How much Nm torque???

[Frank in Thailand]

I'm trying to find out how much torque the terminal should get to have the bus-bar compressed tightly enough to ensure good contact.
Yes, clean and flat materials

The white paper say:
"The torsion should be less than 8Nm when used"
And
"The internal screw with size M4 is used in the pole. "

I don't have M4.
Those who have followed my latest adventure know I also have less 6mm

When known what torque should be absolutely sufficient, I will test each threaded rod with 1Nm extra.
Those that fail (an already have failed) will be re-tapped with M8.

How much torque for M6.
And how much must it be for M8 to obtain the same compression force as M6 did with that torque?

Google did not help me today, probably more due my fuzzy mind then Google

 

[Frank in Thailand]

Metric Bolts - Tightening Torques

Recommended thightening torque metric bolts.

www.engineeringtoolbox.com

Can be a starting point but someone with a lot more clear mind needs to figure this out.

This is for iron.

Tools/ equipment used during installation process:
- Torque wrench 5-25Nm
- 304 stainless steel rods, nuts and washers (M6 and/or M8)
- Weak aluminium terminals with 6 or 8mm thread, 6mm deep
(Normal iron nuts are 4mm)

 

[Bob B]

The general consensus I have seen from other threads is 4 nm ..... or 35 in/lb.

That torsion spec of 8 nm was found to be the max torsion on the whole pad assembly ... not the studs.

 

[Frank in Thailand]

4Nm?

Beter to switch to digital torque meter.
This one can do 0.3-30Nm
That should be accurate enough


Is the 4Nm the same for M6 and M8?

 

[Bob B]

I'm not sure for M8 ..... maybe someone else will check in.

 

[Frank in Thailand]

This thread:
Thread 'Cell terminal bolt torque - you might be wrong!' https://diysolarforum.com/threads/cell-terminal-bolt-torque-you-might-be-wrong.16828/
Informs a lot.

In a nutshell:
3-4 Nm is enough. (4Nm seems to be 700 pounds/315kg of compression)
5 Mm is stretching it, and you might pull the threads
7-8Nm can/will twist the terminals themselves in the housing

The numbers will be slightly different for M8, compared to M6.
The 7-8 Nm stays, as it's thread thickness independent.

I will test on a aluminium heatsink when my taps and torque meter arrives.
I suppose 4Nm will se the sweet spot.

Alternative is laser or cold welding.

 

[ArthurEld]

This thread:
Thread 'Cell terminal bolt torque - you might be wrong!' https://diysolarforum.com/threads/cell-terminal-bolt-torque-you-might-be-wrong.16828/
Informs a lot.

In a nutshell:
3-4 Nm is enough. (4Nm seems to be 700 pounds/315kg of compression)
5 Mm is stretching it, and you might pull the threads
7-8Nm can/will twist the terminals themselves in the housing

The numbers will be slightly different for M8, compared to M6.
The 7-8 Nm stays, as it's thread thickness independent.

I will test on a aluminium heatsink when my taps and torque meter arrives.
I suppose 4Nm will se the sweet spot.

4Nm is the torque most people agree gives a good connection. More than 4Nm is likely to strip a thread. Less is likely to have a bad connection.

Alternative is laser or cold welding.

 

[Frank in Thailand]

Sorry, no cold welding or laser..
Budget isn't sufficient.
Also hard to explain to spend +2000 on equipment for just this job.

I have a mig welder, done tig in the past.
Tig won't work, it gets way too hot.
Even spots would take ages, and really stretching the temperature limits.

Spot welder like used on the cylinder types of cells would work.
But one would need to spot weld a whole lot of layers before it have enough mass to handle the load.

My drilling to M8 will come first.

If that isn't working, the spot welder is easy enough build with parts already available.
(Contactor, contact button, wires, battery)
Nickel strip need to be bought.
On average the strips are 0.15mm thick.. 10 layer should be enough
???

 

[Varney1241]

I drilled mine for 5/16-16 and used a bottom tap.
Secures with locktite assembled the buss bars with bolts. Minimal voltage drop (.001v) between the terminal and buss bar pulling 175 amps.

