Using 4 AWG wire with a SB50 Battery Connector

We are in the process of trying to decide if we want to use 4 or 6 AWG wire for our wiring from battery to the power distribution board. I have heard of multiple teams doing this but I hadn’t seen a full discussion of if this was a good idea and what to watch out for.

The primary reason for not doing this seems to be crimping the wire to the SB50 contacts. Are there other reasons or concerns?

I have seen this done correctly but it seems like it can quite easily go astray like in this picture:


What other failures have you seen and how do you mitigate them?

Do you test these connectors after you make them? What does that test look like?

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I bought some 4awg wire to test making new battery leads, i wasn’t able to get the wire into the Anderson contact enough for my liking so we decided to just use 6awg since that’s what the contact is designed for. If we used less flexible wire it probably would’ve fit better but that just creates another headache.

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Somewhere in CD land is a white paper that shows how to make and use an expansion tool that stretches the SB50 terminal out just enough to get a 4GA to fit.

Found it.

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https://team900.org/blog/Battery-Upgrade/

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We have been using 4 gauge with SB50 for a while now. The wire we use is McMaster 6948K92. With some care getting all the strands into the contact isn’t that difficult. We have more difficulty getting all the stands into the lever connector on the PDH.

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What have you done to be able to get the strands into the PDH? More twisting and straightening? The minimum gauge the PDH is rated in the power input is 4 AWG Bare Stranded, according to REV.

Mark if you could link to this instead, we’d appreciate it because then we can track the analytics on it.

All, we’re still doing this and I’m happy to answer any questions on it.

No, we’ve not seen any interesting or notable failures like the one shown in the OP.

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The paper on the website is saying “You need access”

That’s odd. Should be fixed now.

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How do you know that this is better? Have you done any testing that confirms an improvement?

What would you say to a team on the fence about doing this? How would you convince them that this is a benefit?

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I’d probably not seek to sell this to you as something “better” than most alternatives [1]. It’s certainly not better, on certain metrics, than using the connectors as intended by the manufacturer.

I would only offer this as A Working Methodology for putting 4 AWG wire into SB50s.

Yes we have data that supports this approach, but it’s internal to the organization.

[1] Exception: I have no qualms about saying it’s better than trimming excess strands that don’t fit into the lug.

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I’m going to say this looks like a short strip length failure, not a 4ga wire into the “6ga” SB50 contact issue. I have been using this combo for several years without issues. I find when using high strand OFHC cable, you usually don’t need to pre-stretch the contact, and even then I only slightly flare the entry to help capture rebel strands.

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I wasn’t just talking about the crimp/contact style, more the entire 4 vs 6 AWG debate. Has anyone done resistance testing using the same components just 4 vs 6 AWG cable?

No measured data but we haven’t had a single battery/energy problem in a match since we switched to 2/4 gauge and SB120’s 5 years ago.

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Full disclosure, I’m the one that cut the contacts open :slight_smile:

Have you cut any connections open? What we are seeing is that when inserting the wire strands it appears to fully insert, but my guess is we are seeing some insulation movement along with some birdcaging so the gauge of the wire is changing ever so slightly towards the end.

When I cut the 4awg wire there was a pile of lose strands about 1/8in long in the empty contact section. We are seeing this with other seemingly good 4awg sb50 contacts as well, but only visible if you cut/destroy the contact.

We do not see this with any of the tested 6awg and see a very tight crimp across the entire contact.

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This crimp was made with the wrong size die. I can tell because the flashing on the side of the crimp is too thick. Also, the wire wasn’t inserted far enough.

The flashing on this crimp also looks a bit too thick, maybe not the wrong sized die, may just not crimped hard enough.

Here is a section I did of a #00 ring terminal, and an example of the terminals as finished.

The wire and knock-off burndy crimper and die I used for this specific size.

The steps are not complicated, but must be followed:

-Bleed your crimper’s hydraulic circuit.
-Compress the crimp until the hydraulic circuit is bypassing
-If the flashing is too thick or non-existent you have probably used the wrong die
-Pull-test a sample. A decent 6awg crimp should hold over 300lbf. Also, section and polish a sample or two.

This is how we’ve testing big terminals in the past.
image

image

This was the 6awg ring terminal failure mode.

image

From using a $20 hammer crimper.

tl;dr - crimping in example pictures looks suspect to me, strongly suggest checking die choice and crimper condition/maintenance before drawing any drastic conclusions.

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Oddly enough… I was just testing 4 and 6 cables and crimps!

Yes, there’s a measurable difference between 6 and 4. Its tricky to pack all the strands into a stock Anderson lug, but I can do it reliably. I made the punch and die to expand stock Andersons to be any easy fit on 4; its worth the effort to make a good tool for this!

The “sensible tug” for these wires is “as hard as you can pull”. Really. If you can get it out, its not a good crimp!

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The strands should break at the base before the crimp fails for this style iirc.

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Oh, I should also note: soldering after crimping stiffens the wire to crimp joint… a LOT. Its much more likely to fail with repeated bending. Plus, even rosin flux will add some corrosion over time.

Yes, I saw a small, consistent, decrease in connection resistance with soldering. No, I do not endorse doing this. Its tricky to do without doing the crispy critter thing, and the stiffening above is a big downside.

I’ve read through the paper and it is good but not a lot of teams have access to the tools needed to make the items necessary to do this. We have the press and a small lathe but i don’t believe our lathe could make the swaging tool and we have no way to make the contact holder. It would be cool if someone produced and sold some of these items.

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