Aftermarket iMiEV battery upgrade project

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jonescg
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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg »

tonyw wrote: Tue, 15 Sep 2020, 19:00 I'm sure I'm telling you nothing you haven't already calculated, but...

I would be careful about "desensitising" the current sensing. The current sensor is probably also used to limit the current if Leadfoot Leroy floors the pedal on a steep hill or driveway. If the indicated current is lower, you risk overheating something, and there are electronic components in there that don't like to be overloaded. The motor can probably take a 20% overload briefly, but silicon can't.
The inverter has it's own internal DC and phase current sensors which it uses to do just that - so I think messing with the battery current sensor is probably fairly safe.
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Re: Aftermarket iMiEV battery upgrade project

Post by coulomb »

richi wrote: Tue, 15 Sep 2020, 14:29 I dare say hacking the current sensor won't be enough—it would compensate for the Coulomb counting downward that I assume is happening, but not of course for the trigger at critical low cell Voltage.
Right, but the larger capacity should stop the low cell voltage from happening as soon. Plus, we want to retain protection against low cell voltage. LMO and NMC have similar characteristics at lower SOC.
Not sure from your description, but it sounds like the new cells reach that Voltage at a much higher SoC, right?
Yes.
Likely you'd need to intercept and rewrite the messages from the CMUs to the BMU, and fake the Voltages.
I certainly hope it won't get anything like that complex.
I don't know if anyone has pulled out the BMU hardware to see if it's actually reflashable.
✋ I have found a MUT-3 update CD with iMiEV specific files, but most of the ECU firmware seems to be encrypted. It may be possible to figure out how to decrypt by analysing the MUT-3 PC software, but the keys etc may reside inside the MUT-3 itself. I found that the CMU firmware is not encrypted, and have analysed some of that, but it's hard going, and I've made little real progress.
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Re: Aftermarket iMiEV battery upgrade project

Post by coulomb »

jonescg wrote: Tue, 15 Sep 2020, 14:40 Should quickly add that the original LEV50 cells were LiMnO2 chemistry, not LFP.
Oops, I used "NMO" instead of "LMO". Sigh. I've edited the original post.
LiMnO2 cells maintain a higher operating voltage in the first 50% of the SOC, unlike NMC which tend to show a quick drop off to 4 V and fairly linear drop over the SOC.
Yes. That's the problem, that initial rapid drop-off in voltage.
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Re: Aftermarket iMiEV battery upgrade project

Post by coulomb »

jonescg wrote: Tue, 15 Sep 2020, 19:20 The inverter has it's own internal DC and phase current sensors which it uses to do just that - so I think messing with the battery current sensor is probably fairly safe.
I'm glad to hear that. But there is still the chance that some ECU will compare the current measured in the battery to the current measured in the MCU, and if the two differ by more than a certain amount, it may generate a trouble code. But there are other loads on the main battery (heater, air conditioning, DC-DC), so the two will never be the same, so maybe they won't compare them. [ Edit: However, the battery current reading less than the current consumed by the motor controller might cause problems. ]

There may be other uses for the battery current than for counting coulombs (estimating SOC) and the motor controller. Hopefully we'll find out soon.

I also worry about long term drift of the current sensors; there will be a DC offset introduced. It should be small with high precision resistors, but the current sensor itself won't be perfect, and they may have calibrated out the error and saved the calibration data inside the BMU. But hopefully all that gets reset every time the battery gets charged.

Finally, the BMU may well be assuming LMO characteristics, adjusting the SOC based on current drawn amongst other things. This monkeying with the current might end up making the learned SOC somehow unstable, or drift badly with time. That might mean that the Range Remaining meter is even more divorced from reality than it usually is, and the turtle may turn up at unexpected times.

So there are plenty of potential problems. :|
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Re: Aftermarket iMiEV battery upgrade project

Post by coulomb »

jonescg wrote: Tue, 15 Sep 2020, 14:40 NMC cell discharge curve:
CJs Discharge test NMC.JPG
CJs Discharge test NMC.JPG (27.57 KiB) Viewed 126 times
Compared with the LEV50 curve, from the datasheet:

LEV50 SOC.png
LEV50 SOC.png (119.4 KiB) Viewed 126 times

Here is my rough attempt at overlaying these two, using only the 25°C curve for LEV50. The NMC curve should probably be a bit higher, bringing them a little closer together:

LEV50 vs NMC.png
LEV50 vs NMC.png (94.43 KiB) Viewed 126 times

My original overlay; messy and partly mirror imaged! The NMC curve has the red dots:

Various lithium + LEV50 SOC 2.png
Various lithium + LEV50 SOC 2.png (362.66 KiB) Viewed 126 times
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Re: Aftermarket iMiEV battery upgrade project

Post by richi »

Thanks for that extra data, Mike. It's not half as bad as I'd feared from your earlier comment.

