[PSA] Make sure to properly prepare your connections to aluminium terminal posts in order to ensure low contact resistance.

VagueDirector

Battery Addict
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Jul 20, 2020
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I recently noticed the cell voltages of my 2.3kWh LiFePO4 system were unexpectedly deviating. After running my computer setup with it (~25A@12V) for a few hours, one of the cells was much lower than the others. This is odd as I know they have closely matched capacity. So I opened the case and went probing around with the multimeter. (The cells are arranged as 2P4S for reference.) That's when I noticed that the first parallel pair was at completely different voltages/SOC, one cell was at ~3.15V while the other was at ~3.25V. When I probed a cell terminal bolt and its attached busbar saw a 70mV difference! These bits are directly bolted together, there should be no voltage across them at all when the system is at zero load.

What happened is when I built the system ~6 months ago I didn't sand the aluminium terminals to remove the oxide layer. I was fixated on issues such as cell balancing, cell compression and terminal bolt over torque that I completely overlooked this in the excitement of building a new system. I assumed the cell voltage discrepancy was normal and down to manufacturing tolerances.

To fix it I completely redid the connections by sanding the terminal posts and busbars with fine grit sandpaper, and then immediately applying dielectric grease to prevent oxidation. After re-assembly the cell voltages as read on my well calibrated BMS are now always within 5mV of each-other. There is also <0.5mV between the terminal bolts and the busbars. I've also noticed the batteries now run a little cooler under moderate load, as they are no longer sinking heat from poor connections.

Some images of the system for context:
1608365804128.png1608365861402.png
 
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Off-Grid-Garage

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I'm in the same boat. Built the system in a 16s configuration and did not worry about cleaning or sanding the terminals. The consequence is now that I have some cells peaking high or low all the time. Loosening the bolt just a quarter turn and tighten them again mostly fixes it temporarily. Voltage differences up to 0.1V I have observed at 50A load on the 48V pack.
So, in my over-excitement, I have totally forgotten about all this and just wanted to get the battery going. Now I have to remove everything again and sand/clean all contacts properly.
1613519258105.png
 

Bazzar

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I just made a post about this myself. Seems like a commonly overlooked detail that can make a world of difference.
I used a green scotch bright on the terminals and busbars and clean them up after with cotton swabs and a bit of rubbing alcohol.
 

Off-Grid-Garage

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What are you guys using in between, any grease like this?
It sounds ideal...

Conductive Carbon Grease​

Lubricates and improves electrical and thermal connections between sliding surfaces, while providing protection from moisture & corrosion. Excellent for use on switches and EMI shielding applications. Industrial, trade and hobby use.

• Prevents normally closed switches from corroding in place.
• Reduces make-break arcing and pitting of switch contact surfaces
• Improves the connection between irregular or pitted contact surfaces
• Reduces EMI noise by maintaining a continuous path between conductive surfaces
• Thermally stable up to 200°C
• Density: 2.7 g/ml
• Electrical resistivity: 117 ohms/cm

1613524075235.png
 
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zzyzx

Apprentice Neanderthal
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Aug 20, 2020
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96
Very nice build. (y)
To fix it I completely redid the connections by sanding the terminal posts and busbars with fine grit sandpaper, and then immediately applying dielectric grease to prevent oxidation. After re-assembly the cell voltages as read on my well calibrated BMS are now always within 5mV of each-other. There is also <0.5mV between the terminal bolts and the busbars. I've also noticed the batteries now run a little cooler under moderate load, as they are no longer sinking heat from poor connections.

Some images of the system for context:
What case did you use and can it really support the weight of your 8S battery?
 

Just John

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Aug 15, 2020
Messages
2,381
What are you guys using in between, any grease like this?
It sounds ideal...

Conductive Carbon Grease​

Lubricates and improves electrical and thermal connections between sliding surfaces, while providing protection from moisture & corrosion. Excellent for use on switches and EMI shielding applications. Industrial, trade and hobby use.

