Replaced corroded ground straps

[shifty35]

I'd noticed the ground straps in the Insight weren't looking too good. Neither were broken, but one was slightly frayed. Both had a fair black / greenish corrosion look to the copper. I'd made up my mind to replace them last July, but just now got around to it (it helps that I just bought a house and have a garage to work in).

Not wanting to replace them with OE quality, since OE is obviously not that great, my experience with car stereo work told me to go big

I replace them with short lengths of 4GA oxygen free copper ground cables with crimp on ring terminals. I also cleaned all of the mating surfaces with a wire brush prior to reinstallation. I pulled the negative battery terminal before hand to reset the IMA, as I'd never done so before.

Initial results seemed fantastic... I had to really abuse the assist to get the first bar to drop off! I'm talking at least 3-4 minutes of prolonged assist, using the friction brakes to decelerate rather than regen as normal - harder than I would ever have a reason to actually drive it. Eventually I got it down to 2/3 SoC where it recal'ed as it typically does.

After recharging (post-recal), I've noticed that regen becomes limited (although full assist is available?) as battery temps rise.

I'll post more results when I get them, but it definitely seems like an improvement to me.

Next I'll be replacing the battery terminal and negative terminal strap to ground with something similar. I think this car's electrical performance is a bit too important to skimp on.

Now hopefully that IMA light will come on in the next 16k so I can get a free battery...

[joecvt]

Originally Posted by shifty35

... I pulled the negative battery terminal before hand to reset the IMA, as I'd never done so before ...

Since your ground straps were not too damaged and possibly still functional, how do you know the improvement you saw came from the replaced ground straps and not the IMA reset that you have never done before? Both things that you did could fix a problem.

JoeCVT = Just your average CVT owner

[shifty35]

Eh, I was hoping that the combination might eliminate the recal behavior, which it didn't. The IMA reset seems to me like a typical recal, although clearing out the MCM's memory may have some additional effect.

One of the ground straps, which was slightly frayed, broke in half as I straightened it to measure it. Second thoughts say they were probably pretty bad.

Typically while driving at night I have difficulty maintaining SoC in the HV battery - I used to attribute this to high 12v load, frequent FAS'ing, and driving to minimize braking (and therefore regenerative braking). With a few decent regen stops, SoC easily got up to full and stayed there. Never seen that happen before at night.

More info will be available after my commute tonight.

[joecvt]

Originally Posted by shifty35

One of the ground straps, which was slightly frayed, broke in half as I straightened it to measure it. Second thoughts say they were probably pretty bad.

I imagine if it was that brittle to break, chances are that is wasn't doing a good job as a ground wire either.

JoeCVT = Just your average CVT owner

[Mike Dabrowski 2000]

A caution about the ground straps.
While bigger is better electrically, the bigger wire is likely stiffer, and will work harden and fail. I replaced both of my ground straps last year with some #6 insulated stranded wire. The copper fatigued right where the ring terminal meets the wire insulation after only 4 months. The engine vibrates a lot, so it is very important that the straps are dissipating the vibration over the whole strap rather than at any transition point, or they will not hold up, no matter how thick they are.
Recals seem to be related to subpack to subpack balance rather than the ground straps. The IMA HV is floating relative to the chassis ground, and actually has a ground fault detection, so the two straps effect the ECM operation more than the IMA in my experience.

[shifty35]

Originally Posted by Mike Dabrowski 2000

A caution about the ground straps.
While bigger is better electrically, the bigger wire is likely stiffer, and will work harden and fail. I replaced both of my ground straps last year with some #6 insulated stranded wire. The copper fatigued right where the ring terminal meets the wire insulation after only 4 months. The engine vibrates a lot, so it is very important that the straps are dissipating the vibration over the whole strap rather than at any transition point, or they will not hold up, no matter how thick they are.
Recals seem to be related to subpack to subpack balance rather than the ground straps. The IMA HV is floating relative to the chassis ground, and actually has a ground fault detection, so the two straps effect the ECM operation more than the IMA in my experience.

I think I left enough slack in the cables to give them some room to move. It's pretty high quality car stereo grade cable, very very fine strands.

I think the key relation of the ground cables and the IMA lies in the DC-DC operation. Bad cables may cause the DC-DC to be overactive and lead to excessive background charging.

I did notice this morning that the HV battery stays fully charged with very little effort compared to before. But as suggested before, this may be due to the IMA reset. I have forced one recal since the reset, and the improvement seems to remain. I will likely replace the negative battery terminal and ground strap with something a bit higher quality as well just to get the mod bug out of my system.

On a slightly related note, has anyone measured the voltage drop across the IMA HV cables? They are pretty long, and it is unlikely Honda went with a super high quality cable. Even a 2-3v drop would cause a lot of resistive heating.

But with copper prices these days, replacing the HV cables with something great for an extra 200-300 watts out of the IMA is a tough sell.

[dtlee]

i measured about 0.6Ohm across my old ground strap and 0.2Ohm across my new ones

[shifty35]

Most wire is rated in terms of ohm / foot, and is pretty easy to find. I'd think the terminals / connections are more important in determining the overall resistance of the connection.

But it's an interesting experiment for sure.

[Mike Dabrowski 2000]

The ground straps are not part of the IMA current path. The IMA is actually totally isolated from chassis ground, with ground fault sensing in the event of a short due to a crushed HV cable.

[shifty35]

Originally Posted by Mike Dabrowski 2000

The ground straps are not part of the IMA current path. The IMA is actually totally isolated from chassis ground, with ground fault sensing in the event of a short due to a crushed HV cable.

I haven't suggested they are a part of the HV system. My use of the term "IMA" includes the DC-DC as well as all the 12v logic controlling it. Sorry for the confusion.

The ground straps between the engine and the chassis are keep the ground potential the same everywhere. If the engine or trans were allowed to "float" to a different potential, sensors and all kinds of things would start going awry, as it pretty well documented.

The IMA motor, being a large rotating magnet, could induce all kinds of strange potentials within the engine bay while the engine is running. These ground straps are critical to keep everything in sync.

The DC-DC is grounded just outside of the IPU box in the rear. My thought is that the quality of the ground paths may effect DC-DC performance.

Just a theory. Either way, I've also replaced the ground strap from the battery to the chassis. All still seems to be going pretty well.