Why do hybrid battery control module connectors get corroded?

The voltage potential from pin to pin is ... 19v maybe, unless the arcing is across rows, but that would blow pins off at the base, not cause corrosion wouldn't it?
Being DC, the electron flow is one direction, are there tell-tale signs that one end of a busbar corrodes more than the other?

T1 Terry

 

I tend to agree... I think it was Jack at saltyhybrid.com who first described it as "micro-arcing" between pins. But maybe that is not as accurate as simply saying the corrosion on that first pin creates signal noise that screws up the ECU's ability to produce accurate charge rate data.

 

This isn't high current flow across any two connector pins (at least not initially). It's the high voltage potential that makes the materials "more reactive" - and more likely to form corrosion. I might think that vibration is also a factor by causing fretting or wear at the terminal to pin interface.

IDK what the voltage threshold is to make this all happen, but all I can do is guess based on the observations. The orange HV connector is the one that "always" has problems. I do not see or read about corrosion at the low voltage connectors.

I would think that they chose to use gold plated terminals to help reduce corrosion problems, but they still happen.

I haven't seen enough ecu failures to know if any particular group of terminals "gets hit" more often than others. I just deal with it when the car is in my bay.

Posted via the PriusChat mobile app.

 

A constantly-applied potential of even 12 volts is enough to really speed up the growth of malachite on connector terminals ... that's what used to be seen under the hoods of old cars before we had good weathertight sealed connectors. A pin on a constant unswitched +12 circuit would pretty much always be more covered in green stuff than its only-intermittently-powered neighbors.

I strongly suspect (but haven't tried to find out for sure) that the speed of the reaction depends on the voltage gradient. So if you have a terminal at +12 that's an inch away from something grounded, there's a 12-volt-per-inch gradient there. If it's half an inch from something grounded, that's a 24-volt-per-inch gradient, and so on.

The orange connector has a bunch of terminals all pretty close together and not far from a grounded case, and the pin-to-pin voltages are anywhere from 14-ish up to a couple hundred depending on which two pins you pick.

I've long thought that generating a plot of the voltage gradients (taking all of the pins into account) superimposed on the geometry of the face of that connector would be a fun graphing exercise, only so far I haven't had the time for that much fun.

 

There's no time for fun? I'm pretty sure that leads to heart disease...

 

Haven't had time, so far, for that much fun.

So if there's somebody else with time to generate that plot, I haven't deprived them of it.

 

The more I think about this situation the more I think about it from the perspective of a sound engineer and why they spend so much money to ensure the clearest sound possible by reducing signal to noise ratios. As in corrosion in the ECU plug all the way up until the plug and ECU fry is more noise than signal, which screws up the ECU data.

 

On the module busbars that link each module in series, one end is always more built up with corrosion than the other. Electron flow is the reverse to that of conventional wisdom, electrons flow from the marked negative side to the marked positive side, yet another example of early wisdom being completely wrong.

The voltage and current need to be high enough to ionise the air gap ..... you can't make a spark plug arc the gap with even 48v, I doubt you could using the full prius battery voltage

T1 Terry

 

Batteries produce DC voltage; in the case of my car, it's 200-300 volts. This tends to create a high potential for electrolysis, which causes corrosion. There are some metals, such as gold, which will resist corrosion, but they tend to be very expensive. It's much more cost effective to use a dielectric grease once the terminals are connected.

 

Electrolysis occurs between dis similar metals when current passes between the dissimilar metals, the voltage has little to do with it, the current key element.
The point we are trying to establish is the cause of the corrosion between two similar metals, there is not 200vdc to 300vdc between each terminal in the multi pin battery computer plug, at the very highest there might be 19v, 9.5vdc per module, 2 modules in series are voltage sensed by the battery computer. That is enough to cause an arc if a good contact is not made and this corrosion build up is enough to create the heat in a single pin to allow it to pull back out of the socket in the battery computer.
19vdc is not enough on it's own to cause this type of corrosion to form, creating the poor contact that then generates the heat, something else needs to be involved, some chemical compound, like the leaking acid/water mix in lead acid battery causes a reaction in the lead to lead or copper or brass to create that type of corrosion.