 

[Frank in Thailand]

@Varney1241
Just curious, how did you measure?
When I push or pull 175A, I have a "huge" difference in the cell voltage.
(Compared to mild 10-20A push or pull)
Absolutely more then 0.001v
Then again, I don't push or pull 10 kw often

How to measure a good contact connection?

I have parallel, so my internal resistance meter will show for 2 cells.
It's totally accurate up to 0.0001v

Sure, easy enough to see In real life, push +100A and if a connection gets warmer then the rest.. it ain't as good as the rest.

Are there alternative ways to test?

 

[Itohmamma]

I would think an appropriate test would be the resistance after torquing them down. All should be equal to each other equal busbars.

 

[Frank in Thailand]

Yes, but you will need to have battery resistance tester like the YR1035+ (about $35)
I have.
As we are talking about milliohms, the slightest difference on the busbars surface (oxidation) will have huge effect on the readings.
So does the state of charge and temperature.

When you have spotless clean terminal and busbars (as much oxidation free as possible), use proper antioxidation grease like oxiguard, and use as much similar torque on all the nuts clamping down the busbar, you have the most equal contact on all cells.

Afterwards, sure, you should test.
There might have occurred more oxidation (too much) on a connection.

Sad news, more torque isn't going to help.
Remove and clean is the only solution.
More torque will only strip the thread.

3.5-4Nm is in lesser quality threads already too much.
(With the use of loctite in the thermal tread and stud, this is greatly improved, do use primer as aluminium and stainless steel need activator)

It's a great "after putting Humpty Dumpty together" test to see if things are Ok.

But will cost you.
Simple multimeter won't be able to measure milliohms.

Aluminium oxidises in 30 seconds enough to have measurable outcomes when used with LiFePO4.

If you apply oxiguard (or similar) after cleaning the terminal (and busbar) it won't be a problem.
Thin layer is enough.

Please be careful not to lubricate the stud (or nut), as that will affect the torque.
3.5Nm torque on a lubricated stud is a lot more force....
And stress on the weak threads on the terminals.

Do you need a torque meter? Yes.

Do you need the milliohms meter? Not for this, but can be interesting when making larger battery packs, combining internal resistance to have the same over the whole pack, to increase stability.

Laser welding still will give the best results.
You probably am able to find a shop closeby, who can do this not too expensive.
That is how it is intended to be used, and will give the best contact

 

[time2roll]

3-4 Nm is enough. (4Nm seems to be 700 pounds/315kg of compression)

I have welded 6mm nuts on my terminals and set them to 3 Nm. Works fine at 80 amps. So many have searched for the maximum torque.... I am inclined to find the minimum torque when the possibility of pulling threads is so great. I think Off-Grid Garage did a bit on this and found minimal torque worked fine.

I would be curious of a test at 1 Nm or 2 Nm and see if the bus or ring gets warm.

 

[Itohmamma]

Yes, but you will need to have battery resistance tester like the YR1035+ (about $35)
I have.
As we are talking about milliohms, the slightest difference on the busbars surface (oxidation) will have huge effect on the readings.
So does the state of charge and temperature.

When you have spotless clean terminal and busbars (as much oxidation free as possible), use proper antioxidation grease like oxiguard, and use as much similar torque on all the nuts clamping down the busbar, you have the most equal contact on all cells.

Afterwards, sure, you should test.
There might have occurred more oxidation (too much) on a connection.

Sad news, more torque isn't going to help.
Remove and clean is the only solution.
More torque will only strip the thread.

3.5-4Nm is in lesser quality threads already too much.
(With the use of loctite in the thermal tread and stud, this is greatly improved, do use primer as aluminium and stainless steel need activator)

It's a great "after putting Humpty Dumpty together" test to see if things are Ok.

But will cost you.
Simple multimeter won't be able to measure milliohms.

Aluminium oxidises in 30 seconds enough to have measurable outcomes when used with LiFePO4.

