for short periods. Since the distance is short 0.063 would work but would have more voltage drop and build more temp, but for short start burst this is min. Lets say the hole for the lug is 5/16 = .32. Assume the strap is 3/4" wide. The total area is (.75-.32) x 0.63 = 0.027 in-sq. This is about 1/4 way between a #4 and #6 wire. Well the voltage drop for a #6 wire is only 0.07 volts (assuming 350 amps and 0.5 ft and 0.021 in-sq equiv to #6 awg). The temp for continuous ops would be too high even with twice the area.
Think about this. Take a case where you are using a large wire say #1 or #2 and the first part is the "Lug". The 0.63 copper strap is not any worse really if the lug thickness is the same, at least in the contact area. In reality 0.125 is too thick and 0.63 is a little shy but would work. One thing you could do is make it wider. Assume you need 0.05 in-sq. So 0.05 = (X-0.32)*0.063 > X = approx 1 inch wide.
In a word this metal part will get very hot. Ideally you would need the cross section but 0.063t will work is about 1 in wide.
Here is more info. From what I am reading and all my data you should have at least 0.035 in-sq (about a #4 wire).
When you look at it AREA, it has to do with length of the wire (strap) run, amps carried, desired voltage drop, max temp and weight.
Since the strap is out in the open you don't have a heat problem, and the time you run it is short and it has time to cool. I you arbitrarily want to keep it under say 400F for continuous op (which is not a bad idea) you would need more area, say the size of a #2 wire (about 0.0521 in sq). A 0.75 in strap X 0.125 in (with 5/16 hole) gives you that. Do you need the thickness? Well not really but it can't hurt. The length of the strap is so short that weight is not an issue.
http://www.skytecair.com/Wiring_Experimental.pdf
PS: The starter relay that B&C sells not only is harder to install, it may not made for vertical mounting? In the past van suggest you mount the relays (contactor's, solenoid), both starter and master, side ways to avoid the effects of G-force during maneuvering. In the past pos G's could engage the starter contactor. Well the side ways solution caused great wear on the contactor size the solenoid was galling in that position. The solution was to mount the starter relay upside down so pos G's caused it to stay open. Since Neg G's are less this works. Master relay you want Pos G's to keep it closed. My point is, are the B&C units made to be mounted on the vertical?
A Zillion is a lot
Two strips....
Linear Mode
