diy solar

diy solar

Fire!! Never cover LiFePO4 with wood!!!

The stud is not your electrical connection, the bus bar to terminal mating surface is. Stainless is a poor conductor whether it's got loctite on it or not. These studs and the limited number of aluminum threads is not ideal in a lot of ways. I'd say helicoils is probably the best/strongest solution. Red loctite is another path that I'd argue is significantly better than raw stainless to poor aluminum threads, but opinions vary.
The main reason to be careful using Stainless threads in these soft aluminum terminals is galling. Stainless threads will quickly degrade the aluminum threads if they are tightened and loosened repeatedly.

If only being exercised once on new cells, a stainless grubscrew secured with Loctite Red is the best way to convert a fragile aluminum female threaded terminal to a robust male thread.

In my case, I use brass nuts to avoid galling of the nut on the stainless grubscrew as well.

And you are absolutely correct, grubscrew composition has nothing to do with conductance and everything to do with mechanical clamping force (as well as a bit to do with avoiding corrosion).
 
In my job (military defense contractor), the application of Loctite is only a drop. Apply it to the screw/stud. You will see the drop wick a little around the screw, continue until it covers a 2-4 threads. As the screw goes into the nut/terminal, it will coat the thread surfaces. Once it's tightened, it will cure the Loctite when the two metal surfaces of the thread compress.

Loctite is anaerobic. It will only cure in the thread areas that are in close contact. Having liquid Loctite in the bottom of the hole won't cure, but will be leaking out for a while. Just a drop is all you need

I've been using several different flavors of loctite in different applications for many years and the process you describe is right for most of them. These studs and shallow aluminum threads have some unique challenges. Give it a shot with some 271 and see how it works. Even a single drop near the end of the threads will push back out the hole due to the air pressure as the stud is screwed in. I thought it would be a simple easy thing until I tried. The curing also has to do with the activity of the metal and that's why it's critical to use primer when curing loctite on stainless and/or aluminum (neither are very active metals).
 
Please don't use stainless steel scrub screws in the aluminium cells. They will corrode.
Use normal galvanised fasteners
Stainless is good. Aluminum is an anode and will be sacrificial to the stainless. Somewhere in the corrosion control handbook, near the back, they explain the surface area issues on galvanic couples. A small aluminum screw in steel block is really bad due to the large noble material and small anode. Using a small noble stainless steel screw in a large aluminum block is recommended.

The bigger question that I have is the buss bars. Equal surface areas, copper against aluminum. This and the electrical contact could cause corrosion. A little moisture in there and the aluminum will pit. As the pitting increases, the amount of aluminum surface contact will drop, accelerating more corrosion.

Is anyone using Noalox? Anyone seeing corrosion?

 
Using plated busbars and tinned lugs instead.
Tin/lead is better than bare copper. Closer to Aluminum on the galvanic scale.

They could be using the 8000 series aluminum alloy in the cells. That's what's mentioned in the video. By alloying aluminum, they can avoid the corrosion issues. My belief is that the cheapest, most popular cells don't search out the best aluminum, just the most available/cheapest.

I haven't seen anyone with a discussion of corrosion. Maybe it's not an issue, or I haven't spent enough hours on the board.

 
Tin/lead is better than bare copper. Closer to Aluminum on the galvanic scale.

They could be using the 8000 series aluminum alloy in the cells. That's what's mentioned in the video. By alloying aluminum, they can avoid the corrosion issues. My belief is that the cheapest, most popular cells don't search out the best aluminum, just the most available/cheapest.

I haven't seen anyone with a discussion of corrosion. Maybe it's not an issue, or I haven't spent enough hours on the board.

Plenty of discussions about it. I personally recommend using noalox or ox-gard or any of the many brands specifically designed for the problem. Many will disagree or emphatically tell you about silver paint, or very expensive carbon based solutions.
 
