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Too Many Connectors on the Master Relay

rockitdoc

Well Known Member
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I have an 1/8” copper bar, and two 6AWG ring terminals to connect to my master contractor. Even with a thin jam nut, I’m left with only one thread showing when tightened. I tried replacing the thicker nut already on the contractor with a jam nut, but the stud on the contractor gets loose when that nut is loosened, so I’m reluctant to remove that nut. What is an acceptable method to get these three thickish bits together on the contractor. Oh, yeah, the starter contractor has the same issue, so switching to that post doesn’t help.
 
Why do you have too many cables? I have one 6g from bat to bat solenoid, and one wire from the master solenoid to the bus
 
I have an 1/8” copper bar, and two 6AWG ring terminals to connect to my master contractor. Even with a thin jam nut, I’m left with only one thread showing when tightened. I tried replacing the thicker nut already on the contractor with a jam nut, but the stud on the contractor gets loose when that nut is loosened, so I’m reluctant to remove that nut. What is an acceptable method to get these three thickish bits together on the contractor. Oh, yeah, the starter contractor has the same issue, so switching to that post doesn’t help.

If you twisted the stud you may have damaged or destroyed the contactor. Been there, done that.
 
Multiple wires in one crimp

You could crimp multiple wires into a larger terminal. Two 6 AWGs will definitely fit into a 2 AWG terminal, maybe a 4 AWG terminal, if loose in 2AWG terminal, fill with extra strands. BTW this method is Nuckolls approved.

If you rotate the stud on the contractor that is not good, seems to have an anti-rotation feature molded into the case, can’t guarantee they all have that though. https://photos.app.goo.gl/AhhRrfY7XhUsvtLW8
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If my math is correct, a 1/8" thick copper bar only needs to be 0.164" (well less than 3/16) wide to have the same cross sectional area as 6AWG wire.

You could:
1. use a thinner bar
2. machine down the ends of your present bar
3. put one 6AWG ring connector on each end
4. drill a hole in the middle of the bar and connect both ring terminals there
 
I have an 1/8” copper bar, and two 6AWG ring terminals to connect to my master contractor. Even with a thin jam nut, I’m left with only one thread showing when tightened. I tried replacing the thicker nut already on the contractor with a jam nut, but the stud on the contractor gets loose when that nut is loosened, so I’m reluctant to remove that nut. What is an acceptable method to get these three thickish bits together on the contractor. Oh, yeah, the starter contractor has the same issue, so switching to that post doesn’t help.

The contactor comes with a nut installed on the stud. You MUST keep a wrench on that nut as you tighten the nut to hold the terminals.
If you don't, the stud will turn inside the solenoid and the contact foot will not be parallel to the contact disc and reduce the capacity of the contact.
 
The contactor comes with a nut installed on the stud. You MUST keep a wrench on that nut as you tighten the nut to hold the terminals.
If you don't, the stud will turn inside the solenoid and the contact foot will not be parallel to the contact disc and reduce the capacity of the contact.

I’m replacing the contactor.
 
If my math is correct, a 1/8" thick copper bar only needs to be 0.164" (well less than 3/16) wide to have the same cross sectional area as 6AWG wire.

You could:
1. use a thinner bar
2. machine down the ends of your present bar
3. put one 6AWG ring connector on each end
4. drill a hole in the middle of the bar and connect both ring terminals there

What he said. And, depending on your wiring diagram, you can run the alternator B lead to your master buss bar or master fuse block.
 
Buss bar

That's an interesting solution. I will be making cables soon.
Are you suggesting a hole in the buss bar in between two components with a bolt, washer & nut?
Just curious.
 
What's on the other end of the copper bus bar? Could you move a wire from the master relay stud to the stud of the device on the other end of the copper bar?
 
That's an interesting solution. I will be making cables soon.
Are you suggesting a hole in the buss bar in between two components with a bolt, washer & nut?
Just curious.

My main alt B lead is 6AWG, but my backup alt B lead is only 10AWG. I’m just going to put them together in a ring terminal that will accomodate both. Probably a 2AWG lug will work. If not, I’ll put a bolt with nut in middle of copper strap between contactors as suggested.
 
Are you suggesting a hole in the buss bar in between two components with a bolt, washer & nut?
Just curious.

Yes. A hole in the middle should have no more effect (electrically) on the bus bar than the two holes in the ends. Given that starter current doesn't have to go through the connectors that attach there, the hole can be a smaller diameter.
 
B lead from alternator to main bus.

Why not connect B lead from alternator direct to main bus.
There is no need to have the B leal from the alternator go trough a contactor
unless the installation is non standard.

Good luck
 
Why not connect B lead from alternator direct to main bus.
There is no need to have the B leal from the alternator go trough a contactor
unless the installation is non standard.

Good luck
Main bus is behind FW. So, more big gauge wire than needed. In my case two 6AWG wires instead of one.
 
I have an 1/8” copper bar, and two 6AWG ring terminals to connect to my master contractor. Even with a thin jam nut, I’m left with only one thread showing when tightened. I tried replacing the thicker nut already on the contractor with a jam nut, but the stud on the contractor gets loose when that nut is loosened, so I’m reluctant to remove that nut. What is an acceptable method to get these three thickish bits together on the contractor. Oh, yeah, the starter contractor has the same issue, so switching to that post doesn’t help.

I usually mount the B lead shunt near there, therefore have at least one more usable stud in the circuit that I can mount any additional terminals off if needed.
 
