Ampster
Renewable Energy Hobbyist
How does the tensile strength of aluminum compare to SS?
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link to proper studs and nuts for eve cells?
- Thread starter bgflyguy
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I suspect that surface area does matter. I thought about figuring out the surface contact area for the bolt, when fully inserted, but I need to get some actual work done so I can pay the bills (for all my solar components!).
Bob B
Emperor Of Solar
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I started a new thread about the current flow question. It seems there is interest in this, but it may be buggering up the main discussion.
diysolarforum.com
Current flow from battery cell to bus bar
The discussion came up on another thread about whether or not current flows to the bus bar thru the stud. That discussion was surrounding the use of the stud / flange nut type of connection using a stainless steel stud and nut and an aluminum pad on the battery cell. I wanted to separate the...
diysolarforum.com
Sorry, just saw this post today. From the blog post "Yield Strength in Exhaust Tubing, Aluminum vs Stainless Steel":
My take is that 6061 is better than stainless steel for our battery connections, assuming you don't heat it up. It won't have corrosion problems and has better conductivity.
Taking the plunge, I just ordered M6x15 and M6x20 aluminum hex head bolts. I didn't like the length of the (assumed) stainless steel bolts that came with my cells. I was going to replace them anyhow, so I figured I might as well go with aluminum.
I've posted this before, but it's worth seeing again. The chart is likely referring to pure aluminum, or at the very least, an alloy that may be a better conductor than 6061.
Here is a more impressive chart directly comparing "6061-T6 Aluminum vs. AISI 416Se Stainless Steel", from the MakeItFrom website. 6061 is on top, stainless steel on the bottom. There are many more comparisons on that website. Their tensile strength comparison contradicts the one quoted above, but the two are close enough that I'm OK with 6061.
CAVEAT: I don't know enough to find a truly authoritative source. So I'm going with the theme, "If it's on the Internet, it must be true."
Dhopewell
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I did the estimate for this but didn’t write it down. If you aren’t interested in nerding out now is the time to stop reading.
it turns out there is plenty of contact surface to carry current through stud and nut, but SS has 1/10 the conductivity of copper and the current needs to travel about 6mm from the middle of stud to middle of nut in a 100mm2 conductor. So imagine a 10mm2 conductor.
LF280 terminals have 200mm2 of contact surface and current travels 1mm into my lug. So, the stud path has 6 times the distance and 1/20 the conductivity, ohm says a little less than 1% of current goes through stud. All copper connectors would raise that to around 10%. That would reduce voltage drop at terminal from nearly nothing to ~90% of nearly nothing.
it turns out there is plenty of contact surface to carry current through stud and nut, but SS has 1/10 the conductivity of copper and the current needs to travel about 6mm from the middle of stud to middle of nut in a 100mm2 conductor. So imagine a 10mm2 conductor.
LF280 terminals have 200mm2 of contact surface and current travels 1mm into my lug. So, the stud path has 6 times the distance and 1/20 the conductivity, ohm says a little less than 1% of current goes through stud. All copper connectors would raise that to around 10%. That would reduce voltage drop at terminal from nearly nothing to ~90% of nearly nothing.
Ampster
Renewable Energy Hobbyist
Thanks that confirms my choice of SS studs but there are good reasons for other options. I take issue with the term "proper" in the title. Appropriate is softer but it is really a personal choice based on how one wants to approach the issue. This was never an issue on EV conversion forums because vibration was the biggest driver of connector stability.
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ArthurEld
Solar Wizard
Are you guys saying that shorting a stainless steel screw will cause less sparks?
Dhopewell
New Member
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No, I don’t think that SS is less spark prone. Higher resistance doesn’t mean high resistance. A dead short across lifepo cells will instantly melt stainless. Same for inverter precharging - maybe the spark is less likely to scar the conductor but it will still spark. A resistor seems to be needed to stop that.
ArthurEld
Solar Wizard
I wasn't planning to try it. But I thought since stainless is less conductive it might not cause as much molten metal.
I'm still trying to come up with a good looking cover for my battery terminals.
I'm still trying to come up with a good looking cover for my battery terminals.
I'm going to use kapton tape, but there are vendors on Alibaba that can sell you busbar end covers, or bubar whole covers
Ampster
Renewable Energy Hobbyist
I am just putting a piece of plexiglass or acrylic over my batteries, I don't need covers for each buss bar.
That's the route I'm going to take. I have some scrap plexiglass around here somewhere.
ArthurEld
Solar Wizard
Plexiglass could be good. It would probably need a frame. Or maybe hinges.
This would probably work well-
This would probably work well-
Ampster
Renewable Energy Hobbyist
I ordered the same insulated 10mm wrench from Alibaba, washers, grub screws, DIN 6923 hex flange nuts and used my Bondus hex T handle to hold the grub screws 1/4 turn off the bottom.
15.95US $ |1000v High Voltage Insulator Insulated Offset Box End Wrench Iec60900 Vde Certification Insulation Ring Spanners Handle Tools - Wrench - AliExpress
Smarter Shopping, Better Living! Aliexpress.com
a.aliexpress.com
My crimped and soldered balance lead Y lugs don't fit completely around the grub screws with the washers I've chosen, I might downsize to smaller washers later.
Amy is sending me wider rectangular busbars, once they arrive I'll heat shrink and kapton tape my terminals.
Thanks for posting the Amazon links. I ordered the same grub screws and nuts as you did. I also ordered some blue Loctite for the grub screws. They are scheduled to be delivered today. I am going to use whatever hardware comes with the cells to balance them to make sure all is well before using the grub screws.
I noticed you have your MRBF fuse directly mounted to the cell. Do you intend to leave it there? I am planning on doing the same if you don't see a problem with it. I know there has been discussion about having the fuse directly mounted to the cell but in my case I don't think it will be a problem since my cells will remain stationary.
My 8 cells are scheduled to be delivered Friday. So I need to get moving on my build although I will be taking it slow. Thanks.
ArthurEld
Solar Wizard
I think I read somewhere about being careful not to put too much stress on the stud when mounting the terminal fuse blocks. Since mine will use a big cable I plan to attach the cable to something so it will never put stress on that terminal. I think it might be good to put a non conductive spacer under the unsupported part of the fuse block too. I bet some people make up some kind of mount for extra support so the cell terminal screw doesn't have to hold everything.
John Frum
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kaptop tape may be ugly but it works.
Thanks, those are good ideas. Since I am leaning towards a 24 volt system as opposed to a 12 volt system my cables will not be too large but I will support them.....good idea. I might be able to get by with 4 AWG but I haven't even decided on an inverter yet. Using the online calculators I could get a 2000 watt 24 volt inverter and 4 AWG would be ok up to 4 feet. I don't really need a 2000 watt inverter. Anyways got to get the pack built first. Then I will decide on an inverter.
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