Is it the electrolyte leaching along the voltage sensing cable, fumes from the leaking electrolyte entering the plug/socket enclosure, moisture and dust? Something else?

T1 Terry

 

Everybody mark your calendars, 'cause I'm going to agree with Paul here.

Yes, it is the flow of current that is key in electrolytic corrosion.

Question: where does the voltage come from to make that current flow?

Answer: doesn't matter. If you do have a junction of dissimilar metals (some volts different from each other in the galvanic series) getting damp in the environment, then that's a battery right there and you don't need anything else. The voltage of the junction makes the current flow.

If you're dealing with similar metals, then there isn't that intrinsic source of voltage to make electrolytic corrosion happen. But a tendency for current to flow can just as easily exist because of some other source of voltage. A voltage because the terminals happen to be connected to a bunch of NiMH battery modules, for example.

Note you can also use external sources of voltage to oppose the corrosion process. If you have, say, dissimilar metals producing a voltage tending to make a corrosive current flow, and you use an external DC power supply to impress an adequate current in the other direction, you'll have built an impressed-current cathodic protection system.

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You seem to be thinking in isolation about two terminals wired to adjacent blocks in the stack. Don't forget that the orange plug at the ECU has all of the terminals from all of the blocks in close proximity to one another, including terminals over 200 volts apart. Toyota has put the terminals into the two rows in an interesting order that seems intended to keep the voltage gradients (in V/mm, say) reasonably low, but to calculate what the steepest gradients are on that plug requires taking into account all of the voltages present on all of the terminals. There's been some discussion of that, and a link, upthread.

This type of corrosion was routinely seen on engine-compartment terminals in older cars before weatherproof sealed connectors were as good as they now are. The ones most affected were those constantly powered from the 12-volt battery.

 

Settle down, it's just a technical discussion.
It's not current flow (amperage) that causes electrolysis, it's voltage potential.
A high voltage will not cause current to flow unless it has a path through a conductor.
When dissimilar metals come in contact, they form a weak battery, which can cause electrolysis, given time.

 

I'd actually prefer no one settle @ChapmanF down... The more we rile him up the better! He's at his best when he gets all wound up about stuff.

 

Right, as long as it stays a technical discussion, it's all good.

So we have it's not current flow, it's voltage, and we have occurs when current passes, the voltage has little to do with it.

Partial credit to each.

Motion of electrons is the key thing happening in corrosion: they move from the molecules of one substance, leaving positively-charged ions, and toward another, where negatively-charged ions result. There has to be a path for those traveling electrons and a path where the same amount of charge moves the other way, say as ions moving through a layer of damp.

But that motion of electrons (current, by definition) doesn't happen just because they're bored. There has to be a voltage motivating them to move. That can be the voltage difference between dissimilar metals on the galvanic series, or it can be a voltage from any other source, such as a big ol' battery that just happens to be part of the picture.

 

Not to put too fine a point on it, but the amount of current flow in an electrolysis reaction is minuscule.
It happens in proportion to the voltage. Deal with it, we're not all perfect.

 

The current flow, of course, is in exact proportion to the amount of electrolysis happening, because the current flow is exactly how it happens. The voltage needs to be adequate to make it happen (where 'adequate' depends on various conditions).

Electrolysis reactions can be useful, and can happen on minuscule or massive scale, with current flow to match.

 

You win.
I guess.

Can't let anything go I see.

 

And the flow of the electrons that are causing this corrosion has more the characteristic of signal noise and not just simply the signal itself... Do you agree or disagree?

 

Of course there is always some tiny amount of current in any reaction, so you win on a technicality.
Congratulations.

 

I didn't know I was trying to win? I thought we were trying to work together to figure out the cause?