Aftermarket iMiEV battery upgrade project

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nuggetgalore
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Re: Aftermarket iMiEV battery upgrade project

Post by nuggetgalore »

coulomb wrote: Sun, 04 Apr 2021, 17:07
nuggetgalore wrote: Sun, 04 Apr 2021, 16:46 I doubt that the shock from connecting two packs with 2 or 3 volt difference could kill a cell, but maybe I am wrong again?
I agree, paralleling the packs with such a small voltage difference would not have caused much current to flow, much less killed a cell.

I thought you measured the 25 V on the bench, with a power supply limited to 25 V. If it's still buried in the pack, by guess is that a link has gone open circuit or high resistance.
Still buried in the pack when I measured the high volt across that cell. I have removed the cell from the module and it is definitely dead.
coulomb wrote: Sun, 04 Apr 2021, 17:07
I can imagine about a 25 V drop (7.5%) of the main pack under load; if there was an open circuit link, most of that 25 V would appear to be that cell's voltage. Actually, I would expect it to appear to reverse in voltage.
Edit: Not quite correct.
Thanks for pointing this out, yes it must have been reverse, as the good cell volts did not change but the pack volt went down as I drove a few km up hill with the main pack behaving normal.Yes it must have been reverse volt while driving, but it was actually while charging that I was able to measure module and cell voltages where I found the discrepancy of pack voltage v cell volts x 88. I did not measure module or cell volts while driving, I can only observe (relatively safely) what the EvBatMon app displays with large digits and the millivolts measured across the current shunt between the two packs.
coulomb wrote: Sun, 04 Apr 2021, 17:07 Luckily the main pack was there to limit the reversal.

So maybe the cell is OK after all.
Dead as a dodo. Does not even light a tiny torch light globe.
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Re: Aftermarket iMiEV battery upgrade project

Post by nuggetgalore »

nuggetgalore wrote: Sun, 04 Apr 2021, 18:29

Dead as a dodo. Does not even light a tiny torch light globe.
I still have no idea why this cell died and coincidentally showed up as I paralleled the two packs the first time (with practicably no voltage difference ie no current shock).
I replaced that cell with the one spare I had left and charged and driven the car successfully now for several hundred km.
I get a realistic 120 km range. I think I can detect a very small increase in energy use per km due to the added weight of approx 100kg by comparing trips I recorded prior (CaniOn) with similar trips now. In the big scheme of things I consider it negligible. The bigger question is how long until the next cell dies for no apparent reason. So far they all appear to be ok.

Here a few observations re the current draw while charging and driving.
Scanners and apps show the amps exactly as before what goes in from charger to battery resp out to inverter. I have a current shunt showing what goes in and out of the additional pack.
Standard charging at 12.5 A from 240 VAC indicates 7 or 8 A DC (depending on app or scanner).
Strangely only about 2.5 to 3 amps go to the additional pack.
But the reduced current into the main battery reduces the difference of the voltages of the lowest to the highest cell considerably (from >0.04 to <0.02 V) during charging (for other reasons charging stops just short of the pack getting to 361V, resp cells to 4.11V).* The same is true for discharge under load, the voltage differences shown on EvBatMon are considerately smaller than before with either of the packs.

I had a mate recording videos of the EvBatMon app next to the DMM showing the current in mV that is drawn out or charged back to the additional pack while I was driving.
The amps to and from the additional pack read as much as 60 to 70% of the total current drawn or regenerated (opposite to when charging of the wall).
Quite often after stopping, there is a current of a fraction of an A up to 2 or 3 A flowing either one way or the other for a few minutes until the packs are equal.

