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robo
14 June 2013, 2020
Three questions about (2/0 Magna) cable lugs:

1. How much of a lug mounting hole mismatch is/is not tolerable? E.g. using a 3/8" holed lug on a 1/4" CALB cell terminal. Angled lugs with 1/4" holes seem hard to find.

2. How much could a flat lug be realistically bent? 20 degrees...40 degrees...none? Obviously no bending is best...and repeated bending is worse with work hardening and brittleness (this can include high frequency vibration...ask me how I know).

3. Finally, I have a cable clearance issue on an Alltrax terminal that a 1/4" conducting spacer would solve well (sandwiched between cable terminal and Alltrax terminal). Could/should this be done with a copper or aluminum washer/spacer? I would protect this junction to avoid shorting against the spacer.

Just trying to stay alive while being practical.

ARC EV Racing
15 June 2013, 0319
2. I've gone to about 45 degrees in the past. As you say no bending is best but I've probably done this a couple of times per build and never had a failure yet.

Never run into you other two issues so I'll leave that to others to comment.

Athlon
15 June 2013, 0543
hole mismatch is not a real issue as long the bottom of the lug still in a good contact with the conductive parts , the current is not carried inside the screw but by direct contact between the lug and the terminal , I used several time M10 lug on M8 terminals and never got any issue .


Interposing something between the terminal and the lug can be triky as you are adding a point of failure , be sure to use clean flat brass washer , NEVER NEVER use iron or steel washer , motor current is AC , steel when working with AC is an high impedance (almost insulant) material so will turn red hot in a very short time.


4563

in this picture you can see the difference between AC motor wire when used with a direct contact between the Curtis Terminal and the wire (above) and with a steel nut interposed between the motor contact and the lug (below) , current was as little of 250A , but the steel turned red hot in a few moments.

lugnut
15 June 2013, 0559
I second what ARC and Athlon have told you. Plus, I ask why is there a mismatch in #1 of a 2/0 lug and 1/4" terminal? It doesn't sound like 2/0 is warranted for capacity of a cell using 1/4" terminals. Is a 1/4" fastener sufficient to properly clamp and secure a 2/0 lug and cable?

Having said that, I have actually had similar situations (1/0 on a M6) where I had to find undrilled lugs and drill them to the proper size.

robo
15 June 2013, 1139
Thanks guys.

Arc-ev, thanks. I suspected people are bending lugs. Glad you've had good results.

Athlon, thank you for the interesting info. I hadn't considered brass (and I agree, steel is not an option). I'm now considering using stacked lugs as spacers with the round cable crimp part removed (probably just two of them). In this case, I know the tinned copper is rated, tested, same shape, and not a dissimilar metal (to help obviate corrosion which would be really bad in a connection like this).

Lugnut, good concerns. I have .25"/M6 flat lugs for 2/0, so they "should" be structurally good. But, I couldn't find non-flat/pre-bent lugs for M6. Just for 3/8". That's why I asked about hole mismatches and/or bending (the .25") flat lugs. From your comment, bending the .25" lugs without good cable support now sounds like possible trouble...and maybe that's why pre-bent M6 lugs are hard to find.

I'm doing everything with 2/0...partly for convenience and partly for lower resistance with relatively longer cable runs to my pannier cell packs.

robo
15 June 2013, 1155
Also, here's wikipedia's table of various metals' resistivity:

http://en.m.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

I imagine choosing an appropriate conductor also includes other factors like corrosion resistance, material strength, and in the case of gold...the cost!

Too bad superconducting cables & lugs aren't available...at least at practical temps.

podolefsky
15 June 2013, 1501
Second what was said about about 3/8 hole with M6 screw should be fine. You'll still have lots of contact area. I'd recommend making a little spacer from 3/8" OD aluminum tube. That will help keep the lug centered - not a big deal, but something I've done just because.

Some copper lugs can be bent, but I've had bad luck with Magna lugs. They're pretty brittle. I've never been able to bend one without it breaking or severely weakening.

Also 2nd on brass washer, or 1/4" thick bushing. McMaster has brass bushings - that will keep you from having to stack washers, which makes even more points of contact.

My 2c on 2/0 is that it's slightly overkill for a 450A controller, but since the cost over 1/0 or even 2 AWG is pretty small, you might as well if you can fit it. Alltrax actually recommends 4 AWG cable for their 450A controllers, which seems pretty small to me (I've run 100A through 4 AWG and it gets hot fast).

I just did a build with GBS 200Ah cells - they use M6 screws even though they're capable of well over 1000 A. We used 2/0 cable. I have M6 screws holding my handlebars on - I would hope they'd be strong enough for a cable lug.

robo
15 June 2013, 2051
I'll look into a brass bushing with an eye out for adequate surface area.

Awhile ago, I ordered both Magna and AC Terminal brand lugs from here:

www.cloudelectric.com/category-s/297.htm (http://www.cloudelectric.com/category-s/297.htm)

The AC Terminal lugs look as thick as the Magnas. Nice lug and a bit cheaper. They also bend pretty well. I bent a flat lug to ~30 degrees and it didn't feel any less stiff during the bend.

Haven't bent one of the Magnas yet, but now I know what to expect.

lugnut
15 June 2013, 2109
I just did a build with GBS 200Ah cells - they use M6 screws even though they're capable of well over 1000 A. We used 2/0 cable. I have M6 screws holding my handlebars on - I would hope they'd be strong enough for a cable lug.

The GBS cells have 4 screws per terminal, right? And the handlebars likely have more than just a single M6 threaded into aluminum. A single M6 screw is very strong. But you need to consider the structure and material of what is being compressed and secured.

podolefsky
15 June 2013, 2133
The GBS cells have 4 screws per terminal, right? And the handlebars likely have more than just a single M6 threaded into aluminum. A single M6 screw is very strong. But you need to consider the structure and material of what is being compressed and secured.

The 200 Ah GBS pic online is 4 small screws, but the ones we got were a single M6.

podolefsky
15 June 2013, 2145
I'll look into a brass bushing with an eye out for adequate surface area.

Awhile ago, I ordered both Magna and AC Terminal brand lugs from here:

www.cloudelectric.com/category-s/297.htm (http://www.cloudelectric.com/category-s/297.htm)

The AC Terminal lugs look as thick as the Magnas. Nice lug and a bit cheaper. They also bend pretty well. I bent a flat lug to ~30 degrees and it didn't feel any less stiff during the bend.

Haven't bent one of the Magnas yet, but now I know what to expect.

I've used 1/8 thick copper bar for some short runs where I didn't need the flex of cable. I've also got a lug bolted to bent copper bar, all sealed in heat shrink, going to controller negative. I bent it 90 deg no problem. Not sure why magna lugs are so brittle.