G3 Wire Harness

I'm not always this enthusiastic about a product Azusa promotes, but I totally agree this one fills a genuine need, because Toyota would sell you one of these for gen 1 or gen 2, but they stopped selling it for gen 3 and just said "if you need it, buy a whole battery".

The nickel-plated bus bars and wide SS flange nuts all seem well chosen. Nice package.

There are a few bits on the sell page that do seem pretty superfluous:

• To be as efficient or more efficient than OEM in transmitting a signal between the battery modules and the ECU.
• Voltage sensor tabs are made of a better conductive copper alloy compared to the OEM
• Wires' operational temperature rating is greater and internal resistance is lower, compared to the OEM.

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... these wires connect blocks in the battery to voltmeter circuits in the smart unit. Voltmeters by nature are high impedance. Milliohms added or subtracted in these wires won't rise to the level of rounding error.

I am glad the listing mentions the color code doesn't match factory. Even better if some label on the harness itself says that, just so no tech ends up looking at it and getting confused.

Some information I would like to see and don't see would be the actual type of wire insulation used. Although this harness looks innocent enough, it is a high-voltage part, with wires that can be more than 240 volts different crowded together in a tight space (especially where they are bundled through the orange tubing). And the wires are very thin, which I suspect Toyota gets away with by using a very thin insulation that nevertheless has the requisite high-voltage performance. Similar thin wires commonly available for purchase might not have a suitable rating on this score—which is arguably more relevant than, say, higher copper conductivity.

 

IR is resistance on the power path.

This harness isn't any part of that path; it just connects 14 sample points along the path to high-impedance voltmeters. You could make the wires in this harness out of audiophile-grade oxygen-free copper or the belt wire out of old tires and it wouldn't affect the IR either way.

That said, I do believe this harness ships with a set of shiny nickel-plated busbars included, and those are part of the power path, so that part of the kit could legitimately affect the IR of the assembled battery. By how much? I don't know. It would be straightforward to measure ten samples of stock copper busbars and ten samples of the nickel-plated ones on a microohmmeter and report the numbers; that's been talked about a few times over the years, but I'm not sure anybody's gone and done it.

 

You might be confused, or you might have escaped taking electronics in school.

The nickel bus bars are part of the power path, sure enough. This harness, and even its "better tabs", are not. The harness only connects those points along the path to voltmeters to sample their voltage.

An ideal voltmeter draws no current whatsoever. Any real voltmeter draws a tiny amount, but so tiny that one wire isn't going to "transmit better voltage readings" than another. It matters more that the wires are insulated appropriately for the voltages and temperatures they're going to see, and not too mechanically frail to hold up to expected vibrations and stresses.

(By the way, I haven't seen details on what this harness uses for insulation. I strongly suspect that Toyota gets away with making the wires in their harness so thin by using some unusual insulation to get the right safety margin for the voltages involved.)

I guess that wouldn't surprise me, and there have been other suppliers of alternate bus bars too, who might also have made videos. There have been a lot of bus bar discussions here over the years.

It would be straightforward to measure ten samples of stock copper busbars and ten samples of alternate ones on a microohmmeter and report the numbers; that's been talked about a few times over the years, but it's not something I remember seeing in any videos about them.

 

None of the current powering the car flows through those wires. None. IR is not affected by them.

Voltage drop is proportional to current. Did you miss the part about voltmeters drawing practically no current? There is practically zero current flowing along those wires.

Want to quibble about the difference between 'zero' and 'practically zero'? Ok. But the car's voltmeters report down to hundredths of a volt only, as you've seen on countless live-data screenshots. You could take a hundredth of a volt, divide it by the difference in resistance between this wire and a stock wire, and see how large the current would need to be to make any difference the car could even detect. It would come out larger than 'practically zero'.

[Edit: an even simpler way to see it: PriusChat member landspeed dissected a gen 2 battery ECU and found that where each sense wire enters, a 1000 Ω resistor is in series. So, what's the difference in resistance between one of these wires and one of the Toyota wires, and what is that difference in proportion to 1000 ohms?]

A wire carrying practically zero current is the same voltage at both ends. That's how it will "transmit" the voltage to the voltmeter. Doesn't get much better than that.

Heat generation is proportional to current squared. If 'practically zero' sounds already pretty darned small, wait till you square it. (Remember values less than one get smaller when you square them.)

there's almost some useful information there by accident. So what is the insulation on these wires? What is its dielectric strength and heat rating, and how do those specs compare to OEM? Also, where did you get the OEM specs?

It's quicker now, too? This wire will be the same voltage at both ends faster than the wire Toyota uses? There's a speed-of-light accelerator installed?

You clearly have mad skillz for writing prose like this post that throws together concepts you've sort of heard of. You could go further if you wanted and even learn about them, but clearly you can go on writing stuff like this post without bothering.

 

Did you find an AVS marking on the OEM wires, or have you decided by "examining" them that they are "like" AVS wires?

The AVS 60 V nominal voltage rating makes me think Toyota would not have been likely to choose AVS for this harness, where Uₒ and U of ~ 270 V can be seen.

We're seeing the same temperature ratings here, and roughly the same resistance ratings. You've used "IR" here, a term specific to batteries and other voltage sources, where talking about a wire. This is just resistance.

I assume FLRY-B is what you know the new harness to be made of, which also seems like a choice Toyota might not have made for this harness, given the same 60 V nominal rating as AVS.

Also you said IR where you meant resistance again. But we can use the figures you've given (and assume the 50.2 mΩ/m figure you found for AVS is close enough for whatever wire Toyota really used): the difference between 50.2 and 37.1 is 13.1 mΩ/m.

Let's say the longest wire in that harness is about a meter, so there's a difference of 13.1 mΩ for that one (and smaller for all the others).

We can even assume (for argument's sake, as it gives you the most benefit of doubt) the ECU's voltmeter input impedances are not any higher than the 1 kΩ resistors that landspeed found right at the input pins. So, by how much would a typical block reading of 14.40 volts change if we changed a total voltmeter impedance of 1000.0502Ω to 1000.0371Ω?

The change is 26 times too small to make any difference in the last decimal place of 14.40.