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Peak current handling of S604 gold "DB" style contacts

 
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jmfpublic(at)comcast.net
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PostPosted: Tue Jan 24, 2006 5:45 pm    Post subject: Peak current handling of S604 gold "DB" style contacts Reply with quote

Bob, or anyone,
I'm wiring my engine compartment to the instrument panel with a CPC2 series Amp connector to allow the panel to be removed from the plane and assembled on the bench. One of the wire pairs from the engine compartment is the 5 amp breaker switch to the field terminal on the BC20 alternator. I recall that Bob has suggested a mean current draw of 4 amps max for the gold plated 0.040 DB style pins and sockets, which have the part number S604 on the B&C site. Could I use a pair of these to carry the current through the field circuit breaker and switch? If the overvoltage crowbar on the LR-3 regulator shorts the field, there will be a momentary current draw of much larger magnitude. The data sheets for this series of breakers at 5 amps suggests 50 milliohms internal resistance, and if I use 12 feet of 20 gauge wire, this will add 120 milliohms to the circuit. I don't know the internal resistance of the crowbar. If set to zero, this leaves 170 milliohms plus the contact resistance of two series pairs of the pin and socket. I have not measured this resistance, but the Tyco (Amp) site suggests 10 millohm maximum. After doing some reading, I find that the CPC series with "size 20" pins and sockets is rated at a single circuit of 8.34 amps continuous with a 30 degree C rise in temperature. The breaker will open in 0.2 to 0.6 sec at 1000% load.

When the crowbar fires, the instantaneous current before heating is 16 volts/0.18 ohms, or 89 amps. The bimetal thermal breaker should raise its electrical resistance much faster than the wiring because it is enclosed. I'm not sure. The convenience of routing all wires through this one or two CPC connector set is attractive, but I could run the wires through a grommet in the panel, directly to the breaker. It is harder to take apart this way, but at this point, I have convinced myself that the direct route to the Fast-On tab on the breaker is the best way. Having spent several hours researching this, I thought I'd share it with the list.

The two Tyco PDF documents of interest are: instruction sheet 408-7593 and 108-10024-3 on the web site.

Jim Foerster, J400, still wiring...


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