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My main alt B lead is 6AWG, but my backup alt B lead is only 10AWG. I’m just going to put them together in a ring terminal that will accommodate both. Probably a 2AWG lug will work. If not, I’ll put a bolt with nut in middle of copper strap between contactors as suggested.

When I add nominal circular mils of stranded aircraft wire the result implies a 6 and a 10 awg wire will fit into a 4 awg terminal with room to spare. You could put a stub of 12 awg in to fill the space.

Hope my spreadsheet is not too cryptic.
.
 
I just ran into this same issue on the master contactor. Not saying you haven't, but investigate if you have room on any other contactor posts electrically identical to it. I moved a couple of wires to the ANL fuse holder and a couple of wires to the contactor for my ground power input. Each master contactor now only has one wire on the bus side. I've got two alternators, two batteries, a VP-X and two additional fuse blocks + a ground power connector so a lot going on.
 
This isn't a very good photo but it does show how I did it, using a 1/16" x 1" copper bar from McMaster, not expensive. There was plenty of room to add whatever connections I wanted to it.

z4CjykD.jpg


Dave
 
Here's mine...

Here's mine --

My airspeed gets whacky at 76.47 KTS, and my VOR needle wobbles...a lot...

(humor)
 

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Here's What I Did

I used the Knuckolls/previous response (thanks) method of combining the 6AWG and 10AWG into one ring terminal.

The 6AWG and two 10AWG wires fit inside a 4AWG lug nicely. I un-twisted them a bit to combine and then twisted them together a bit. Crimped on the 4AWG lug and then covered with shrink. Should work splendidly.

Wires From Alternators to Contactor.jpg

Alternator B Leads at FW.jpg
 
I used the Knuckolls/previous response (thanks) method of combining the 6AWG and 10AWG into one ring terminal.

The 6AWG and two 10AWG wires fit inside a 4AWG lug nicely. I un-twisted them a bit to combine and then twisted them together a bit. Crimped on the 4AWG lug and then covered with shrink. Should work splendidly.

View attachment 37786

View attachment 37785

The engine wags a lot more than you might think. Keep an eye on that short wire from the B&C...
 
You can run the alternator B lead to your master buss bar or master fuse block.


Thats the way my 310B is. Only 1 big wire on battery solenoid, 1 wire from it to the starter solenoid, and only 2 big wires on the input of the starter solenoid, the wire to the main bus and the input to the solenoid.
The alternator big charging wires connect together at one end of the main bus, and the battery big wire connects to the other end of the main bus. This is a 1967&1968 310L/N wiring schematic, my 1957 310B was converted from gens to the 310L alternator system back in 1974. My Alts are not exactly like this, this shows the output from the Alts going thru their respective shunt and than tying together at a fuse block.. mine do not tie at the fuse block, they run separately through the 70amp breakers and tie together at the main bus

rsNjSX9.jpg


dg9hz7S.jpg
 
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More Slack and a Boot/Covers

Added some more slack to that Alt B lead from the backup and booted the lead at the Alt and put covers on the Midis.

Alternator B Leads on fW.jpg
 
I used the Knuckolls/previous response (thanks) method of combining the 6AWG and 10AWG into one ring terminal.

The 6AWG and two 10AWG wires fit inside a 4AWG lug nicely. I un-twisted them a bit to combine and then twisted them together a bit. Crimped on the 4AWG lug and then covered with shrink. Should work splendidly.

View attachment 37786

View attachment 37785


What is the purpose of the 10AWG wire if it terminates at the lug end of the 6AWG wire?

It could have been connected to the same wire at the fuse block with the same results.
 
What is the purpose of the 10AWG wire if it terminates at the lug end of the 6AWG wire?

It could have been connected to the same wire at the fuse block with the same results.

There are two alternators. Each with a B lead to the contactor. Each B lead has its own midi fuse. 100A for the 60A alt and 70A for the 40A backup alt. The two B leads come together at the contactor but they are independent until then.
 
There are two alternators. Each with a B lead to the contactor. Each B lead has its own midi fuse. 100A for the 60A alt and 70A for the 40A backup alt. The two B leads come together at the contactor but they are independent until then.

I understand that. My point is your connection of the 10AWG to the 6AWG should have been made at the fuse block on the right hand lugs to avoid an unnecessary wire run of the 10AWG along side the 6AWG and crowded issues at the master lug.

It will work just fine the way you have it, it's just overkill.
 
I understand that. My point is your connection of the 10AWG to the 6AWG should have been made at the fuse block on the right hand lugs to avoid an unnecessary wire run of the 10AWG along side the 6AWG and crowded issues at the master lug.

It will work just fine the way you have it, it's just overkill.

I get it. You mean put a jumper across the 100A and 70A midi fuses, then just run one 6AWG down to the contactor. That would work, but you still have to deal with two thick connectors at the fuses which have shorter studs.
 
I get it. You mean put a jumper across the 100A and 70A midi fuses, then just run one 6AWG down to the contactor. That would work, but you still have to deal with two thick connectors at the fuses which have shorter studs.

Rather than stacking terminals at the fuse holders one could make the jumper with the 10 awg and 6 awg crimped into one terminal. This reduces stack height and removes one FMEA failure mode - loose nut where 10 and 6 terminals are stacked makes both alternators inop. (I'm presuming a best practices crimp is more reliable than a bolted connection but I don’t have statistics on that.)

Up to you whether you want to do it but the 10/6 combo wireset you made between fuses and contactor can be flipped and the 10 shortened.

BTW the BC410-H is not a 40A alternator. It makes 32A at 2,700 Lycoming RPM.
 
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