CATL 271Ah 'Grade A' prismatic cells from Shenzhen Basen - Cell terminals without threading

[thegoogler]

This question is much discussed in many threads around this forum. Msny users here do choose thread locker. After trying both, and finding that epoxy is much stronger, that’s just what I chose. Many have found that LokTite does not bond well to the aluminum without using an “accelerant“.

It is very important to use one, or the other. These aluminum terminals a very soft, and the threads are shallow. It is scary to feel one of your studs pulling out as you gently tighten a nut. I was able to salvage that terminal by fixing the stud with epoxy. That was what tipped me to now using epoxy with the very first install of every stud.

it is certainly possible to repair a damaged terminal thread with a heli-coil insert. But I have 48 cells (96 terminals) in service, and I don’t want to mess with a bunch of heli-coil repairs if I can avoid it easily and cheaply with the epoxy.

Thanks, that's good info.

My big concern with helicoils is they are stainless steel being mounted into aluminum, which risks galvanic corrosion over time. I would not use anything in aluminum other than zinc. YMMV of course.

 

[Johncfii]

Thanks, that's good info.

My big concern with helicoils is they are stainless steel being mounted into aluminum, which risks galvanic corrosion over time. I would not use anything in aluminum other than zinc. YMMV of course.

I agree with you about this, though I think that not all heli-coils are stainless steel.
But this is the exact reason why I install black-iron-oxide coated studs in my terminals.
I can’t understand why so many readers of this forum go out of their way to use stainless steel studs.

 

[Gazoo]

I agree with you about this, though I think that not all heli-coils are stainless steel.
But this is the exact reason why I install black-iron-oxide coated studs in my terminals.
I can’t understand why so many readers of this forum go out of their way to use stainless steel studs.

As you know, most, including myself, have used a thread locker which seals the deal. But I don't understand why galvanic corrosion is a problem. According to what I have read galvanic corrosion happens when two dissimilar metals are used in the presence of an electrolyte. There are no electrolyte concerns with LFE cells unless they are leaking or venting and that should not be happening. I am no expert on this so I am probably missing something. Maybe in a humid salty environment it would be a problem if not using a thread locker?

 

[Pyrofx]

Half the world of OEM parts helicoil aluminum parts.
Dont start manifesting theoretical problems.
You do realize that technically, the bumble be shouldn't be able to fly......

 

[Johncfii]

As you know, most, including myself, have used a thread locker which seals the deal. But I don't understand why galvanic corrosion is a problem. According to what I have read galvanic corrosion happens when two dissimilar metals are used in the presence of an electrolyte. There are no electrolyte concerns with LFE cells unless they are leaking or venting and that should not be happening. I am no expert on this so I am probably missing something. Maybe in a humid salty environment it would be a problem if not using a thread locker?

Admittedly, these are probably trivial issues. But why not easily reduce the possibility of even trivial problems by using less expensive non-stainless-steel heli-coils, and non-stainless-steel studs? At the same time, it is all nothing to lose sleep over.

Humid air will function as an electrolyte, though not a good one. And I have read that fumes from household products can also increase galvanic corrosion, though I don’t know how seriously. It isn’t necessarily the air between the stud and the aluminum, but the air circulating around them that can contribute to galvanic corrosion.

My only question is why the seemingly wide preference for stainless steel studs? I can’t see any advantage unless you are in a severe marine environment, in which case I would also coat them with protectant to exclude air after assembly.

But that’s the great thing about being a DIY’er. Every one of us can choose our own priorities. There are usually several different good ways to accomplish a thing. No need to get worked up about someone else’s priorities.

 

[thegoogler]

I agree with you about this, though I think that not all heli-coils are stainless steel.
But this is the exact reason why I install black-iron-oxide coated studs in my terminals.
I can’t understand why so many readers of this forum go out of their way to use stainless steel studs.

If you've ever had a zinc-plated bolt rust solid, stainless steel seems like magic. If you're unfamiliar with galvanic corrosion then you think "why use anything else?"

As you know, most, including myself, have used a thread locker which seals the deal. But I don't understand why galvanic corrosion is a problem. According to what I have read galvanic corrosion happens when two dissimilar metals are used in the presence of an electrolyte. There are no electrolyte concerns with LFE cells unless they are leaking or venting and that should not be happening. I am no expert on this so I am probably missing something. Maybe in a humid salty environment it would be a problem if not using a thread locker?

