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Discussion Starter · #1 ·
I live in Canada. Currently, the high temperature is around 45 degrees Fahrenheit. When going down a hill and lightly pushing on the brake pedal, the indicator will show full battery regeneration for about ten seconds, but then it will drop down to three bars of charge, even if I keep the brake pedal lightly pressed and the speed above 40 mph. This seems to happen even if the battery isn't even close to being fully charged. I do not feel the battery cooling fan sucking in air from the vent behind the passenger seat while this is happening, although I know this fan works because it comes on when I use the grid charger. So I'm guessing the battery isn't refusing full charge because it's overheated. Why else would it stop charging at maximum power so soon?
 

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Throttling regen is normal behaviour on hills.

The system has time versus power calculations built in and does not just rely on SOC and/or temperature to determine when to allow regen or for how long.

You would need to have a plug in OBDII device (HDS) to gather some proper data or video the behaviour so we can see if it is out of the ordinary.
 

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Discussion Starter · #3 ·
Throttling regen is normal behaviour on hills.

The system has time versus power calculations built in and does not just rely on SOC and/or temperature to determine when to allow regen or for how long.

You would need to have a plug in OBDII device (HDS) to gather some proper data or video the behaviour so we can see if it is out of the ordinary.
I do have a BlueDriver scan tool which reads data from the OBD port and transmits it to my smartphone. Is this an "OBDII device"? What data should I look for, specifically? What I wonder is, you say the system has time versus power calculations, but what would be the purpose of this? Why would it not want to charge the battery at the maximum power if it's not overheating and it's not close to being full? Or were the designers afraid of the battery being full even if it isn't indicated as being so, and being overcharged?
 

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Peter may be referring to a more complex OBD-II device than you probably own, that can read the data that the IMA module puts out. Some of this information can be read with the "live stream" feature of a regular OBD-2 reader.

It is unlikely your battery is overheating. The IMA system would likely throw a code and light the IMA light on the dash. I actually simulated this (by accident) on a road trip this month by forgetting to plug in the fan on the battery module. It actually took quite a while before the pack got hot enough for its computer to disable it. (Plugged it back in and it is fine now.)

More likely, it sounds like this is a new problem. It is possible you have a weak cell and its voltage is dropping further than the others, and the IMA is reducing power to prevent it from reversing. Actually, that last sentence was a total guess, because none of us have much insight into the decision making software inside the BCM, MCM and ECM.

Hard data is king. Play with your OBD-2 reader and get familiar with the live stream data that it produces. If you really want to go down this rabbit hole (do you like to explore rabbit holes?) then you probably want to get an OBD-2 reader that can read the IMA ECU including IMA voltage and current as well as problem codes (the MCM I think provides this.) If you search "Autel" in the search box above, you may find some threads about what I use and what @minor4326 recently acquired for this purpose.
 

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Discussion Starter · #5 ·
It is possible you have a weak cell and its voltage is dropping further than the others, and the IMA is reducing power to prevent it from reversing. Actually, that last sentence was a total guess, because none of us have much insight into the decision making software inside the BCM, MCM and ECM.
Wouldn't that cause it to throttle assist rather than throttling regeneration?

Peter may be referring to a more complex OBD-II device than you probably own, that can read the data that the IMA module puts out.
Is there one you'd recommend?
 

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Wouldn't that cause it to throttle assist rather than throttling regeneration?
Sorry, I read this wrong!!!!

So yeah, this potentially could happen with regeneration too. I have a modified IMA which shows me stick voltages on my cell phone in a bar graph. A weak cell could reach the peak charge voltage before the others.

Peter is likely right in that there are time vs power calculations going on.

I have seen this backoff functionality happen on my car on downhills, now that I better understand your question. But it has to be a big downhill. And yeah, now that you mention it, it does feel like it would be related to temperature. If the IMA is throttling performance it would be because the designers might be considering the fact that the cells have thermal mass, and it might take some time before the heat makes it to through the case and is picked up by a sensor. They may also be trying to limit gas production within the cell, perhaps localized??? Wish we could ask the designers.

Is there one you'd recommend?
I use the Autel MD-802 All Systems, but this model is not sold new any more. It cost about $250 and can scan pretty much any car any model year. On the Insight it can read all the ECUs. Autel's newer systems are a lot cheaper but you specify which model car you want to use. @minor4326 just bought one and has the latest info.

You can also use Peter's OBDIIC&C which is focused on the IMA functions and intended for the Insight. It is highly recommended by members.
 

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It is unlikely your battery is overheating. The IMA system would likely throw a code and light the IMA light on the dash. I actually simulated this (by accident) on a road trip this month by forgetting to plug in the fan on the battery module. It actually took quite a while before the pack got hot enough for its computer to disable it. (Plugged it back in and it is fine now.)

More likely, it sounds like this is a new problem. It is possible you have a weak cell and its voltage is dropping further than the others, and the IMA is reducing power to prevent it from reversing. Actually, that last sentence was a total guess, because none of us have much insight into the decision making software inside the BCM, MCM and ECM.
I think it's more likely the MDM temperature. Do you know if the MDM fan is running? (Not the IMA battery fan, the other one.)

I have seen this behaviour with stock NiMH batteries, LTO, and with LiBCM. So we know it's not:
  • Imbalanced cells (ruled out by LTO w/ BCM Fooler)
  • IMA Pack Temp (ruled out by LiBCM because it only ever sends 1 temperature)
 
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Discussion Starter · #8 ·
I think it's more likely the MDM temperature. Do you know if the MDM fan is running? (Not the IMA battery fan, the other one.)

I have seen this behaviour with stock NiMH batteries, LTO, and with LiBCM. So we know it's not:
  • Imbalanced cells (ruled out by LTO w/ BCM Fooler)
  • IMA Pack Temp (ruled out by LiBCM because it only ever sends 1 temperature)
Thank you. Where is the MDM fan? I suppose I can see if it's running through these ODB port readers the others mentioned above, or is there another way? If I can at least access it, I can see if it's clogged and maybe clean it and its channels (I suspect my car's previous owner had a dog riding with her a lot of times). Is there something else that would be causing the MDM to overheat? I occasionally get a "High voltage short circuit" error code when it rains, if that has anything to do with this.
 

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Having let this simmer, one possible cause is a weak cell that is causing one of the stick pairs to report a higher voltage than the rest during region; perhaps the voltage difference reaches a threshold and the MCM backs off the current which will keep that difference the imbalance from growing further. This isn't something you are able to see or confirm with an OBD2 or other scanner. Actually seeing if this is the situation requires monitoring the pack voltages going into the BCM, which requires a custom built tool that I think only four people here have built and then correlate that to actual current draw, something which I don't think anyone has done.

The cooler weather may be at play here. I am dealing remotely with a pack that started throwing IMA codes when it got cold outside.
 

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It's not anything to do with the status of the IMA battery. LTO w/ BCM Fooler (so constantly equal reported stick voltages) can still have this happen. LiBCM (so no BCM at all) can still have this happen.


perhaps the voltage difference reaches a threshold and the MCM backs off the current which will keep that difference the imbalance from growing further.
Not that it matters, but to my knowledge, the comms the MCM gets from the BCM on BATTSCI don't include this type of information.

MCM gets:
  • SoC
  • 4 Flags (throttle assist, throttle regen, etc)
  • Battery voltage
  • Battery current
  • Battery temperature (highest and lowest)
  • Some check bits that the MCM originally sent to BCM over METSCI
  • P Codes
  • Request for MCM to force charge IMA battery
 
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