* francisco.shi probably knows the answer to this with his knowledge of SoC and coulomb counting.
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Re: Aftermarket iMiEV battery upgrade project

Post by francisco.shi »

I assume you have two packs connected in parallel.
So if they had different impedance then one would put out more energy than the other.
Let's say we have 2 packs of the same capacity and one has 1Ohm and the other 0.5Ohm internal resistance. We put a load of say 10A. So the voltage will sag to 3.3V (1 Ohm in parallel with 0.5Ohm gives you 0.33ohms)
So now we get that 3.3v into 1 Ohm is 3.3A and 3.3v into 0.5Ohm is 6.6A.
Let's say we do this for 1min. So the pack with 0.5Ohm has supplied 6.6Amin and the other pack has supplied only 3.3Amin. So one pack has discharged more than the other. When you remove the load the pack that has more charge will now try to charge the pack that has less charge hence thehe current flow. If both packs were made of the same cells (and same age) the difference will be so small you wouldn't notice it. Also note that the length of cable connecting the packs is part of the internal resistance. So if one pack is in the front the other in the back and the inverter is at the front the pack at the back will appear to have higher internal resistance.
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Re: Aftermarket iMiEV battery upgrade project

Post by nuggetgalore »

francisco.shi wrote: Fri, 16 Apr 2021, 15:40 I assume you have two packs connected in parallel.
So if they had different impedance then one would put out more energy than the other.
Let's say we have 2 packs of the same capacity and one has 1Ohm and the other 0.5Ohm internal resistance. We put a load of say 10A. So the voltage will sag to 3.3V (1 Ohm in parallel with 0.5Ohm gives you 0.33ohms)
So now we get that 3.3v into 1 Ohm is 3.3A and 3.3v into 0.5Ohm is 6.6A.
Let's say we do this for 1min. So the pack with 0.5Ohm has supplied 6.6Amin and the other pack has supplied only 3.3Amin. So one pack has discharged more than the other. When you remove the load the pack that has more charge will now try to charge the pack that has less charge hence thehe current flow. If both packs were made of the same cells (and same age) the difference will be so small you wouldn't notice it. Also note that the length of cable connecting the packs is part of the internal resistance. So if one pack is in the front the other in the back and the inverter is at the front the pack at the back will appear to have higher internal resistance.
Thanks for that explanation. There is a further complication in that the two packs are different chemistries.
One pack,the original iMiEV LMO LEV50s are degraded to about 65%.
The other pack with the so called "60 Ah" NMC LIYUAN cells that gave me about the same range as the degraded old cells at first but then dropped of (maybe because of the failed cell although the BMS did not show any bad cells while they were installed as the sole traction pack).
The discharge curves show that this is not a good marriage, but like in real life one has to make compromises....and so far it is working as good as I could hope, the accidental reset of the battery health a definite bonus now.
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Re: Aftermarket iMiEV battery upgrade project

Post by brunohill »

Hey Andreas,
Does your iMiEV have Chademo? Are you brave enough?
Last edited by brunohill on Fri, 16 Apr 2021, 20:58, edited 1 time in total.
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Re: Aftermarket iMiEV battery upgrade project

Post by francisco.shi »

The different chemistries shouldn't be a problem as long as you don't exceed either of the voltage limits. If the voltages are not the same then one will be underutilized.
And each pack should have its own BMS.
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Re: Aftermarket iMiEV battery upgrade project

Post by nuggetgalore »

brunohill wrote: Fri, 16 Apr 2021, 20:45 Hey Andreas,
Does your iMiEV have Chademo?
yes.
brunohill wrote: Fri, 16 Apr 2021, 20:45 Are you brave enough?
No, not yet anyway!
I have fast charged the original pack only once, but the previous owner did it all the time.
The aftermarket pack I charged twice at Monash Uni Chademo to check if it is working, but since the battery was about 3/4 full it only charged for for a few minutes at more than about 8 A which is the same rate as the OBC pumps in and I stopped at 80%.
I cannot see any real problem once I have a better BMS on the additional pack. Currently I only have cell balancers that start balance if they detect 100mV difference, so far the worst is only
40 mV while charging and I do keep a keen eye on it.
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Re: Aftermarket iMiEV battery upgrade project

