Corrosion - electrolyte leakage?? Outgassing? Has anyone seen this?

[Solar Steve]

Wondering if anyone else on the forum has seen this - after operating this 4s pack daily for about a year (in series with another 4s pack), I've noticed this white corrosion on the heat shrink and in particular on the thermocouple leads from the BMS, which has the insulation partially eaten away, although none of the other wires are affected. I can also smell a faintly sweet smell, which makes me suspect electrolyte leakage somehow, but the cells and in particular the vents appear undamaged. Charging rates in the system never exceed about 0.25C, and the cells appear to still work normally. If this is electrolyte leakage, what are typical leak points?

 

[740GLE]

Any chance you can inspect the bottom of the cells?

 

[S Davis]

Are the sensors between the cells?

 

[robby]

I saw this post when it came out and I was puzzled and did not reply.
After 4 days a post like this would normally have gotten a lot of replies but I guess everyone is also stumped, so I am just going to throw out my wild idea.

I see zero leakage from the battery! Corrosion would normally form on the Metal first, but in your case the metal is fine and it's just some white stuff on the Heat shrink tubing and on the one temp sensor. The temp sensor makes thing even more confusing but there is one clue that makes me believe this is not from the battery itself.

On closer inspection I noticed that the same white stuff is on the Wire that is connected to the Positive Terminal on the Front of the wooden box. That terminal is not even in contact with the battery!
It almost looks to me like you used marine grade heat shrink tubing and the adhesive was factory applied to the outside instead of the inside of the tubing. Either that or some kind of chemical was on your hands when you did the wiring or possibly you used a lot of solder flux and it is now drying out and showing up.

 

[SparkyJJO]

I'm going to agree, it looks like it may have something to do with that heat shrink.

 

[MisterSandals]

OP, can you put a loose piece of shrink wrap in that box to see what happens? Would be interesting to shrink half of that piece for a more complete test.

 

[12VoltInstalls]

same white stuff is on the Wire that is connected to the Positive Terminal on the Front of the wooden box. That terminal is not even in contact with the battery

It wipes off with a rag, I’d bet. Cheapo dielectric compounds dry out and turn white over a relatively short time.

The emf around the connectors and that fact that it is outside the box as well makes me believe that it could be something on the heat shrink drying and showing the residue OR attracting something out of the air

 

[Shimmy]

It wipes off with a rag, I’d bet. Cheapo dielectric compounds dry out and turn white over a relatively short time.

The emf around the connectors and that fact that it is outside the box as well makes me believe that it could be something on the heat shrink drying and showing the residue OR attracting something out of the air

My first thought was termites... but I am scarred from past experience there. Salt would also do similar things.

But, the negative terminal with two wires in a single lug... you might want to check temperature during discharge. Unless the terminals are designed for two cables it is easy to have a bad connection there.

 

[RCinFLA]

Without further examination, I would guess you got some really crappy bus bars that had a terrible plating job, probably due to contaminated pre-clean prep of base material.

It also looks like tin plating without any nickel barrier layer but that would take a closer examination to be sure. It looks so thin it might be electroless tin plating. Top left bus bar looks like almost bare copper.

Better to have just nickel-plated bus bars for interfacing to aluminum battery terminals. Bare copper to aluminum is a no-no.

 

[robby]

Solar Steve has not come back since he made the thread.
I am wondering if it is actually @Steve_S playing a prank on us? To test our intelligence.
I recognize that Avatar picture Solar Steve is using and it looks like a picture of younger happier Steve_S when he was in his prime.

Just Kidding Steve from one fossil to another

 

[12VoltInstalls]

Without further examination, I would guess you got some really crappy bus bars that had a terrible plating job, probably due to contaminated pre-clean prep of base material.

It also looks like tin plating without any nickel barrier layer but that would take a closer examination to be sure. It looks so thin it might be electroless tin plating. Top left bus bar looks like almost bare copper.

