A bolt by any other name, is still a bolt

Boondock Saint

Solar Addict
I want to replace the M6 bolts that came with my batteries from China with SS and slightly longer.

The busbar is 1/4" thickness and I'm not convinced I'll need washers / lock-washers. I would however like for the head to be as large of surface area as possible. I don't know if that's even a variable.

The hole depth in the battery is 6mm. The busbar is appr 6.5mm. In order to bottom out a bolt against this busbar I need appr 12 - 13mm bolt thread length.

Then there's the thickness for the leads from the BMS terminals.

I have ZERO aspiration of going to any big box store and finding SS M6 bolts with this thread length.

So I'm asking all the rocket surgeons here for resources they know and trust to purchase more than qty = 70 pc.

THANKS in advance.
 
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svetz

Works in theory! Practice? That's something else
Home Depot and Lowes carry stainless steel M6, Lowes might have the correct length. Amazon has a bigger variety.
 
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Boondock Saint

Solar Addict
Sure sure, but every time I go TO THD they never have the metric stuff in stock, always a time waster.

I have a few selections from Amazon I'm looking at, but I can't say as to the quality of the products.

There's no Tacoma Screw or Fastnal place around where I'm at now.


I found some resources in this DIY thread to follow up on.
 

Boondock Saint

Solar Addict
I had not considered the "M6 x 30mm Socket Set Grub Screws Cup Point 201 Stainless" type of threaded connection, but I see the benefits of it now. Being able to torque this and then hold it in place while torquing a nut down seems like a good idea to prevent stripping the cell threads and having to tap again.

30mm seems excessive though and would leave too much above the nut to try and insulate, more work.


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labeeman

Solar Enthusiast
I use ebay for my hardware only takes 3 or 4 days to get and in large quantities, I needed 500 m6 flange nuts for my batteries no store around me will have that many.
 

Boondock Saint

Solar Addict
Righton. I have them in my cart already. I spoke with this most excellent customer service gal at boltdepot.com.

I need 66 so I ordered 70. They will ship the dreaded USPS but will add tracking and signature required for no additional cost. :D

I found there the Metric set screws, Allen, Cup point, Stainless steel 18-8 (A-2), 6mm x 1.0mm x 20mm and also the Metric flange nuts, Class 10.9 steel plain finish, 6mm x 1.0mm

8736 - Metric set screws, Allen, Cup point, Stainless steel 18-8 (A-2), 6mm x 1.0mm x 20mm $0.26 $18.20
17696 - Metric flange nuts, Class 10.9 steel plain finish, 6mm x 1.0mm $0.08 $5.60

If I understand this correctly, one would use an allen wrench to set the screw in place, mount the HW, then while keeping the screw secure by fores, set the flange nut tight. That about sum it up?

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Boondock Saint

Solar Addict
Would you agree that the two products listed are an appropriate combination when used as prescribed for the stated reasons?

PayPal is waiting me for me to make up my mind :D


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jjkd

New Member
I use 20mm set screws, flange nuts and dished washers with stock/thin busbars, and 25mm for my system with 1/4 inch busbars.
 

Boondock Saint

Solar Addict
I use 20mm set screws, flange nuts and dished washers with stock/thin busbars, and 25mm for my system with 1/4 inch busbars.

Oh NOW you show up, where have you been all day? :D JK

I really want to have as little of the screw surface exposed after the nut as possible. How much extra did you end up with on the 25mm set?

Would you NOT go 20mm with the 1/4" BB?

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bgflyguy

Solar Enthusiast
I just went the grub screw and flange nut route. 15mm worked for me, but barely. 20mm would have been better.

I added red loctite so I could torque the nuts. Buy the inactive metal variant. I went with what was on the shelf and they slipped a bit. Someone on here recommended taping the terminals and using a drill bit by hand to cut the tape off the holes. It's definitely worth the extra time to keep it tidy.

Keep the surfaces clean and scratch free and use acetone and anti corrosion something. Off grid garage on youtube went through a whole thing polishing his terminals because of bad connections. I was seeing the same behavior as him. mine was worse because of higher amps. I had hot terminals at 100a. You could see the extra resistance pulling the cells out of balance on the bms. Take the time to get it right while you are swapping to the grub screws. It makes a difference.
 

Gazoo

Dumb Dumb
Ya roger that.

So that's 1 vote for the 20mm and 1/4" combo.

Anyone else?

Beuller . . . Beuller . . .


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I used 20mm grub screws and with the 2mm busbars doubled up there is pleanty of room for the BMS ring terminal. I also used a thread locker. Holding the grub screw with an allen wrench while tightening the nut is fine. But how are you going to measure the torque applied to the nut? There are torque wrenches that will work but they are expensinve.

If you screw in the grub screw with a thread locker applied, then you don't have to worry about the grub screw turning while tightening the nut and can use a traditional torque wrench. If too much torque is applied the grub screw will strip upwards because the nut is pulling up on it. Ask me how I know... :)
 

jjkd

New Member
Oh NOW you show up, where have you been all day? :D JK

I really want to have as little of the screw surface exposed after the nut as possible. How much extra did you end up with on the 25mm set?

Would you NOT go 20mm with the 1/4" BB?

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My digital caliper shows 5.81mm above the flange nut, so it seems to me that you could get away with 20mm as long as you don't have much extra going in there. The terminals where the BMS monitor ring terminals are attached show about 1mm less, so I'd guess you'd be pretty much flush plus or minus a bit. This is on 280 AH cells that seem average in all respects.
 

Boondock Saint

Solar Addict
Ya to be honest I think the 20mm offering is the one to go with. I thank you for your expert advice

I'm gonna pull the trigger now.

Cheers
 

time2roll

Photon Sorcerer
My local Ace Hardware has these. Picked up a couple 8, 10, 12 mm length to test fit what is needed for each terminal depending on the number of wires stacked.

In hindsight I might prefer the conductivity of aluminum or copper screw for my next build.
 

Boondock Saint

Solar Addict
I also used a thread locker. Holding the grub screw with an allen wrench while tightening the nut is fine. But how are you going to measure the torque applied to the nut? There are torque wrenches that will work but they are expensinve.

If you screw in the grub screw with a thread locker applied, then you don't have to worry about the grub screw turning while tightening the nut and can use a traditional torque wrench. If too much torque is applied the grub screw will strip upwards because the nut is pulling up on it. Ask me how I know... :)
I could use threadlock to the extent it doesn't affect the battery thread to screw current contact area.

I probably won't use a torque wrench on the flange nut, just "prett damned tight" and some threadlock and call it good. 64 times . . .


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