Post by nuggetgalore »

francisco.shi wrote: Fri, 16 Apr 2021, 20:49 The different chemistries shouldn't be a problem as long as you don't exceed either of the voltage limits. If the voltages are not the same then one will be underutilized.
For better or worse, the two packs are combined by a relay designed for EVs that energises when the main pack relays are on. Additionally I have a low amp fused manual switch connecting the two packs that allow me to observe the voltage difference and/or current flow between the packs when the car is switched off. That way I make sure the two packs are always exactly the same volts when the car is switched on.
francisco.shi wrote: Fri, 16 Apr 2021, 20:49 And each pack should have its own BMS.
Yes I know, I am working on that but shortly the car gets mothballed for 3 months and if it has not died by then I get cracking.
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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg »

Might pay to make that fuse a bit more than 'low'. Perhaps rated to 50 amps or something? It wouldn't need to be a high voltage fuse as the potential across it should only be in the tens of volts at worst, but it would need to be a fast acting one.
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Re: Aftermarket iMiEV battery upgrade project

Post by nuggetgalore »

jonescg wrote: Sat, 17 Apr 2021, 11:05 Might pay to make that fuse a bit more than 'low'. Perhaps rated to 50 amps or something? It wouldn't need to be a high voltage fuse as the potential across it should only be in the tens of volts at worst, but it would need to be a fast acting one.
The potential between the two packs has never been more than about 3 V when I connected them after a few hours disconnect. When they are not connected, the LEV50 cell pack loses a tiny bit more of the top than the aftermarket one .
The spare cell I had was still 4.11 V after sitting on the shelf for months, a feature I found was common with these cells when I charged them up originally. But as soon as a small load is attached, they drop the voltage at a great rate and a lot different from one to the others.
I have high voltage fuses but maybe I should get a fast acting one.
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Re: Aftermarket iMiEV battery upgrade project

Post by nuggetgalore »

Since I added my two bobs worth to the winter solar discussion, I may as well post an update on the aftermarket iMiEV saga.
On the whole I am reasonably happy with what I have , 120 km range on a warm day if driven straight after full charge. The cooler weather and a bit more degradation of the LIYUAN cells give me about 100-110 km now, admittedly I drive somewhat less range minded than before the duplication. I just have to hope the next complete cell failure does not happen anytime soon......
This actually leads to a question I was going to ask earlier, any chance that one or more of these same cells are in Australia waiting for a home?
LIYUAN BATTERY CO.,LTD
NMC- lithium battery
3.6V 60 Ah
Or maybe some LEV50s? 65-70 %

On a more technical note, my observation is that the cells on both packs charge and discharge with less voltage differences than when they were used on their own, the obvious reason (caution:opinion!) is the currents both ways are about half* and therefore less stress.
*It depends on the SoC how much the currents vary.
For instance charging total DC current (as per scanners) is 7A, the NMC pack draws 4.5A when nearly empty, about 3.5A half full and then reduces to 2.5 for the last quarter or so while the OBC still supplies the full 7A.(by the way,the EvBatMon app claims it is 8A (could be 7.5?).
Under load, it appears the current drawn from the additional pack is always a bit more than half, but not as pronounced anymore as in the beginning. At rest after a good run, the current exchange between the two packs can be a much as 2A for a few minutes and it can flow either way depending on SoC or if there was strong regen prior to the stop.
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Re: Aftermarket iMiEV battery upgrade project

Post by francisco.shi »