Happens a lot in automotive, RV, and especially marine environments. If your battery is air-tight and in a low humidity environment you may well be fine for the life of the battery. And depending on your situation (such as a boat where the battery is not air tight) you may prefer the risk of galvanic corrosion over the likelihood of normal corrosion of zinc.

Practically speaking it's a low risk problem, but so long as I'm optimizing for some scenarios (i.e. battery compression, correct nut torque, etc) why not optimize for this as well? I'm an engineer, there's no problem that can't be tweaked and tuned unnecessarily.

 

[Gazoo]

But that’s the great thing about being a DIY’er. Every one of us can choose our own priorities. There are usually several different good ways to accomplish a thing. No need to get worked up about someone else’s priorities.

Not worked up here and was just asking. In my situation corrosion is not a problem. But I am a curious type of guy and enjoy learning things.

Practically speaking it's a low risk problem, but so long as I'm optimizing for some scenarios (i.e. battery compression, correct nut torque, etc) why not optimize for this as well? I'm an engineer, there's no problem that can't be tweaked and tuned unnecessarily.

I agree with you. I just don't know how far into the weeds one has to go to accomplish a benefit. For example cell compression using springs...I am not going there but do have my cells in a fixture. Correct nut torque is important as are other things.

My 8 EVE cells are in a climate controlled environment and I will be rebuilding my pack using braided busbars. I am currently using the solid busbars that came with my cells. I will be adding a corrosion inhibitor not because I am worried about corrosion, but because some of them claim to improve conductivity.

MG Chemicals Carbon Conductive Grease is a possibility as is Gardner Bender OX-100B. I don't know one is better than the other, but there is a big difference in price. It's my understanding NO-OX-ID is good stuff and is also conductive. No doubt they all accomplish the same thing regarding corrosion as do many other products.

Like I said I am not an expert, regarding anything actually, and I learn new things every day. I certainty don't have anything against what others do with their system. I find all of it interesting.

 

[ArthurEld]

Corrosion inhibitor won't hurt anything. It's more like insurance even if you don't think you need it.
Many things can start corrosion. Like one drop of sweat or a sweaty fingerprint.
I think the electrical connection alone can start corrosion.

 

[Johncfii]

Not worked up here and was just asking. In my situation corrosion is not a problem. But I am a curious type of guy and enjoy learning things.

Didn’t intend at all to imply you were getting worked up. I’ve read enough of your posts to know you are a thoughtful person. Darn written communication sometimes doesn’t always shade intended meaning exactly right ... I meant to say the I wasn’t trying to tell anyone else what is THE best way.

 

[Gazoo]

Darn written communication sometimes doesn’t always shade intended meaning exactly right

It's ok. I get your meaning that it was a general statement and I didn't take it personally. I know you are a thoughtful person too...

 

[Influencer]

Great convo!!! I'll probably just make the threads and epoxy them in. It'll be a stationary battery for the most part. I'll try and find black-iron-oxide coated studs since I live in a relatively humid area.

I realized I had not set my 10A power supply's amperage to the maximum. I didn't understand that you could only adjust the max current while actively shorting the leads when it's not connected to anything (and was too afraid to adjust anything with it connected to the battery). Now it's charging at about 7 amps instead of about 3. I'm not rushing on the top balancing since I'm out of town this weekend and won't be able to capacity test until next week. I'll charge it up as much as I can while I'm here, then leave the cells in parallel while I'm gone and finish charging when I get back.

When they're wired in parallel, can you get an accurate voltage of the individual cells by using the multimeter on their terminal studs/bolts? Also, where's the best places to put the multimeter leads to get the most accurate general voltage of the entire battery (when they cells are in parallel)?

 

[time2roll]

Anyone use an aluminum screw?

 

[Gazoo]

I didn't understand that you could only adjust the max current while actively shorting the leads when it's not connected to anything (and was too afraid to adjust anything with it connected to the battery)

I don't think the current adjustment matters if the leads are shorted together or connected directly to the cells because the cells IR is so low.

What definitely does matter is that the voltage of the power supply is set before it's connected to the cells.

When they're wired in parallel, can you get an accurate voltage of the individual cells by using the multimeter on their terminal studs/bolts? Where's the best places to put the multimeter leads to get the most accurate general voltage of the entire battery (when they cells are in parallel)?

The best place is right at the cells terminals. My meter probes will reach them and I am using the standard busbars.

