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Broke terminal bolt on new Victron MPII inverter

HalfBaked

HalfBaked

Ever the student
Joined
Jun 6, 2023
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215
Location
Upper Mississippi Delta
Yesterday, after nearly a week spent fully assembling a new complete system ordered from CC, I was torquing all the connections. The final connection to the Victron MPII 3kva inverter negative, the terminal bolt twisted off. The torque spec is 12nm, my wrench goes to 11nm and had just successfully torqued over 20 other connections.

While doing a little research on the issue yesterday I found someone with the exact model inverter, who broke the exact same bolt. https://community.victronenergy.com...ii-battery-terminal-bolt-snapped-sheared.html

I sent an email first thing this morning to CC to see how to proceed, will update as it evolves.

Meanwhile, does anyone know a fix, or will any attempt invalidate the warranty?

Considering getting a Phoenix to fill in until this is fixed.

Thoughts?
 
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Ouch.

This is why I rarely use a torque wrench. Have you had yours calibrated recently? They are famous for getting out of true and then you're over or under torqueing everything without knowing it. Also since your wrench only goes to 11nm, you were torquing at the very end range of your wrench and I could see that the end range would be a likely place where it dramatically becomes less accurate. Instead, using a (calibrated) wrench that goes from 0nm to 33nm, would likely give you a much more precise torque.
 
Regarding the wrench, it was new, seemed to be working as expected for the previous nuts. I only have a photo at the moment.
 

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Brett V said:
Harbor Freight ?
Click to expand...

Sure looks like it. I have one that I have used for 15+ years and never had an issue. But, the click (light thump really) is so light at the smaller settings that it can easily be over torqued if you're not paying attention.

ETA: If it were me, I'd have it torn apart trying to fix it myself.
 
One wonders where manufacturers get these torque figures from. For example, the installation manual for Sunsynk 3kW it shows 5.2Nm is recommended.
 
So an update...

Since the inverter is new, I didn't want to do anything to invalidate the warranty so I contacted Current Connected via email. Got a reply within an hour, RMA started with Victron, new PCB is on the way to CC.

Instead of being down for who knows how long, I decided to order a second MPII, as I am beginning to learn about redundancy. 1 is definitely none. This will also open up other dual inverter options.

Dexter @ CC has been really helpful through the entire process and has made it as painless as possible, including a significant unsolicited discount on the new inverter. This company knows how to treat customers, whether ordering or warranty support, things tend to happen today rather than tomorrow.

I'll continue to update as it goes.

And I don't think I can ever trust another torque wrench.
 
Grend said:
One wonders where manufacturers get these torque figures from. For example, the installation manual for Sunsynk 3kW it shows 5.2Nm is recommended.
Click to expand...
Doesn’t the manual state max torque? I can see how some think that’s the torque spec.
 
HalfBaked said:
So an update...

Since the inverter is new, I didn't want to do anything to invalidate the warranty so I contacted Current Connected via email. Got a reply within an hour, RMA started with Victron, new PCB is on the way to CC.

Instead of being down for who knows how long, I decided to order a second MPII, as I am beginning to learn about redundancy. 1 is definitely none. This will also open up other dual inverter options.

Dexter @ CC has been really helpful through the entire process and has made it as painless as possible, including a significant unsolicited discount on the new inverter. This company knows how to treat customers, whether ordering or warranty support, things tend to happen today rather than tomorrow.

I'll continue to update as it goes.

And I don't think I can ever trust another torque wrench.
Click to expand...
Did they have a recommendation for low torque fasteners?
 
Maybe something like this?

RIMKOLO 1/4" Drive Torque Screwdriver Wrench Set, 36-Piece 10 to 65 In.lb Torque Wrench Set for Maintenance Tools Bike Repairing and Mounting https://a.co/d/4iQRlls
 
Soft metal (brass) plated (hidden) for terminal studs just ticks me off. Some of the other places I’ve found them with either no torque specs or buried in the literature(mouse print). Trolling motor HD connect, and Buss breakers.
IMG_0866.jpegIMG_0867.jpeg
 
Skypower said:
Soft metal (brass) plated (hidden) for terminal studs just ticks me off.
Click to expand...
There are a LOT of plated brass terminals in the solar industry. Brass is a good conductor - what would you recommend instead?
 
HighTechLab said:
There are a LOT of plated brass terminals in the solar industry. Brass is a good conductor - what would you recommend instead?
Click to expand...
In my opinion, a fastener should never have to be depended on as a current conductor. What is lost by the low torque of a better conductive fastener is offset by what could have been a better compressive force between the actual working contact surfaces. However, I understand why Victron did this in this case. Viewing the OP picture closely, it appears circuit board top surface is a thinner foil and the back probably has the thicker conductor so the stud is part of the conductor through the board to the top. Not what I would like. Depending on the plating process, plating brass can lead to “hydrogen embrittlement” right at the root of the threads. The failure could be this, just plain bad luck or possibly a bad torque wrench. My fastener of choice (but not for this case) would be zinc, tin or silver plated steel with the tensile strength of a comparable grade 5 bolt. Nothing fancy, stainless is over rated. If you’re worried about galvanic corrosion between alloys use a good non carbon or non metallic containing dielectric in and around that junction. NO-OX-ID A Special or “Marine Green grease” are excellent because they are Ph neutral thus can’t work like an electrolyte and keep air and moisture away from the juncture.
 
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HalfBaked said:
And I don't think I can ever trust another torque wrench.
Click to expand...

I do use a torque wrench but don’t trust it. What I mean is I set the torque setting then slowly start to tighten it. “does this feel right?” as I go. I only tighten to what feels right or reasonable. I might go a tad more than that to see if I hit the click of the wrench, if not I’ll stop. So I trust my own hands first and the wrench second. To set the wrench and trust it completely is just asking for trouble.

Before I learned this skill, I completely bent and wrecked my rebuilt-by-me carburetor because I over tightened it. I didn’t own a torque wrench at the time and assumed I should just tighten ‘er down good and tight. Car got about 2 miles to the gallon after that…

What I’ve learned over the years both with and without a torque wrench, generally it’s better to go a little light than too tight. Especially with plumbing, but it works good for about anything.

When I started using a torque wrench to tighten my lug nuts on my car and truck wheels, I was amazed at how light the spec torque is. For years I had really been cranking down on them, which I now know isn’t necessary. Unsure of the accuracy of my torque wrench, I went to the local tire shop, who know what they’re doing and they had the same result as my torquing.
 
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