Battery bus bars

Cleaning and polishing bus bars. One way.

 

Coles Notes summary:

Bus Bars: soak in sulfuric acid, followed by vinegar soak. Polislh with 2500 grit wet/dry sand paper.
Nuts: spray generously with Carb Cleaner or similar.

 

My understanding had always been that the nickel-plated ones were nickel-plated copper.

If somebody out there is selling nickel-plated stainless bars, we should know who that is, 'cause yeah, that'd be weird.

 

If "all" the aftermarket busbars are plated stainless (which doesn't make much sense to me anyway), wouldn't that show up as (much) higher internal resistance numbers on scan data?

It might be true, but I don't care enough to open my pack up and remove the plating on one if my busbars.

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I wonder if something that hasn't been considered regarding the plated busbars is thermoelectric effect. Copper and nickel have somewhat different Seebeck coefficients (6.5 for copper, −15 for nickel, relative to platinum). I don't know what the material is of the battery module terminal studs. That might lead to an effect (not sure how large) where current flow moves some heat from one end of each bar to the other.

 

Yeah, I'm more inclined to keep and clean my original bus bars. Although $120 for a new OEM is not bad but it seems nobody has them in stock except Ebay shipped from Japan....which hopes to be correct OEM. I think I see it listed as item #11 on the hybrid battery parts item page


8216547040 is the part number for wire #2 $67.05 From Olathe Toyota. but that is only half of them?

 

Well, the resistivity of stainless steel is 41X higher by this source:

https://www.thoughtco.com/table-of-electrical-resistivity-conductivity-608499

45X is plausible for some other stainless steel alloy though. Not sure why they would use stainless steel when aluminum conducts much better (1.7X more resistivity than copper).

What really matters is the resistance of the part, and that in turn depends on the part's geometry. The frames of most cars are stainless steel and large currents pass through them without causing problematic heating, but that is because the cross section (perpendicular to the current direction) is large. I can believe that when Toyota designed these bus bars they made them as thin as possible to save on copper costs. Replacing them with a bus bar of the same size made of stainless steel might very well result in a part with too much resistance for the peak current. (Which would be a problem for regular NiMH cells too, right?) However, if the stainless steel part was made thicker it would eventually have the same resistance and would work just as well (albeit probably also requiring longer bolts, and it might be too thick to fit).

Has anybody measured the resistance of the two types? Measuring very small resistances on most DVMs isn't possible, but force 10A through the part and it should be possible to measure the voltage across it easily enough, and then derive the resistance from that. From the known part resistance and the known peak currents we can estimate how much power is dissipated in the two types of bus bar.

 

It's way easier and less toxic exposure to your body to just toss 'em in a rock tumbler for 24 hours. Nearly effortless way to get 'em clean.

 

I used to buy solid nickel bus bars that were nice... Trying to find the link for those right now...

 

As far as sulphuric acid, not sure I'd want to mess with that. Acetic acid at 5%, aka vinegar, seems like it would do the trick, just take a bit longer. I've got a bottle of "short stop", a darkroom concentrate of acetic acid. It might be a bit stronger than vinegar.

 

I think frames are typically steel, sometimes of exotic high-tensile types, but very uncommonly stainless.

To measure anything like one of these busbars meaningfully, of whatever material, you would probably look at something like this, a combination of a high-current source and a voltmeter with resolution in microvolts.

 

Getting to the point where I’m dealing with acid and bus bars, I’ve already made sure I have the proper procedures to handle 250 volts DC which can kill me, it’s also having the proper procedure for handling sulphuric acid.

 

Right you are, steel, not stainless steel. Except maybe in vehicles with tubular frames, like a custom off road buggy or a dragster.

Exactly, not easy to measure the resistance of objects which are good conductors. Unless one is careful most of the resulting value will be from the junction resistances where the meter probes touch the test object. Using the sort of DVM most people have it would be impossible to distinguish between a copper and a steel bus bar, both will read as 0 Ohms, or more likely, values dancing around near that value as the probes slide a bit on the surface during the measurement.

These bus bars are what, around 0.1 mOhms? That is a rough guess based on ~100A max current and ~1W power dissipation, using
R =P/(I^2). My best DVM can measure 0.1mV resolution on the 200 mV range. 40X that resistance with 10A going through it is 40mV, which it could see. Just. (To 0.7% accuracy, +5) But for the copper ones that would only be 1mV. In theory the DVM could resolve it, but I wouldn't bet money on it. Probably need to make special leads to bolt securely to the ends of the bus bar. In any case, I don't have a DC power supply which will current limit above 2A, so this is all hypothetical for me.

 

Sulfuric acid seems like much too strong an acid to just remove a little corrosion. Try vinegar and a toothbrush.

The rock tumbler would probably nick the surface considerably, unless it was brand new and no rocks had previously been in it.

 

The key is a proper 4-wire measurement. In the photo of the micro-ohmmeter above, the banana jacks are kind of cropped out at the bottom, but there are four of them. Two supply the current across the thing under test, while the other two measure the voltage. Because the voltage connection junctions are carrying virtually no current, their resistances drop out, leaving an accurate measurement.

As it happens, what's being measured in that photo (at 0.2776 milliohms) is about an inch of copper pipe-support strap, which is maybe not too much different from a battery busbar.

 

There's no justifiable reason to use acid on bus bars. Just put 'em in a rock tumbler for 24 hours and you're done...

 

One of the ways Honda caught up to Toyota in the early years of hybrid technology when Toyota was way ahead of them was building the first Honda Insights on an all aluminum chassis with mostly plastic bodywork, which made their car a thousand pounds lighter than a Prius. Because of this it accelerates faster, requires less total horsepower and gets better MPG. If I owned a shop with extra space I'd have one of these 2001 Insights in a corner where I'd convert it to all electric and take it to the race track often.

 

Seems like if the steel bus bars get hot enough to damage the LiFePo4 cells they are probably also hot enough to do bad things to the OEM NiMH cells. Since measuring the resistance is clearly not something that most of us are going to be able to do with the tools at our disposal, how else could one determine the material of the bus bar? Destructively would be pretty easy - drill a hole through it or cut it in half. Not great if one doesn't have a spare bus bar though. Are the steel ones different in dimension (tell the difference with a caliper) or weight? A magnet might be able to tell the difference, but that would depend on what sort of steel is used, some are not ferromagnetic despite containing iron.'

Edit: looks like OEM bus bars are just copper, not nickel plated copper. Are there nickel plated copper bus bars too?