Carbon paste isn't that pricey; messy though, just a little dab will do.
I will be happy to stick with the under $4 solution that has worked fine for 40 years, but of course everyone is welcome to make their own decision.

I will also point out the thread owner used silver paint. I doubt it cased the fire, but anything is possible since it was pointed out to me that silver is very prone to corrosion.
 
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Carbon paste isn't that pricey; messy though, just a little dab will do.
If it's working, then its a solution.

Personally Carbon is on the opposite end of the scale from aluminum. My company scrapped carbon fiber structures due to corrosion on aluminum. There are ways to make it work. Boeing has done it.... maybe. They coated the interface between aluminum and carbon to electrically (galvanically) isolate them. That's not good for an electrical battery post.

 
As far as how a terminal connection could go south, with that many cells in parallel, and non matched bus bars, and triple stacked in some places... Well, one cell lags behind the others due to higher contact resistance, once you hit the knee, or close to it, that slow charging cell can see 80% of the total current instead of its share.

With a 100mv drop at that terminal, to get 25w dissipated power, you would need P= V*I 25/0.1=250A. Of course this is all guesswork.

What is the voltage of this battery pack?
That's an easy comment.

You probably didn't look close enough.

All Bus-bars that make the series connection are the same, same thickness, same wide.
That is where the real power is.
Parallel, that can be a thin copper wire as all it does is Ballance the 3 cells in parallel.

Apparently you never went to the complexity of 3 cells in parallel.
It's not possible to stack just 2 Bus-bars, unless you make one with 3 holes.
That would be a challenge.

The cells got delaminated as they wherent compressed for months a year ago. Capacity is still good, a few Ah less. They do have slightly different distances between the rods.

You didn't read closely enough, as you ask questions that already have been answered.

Once again: S16 LiFePO4. (That is nominal voltage 51.2v)
S16P2 280Ah and
S16P3 152Ah
Voltage before I closed the door, little over 53v
Discharge in the night, at start about 750w, (airconditioning and refrigerator need to work harder with higher temperatures) later down to 250 watt or less.

I looked again in the morning, 09.00.
Little bit hazy weather, absolute low solar production.
Perhaps 20A, 30A tops.

The bus-bar connections where good. And yes, I touched them to feel if anything got more hot during 100A charge. The ones I can't touch, I have temperature sensors.

If it was the force down on the threaded rod that got the terminal out of the plastic cover, or the wire from terminal sensor that got damaged, we will never know.

What we can tell is that the fire didn't start until 7 or 8AM
It wasn't smoldered that far, just the edge.

I best guess is that the weight made the terminal move.
During the sun rise (at 08.00 my eyes where still closed) there might not have been cloud cover before 09.00.
With 14kw of solar, even the early morning can produce quite some.
Perhaps even up to 50A

With the damaged terminal, that's what most likely made the fire.

You are free to test at your installation alterative ways to set fire!
 
Using plated busbars and tinned lugs instead.

As you can see, I tinned all my coper Bus-bars.
That took weeks to do as I do not have professional tinning installation.

The ones used from the seller are zinc plated.

If I ever need to redo plating, it will be zinc, as it looks a lot better :)
(Stay shiny where tin gets gray)
 
That's an easy comment.

You probably didn't look close enough.

All Bus-bars that make the series connection are the same, same thickness, same wide.
That is where the real power is.
Parallel, that can be a thin copper wire as all it does is Ballance the 3 cells in parallel.

Apparently you never went to the complexity of 3 cells in parallel.
It's not possible to stack just 2 Bus-bars, unless you make one with 3 holes.
That would be a challenge.

The cells got delaminated as they wherent compressed for months a year ago. Capacity is still good, a few Ah less. They do have slightly different distances between the rods.

You didn't read closely enough, as you ask questions that already have been answered.

Once again: S16 LiFePO4. (That is nominal voltage 51.2v)
S16P2 280Ah and
S16P3 152Ah
Voltage before I closed the door, little over 53v
Discharge in the night, at start about 750w, (airconditioning and refrigerator need to work harder with higher temperatures) later down to 250 watt or less.

