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I heard about this on the Go Hypermiling podcast, and I wonder if that's what I experienced in my first-gen Insight. What is a SoC crash, at what cell temperature does it happen, and where does the energy that was stored in the pack go?

I have a few clues, although not claiming to be an authority.

If your battery pack is already going bad, hot weather will make it worse. The fans will kick in and put a drain on the pack....normally not so big a deal, but one weak or unbalanced cell is enough to cause a recal. Use of the A/C is also a big draw, although I'd recommend it's use to protect the batteries.

Hi Robert;

The thermal SoC crash that we referred to is an instrumented, automatic routine put in place to contain any potential damage to the battery pack under certain high temperature conditions.

While the earlier Honda hybrids implemented a somewhat more hard-wired approach to this process, it also remained a bit more discreet than the later generation IMA's.

In any case, when such an event occurs, the SoC is usually invalidated and the system is forced to re-discover its actual position on the charge curve. Under normal situations the charging process ends with the discovery the effective upper voltage levels and life goes on with the operational changes that entails. When this happens the instrumentation is effectively re-calibrated for the current temperature ranges.

Now, if a problem is found during the charge process then the system may enter a state often referred to as a managed mode. I am not sure if this works the same way for earlier Honda hybrids but the later versions have this mode at both ends of the temperature scale. In the case of a very warm day, the system will aggressively manage the charge and assist patterns to the point that you may get almost nothing of each and the car will invariably stressed with poor acceleration until it slides back into a safer range.
If this happens under any other circumstances then I would have the car looked at. It could be something simple (like a bad fan driver or IPU vent obstruction) or it could be a condition of potential thermal run-away withing a battery module.

Maybe this will also help a bit:
Understanding your HEV NiMH battery pack (http://www.cleanmpg.com/forums/showthread.php?t=24829)

Cheers;

MSantos

Thanks for the explanation, msantos. The IMA system is occasionally unpredictable, and it doesn't give me as much feedback as I'd like on why assist or regen is cutting out.

I have been grid charging my stock battery pack more or less nightly for a few weeks now. I leave the BCM (and everything else on the IMA fuse) running. One morning, I unplugged the charger and noted 166V. A few hours later, I had 162V and 16 bars instead of 20+ bars on the SoC gauge. I expect a small decline in pack voltage, but I was not expecting a 4V drop and a recalibration.

Honda doesn't turn the battery fan on soon enough for my taste, so I'll have to fix that. Meanwhile, I've felt my battery module get pretty hot once the battery is full - at least 120°F.

Btw, Chuck, the Insight doesn't have electric air conditioning. Unfortunately, mine doesn't have ANY air conditioning, yet. It took a long time for me to come to terms with the fact that I need to drive with at least the driver's window down, even on the interstate.