Source of Belleville washers for 300kgf fixture?

HaldorEE

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So if I understand correctly, your saying that finger-tightening a socket is applying twice the recommended torque to busbars/terminals, correct?

I just finger-tightened (through a socket( the 1/4” nuts on single-cell jig I made and when I then used the torque-wrench to apply what I’ve estimated to be 12psi / 165lbs I added anew turn or so to the nut (confirming that a socket finger-tightened applied well under 165 lbs, but your 62 lbs sounds very credible).

Was that as tight as you could go by hand or just snug?

p.s. you could probably start a side business hand-tightening various battery-related things and letting us know the approximate range. I’ve been hand-tightening my bus-bars with a Philips-head screwdriver, for example, and would love to know what force is possible to apply by hand using a Philips head bit between finger-tips.
More like 60%. I don't know where the 4 N.m torque spec came from.

I am just going to lock tight the grub screws in and torque the nuts to some value. I need to do more reading to find out how much.

I am going to sand the battery terminals and bus bars, then apply antioxidant cleaner to make the contact as good as it can be.

I have used ProGold for audio connections. That should work and not risk doing anything bad.
 
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fafrd

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More like 60%. I don't know where the 4 N.m torque spec came from.

I am just going to lock tight the grub screws in and torque the nuts to some value. I need to do more reading to find out how much.

I am going to sand the battery terminals and bus bars, then apply decide cleaner to make the contact as good as it can be.

I have used ProGold for audio connections. That should work and not risk doing anything bad.
You are ahead of me in your build and I’ll be interested to follow in your footsteps since it sounds like you are approaching many of these design consideration much the way I’m planning to.

When I built my first 90Ah 8S LiFePO4 battery last year, I didn’t do any of this stuff and it shows. I now understand that I received two capacity&leakage-deficient cells in that batch and have 2 new cells on the way for a rebuild, so I’ll probably do a rebuild of that battery using all of the knowledge I’ve gained from this Forum (from you and others).

I’m in no rush for my 280Ah build since it’s intended to be the heart of an off-grid solar build that may push out to 2022 or even 2023 now that the tax credit deadline has been extended for 2 years...
 

cinergi

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20 in.lb torque is only 2.6 N.m, no wonder people are having problems stripping threads when tightening the screws on their EVE load cells.

I am definitely going to use a torque wrench when installing the nuts on my bus bars. I think I saw a figure of 4 N.m recommended in another thread? That would be 35 in.lb

Yes, 4 Nm for M6x6 in aluminum.
 

fafrd

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For all the experienced pros on this thread, I’m deciding I probably should invest in a finer-range torque wrench than the 0-600 in-pounds ‘bend-gauge’ model I use for automotive work.

Someone recommended a smaller-range wrench of the same style but I am mulling getting one of the ‘click-type’ torque wrenches like this: https://www.amazon.com/EPAuto-4-Inc...rds=Small+Torque+Wrench&qid=1610342749&sr=8-3

I’ve never used this style of torque wrench before and would appreciate any insight more experienced Forum members can provide before spending my money...
 

HaldorEE

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For all the experienced pros on this thread, I’m deciding I probably should invest in a finer-range torque wrench than the 0-600 in-pounds ‘bend-gauge’ model I use for automotive work.

Someone recommended a smaller-range wrench of the same style but I am mulling getting one of the ‘click-type’ torque wrenches like this: https://www.amazon.com/EPAuto-4-Inc...rds=Small+Torque+Wrench&qid=1610342749&sr=8-3

I’ve never used this style of torque wrench before and would appreciate any insight more experienced Forum members can provide before spending my money...
That is still too big.

I have one like that in 1/4", 3/8" and 1/2" drive. 20 in.lb is lowest setting on it.

A bicycle torque wrench might be a better choice. This one looks interesting.

 

fafrd

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That is still too big.

I have one like that in 1/4", 3/8" and 1/2" drive. 20 in.lb is lowest setting on it.