A bit of an update on the Imiev battery hacking project.
I got back the Imiev I was working on before with new batteries. I have a board made (that I am using for another project) and it turns out the processor is too slow and the car finds out I am messing with the messages.
So I have had to go back to using a faster processor. So I will need to remake the board. I managed to get 200km of range out a fully charged battery.
I am still unsure how low to let the batteries go before going into turtle mode. The original BMS seems to go down to about 3.5v per cell and that is empty but I would have expected to go down to 3 or 3.2v.
While I am at it I have also been trying to hack into the inverter so I can get one pedal driving and cruise control as well as getting the brake lights to come on while in regen. I managed to get the inverter to do what I want without the EV-ECU finding out.
I got the one pedal driving more or less working. I did a bit of testing yesterday today and drove about 150km without using the brakes. I also got far more regen braking than before (in B mode) which is enough to stop on a yellow light still without needing the mechanical brakes. The only time when i have had to use the mechanical brakes was when a cat decided to run in front of me and check my reflexes. I have also managed to get much faster accelerator response.
One problem I have is that the motor rubber mounts are so soft that if you floor it will cluck. It also shakes at very low torque settings. I am not sure how they managed to make the transition from driving to regen so smooth. I am guessing they may be avoiding low torque settings and keep the bushes loaded. I can't do this because when the car stops I set the torque to zero so it doesnt crawl which means I can't preload the bushes because the car would start to move. Also if I try to implement a hold function I will need to have good response around zero torque.
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Re: Aftermarket iMiEV battery upgrade project

Post by dracekvo »

Nice work. I wait for next update.
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Re: Aftermarket iMiEV battery upgrade project

Post by Travers »

Nice one
Eagerly following.

Have you also tried increasing overall output? As I understand this drive is basically the same as the outlander which have them rated at 60kW.
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Re: Aftermarket iMiEV battery upgrade project

Post by francisco.shi »

It appears that it probably can do higher output. The EV-ECU seems to aim at limiting the maximum output by limiting the torque once the current increases to a certain point.
When I did the first test I floored it and the needle starts to go up until it hits the maximum but the motor keeps going. Then it cuts out. I am not sure who makes the decision to turn the power off and how it is done. What I will do is change the reported current to say double what the BMU reports and see if it cuts out at half the power. If it does then it means it is the EV-ECU making the decision.
The needle on the dash is reporting battery current. If this is the case then I would say it would be possible to put a bigger fuse and increase the output power.
Currently when driving in the original mode the maximum current out of the battery is about 180A.
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Re: Aftermarket iMiEV battery upgrade project

Post by francisco.shi »

I managed to get control of the GOM so I should also be able to get the range remaining to read correctly as well.
GOM
GOM
20210712_100913.jpg (1.25 MiB) Viewed 22840 times
The car is charging now so I wrote a big number just to confirm I can control the display.
For the time being I am adjusting the estimate by 94/50 which is the ratio of the Ah of the new cells to the old cells.
I did try to modify the odometer reading but it seems that is stored in the instrument cluster.
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Re: Aftermarket iMiEV battery upgrade project

Post by adoepner »

Well done!

Watching with great interest from Canada! I'd love to be able to upgrade my Miev to 94 AH and move the existing cells to another application (like a DIY powerwall). I already have the cells from one salvage 2012 - using only some of them for a Torqueedo electric outboard and a home sump pump backup.

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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg »

Hey @nuggetgalore - we never saw any pictures from your paralleled packs. Care to share?
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Re: Aftermarket iMiEV battery upgrade project

Post by francisco.shi »

@adoepner
So far I have done 180km on one charge.
I think it will do 220 down turtle mode.
I will do a full charge and run it until the charge message starts flashing and will let you know how far it goes.
I got the GOM working so I will check to see how accurate it is.
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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg »

@francisco.shi these are the 94 Ah cells in place of the original LEVs?

Looks like the trick is to hack the BMS alright.
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Re: Aftermarket iMiEV battery upgrade project

Post by francisco.shi »

Yes. They are almost the same physical size so they fit with very little mods to the pack.
With the new batteries these Imievs are a pretty useable car. It is a pity Mitsubishi doesn't make them anymore. I reckon they could sell them cheap and would sell well.
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Re: Aftermarket iMiEV battery upgrade project

Post by nuggetgalore »

jonescg wrote: Tue, 13 Jul 2021, 08:26 Hey @nuggetgalore - we never saw any pictures from your paralleled packs. Care to share?
Thanks for reminding me. I was reluctant to post pictures before I had some cell monitoring in place and then forgot.
The car is mothballed for three months while I am in covid free central Queensland. A mate of mine is checking the batteries regularly , no problem with the traction, but the auxiliary 12 V has needed a recharge once.
When (or maybe I should say "if") I get back to Melbourne, I post some pictures of the back seat passengers....
By the way and off topic, but my mate also had to take a picture of the odometer, so I can send it to our Victorian government who on one hand gives us a $100 dollar discount on rego but from now on charges a road tax of average $350. What a pack of penny pinching
A..e holes!
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Re: Aftermarket iMiEV battery upgrade project