 

[Johncfii]

I didn't understand that you could only adjust the max current while actively shorting the leads when it's not connected to anything (and was too afraid to adjust anything with it connected to the battery).

That’s not exactly correct. In this case, the way to adjust a PS that regulates both voltage and current:
1. With the leads not connected, adjust the current limit up a small amount, perhaps 10% or 20% of full CW.
2. Adjust the voltage to your desired charge voltage, say 3.65 volts per cell.
3. Connect the leads to the battery.
4. Leave the volts adjustment unchanged, but increase the current limit knob to your desired maximum, say 10 amps.

Over hours, the battery terminal voltage will slowly rise towards your set voltage. As it nears your set voltage the current flow will taper off.

 

[Influencer]

Cool, I've had it set to 3.6v to be safe. Once I'm back from my trip, I'll do the final charge and do the capacity test.

 

[ed1380]

I suggest a machine shop over a mechanic shop.

some mechanics are utter idiots and shouldn't be trusted with a screwdriver. also a machine shop would have a steady arm and more experience with tapping aluminum

 

[Frick]

Tapping aluminum by hand is easy, it’s soft and cuts well. It can be very sticky though depending on the alloy and this can cause it to stick to the tap and gall the threads something terrible.

USE LUBE. Specific for aluminum tapping lube is great, but wd40 will work too.

i would also get a blind tap and not a through tap since you have limited depth and want all the threads. I’d be surprised if you couldnt get a tap with handle and lube for 15$. Go slow, let the tap find the center of the home and guide itself in straight. One smooth turning in without reversing directions cuts the best threads.

 

[Sanwizard]

Basen offered to pay for me to get the terminals threaded. I'd prefer that they just send me a new cell, but at least they offered that much. What kind of shops tend to be willing to do this kind of thing? I'm going to call around, but if anyone knows about how much it would cost me that'd be good to know (I'm in the Portland, OR area, if someone knows a good place).
Even if I do it myself, at least I'll know what to quote Basen at for my trouble.

From skimming through that forum post and video, tap-and-die looks to be pretty straightforward for someone who hasn't done it before? It seems there are kits online for about $50, are these good enough without additional investment? I guess I can use it once and then return it, lol.

In the mean time, I have the cells charging in parallel. Ideally I'd wait for the fix, but I want to be comfortably within the Basen and Alibaba return periods after I capacity test the cells. On the threadless cell, I have the bus bars taped on with electrical tape in the meantime... The power supply reads 3.5v as of this morning, and the lower voltage cell is up in the 3.4v range. The voltage reading has dropped a few times, but in general has trended upward.

I notice when I use the multimeter on the cell with the lower voltage, the voltage reading doesn't settle quickly like on the other cells' terminals. Does this mean anything? I have been taking the reading from the stud/nut and I know those are less conductive than the bus bar.

Home depot has taps and dies.

 

[Influencer]

I finished top balancing last night. Looks like my cheap 'Kungber' power supply was slightly hot voltage wise, as I started getting 3.65v at all the cells on my multimeter when the power supply was still sending current. I planned for this and was monitoring it closely. With the individual cells all reading 3.65v, The current only zero'd out when the power supply voltage was turned down to 3.4v. Unless my multimeter is reading high. Hopefully it was a successful top balance.

This afternoon, I just started the capacity testing. I'm using one of those cheap aliexpress capacity testers that Will recommended, and simultaneously taking readings from a shunt, and monitoring from the BMS app as well. What concerns me is that the capacity tester is designed to draw 185w max, but even at its max settings it is only drawing 130w, staying below 10 amps. In will's review of it, it seemed very easy to turn up the tester beyond its max wattage. Does this just indicate an issue or design change with the capacity tester?

 

[Influencer]

Results of the capacity test were 272 Ah / 3479 Wh from the aliexpress tester, and 3530 Wh from the shunt. The shunt (and the BMS app if I remember correctly) also consistently read a few .1 volts higher than the capacity tester. Whichever is more accurate, I'd say that's satisfactory.

The first cell that dropped to 2.5v was also the cell which came threadless. I tapped the start of those threads, but need to get a bottom tap to finish them, so the bus bar wasn't as tight on that cell while top balancing, or during the capacity test.

They also agreed to refund me for the $70 for doing the thread myself, so as long as I see that in my paypal soon, I'll be pretty satisfied.