I looked again in the morning, 09.00.
Little bit hazy weather, absolute low solar production.
Perhaps 20A, 30A tops.

The bus-bar connections where good. And yes, I touched them to feel if anything got more hot during 100A charge. The ones I can't touch, I have temperature sensors.

If it was the force down on the threaded rod that got the terminal out of the plastic cover, or the wire from terminal sensor that got damaged, we will never know.

What we can tell is that the fire didn't start until 7 or 8AM
It wasn't smoldered that far, just the edge.

I best guess is that the weight made the terminal move.
During the sun rise (at 08.00 my eyes where still closed) there might not have been cloud cover before 09.00.
With 14kw of solar, even the early morning can produce quite some.
Perhaps even up to 50A

With the damaged terminal, that's what most likely made the fire.

You are free to test at your installation alterative ways to set fire!
Man...People try to help you sort through a problem and you get abusive. Good grief.
 
I have to ask...what's with the loctite? If you aren't mobile then why do you need loctite for a battery bank that isn't going to move? Wouldn't a good nut, flange nut or double nuts be adequate?
 
Plenty of discussions about it. I personally recommend using noalox or ox-gard or any of the many brands specifically designed for the problem. Many will disagree or emphatically tell you about silver paint, or very expensive carbon based solutions.
I totally agree.

Sadly noalox and ox-gard aren't available in Thailand, and shipping+ tax will make one tube over $75.
(Not the $4 one, that will be about 22,50, but I doubt it's enough for 160 terminals)

Oxidation of silver isn't a problem.
The conductivity of silver oxidation is close to non oxidized silver.

Copper oxidation isn't a real problem (with copper to copper) sure the oxidation changes the way the electrons behave, 2 oxidated copper (with thight contact) counteract eachother makeing a good contact again.
This is the reason you don't need to clean each strand of wire, but just compressing them is enough.

Aluminium is the bad boy here.
Milliseconds after you cleaned it already oxidises, and after a few minutes that far that it will interfere with the contact.

Covering the terminal contact areas with a little drop of silver paint after cleaning creates a seal, like oxi-guard or noalox.
With the big difference that silver is conducive and noalox/oxi-gard are not. (Di-electric grease)

I agree that different metals is asking for troubles.
Not the trouble I encountered!!!

Best is to use aluminium bus-bar and if you can get, aluminium threaded rods.
With aluminium nuts.

Once you start with different metals..
You are screwed.

Most likely not in the period of installation, but 15-25 years.

Most cells don't have environment that speed up the galvanic corrosion process.
No aviation or salt water.
No huge temperature swings.

304 stainless steel is the most "Neutral" out there, it doesn't get eaten away from galvanic corrosion.

Yes, that makes the aluminium and the copper the sacrifice metal.
Tinning or zinc plated makes that the sacrifice metal.

Inside the aluminium threads?
Zinc plated grub screws get damaged just by being in the box together.
There will be bare metal.
If you don't believe me, place it a few hours in salty water and lay it outside for a few days.
All those rust spots are damaged areas.

At those locations the bare iron have full contact with the aluminium. The zinc surrounding is corroded quickly.

Loctite is a good solution.
Not just because it locks the nut, it also seals the thread.
No oxigen = no galvanic corrosion.

There are many discussions about it.
Most people use the brass bolts they get with the cells.
Or what ever they had available.

I'm yet to see an eaten away thread hole from galvanic corrosion.

That has a real clear signature.
No smooth walls like stripped thread, but uneven.

As long as no one is able to show the galvanic corrosion problem in the thread, it only exist in theory.

Outside the thread, the contact that have air exposure...
Yes, absolutely.
Anyone with a car, that cleaned their lead acid terminals from the white/blue/green powder know what that looks like, lead and copper with probably some acid air., And different temperatures.

That is a whole different story.

