Battery Terminals - Studs, bolt sizing and ring terminals

[Barold]

So when people build their banks with large LFP cells which come with these relatively small M4 terminal screws, what is the thinking on terminals? for instance my existing battery cables (to charger, breaker, load) are 2 gauge or some even bigger and have the clamp terminals on them. Am I to cut the cable and crimp on new ring connectors to pile together? I can see the balance leads fitting fine but at the positive terminal, I've looked at the Blue Seas terminal fuse blocks but believe there is a mismatch in holes (the terminal fuse block has an M10 hole). Anyone have ideas/solutions?

Thanks!

 

[Leon]

I'd like to know the answer to this too. At the moment I'm tossing up between CALB cells with their M8 terminals and aluminium case cells with M4. I wonder if those puny screws are more trouble than the slightly lower cost is worth.

 

[LukeVader]

What are those m4 base posts made of on the cells? Is there a way to weld/solder some kind of thread adapters into the top of those cells kinda like these in this picture?

 

[EllaBella]

I'd like to know the answer to this too. At the moment I'm tossing up between CALB cells with their M8 terminals and aluminium case cells with M4. I wonder if those puny screws are more trouble than the slightly lower cost is worth.

This is the exact same problem I'm facing. The 100ah CALB cells are 3.3kg each versus the aluminium case are 2kg. But the M8 terminals are far more durable and the M4 terminals appear to be very short and not having much thread left once you've added bus bars and balance cables.

 

[EllaBella]

I'd like to know the answer to this too. At the moment I'm tossing up between CALB cells with their M8 terminals and aluminium case cells with M4. I wonder if those puny screws are more trouble than the slightly lower cost is worth.

For me it's not just the puny screws but also the weight difference. The CALB cells are pretty heavy.

 

[ghostwriter66]

This is the exact same problem I'm facing. The 100ah CALB cells are 3.3kg each versus the aluminium case are 2kg. But the M8 terminals are far more durable and the M4 terminals appear to be very short and not having much thread left once you've added bus bars and balance cables.

Use washers with larger surface areas to maximize connectivity between what you are connecting and the base of the battery terminal and of course you can also by much longer screws to ensure that they reach all the way done to the base ...

Its not the size of the screw -- but how much surface contact you have ....

 

[EllaBella]

Use washers with larger surface areas to maximize connectivity between what you are connecting and the base of the battery terminal and of course you can also by much longer screws to ensure that they reach all the way done to the base ...

Its not the size of the screw -- but how much surface contact you have ....

Thank you, I was worried that the bus bars provided on a lot of the M4 cells wouldn't be thick enough, like in Will Prowse's videos and that the provided screws wouldn't be long enough with the bus bars doubled up, but if I buy a flat strip of copper I can just make thicker bus bars myself and use longer M4 screws.

 

[ghostwriter66]

Thank you, I was worried that the bus bars provided on a lot of the M4 cells wouldn't be thick enough, like in Will Prowse's videos and that the provided screws wouldn't be long enough with the bus bars doubled up, but if I buy a flat strip of copper I can just make thicker bus bars myself and use longer M4 screws.

where I work I often have to make my own busbars because of distance and timing ... but I make my own by sometimes taking copper pipe -- lay it on cement -- put a board on top of the pipe ... and then run my truck over it a couple of times ... makes great CHEAP bus bars ...

Also I have found that Tractor Supply, ACE, and HomeDepot all have M5/6/7 type screws of various length ... as does EBay ...

 

[Steve_S]

There is a few of points to KNOW with LFP cells.
1) You "never" want to bottom out the screw in the hole. You could go through the top or damage the cell.
2) The screw is NOT the current carrier. It is the top surface of the "post" and connection to busbar. Typical post is 20mm wide. (varies by manufacturer)
3) Full surface contact between the Bus Bar and Post top is essential. A light coating of No-Ox / Ox-Guard between the post & bar is prudent. Most especially in a Marine environment but any mobile application or if in a damp area. Generally just a good idea period.
** NOTE, best to wipe off the terminal tops with rubbing alcohol so there are no machine oil residues left BEFORE no-ox applied & bus bars attached.
4) Tighten your screw and BY HAND spin it down as tight as you can, then back it off 1.5 turns (preventing bottoming screw). If you need to use a washer (use stainless, NOT Galvanised or zinc coated)
5) NEVER over tighten the screws, stripping these holes is nasty !
6) DO NOT USE SAE SCREWS !!! These are Metric ONLY !
7) If you need to buy screws, use Stainless ! or Copper/Brass. NO Zinc or Galvanised !
8) If you need to make bus bars, best to use 110 Copper Bar Stock, drill slightly slotted holes (matched to bolt size) so there is little back & forth movement. (pipe bashing is, well a BODGE JOB )
9) IF you have a mobile installation subject to vibration & movement, the use of a "little bit" of Loc-Tite Blue is fine just don't goop it a tiny dab will do. Alternatively, a lock washer or serrated type washer can be used. BTW: a dab of nail polish works just as well and is cheap BUT not accepted by electrical wizards... <<grins>>

The screws for the bus bars rare not intended or designed to handle stresses. Ensure than when you assemble your pack that everything is snug and that the pack itself is bound together with either strapping, 2-way tape so none of the cells can move independently or twist, they should be assembled so the pack of cells is essentially "one solid block". That will prevent any vibration issues, potential twisting when being handled.