Do you have a handle on how far it'll actually drive until power gets reduced? (i.e., not just lighting the turtle, but actually acting like one.)
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Re: Aftermarket iMiEV battery upgrade project

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richi wrote: Tue, 15 Sep 2020, 20:41 Do you have a handle on how far it'll actually drive until power gets reduced? (i.e., not just lighting the turtle, but actually acting like one.)
After the 12%/10% turtle light, I believe that when the estimated SOC gets to 0%, the car stops dead. Like a turtle 🐢 on its back :o
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Re: Aftermarket iMiEV battery upgrade project

Post by brunohill »

Good luck Mike. I see Wolftronix still hasn't got his hacked LEAF BMS working. If only they were reflashable with the voltages and currents just written in HEX.
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Re: Aftermarket iMiEV battery upgrade project

Post by richi »

Mike, sorry to keep hammering this point, but have you tried it? If I'm misunderstanding what you're saying, then I apologise.

You see, I have a sneaking feeling that the light is triggered by the Coulomb counting downwards, but the actual power reduction and final shutdown happens on lowest cell Voltage. This is how the Outlander seems to behave.

If I'm right, you might get lucky: The GOM will be utterly wrong, but you might still get 200 km of real, usable range without changing anything. Then a simple add-on OBD-polling app can replace the GOM and you can stick some tape over the turtle ;)
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Re: Aftermarket iMiEV battery upgrade project

Post by nuggetgalore »

oulomb wrote: Tue, 15 Sep 2020, 20:57
richi wrote: Tue, 15 Sep 2020, 20:41 Do you have a handle on how far it'll actually drive until power gets reduced? (i.e., not just lighting the turtle, but actually acting like one.)
After the 12%/10% turtle light, I believe that when the estimated SOC gets to 0%, the car stops dead. Like a turtle 🐢 on its back :o
I test drove my iMiEV three times down to turtle (GOM still reading several km to go). On two occasions, with aircon on I drove at least 4 or 5 km after GOM said zero, it failed to shut the aircon off and reduce available power.
But yes, SoC was not zero, so don't know at what stage SoC the predicted slow down or stop would have happened.
Back to the 93Ah cells:
I still wonder at what voltage the cells stop charging, is it 4.1 V? Or does it depend on how far the pack has run down? Putting it an other way, if the pack would be (artificially) drained below the 49 Ah level when it goes to turtle , would it accept a charge to 4.1 V or does it stop charging at about
the 49 Ah input?
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Re: Aftermarket iMiEV battery upgrade project

Post by richi »

Andreas, sorry but that's not what I'm asking. I want to know what happens to Graeme/Mike's car with the 94 Ah cells.
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Re: Aftermarket iMiEV battery upgrade project

Post by nuggetgalore »

richi wrote: Tue, 15 Sep 2020, 22:08 Andreas, sorry but that's not what I'm asking. I want to know what happens to Graeme/Mike's car with the 94 Ah cells.
Yes, we are on the same page, I too would like to know how the "brain" in the iMiEV restricts the use of more cell capacity. Is it happening at charging or at discharge, or both?
My post(s) referring to my car are to highlight what normally happens, comparing that with data on the 94 Ah cells hopefully may shed some light on where to look for solutions.
Of course I have a vested interest in this, as I may encounter similar issues with the 60 Ah cell project.
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Re: Aftermarket iMiEV battery upgrade project

Post by wovenrovings »

There is another guy in brisbane, Danie Rykiert, that has put a second 150AH pack in the back of his Minicab. Not sure if he is an AEVA member. Anyway he has it spliced into the wires to DC wires to the motor controller. He has reported seeing over 200km on the GOM and fast charging of 47kW. This experience may lend hope to the idea that tricking the current meter from the battery might work.
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Re: Aftermarket iMiEV battery upgrade project

Post by stealthhack »

richi wrote: Tue, 15 Sep 2020, 22:08 Andreas, sorry but that's not what I'm asking. I want to know what happens to Graeme/Mike's car with the 94 Ah cells.
I am waiting too for Graeme's news on the battery project, can't wait for a solution on the BMS "seeing" all the capacity! 8-)
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Re: Aftermarket iMiEV battery upgrade project

Post by tonyw »

We're ALL waiting!

Now what can we Southerners do to help in this investigation? Send pizzas? Beer?
cheers

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Re: Aftermarket iMiEV battery upgrade project

Post by coulomb »

tonyw wrote: Wed, 16 Sep 2020, 19:28 We're ALL waiting!
No pressure, then :oops:
Now what can we Southerners do to help in this investigation? Send pizzas? Beer?
You could find me a decrypted BMU image to analyse. Someone must have one, or know how to get one. But it might be tricky. 😐
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