Multiple power wires for radio

[GLPalinkas]

I have searched hi/lo to find an answer to this question.

VHF Radio power connection - I remember reading somewhere (probably lectric Bob) that one should supply multiple power wires to the connector as the King radio installation manual shows (4 different pins on the main connector). Question is do I really have to run 4 wires from the buss to the connector or can I loop off the back of one wire run to other pins. I think maybe 2 wires with loops to 2 other pins would be prudent but want to get it right. Also, if looping to other pins is recommended how the heck do you put two wires into one Molex connector pin?

My last aircraft wiring job was in the 60's (F-4's) and just a FEW things have changed.....LOL

[N57 OZ]

Hi Gary, you have pretty much answered your own question, getting two AWG20 into a molex is a pita, much easier to run multiple supplies from the bus, some radios have up to 4 pins that need +12v at them, its more to do with were components are laid out on the board. Also remember if you run more supplies then they can be smaller so easier to get into a crimp pin.

[Bob Axsom]

I know of no functional reason to run more than one power wire to the radio. you can use a stub or several three or four wire butt splices to join the wires from the pins instead of trying to terminate multiple wires in connector pins. The same is true of the multiple ground requirements. We used those on the F-101 and even though we started using a woven braid and crimp pins on the F-4 wire bundles, splices were common on Uncle MAC's products. Wiring hasn't changed that much.

Bob Axsom
McDonnell Aircraft Company Employee 86305
Just Like my USAF serial Number - You never forget

[GLPalinkas]

Thanks for the info guys. I appreciate it.

[Jekyll]

Multiple power inputs allow multiple busses to power your radio. This will help keep your radio functioning if you experience system failures.

Jekyll

[SteinAir]

Originally Posted by Jekyll

Multiple power inputs allow multiple busses to power your radio. This will help keep your radio functioning if you experience system failures.

Jekyll

Sometimes yes, but sometimes no (for example, remove power from one side of an SL-30 and the radio is useless - and it has 2 power inputs, 1 Nav and 1 Comm). It's not always for redundant paths of power. Some radios have multiple power inputs on some connectors for the simple reason that the engineering wizards who designed the thing didn't find a way to connect power from multiple PCB's inside the radio, yet 'some' of the stuff is connected. Most of the radios with multiple power inputs will not work properly if you loose just one of them. Heck, Icom has powers that simply jump out and back into the same connector for this very reason. So does King on some of their stuff. Same story goes from grounds on many of these radios.

To me, unless they are truly multiple power inputs (and they rarely are on radios) then running multiple power wires to the buss is just a waste of wire, weight, money and time. Most of the shops I know will follow the mfgr's instructions, which sometimes is to just jumper them together and run a fatter wire to the buss. In the case of some King (KX-155) radios they specifically say they want parallel runs of AWG18 wire for the powers and grounds, while in some radios they specifically want certain wires jumpered together.....Depends on the radio and the mfgr.

Now when you're talking about EFIS's that is an entirely different story. Some of the EFIS mfgrs (such as GRT) have interanlly diode isolated multiple power inputs where multiple streams of power may be input. In this case then yes, it could/might be a wise idea depending on your power architecture.

Anyway, hope this helps....I'm always good for "muddying up" the waters!

Cheers,
Stein.

[GLPalinkas]

I appreciate everyone's thoughts. Since I buy most of my wiring stuff from SteinAir (great prices, quick shipping, RV guy, etc) I will take his advice and run a larger size wire from the buss and use a multiple wire butt splice to power each point on the radio as per the King installation manual. It also solves my "multiple wires into one Molex connector" issue.

Thanks again for all of the help.