The Devil is ALWAYS in the Details !
Hope that helps
Steve

 

[ghostwriter66]

There is a few of points to KNOW with LFP cells.

8) pipe bashing is, well a BODGE JOB

and YES - I had to look the word up ...

 

[EllaBella]

I was just worried with the screws not being long enough to have enough threaded and the vibrations from the van causing a screw to loosen or even rip out if I go over a nasty pothole. Also with the bus bars on most cells looking very thin and probably needing to be doubled up unless I buy or make my own.

If the copper pipe method works for people then it's fine, there are far worse ways of making bus bars ?

Do you have that copy and paste saved to your desktop? ?

 

[ghostwriter66]

I was just worried with the screws not being long enough to have enough threaded and the vibrations from the van causing a screw to loosen or even rip out if I go over a nasty pothole. Also with the bus bars on most cells looking very thin and probably needing to be doubled up unless I buy or make my own.

If the copper pipe method works for people then it's fine, there are far worse ways of making bus bars ?

Do you have that copy and paste saved to your desktop? ?

No .. just a fast typer .. LOL

But @Steve_S is right about making sure you don't hit bottom with the screws to punch through ... and using loc-tight to keep the vibration down

 

[Bob B]

I am also thinking the screw carries some of the current. There is a connection to the battery post on the bottom of the busbar, but there is also a connection on top of the bus bar from the screw / bolt washer.
The terminal connection is also on top of the busbar.

 

[EllaBella]

No .. just a fast typer .. LOL

But @Steve_S is right about making sure you don't hit bottom with the screws to punch through ... and using loc-tight to keep the vibration down

I meant about the copy and paste with Steve's post, sorry for the confusion.

 

[mburris]

There is a few of points to KNOW with LFP cells.
1) You "never" want to bottom out the screw in the hole. You could go through the top or damage the cell.
2) The screw is NOT the current carrier. It is the top surface of the "post" and connection to busbar. Typical post is 20mm wide. (varies by manufacturer)
3) Full surface contact between the Bus Bar and Post top is essential. A light coating of No-Ox / Ox-Guard between the post & bar is prudent. Most especially in a Marine environment but any mobile application or if in a damp area. Generally just a good idea period.
** NOTE, best to wipe off the terminal tops with rubbing alcohol so there are no machine oil residues left BEFORE no-ox applied & bus bars attached.
4) Tighten your screw and BY HAND spin it down as tight as you can, then back it off 1.5 turns (preventing bottoming screw). If you need to use a washer (use stainless, NOT Galvanised or zinc coated)
5) NEVER over tighten the screws, stripping these holes is nasty !
6) DO NOT USE SAE SCREWS !!! These are Metric ONLY !
7) If you need to buy screws, use Stainless ! or Copper/Brass. NO Zinc or Galvanised !
8) If you need to make bus bars, best to use 110 Copper Bar Stock, drill slightly slotted holes (matched to bolt size) so there is little back & forth movement. (pipe bashing is, well a BODGE JOB )
9) IF you have a mobile installation subject to vibration & movement, the use of a "little bit" of Loc-Tite Blue is fine just don't goop it a tiny dab will do. Alternatively, a lock washer or serrated type washer can be used. BTW: a dab of nail polish works just as well and is cheap BUT not accepted by electrical wizards... <<grins>>

The screws for the bus bars rare not intended or designed to handle stresses. Ensure than when you assemble your pack that everything is snug and that the pack itself is bound together with either strapping, 2-way tape so none of the cells can move independently or twist, they should be assembled so the pack of cells is essentially "one solid block". That will prevent any vibration issues, potential twisting when being handled.

The Devil is ALWAYS in the Details !
Hope that helps
Steve

What thickness copper bar stock? It will be for a 16s x 3.2 x 180ah.

 

[onemorebattery]

In case anyone is wondering if there is a difference in electrical conductivity between C110 bar stock and the C122 copper tubing at Home Depot the answer is no. Both are 99.9% copper. There is a slight difference in chemistry due to the way the copper is processed. C110 contains a maximum of 0.04% oxygen and C122 is maximum 0.02% phosphorus.

C110 Copper

C110 Copper O60 (soft / annealed) temper
Physical and Mechanical Properties	Ultimate Tensile Strength, psi	31,900
	Yield Strength, psi	10,000
	Rockwell Hardness	F40
	Machinability	20% of free-cutting brass rod (C360)
C110 Copper H02 (half hard) temper
Physical and Mechanical Properties	Tensile Strength, psi	42,100
	Yield Strength, psi	36,300
	Rockwell Hardness	B40
	Machinability	20% of free-cutting brass rod (C360)
C110 Copper H04 (full hard) temper
Physical and Mechanical Properties	Tensile Strength, psi	50,000
	Yield Strength, psi	45,000
	Rockwell Hardness	B50
	Machinability	20% of free-cutting brass rod (C360)
Chemistry	Copper (Cu)	99.9%
	Oxygen (O)	0.04% max

C122 Copper

C122 Copper
Physical and Mechanical Properties	Ultimate Tensile Strength, psi	32,000
	Yield Strength, p	10,000
	Machinability	20% of free-cutting brass rod (C360)
Chemistry	Copper (Cu)	99.9%
	Phosphorus (P)	0.02% max