# DIY bulkhead terminals



## GoElectric (Nov 15, 2015)

Hi - I'm finding it difficult to determine what size terminals I need to withstand the required torque for bolting on a lug 2/0. I thought I had a decent spec for the torque: 90 inch-pounds, but an engineer ran the calculations and said that would require a 7/16 bolt (copper). 

It seems most high-current connectors are either 5/16 or 3/8, silver-plated copper, so I'm guessing my 90 inch-pounds is wrong. I got that from a torque spec on a LiPO prismatic. What are you using??

I'm making my own bulkhead connectors out of 3/4 or 7/8 copper rod, but don't have any nuts (yet) to test different diameter threads. 

Will be using Nordlok washers and corrosion-inhibiting thread paste:

https://www.galco.com/buy/Burndy/PENA134

Thanks,

Jim


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## major (Apr 4, 2008)

3/8" Brass.......


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## skooler (Mar 26, 2011)

Why not just buy the proper kit? So cheap and readily available.

Sent from my SM-N9005 using Tapatalk


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## GoElectric (Nov 15, 2015)

Hi Skooler,

The problem is room - I don't have the room at the end of the box for the terminal and bolt (!) that is what started me on the project. I have to fabricate a custom bulkhead to stand-off the connections. 

I saw a few bulkhead connectors on EVTV, but even the basic ones are $US80 each x4. Since I have to do the custom piece anyway (3D printing a part), I might as well make the connectors too, instead of shelling-out $US400. The really nice connectors are more than double that price, and I thought about them, but that seems over-kill. The cheap connectors are only rated for 250A (http://store.evtv.me/proddetail.php?prod=batterystudblack), and making something is quite simple once I determine what will work. The 3/4" copper will be about $50, machining is free.

Still, I'd like to see what others are using. Brass is only 28% the conductivity of copper, so I'm hoping to find appropriately-sized copper nuts for a few bucks each, but will settle for brass and then maybe 7/8 copper, as I don't want the nuts to get too hot.

I can post a diagram of what I am making, but don't have it now.


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## major (Apr 4, 2008)

Look at the terminals on DC motors. 3/8" brass bolts in a bushing thru a thick wall steel frame. Takes 2000 Amps on the drag strip regularly and 300 Amps all day long. I don't know what your duty cycle is but if it is an EVcar, I doubt 3/8" brass is insufficient. 

major


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## electro wrks (Mar 5, 2012)

Here's the best price Ive found on these bulkhead connectors with free shipping over $40.00: http://www.racerpartswholesale.com/product/LongacreRacingBatteryThruPanel/Longacre_Electrical_Items#minicart_a 

The voltage rating and fire resistance should be checked out for EV use.


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## major (Apr 4, 2008)

How about: https://www.waytekwire.com/item/36664/Electrical-Power-Bushing/


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## z_power (Dec 17, 2011)

These look like ones in Soliton controllers: https://www.bluesea.com/products/category/27/Feed_Through_Connectors


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## GoElectric (Nov 15, 2015)

Thanks guys. I am surprised to hear 3/8 brass is used in DC motors! I do wonder how hot they get though, as the other two offerings which are also 3/8 brass are only rated for 250 amps (although the price is right). I've been basing some of my guesswork on that 250A, which may be incorrect.

I like those "500A" connectors which are 1/2" brass. But they won't work, as my bulkhead is 1/2", and there are other constraints. 

Our feeling in going for copper was brass should work, but if we are going to go to all the trouble of making them, may as well use copper. Still leaning that way....

Anyone-else out there got something with copper terminals? 3/8"?


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## piotrsko (Dec 9, 2007)

Big difference between peak and continuous current ratings. Peak ratings COULD be verymuch higher.


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## GoElectric (Nov 15, 2015)

Here is the first prototype - the knurled finish is because they will be inserted into 1/2 pvc. 

We went with 3/8" threads on 3/4 copper.


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## major (Apr 4, 2008)

I don't like the external threads on copper. I would have threaded a thru hole in the copper bushing and used a brass threaded rod. Some of the large DC motors (9 & 11" dia) have gone to insert molded brass bushings with internal threaded holes both sides for 5/16"-18 UNC hex head steel bolts. {I never was a fan of approach. GE started it} Needless to say with the bushing, it conducts and not the fasteners. But you'll also have to consider how to apply tightening torque and how to loosen it years from now once it has corroded together without twisting off that copper thread.

Pretty looking part though.

major


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## GoElectric (Nov 15, 2015)

Hi Major,

We pondered this question, feedback welcome. In the end it was simplest to do it this way, but had to go to 3/8" to get the strength. As I posted earlier, we are using 90 in-lbs as a spec, but I forgot to mention above when we put a brass nut on it, the thread only just started to fail around 180 in-lbs. Could have gone brass threads though. With nordlok washers (50 cents each) we can rest-easy without having to push the torque.

I thinnnnk the industrial grade corrosion-inhibitor will keep things from sticking-together, but who-knows. 

Thanks again, I think with brass inserts on copper the current rating would not have been an issue.


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## piotrsko (Dec 9, 2007)

Should use fine threads, rolled are stronger than cut. Btw I'm at 50 inch lbs on my sol1 posts 4 years under hood so far no problem so I am at some loss as to why the focus on high torque.


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## GoElectric (Nov 15, 2015)

Hi. If you are talking about me (focused on high torque) okay, but I didn't think 90 in-lbs was much when I read it. I just want the RIGHT torque, and having just rebuilt an ICE, 90 in-lbs doesn't seem like a lot. That was 5/16" though, right?

There must be guys out there who can confirm (or not) 90 in-lbs. 

We thought about fine threads, but you are the first who is in favor. I'll be speaking to a Mechanical Engineer about it this morning, and if I can understand what he says, I'll post it.

What does "rolled are stronger than cut" mean? You can roll threads??

Thanks - I'm not used-to small torques like 90 inch-pounds on a 3/8 bolt, but it sounds like the copper is up to it, which is the main thing.


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