• Prevents normally closed switches from corroding in place.
• Reduces make-break arcing and pitting of switch contact surfaces
• Improves the connection between irregular or pitted contact surfaces
• Reduces EMI noise by maintaining a continuous path between conductive surfaces
• Thermally stable up to 200°C
• Density: 2.7 g/ml
• Electrical resistivity: 117 ohms/cm

View attachment 37317
I use Ox-Gard to keep the aluminum surface from oxidation. Very thin layer you can't see, but can feel (since I just dab a bit on my finger and wipe over the terminal).
 

noenegdod

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Mar 21, 2020
Messages
626
What are you guys using in between, any grease like this?
It sounds ideal...

Conductive Carbon Grease​

Lubricates and improves electrical and thermal connections between sliding surfaces, while providing protection from moisture & corrosion. Excellent for use on switches and EMI shielding applications. Industrial, trade and hobby use.

• Prevents normally closed switches from corroding in place.
• Reduces make-break arcing and pitting of switch contact surfaces
• Improves the connection between irregular or pitted contact surfaces
• Reduces EMI noise by maintaining a continuous path between conductive surfaces
• Thermally stable up to 200°C
• Density: 2.7 g/ml
• Electrical resistivity: 117 ohms/cm

View attachment 37317
As you have noticed, for some reason people around here really dont seem to like this stuff. I have brought it up a couple of times and everyone shies away from the idea.

I bought this brand and am going to use it when it comes time to assemble: https://www.mgchemicals.com/product...tive-grease/carbon-conductive-assembly-paste/

IMO it makes nothing but sense. One of the concerns I have heard were over mess, If you are not a conscientious person you probably shouldnt use it as it will get everywhere. The second issue was the concern over corrosion and the aerospace industry has demonstrated several issues with carbon fiber and aluminum. There has been several ways of solving this problem found. I asked MG chemicals about corrosion in this application and because the carbon is in a carrier (grease) that eliminates the atmospheric contact with the carbon, corrosion isnt an issue. Not only that but it states it inhibits corrosion:

Edit: this brand claims a lower resistivity than the one you posted

Features & Benefits​

  • Resistivity of 23 Ω·cm
  • Improves electrical connections between irregular, pitted or corroded surfaces
  • Ensures electrical contact between loose or vibrating parts
  • Prevents arching, pitting, hotspots and welds
  • Inhibits corrosion
  • Fills gaps
  • Can be used on vertical surfaces
  • Silicone-free
 

ArthurEld

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I think one of the downsides to something like that is that it can make trails for current to follow. So if you are sloppy or make a mistake it can be pretty bad.
 

noenegdod

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Messages
626
I think one of the downsides to something like that is that it can make trails for current to follow. So if you are sloppy or make a mistake it can be pretty bad.

For sure, a lot of seemingly innocuous substances can lead to issue. A parallel with this would be silicone sealant. Every time I take a mechanical component apart that has been rebuilt by someone else, there is almost always a huge amount inside. I have had bearings fail because of ground up silicone plugging them up. Almost universally, everyone uses 10 times or in come cases 100x more silicone than required when putting together case halves and covers.

This stuff will be the same. You need almost nothing. You need enough to have a tiny amount extrude out both inside and outside to ensure it has filled all gaps, divots and scratches.
 

Just John

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Messages
2,381
As you have noticed, for some reason people around here really dont seem to like this stuff. I have brought it up a couple of times and everyone shies away from the idea.

