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Cable terminals.. wouldn't a smaller hole in the middle of a terminal be able to carry more amperage?

ericfx1984

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This is something I was thinking about so a while back I ran into a problem we're the previous owner of my RV had installed terminals with half inch holes.. the problem is the stud that it was mounting to was actually quite small and was only one quarter inch.. as a result these connections were heating up quite a bit because they just weren't making proper contact

So based on this I got to thinking a smaller hole would have had a larger contact patch overall and likely would have been able to properly carry the current or at least carry it a little better

At the end of the day, the whole in the middle of the terminal is really just there for clamping Force.. well there is some current carried up through the bolt to the other side of the terminal where the nut is, by and large most of this current is going to be carried on the pad that the clamping force is clamping the terminal onto

Based on this, I would surmise that a 1/0 terminal with a 1/4" hole in the middle would actually be able to carry more current than the same terminal with a 1/2" hole... Of course this is based strictly on the surface area and contact patch and it also draws the conclusion that the 1/4" bolt or stud has enough clamping Force to properly clamp the terminal to the battery's pad.. thoughts?
 
So based on this I got to thinking a smaller hole would have had a larger contact patch overall and likely would have been able to properly carry the current or at least carry it a little better
you are correct, you should use lugs with the hole appropriate sized to the fastener you are using.

The primary issue with smaller bolts is not the bolt failing - but the material which it's screwing into.
A 1/4 screw has a strength of somewhere around 1750lbs.

But when you screw that into an aluminum terminal - you might end up with only 90lbs.
90 lbs is nothing when you apply the lever of a somewhat stiff cable. (various types of aluminum have different properties)

While a 3/8 is able to handle 4250lbs and well above 300lbs in a aluminum.
 
You still need high clamping pressure and connectors for large diameter wires just have big holes.
efficientPV, I Agree, the screw size provides a place for the current to come up through to the bolt head side, so a small hole means small bolt means less current flow which isn't good....it is a balance.

Bigger bolt also provides more heat dissipation.
 
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I would surmise that a 1/0 terminal with a 1/4" hole

the question is - do you even need a 0/1 for an item which only provides you with 1/4 fastener?

Someone a lot smarter then we probably put that bolt or screw on their item and thought it's sufficient.
 
I should add that the bolt also does conduct current from top to bottom. Any connection is always the weak link in a current path. That is the reason you can spot weld two pieces of metal pressed together as in lithium battery welds.
 
you are correct, you should use lugs with the hole appropriate sized to the fastener you are using.

The primary issue with smaller bolts is not the bolt failing - but the material which it's screwing into.
A 1/4 screw has a strength of somewhere around 1750lbs.

But when you screw that into an aluminum terminal - you might end up with only 90lbs.
90 lbs is nothing when you apply the lever of a somewhat stiff cable. (various types of aluminum have different properties)

While a 3/8 is able to handle 4250lbs and well above 300lbs in a aluminum.
Correct me if I am wrong but a lot of the lifepo4 cell I see only have m6 (1/4") fasteners right?
 
Correct me if I am wrong but a lot of the lifepo4 cell I see only have m6 (1/4") fasteners right?

My EVE LiFePO4 280 Ah cells use M6 fasteners. For the 2/0 cable that attaches to the positive terminal of my battery I used a lug with a 1/4" opening. I agree that the smaller hole in the lug means more surface area.
 
I use 4/0 cable with ⅜ holes on the positive and negative terminals of my pack. However I use a custom bus bar with a ¼ inch hole for the terminal top and a ⅜ hole for the cable lug. My pack is 3P16S so the strain is spread out over 3 cells but I also support the cable to reduce the strain. I also use NoAlox because the cell terminals are aluminum and the bus bars are copper.
 
Correct me if I am wrong but a lot of the lifepo4 cell I see only have m6 (1/4") fasteners right?
many cells are only built to handle 125A so a M6 fastener is sufficient to hold a 2 AWG wire lug.
If you want to have more amps - then you parallels cells and you got two M6 fasteners - which give you double the holding power.

Like I said earlier - it very much depends in the type of aluminum alloy used, it could be 500lbs for a M6. The clamping power could be much higher - the proportion I stated was just to emphasize that it's not a bolt problem. It's the material of the cell.
 
fender washers are bad juju, they are typically galvanized and that oxide is an insulator
The MG is not oxide, it is conductive carbon paste, check it out. It improves conductivity. Only ever use S/S hardware.
 
The MG is not oxide, it is conductive carbon paste, check it out. It improves conductivity. Only ever use S/S hardware.
I was referring to the zinc oxide that is used on galvanized steel fender washers
 
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