A bicycle torque wrench might be a better choice. This one looks interesting.

Well my wife and I have recently started to get into biking, so I’m going to see this as an alignment of the stars and go for one ;).

But I take your response to also mean that these ‘ratchet’ style torque wrenches perform as well as the ‘bend gauge’ style wrenches, correct?
 

HaldorEE

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Well my wife and I have recently started to get into biking, so I’m going to see this as an alignment of the stars and go for one ;).

But I take your response to also mean that these ‘ratchet’ style torque wrenches perform as well as the ‘bend gauge’ style wrenches, correct?
Accuracy is same or probably a bit worse (unless you spend some $$$). That little bike torque wrench looks useful. I ride a bike too.
 

fafrd

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Accuracy is same or probably a bit worse (unless you spend some $$$). That little bike torque wrench looks useful. I ride a bike too.
If they are even in the ballpark of being as usable / reliable as the ‘bend gauge’ style wrenches, I’m in.

Among other things, this will allow me to ‘mask’ my purchase as something I’m doing for our newfound fascination with biking rather than my current obsession with building a large LiFePO4 battery ;).
 

HaldorEE

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If they are even in the ballpark of being as usable / reliable as the ‘bend gauge’ style wrenches, I’m in.

Among other things, this will allow me to ‘mask’ my purchase as something I’m doing for our newfound fascination with biking rather than my current obsession with building a large LiFePO4 battery ;).
Advantage to being single. I can spend ridiculous amounts on my van's electrical system without having to justify it to anyone.
 

HaldorEE

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F.Y.I.

I found a source for 120mm x 16mm, M6 braided ground straps rated at 150A. These would work for diagonal bus bars (eliminating the risk of stress on the cell terminals).


For my application (2000W Inverter), 150A is plenty. If you need the full C rating of the cells, you could double them up.
 

Pyke13

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If we use a spring semi compressed at a mid level state of charge any expansion or compression from there is at 15psi. I may be wrong or over simplifying the issue but it make sense to me to just half compress springs rated at 15psi. That gives half the travel of the spring either way for expansion and contraction at the same rate
 

fafrd

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F.Y.I.

I found a source for 120mm x 16mm, M6 braided ground straps rated at 150A. These would work for diagonal bus bars (eliminating the risk of stress on the cell terminals).


For my application (2000W Inverter), 150A is plenty. If you need the full C rating of the cells, you could double them up.
Nice find. Is 120mm long enough to connect cells diagonally?

Those would definitely solve the issue of any stress on the terminals, but at the cost of longer bus wires and greater I^2R losses. I see these are rated for 150A max, but does that mean they have roughly the same resistance as 3AWG wire (0.197 mOhms/foot or 0.07756 mOhms over 120mm)?

The plated busbars that shipped with my cells are about 1.5AWG (halfway between 1AWG and 2AWG and probably represent about 0.14 mOhms/foot or just under 0.03 mOhms over their 2.5” conductance path.

260% the I^2R losses of standard rigid busbars isn’t the end of the world, but is at least worth thinking through...
 

Pyke13

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I’m sure if you speak to any springs manufacturer they will be able to supply a spring with a 15 psi expansion and contraction rate. It can’t be that hard and I’m sure it’s available off the shelf. No need for custom orders
 

fafrd

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I’m sure if you speak to any springs manufacturer they will be able to supply a spring with a 15 psi expansion and contraction rate. It can’t be that hard and I’m sure it’s available off the shelf. No need for custom orders
Oh one of those, yeah I’d seen those earlier. I had the sense they were very large but maybe I was wrong - what is the diameter and length?

Also, at 15GBP each, it’s not a very budget-friendly solution (we need 4).

But yeah, if diameter isn’t too large to be cumbersome and length isn’t much longer than we need (~1mm per cell, meaning ~1/2” FPS 8S), could be an attractive option.
 
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