Are you saying the tin is migrating up the outside of the polyolefin?

Wow! So that would be migrating up the plastic due to the electrical field?

(I plated the late growth rings on fir plywood under the helm on a 14’ Niagara back in the 90s. I screwed / placed a copper lug with a small bolt to use as a pos(+) busbar of sorts. In searching for some ghost battery drain I discovered these shiny metallic woodgrain highlights and realized that the plywood apparently sometimes was damp enough to be a millivolt conductor and it ‘plated’ the wood between it and the nearest neg(-) connected item which happened to be another lug as a neg(-) busbar. Educational to figure that out)

 

[S Davis]

It looks like there is a wet/stained area coming from where the temperature sensor wire goes between the cells, I bet the sensor bead has compromised one of the cells.

 

[Zoomyn]

Yeesh, hear hoof beats and think Zebras : )

Could be Cat-pee-from-the-factory...

Chinesium plastics & quality control: could be an excess of flame suppressant additives such as Antimony used industry wide in IC & SMD bodies, could be plasticizers mismixed and equalizing, could be excess lubricants from injection/extrusion impellers remaining and being first run after machine service, could be some petroleum loving fungus that got missed during sterilization and/or fungicidal additive steps at the chemical plant that was shipping rail car quantities every hour...

Is it water soluble? If its alive it probably would love a drink & to hitch a ride onto... you

 

[Solar Steve]

more replies than I expected...good idea to check the bottom of the cells. I’m able to see the edges at the bottom by removing the sides, no sign of electrolyte leakage. The thermocouple leads have a bit of odd liquid on them, I wiped everything off, added more heat shrink around the affected leads and will put the pack back in service.

No issues with the bus bars or the multiwire crimp, I have used a thermal imager under high load and everything looks normal. I still think there’s some sort of slow electrolyte leak just based on the smell. I see this and the corrosion in the two packs I built up with used Xuba cells, but nothing similar in packs using matched cells from Amy (Luyuan)...

 

[Solar Steve]

 

[Bud Martin]

BTW, did you use non-tinned ring lug on the positive terminal of the battery, or it is tinned ring lug? I ask because the other end of the cable is non-tinned ring lug.
Using non-tinned ring lug on aluminium can cause issue: Galvanic corrosion.

 

[12VoltInstalls]

thermocouple leads have a bit of odd liquid on them

Thermally conductive paste?

 

[Solar Steve]

BTW, did you use non-tinned ring lug on the positive terminal of the battery, or it is tinned ring lug? I ask because the other end of the cable is non-tinned ring lug.
Using non-tinned ring lug on aluminium can cause issue: Galvanic corrosion.

Positive side is tin plated, but the negative side is copper. I used conductive paste but in subsequent builds I used all plated lugs. Also drilled and tapped extra holes in the busbars for the BMS leads in later builds.

 

[RCinFLA]

You don't want bare copper in contact with aluminum battery terminals. It causes pit corrosion in the aluminum battery terminals.
Grease will help reduce this but better to not to do copper on aluminum. Nickel plating is used as a barrier layer.

 

[sparrowhawk]

Wondering if anyone else on the forum has seen this - after operating this 4s pack daily for about a year (in series with another 4s pack), I've noticed this white corrosion on the heat shrink and in particular on the thermocouple leads from the BMS, which has the insulation partially eaten away, although none of the other wires are affected. I can also smell a faintly sweet smell, which makes me suspect electrolyte leakage somehow, but the cells and in particular the vents appear undamaged. Charging rates in the system never exceed about 0.25C, and the cells appear to still work normally. If this is electrolyte leakage, what are typical leak points?

I have the odd sweet smell coming from one of my battery cells. I can't pinpoint it by sniffing around the individule cells but I can tell which end of string the odor is coming from. I went into more detail about in another thread and don't wish to re write it again. But I don't have any corrosion or any other signs of leakage.