If you apply oxiguard (or similar) after cleaning the terminal (and busbar) it won't be a problem.
Thin layer is enough.

Please be careful not to lubricate the stud (or nut), as that will affect the torque.
3.5Nm torque on a lubricated stud is a lot more force....
And stress on the weak threads on the terminals.

Do you need a torque meter? Yes.

Do you need the milliohms meter? Not for this, but can be interesting when making larger battery packs, combining internal resistance to have the same over the whole pack, to increase stability.

Laser welding still will give the best results.
You probably am able to find a shop closeby, who can do this not too expensive.
That is how it is intended to be used, and will give the best contact

Good information and advice.?

 

[Frank in Thailand]

I have welded 6mm nuts on my terminals and set them to 3 Nm. Works fine at 80 amps. So many have searched for the maximum torque.... I am inclined to find the minimum torque when the possibility of pulling threads is so great. I think Off-Grid Garage did a bit on this and found minimal torque worked fine.

I would be curious of a test at 1 Nm or 2 Nm and see if the bus or ring gets warm.

I'm confused..

First, great that you have the ability to laserweld aluminium!!

Tig aluminium welding is usually not advised as the terminal would get too hot.

My confusion is why you would weld nuts on the terminals?

If they are aluminium, you have made the contact area smaller.

If they are (galvanised) iron, it's less conductive.

Stainless steel is, I was told, not possible to weld with Aluminium (via laser welding)

3-4 Nm.
2.8 can work also, but...
Spotless clean.
When you are knowledgeable about welding aluminium, I don't have to explain spotless...
???

Most mortal souls don't have the skills or patience to clean extensive enough.

By using 4Nm you can compensate some "spots".

It won't hurt, if you use loctite (or epoxy) to give the stud more "grip".

Time will tell.
My experience with mechanics (cars, bikes, constructions) and electrical installations that "just tight enough" will provide probelms in the future.

Vibration, and not moving constructions, expansion and contraction.

It takes a few months or years, then you know why you should give it that little extra.

Aluminium wheels always need to be re-tightened after a few weeks as aluminium "gives" a little before it sets.

Obviously that is a lot more torque, same principle.
Just tight enough with aluminium will not be tight enough over time.

Off-grid garage is playing so often with his cells there isn't enough time for the aluminium to set.

You will be surprised.
Torque the nuts on your terminal studs to 3.5Nm and come back after a few (3-6) months.
You will find that the torque has decreased and you can fasten a bit more to keep the 3.5Nm.

Try the same stud and 2 nuts and iron in between.. it will stay 3.5Nm torque.

Your 3Nm will work fine at start
In 3-6 months it's decreased
6-18 months the clamping force is too little and you will start seeing strange behaviour between the cells.

When you do 3.5-4Nm you won't have that probelm.

Still confused...
Why weld nuts in a terminal?

Pictures please!!

 

[time2roll]

These cells came with the welded aluminum nuts. Actually it is a small threaded cylinder on the terminal, no flats for a wrench.
Fairly common, not sure I understand the confusion.
Have been working fine since October. Maybe I will check the torque again soon.

Again my point was to search minimum torque to complete the electrical connection with reliability. All I read is how to get the maximum the fastener can withstand.

 

[newbostonconst]

I have done fastening for Automotive for 25 years and a good rule of thumb is to snug the fastener and then add more then 1/8 but less then1/4 turn....use this if you are lazy and don't want to look up the torque by fastener size and material.

 

[time2roll]

Does the terminal really need 700 pounds of force (4 Nm torque) to have good conductivity? Is 400 OK? 100?

I keep thinking if there was a 100 pound block of concrete with all its weight focused on that terminal all would be fine.

 

[Scph9002]

4Nm is the torque most people agree gives a good connection. More than 4Nm is likely to strip a thread. Less is likely to have a bad connection.

Then the studs are severely undersized jesus christs...

 

[time2roll]

Then the studs are severely undersized jesus christs...

Not the stud that strips but rather the aluminum cell terminal. Too few full threads to grip.