I bought this brand and am going to use it when it comes time to assemble: https://www.mgchemicals.com/product...tive-grease/carbon-conductive-assembly-paste/

IMO it makes nothing but sense. One of the concerns I have heard were over mess, If you are not a conscientious person you probably shouldnt use it as it will get everywhere. The second issue was the concern over corrosion and the aerospace industry has demonstrated several issues with carbon fiber and aluminum. There has been several ways of solving this problem found. I asked MG chemicals about corrosion in this application and because the carbon is in a carrier (grease) that eliminates the atmospheric contact with the carbon, corrosion isnt an issue. Not only that but it states it inhibits corrosion:

Edit: this brand claims a lower resistivity than the one you posted

Features & Benefits​

  • Resistivity of 23 Ω·cm
  • Improves electrical connections between irregular, pitted or corroded surfaces
  • Ensures electrical contact between loose or vibrating parts
  • Prevents arching, pitting, hotspots and welds
  • Inhibits corrosion
  • Fills gaps
  • Can be used on vertical surfaces
  • Silicone-free
Most of us in the USA have to deal with local electrical requirements, and many require something like Ox-Gard or NoAlox when connecting copper (busbars) and aluminum (battery or cell terminals). It's not that we dislike the product you wish to use, it's that we want to use an approved or even required product. At under $4 for a tube, it's not like money is a problem.
 

noenegdod

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Messages
626
Most of us in the USA have to deal with local electrical requirements, and many require something like Ox-Gard or NoAlox when connecting copper (busbars) and aluminum (battery or cell terminals). It's not that we dislike the product you wish to use, it's that we want to use an approved or even required product. At under $4 for a tube, it's not like money is a problem.
LOL. Most of us everywhere have to deal with local codes. The issue is familiarity. It takes a long time for the general population to become comfortable with a new or different product when they have a) have something they are comfortable using and b) aren't forced to change.

Having said that, it takes forever to have people stop doing something that was once required but is now pointless:


If you went thorough your code, I doubt it specifically states you have to use brand X anti corrosion paste. I know that mine doesn't.

Again, corrosion protection is on the list of features and benefits. Does it meet code in your area? Not a clue and dont care. It satisfies mine.

The MG chemicals stuff is a little more than $4.....
 

Just John

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LOL. Most of us everywhere have to deal with local codes. The issue is familiarity. It takes a long time for the general population to become comfortable with a new or different product when they have a) have something they are comfortable using and b) aren't forced to change.

Having said that, it takes forever to have people stop doing something that was once required but is now pointless:


If you went thorough your code, I doubt it specifically states you have to use brand X anti corrosion paste. I know that mine doesn't.

Again, corrosion protection is on the list of features and benefits. Does it meet code in your area? Not a clue and dont care. It satisfies mine.

The MG chemicals stuff is a little more than $4.....
And Ox-Gard is under $4, thus you have your answer.
No need to try and convert people to your preferred solution, people are free to use or not use things.
Having lived in two houses with aluminum wiring in south Florida, I disagree that it is obsolete and no longer needed. That's just my personal experience.
 

noenegdod

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And Ox-Gard is under $4, thus you have your answer.
No need to try and convert people to your preferred solution, people are free to use or not use things.
Having lived in two houses with aluminum wiring in south Florida, I disagree that it is obsolete and no longer needed. That's just my personal experience.
You have to read and pay attention. If your conductors are not aa8800 you still need to use a corrosion inhibitor. Your houses probably didnt have aa8800 so you still need to use a corrosion inhibitor.

Im not trying to convert, I really dont care what you or anyone else does. I am just trying to present an alternative that may be superior to the current mouse trap, situation dependent, and prevent dinosaurs from attempting to wave away potential progress with ignorance and fear. Information sharing after all is the purpose of forums like this

Saying a Chev spark is better tha n a bmw 1 series based solely on price is kind of silly.......
 

