Adapting 3/8 cables to 8mm terminals?

Isaac-1

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I am updating the technology in my RV (switching from PWM to MPPT, Lead Acid to LiFePo4 and have a small problem, most of the existing cables have 3/8 inch lugs on them, and most of the new equipment has 8mm (5/16) female terminals with 8mm screws. My question is are there adapter studs, etc. that can convert the 8mm female terminals on the batteries, DC-DC MPPT charger, etc. to 3/8 (10mm) male studs or female terminals. I have found such adapters that go from 8mm to battery post, but not to 10mm, I have also found ones that do 10mm to 8mm, but they had female 8mm connections, not male that I would need to work with my existing 8mm female terminals.

thanks Ike
 

Isaac-1

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That would work going the other way, my problem is the hole in the cable lugs is bigger than the screw threads.
 

rmaddy

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Is it really an issue having 3/8" cable lugs on 5/16" terminals? The important part is how much metal to metal contact is there between the flat part of the cable lug and the flat part around the terminal?
 
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12,510
Is it really an issue having 3/8" cable lugs on 5/16" terminals? The important part is how much metal to metal contact is there between the flat part of the cable lug and the flat part around the terminal?
Sloppy terminals is not optimal.
I suggest a stress test.
Use an infrared thermometer to see if the joints are getting hot while you run the system to design capacity.
Also check again periodically.
You don't want things getting loose over time due to vibration.
 

rmaddy

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Sloppy terminals is not optimal.
I agree fully but I am curious how much of an issue, if any, it really is in real life. I wouldn't put a 3/8" lug on 1/4" stud but 3/8" on 5/16" may be "close enough". Once the nut is torqued down it's not likely to move around. But it is an RV so it would be worth testing out or at least inspecting on occasion.

For peace of mind though you might want to replace the cables, or if there is enough slack, cut off the existing lugs and crimp on new ones of the needed size.
 
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The nut staying torqued down that holds the lug on has nothing to do with how large the hole is in the cable lug.
The slop in the joint and torque on the wire could allow the nut to work loose.
That is my concern anyways.
 
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I agree fully but I am curious how much of an issue, if any, it really is in real life. I wouldn't put a 3/8" lug on 1/4" stud but 3/8" on 5/16" may be "close enough".
I'm sure its done often.
Once the nut is torqued down it's not likely to move around. But it is an RV so it would be worth testing out or at least inspecting on occasion.

For peace of mind though you might want to replace the cables, or if there is enough slack, cut off the existing lugs and crimp on new ones of the needed size.
A small service loop is a "good thing"TM.
 

time2roll

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I would not worry one bit to put a lug with 3/8 hole on an 8mm stud. Otherwise replace the lug. I would not use an adapter.
 

12VoltInstalls

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One thing I’ve done is slip a thin plastic tube on 5/16 studs to center 3/8 lugs. I think I recall copper refer tubing works for 1/2” to 3/8”. The piece needs to be about a hair less than one terminal shorter than the tightened stack or you create an ‘internal crimp’ as you tighten on the tube and everything swage locks together. (Don’t ask…)

Having said that I’d prefer to change the terminal end.

I’ve got a hundred or so various on hand. When bought bulk you get nice heavy parts and the price can still be 1/4 or 1/3 of retail onesie twosie prices.
I use a ton of 5/16x8ga and 2ga, 1, 2/0 cable to 5/16 eye and I have either a lot or none on hand.
 
Joined
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Messages
12,510
One thing I’ve done is slip a thin plastic tube on 5/16 studs to center 3/8 lugs. I think I recall copper refer tubing works for 1/2” to 3/8”. The piece needs to be about a hair less than one terminal shorter than the tightened stack or you create an ‘internal crimp’ as you tighten on the tube and everything swage locks together. (Don’t ask…)

Having said that I’d prefer to change the terminal end.

I’ve got a hundred or so various on hand. When bought bulk you get nice heavy parts and the price can still be 1/4 or 1/3 of retail onesie twosie prices.
I use a ton of 5/16x8ga and 2ga, 1, 2/0 cable to 5/16 eye and I have either a lot or none on hand.
Somebody should make a metal insert like the terminal equivalent of this.
45-adapter.jpg
 

Zil

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My first battery bank was Duracell GC2. The studs were 5/16. The mounting hole in the MRBF fuse holders are 3/8. I took a coil of 1/16 (+ -) solid solder and made rings. One ring to keep the MRBF centered on the stud. A NyLoc nut on a flat washer, torqued, held the MRBF tight to the flat of the battery terminal. Note; No washer between the lug and battery. This worked on the road for three years. I did maintenance every six months, checking milli-voltage drop across the connections. A temperature check is not accurate enough to find but the worse connections.
If I could have changed lugs I would have done that. But MRBF is not changeable.
 
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