Post by francisco.shi »

I got an update on range.
I got the car fully charged yesterday and the GOM will read 246km.
Fully charged GOM reading.
Fully charged GOM reading.
20210714_162959.jpg (1.5 MiB) Viewed 22725 times
I then drove it for 207km before the recharge warning started flashing at which point I had a 30km GOM reading.
The cell voltage was 3.5v. The total trip was 215km.
I have added a safety measure so if the cell voltage drops below a certain level it will reduce the SOC to avoid battery damage. Reducing the SOCcauses the car to eventually go into turtle mode.
I have set the minimum voltage a bit high so that If I run flat (according to the measurements) I can still set it lower and get home.
So I would be confident that the car will do 200km on a charge and potentially 240km until totality flat.
I still have a bit of work to do on the bottom end management to make it more predictable.
The driving conditions were all city driving (60kph) with one pedal driving mode.
The one pedal driving allows for far more regen than on B mode so it is possible that part of the gain in range may have been due to the extra regen. In the entire 215km drive I only use the mechanical brakes twice. Both for a yellow light which was a little close for comfort. So the one pedal driving will allow for normal driving without ever touching the brake pedal.
I also got the brake lights to come on during regen.
I will keep doing more testing and see how things go.
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Re: Aftermarket iMiEV battery upgrade project

Post by Sandrosan »

francisco.shi wrote: Thu, 15 Jul 2021, 09:21 I got an update on range.
I got the car fully charged yesterday and the GOM will read 246km.
20210714_162959.jpg
I then drove it for 207km before the recharge warning started flashing at which point I had a 30km GOM reading.
The cell voltage was 3.5v. The total trip was 215km.
I have added a safety measure so if the cell voltage drops below a certain level it will reduce the SOC to avoid battery damage. Reducing the SOCcauses the car to eventually go into turtle mode.
I have set the minimum voltage a bit high so that If I run flat (according to the measurements) I can still set it lower and get home.
So I would be confident that the car will do 200km on a charge and potentially 240km until totality flat.
I still have a bit of work to do on the bottom end management to make it more predictable.
The driving conditions were all city driving (60kph) with one pedal driving mode.
The one pedal driving allows for far more regen than on B mode so it is possible that part of the gain in range may have been due to the extra regen. In the entire 215km drive I only use the mechanical brakes twice. Both for a yellow light which was a little close for comfort. So the one pedal driving will allow for normal driving without ever touching the brake pedal.
I also got the brake lights to come on during regen.
I will keep doing more testing and see how things go.
Bravo Francisco! 8-) I am so happy :D to see you are achiving a great improvement on these lovely cars which have too old battery packs. Shame is for Mitsubishi (and PSA group with the clones) that does not offer any soultion for a battery upgrade. Probably due to the fact they belong to the Nissan Renault group where they decided to push just for Leaf and Zoe. I hope you will open this upgrading market to many of us.
Continue in this way, great enginner!
All the best.
Ciao from Milan, Italy
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Re: Aftermarket iMiEV battery upgrade project

Post by francisco.shi »

The plan is to make a box and sell it as an aftermarket product.
The one pedal driving is so much better.
On the subject of one pedal driving. I think I know why the Imiev is so slow to respond. The motor mounts are very soft and resonate at about 5hz (just a guess I haven't measured it yet) . So in order to avoid the resonant frequency of the motor mounts they put a low pass filter and some other filtering to get rid of the resonance. I don't know why they used such soft mounts. I am considering to change the mounts to stiffer mounts and to avoid doing the filtering and give the car better response. It will be very difficult to get the hill hold to work with the current mounts.
Does anyone have any input on the mounts?
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