304 steel rods with Loctite or Jbweld (or similar Epoxy) are the best.
Applied on the rod, then screwed in.
You can see the Loctite react with the aluminium oxide in the thread.
It turns almost directly black.
Having Loctite on the bottom is useless.
 
Regarding the general discussion of worrying about fires with LiFePO4 cells in general, I see a lot of people using foam insulation around their battery bank which could easily melt and/or catch fire. As an extra bit of caution I would rethink using such flammable material around a battery bank that needs cold temp protection. Rock wool would be good option but would require thicker amount.
 
Man...People try to help you sort through a problem and you get abusive. Good grief.
I don't get abusive.

If he read he known that the issue wasn't the bus-bar, knew the setup, voltage and load.

He starts abusive with claiming how 3 layer only can be a bad thing.
That's not helping.

Many of the comments are helpful.
Some aren't.

To summarize:
-It wasn't a bad thing to cover the cells for a few hours while working above them.
-It was a bad thing to leave them.
-It wasn't the smartest move to lean on the wood, and with even studs, that would not have been a problem...
Sadly.. one works with what one can get. In this situation carbon steel rods, some a little longer.
- this most likely damaged the terminal, when the solar panels started to provide energy, the load was enough to heat up the terminal/rod to start a fire.

Is carbon steel the best choice? No it isn't aluminium is.
Is stacked 3 high bus-bar a problem?
No it isn't. With perfectly flat bars, or soft enough to shape under 700 pounds pressure, 1, 2 or 4 layer make no influence.
Besides, the bars that carried the cell to cell series load are connected to the terminal.
Parallel flow is minimal.

I really appreciate all (most) the comments.
And there are many ways of installation.
One better or worse, difference is probably minimal if the terminals and bus-bar are clean, flat and compressed tightly enough.

For this I can only advice to get a torque wrench, or meter.
Screenshot_20210308_125905.jpg

This thread isn't about how the installation could have done better or worse.

It's about the dangers we face with our installation and how one unthought full action can give huge issues.

With all guidelines followed (or not) pressing a terminal down like I accedently did, can give a fire.

The following of the installation guidelines had little to none influence on pressing the terminal and the actions followed after that damage.

If my installation could have been better? Sure.
I'm also sure your installation can be improved.

Laser welding bus-bar, metallic housing that is laserweld under compression, the list goes on.

We need to work with the materials and equipment available, in the budget available.

That doesn't mean the installation tips are discarded.
They are discussed in many other threads as well, several thousands in the last year.

It will be good to keep this educational for the dangers with our setups, not as guide how to install better.
There are other threads for this.
 
I have to ask...what's with the loctite? If you aren't mobile then why do you need loctite for a battery bank that isn't going to move? Wouldn't a good nut, flange nut or double nuts be adequate?
Our suppliers sadly didn't hire the best thread tapper.
Most of the holes are oversized to make tapping easy.
If you can feel the stud wiggle when incerted in the thread, it's clear that it is not optimal at all.

Adding Loctite or other locking agent fills this gap, and makes chemical reaction with the metal.
It becomes strong.
Stronger then the thread alone would be.
You need to apply about 3.5-4Nm force on the nut.
700 pounds of compression, and also pulling force on that weak thread.

It's extra to lower the risk of pulling out the threads.
 
I have to ask...what's with the loctite? If you aren't mobile then why do you need loctite for a battery bank that isn't going to move? Wouldn't a good nut, flange nut or double nuts be adequate?
The aluminum threads on these cells are very soft and easy to strip when tightened for good contact.
 
Even if using a thread locker the stud can be pulled out. Here is a photo of one of mine that pulled up with the aluminum threads included. That is red loctite you see on the stud. I didn't use a primer but so far all of the other studs are ok. The aluminum is so soft it's really easy to strip. I am not entirely sure why this stud pulled up but I do recall some studs had more wiggle room than others while screwing them in. I have since bought a beam style torque wrench.
 

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