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Avionics Relay

Avionics relay

Was looking for options and found this (and some like it) at Digikey.

Diode across coil:
https://www.digikey.com/products/en...t=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

Resistor across coil:
https://www.digikey.com/product-det...-brumfield-relays/1432794-1/PB1329-ND/1236844


Looks pretty tough. Any downside to using this as an avionics relay? Easy to mount, easy to wire it up.

I use an avionics relay, and after over 1500 Hrs, have not had any issues with it. But I also fly IFR, so I have a switch across the relay contacts in case the relay should fail while flying IFR.

I am using a VF-4 relay, but it's rated at 40ADC....
 
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I found a similar relay at Mouser or Digikey. I think it was a Panasonic that had the mounting tab and faston terminals. Seemed like a good solution to me, but it's not operational yet. Relays are not the most reliable electronic components. I bought a spare at the same time.
 
I'm not sure about the ones you're looking at but there are fail "closed" relays out there whereas when they fail they continue to work, you just can't turn them off, we use them all the time in automation projects that are mission critical.
 
I use this relay for my left and right vital buss feeds on a couple of planes (your Avionics #1 and #2): https://www.alliedelec.com/schneider-electric-magnecraft-92s7d22d-12/70185034/

There are many options like this product to select from. I look for ~30 amp rating, silver contacts, and mounting tabs.

I have 4 of these in the RV-10 mounted at the batteries. One each for left and right normal vital buss power, one each for left and right alternate vital buss power (e.g. left vital buss powered from the right battery, etc.).

I use both contacts on each relay - the connections in parallel. My thought was even with this 30amp rated relay having two contacts in parallel provides some redundancy. As these type of relays only draw 50-100ma they present a small load if you are running only on battery power.

Carl
 
Update: ended up using a DPDT switch with 20A capacity on each circuit. Split the avionics bus with COM1/GPS on one side and COM2/Audio panel on the other and fed each side with one circuit of the two switch circuits. No relay. Switch rated for 10000+ cycles less to fail than a relay.
 
Can I get some opinions about wiring the avionics switch? One switch with two wires from 14v source and two wires to the avionics. Avionics split so neither side goes over 20a load according to the CBs called out.

I don?t like as much having the 14v main run all the way back to the console then avionics supply fed to the panel switch then avionics wires back to the console. Seems too many wires too much length.

Also not keen on having a terminal post for the ship power cable on its way through to the console.

So what if I just have the two avionics wires start at the main contractor and run aft to the panel switch then down to the console? My questions on this are if it is okay to put one added terminal on the main contact with the main power cable, and a second one at the ANL side of the main bus bar? Or can I just put both rings on top of the main wire contact and I?m overthinking it?

I have 10Awg wire for this but it might be overkill given the short length.
 
Terminal count isn't a big deal, as long as you can properly secure the terminals with the proper nut & locking mechanism.

Hard to know your architecture without the schematic; what's the goal? Are they always hot circuits, intended to bypass the master contactor? If always hot, get them as close (minimum joints) to the battery as you can. Regardless, small gauge wires need protection at the 'hot' end; you can do that with ANL type fuses or with fusible links (my preference; they'll never nuisance trip and cheaper/lighter than any fuse/breaker).

edit: Again, hard to know goals. If this is flight critical stuff, do failure analysis: if that one switch comes apart, you lose both feeds. Is that ok? Would it help if a switch failure only took out one half? These aren't questions of probability; they're questions of "what if, and if 'if' happens, how will I work around it?"

Charlie
 
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Thanks Charlie. My question is more about is it okay to stack more ring terminals on top of the main cabin feed? Is there room in the firewall feedthru for a pair of 10 awg wires? They don’t need a dedicated breaker or anl on the firewall side just like the main cabin feed doesn’t. I do have an anl on the alternator output but most designs don’t protect between the main post of the batt solenoid and the CB panel. They wouldn’t have their own breaker coming and going from a switch or relay enroute to the avionics bus in the cabin.

It wouldn’t kill me to put a 14awg link on the forward side of the wire though. I have some sleeving.

What would be the proper nut and locking for a couple ring terminals on top of the main terminal?
 
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If the stud is long enough to add extra ring terminals and still use the proper nut to secure the terminals, and you have the room around the stud to 'clock' the terminals so the crimp areas don't interfere with each other, and you can ensure that the wires can't try to rotate the ring terminals (normal best practices), then go for it.

No way for any of us to know about your firewall feedthrough size. :)

If the feeders being discussed are controlled by the master, you're right; protection not required by convention (but easy enough to do).

No reason to change from the hardware that came with the contactor.
 
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