Just John

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You have to read and pay attention. If your conductors are not aa8800 you still need to use a corrosion inhibitor. Your houses probably didnt have aa8800 so you still need to use a corrosion inhibitor.
I have no clue what aluminum alloy they use for the terminals. That's what I'm concerned with.
I have no clue what alloys they used in the houses, I know they both had connection problems, and the code in Fort Lauderdale required some sort of corrosion inhibitor, and it was very much needed. I was just renting, so not really my problem until of course lights started flickering and arcing.
Im not trying to convert, I really dont care what you or anyone else does. I am just trying to present an alternative that may be superior to the current mouse trap, situation dependent, and prevent dinosaurs from attempting to wave away potential progress with ignorance and fear. Information sharing after all is the purpose of forums like this
For under $4, my personal experience with galvanic corrosion says that is cheap to prevent it.
You are more than free to use your preferred compound. I'm not sure I see anything in the marketing spec that makes it superior. Ox-Gard uses zinc as a sacrificial compound so that corrosion isn't preferentially occurring on the aluminum. Aluminum oxide is a much worse conductor than copper oxide, that is what I am concerned with. I am not sure I see any benefit from using carbon black.
Saying a Chev spark is better tha n a bmw 1 series based solely on price is kind of silly.......
Yes it is, not sure how it is related to good connections on battery terminals.
 
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noenegdod

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Messages
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I have no clue what aluminum alloy they use for the terminals. That's what I'm concerned with.
I have no clue what alloys they used in the houses, I know they both had connection problems, and the code in Fort Lauderdale required some sort of corrosion inhibitor, and it was very much needed. I was just renting, so not really my problem until of course lights started flickering and arcing.

So then you ask the supplier, or you just use a corrosion inhibitor like ox guard, noalox or MG CHEMICALS CARBON CONDUCTIVE PASTE as it is a corrosion inhibitor

I have no clue what alloys they used in the houses

So then you used a little common sense and apply the "wont hurt might (probably will) help" philosophy and apply a corrosion inhibitor.

For under $4, my personal experience with galvanic corrosion says that is cheap to prevent it.
You are more than free to use your preferred compound. I'm not sure I see anything in the marketing spec that makes it superior.

What makes it potentially superior is that (assuming it is equally effective at preventing corrosion) it is also conductive and will reduce the electrical resistance at the connection. Which as a side note, was the entire purpose of this thread......

Yes it is, not sure how it is related to good connections on battery terminals.

Its relevance is that you are saying noalox or oxguard are cheap:
And Ox-Gard is under $4, thus you have your answer.
While the MG chemicals version of conductive carbon paste which is also a corrosion inhibitor is substantially more expensive. Admittedly it is my inference but it would appear that you are implying that that noalox and oxguard is better simply because it is low cost. Typically I would agree if all was equal however our comparison is apples to oranges as the MG material, in addition to providing corrosion protection also reduces electrical resistance at the connection. Therefore your comparing a low buck minimum requirement for transportation to a luxury and functionally superior vehicle. Thats how the comparison is valid.
 

Just John

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So then you ask the supplier, or you just use a corrosion inhibitor like ox guard, noalox or MG CHEMICALS CARBON CONDUCTIVE PASTE as it is a corrosion inhibitor
Good luck asking the cell manufacturer about the composition of their trade secrets.
So then you used a little common sense and apply the "wont hurt might (probably will) help" philosophy and apply a corrosion inhibitor.
I did and do.
What makes it potentially superior is that (assuming it is equally effective at preventing corrosion) it is also conductive and will reduce the electrical resistance at the connection. Which as a side note, was the entire purpose of this thread.....
See below.
Its relevance is that you are saying noalox or oxguard are cheap:
They are cheap, well tested and developed for this specific application. All of them make the same claims.
While the MG chemicals version of conductive carbon paste which is also a corrosion inhibitor is substantially more expensive. Admittedly it is my inference but it would appear that you are implying that that noalox and oxguard is better simply because it is low cost. Typically I would agree if all was equal however our comparison is apples to oranges as the MG material, in addition to providing corrosion protection also reduces electrical resistance at the connection. Therefore your comparing a low buck minimum requirement for transportation to a luxury and functionally superior vehicle. Thats how the comparison is valid.
No, just pointing out they all make the same claims. Some are cheaper than others and much more readily available. Marketing spiel is no reason to choose one or the other, but more than 40 years of practical experience and widespread availability on Amazon, home depot, lowes etc combined with price compell my selection. But I have actual experience with galvanic corrosion, and recommend people use something, simply because it is cheap and won't hurt.
 
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