Future Battery Replacement - A Better Battery?

Hey all,

I've been thinking about the i's range and I got to looking at the lev50 battery spec. With its dimensions it could be replaced with a set or 18650 cells in parallel. Doing some conservative volume calculations I could see 30 of the new Panasonic 3.1 ah cells making a great replacement battery cell. They would need to be built in modules with little fuses a la tesla and could be drop in replacements for the lev 50.

If you look at weight and power 30x 18650 cells would give a 93 ah battery weighing 1.2 kg about 30 % lighter and almost double the range. It would be 2640 cells total. I could see them being $3 a cell in the future maybe even less. That would be $8000 in cells for a really nice battery of 30kwh and a car with an easy 200 km of range.

Maybe I should start soldering cells together in 5-6 years as I plan for my battery death.

What do you think ?

Don.....

Yes. 16 kWh I-MiEV will be a joke in some years, no doubt about that.

Neat idea. Do you know what the charge and discharge rates are on the Panasonic's?

If Ben Nelson still has the flooded i-MiEV, this information could help him (and other's with dead packs) get the car under its own power, or help some of us make a killer BRE (battery range-extender).

Sometimes I play with that idea.
Often to replace a damaged cell, but it could be for the whole pack.
$ 3 / cell? I think we should go to recognized quality manufacturers (Panasonic, as Tesla?), we can not think of thousands of cells and 1-2% fail.

Having just completed a Lithium (NMC) installation into my second Sparrow - that's the easy part - just a packaging and wiring exercise.

The more significant issue I see with doing anything with the i-MiEV is to figure out how to either integrate with its existing BMU or else fool the BMU into thinking everything is ok and have a completely separate Battery Management System.

As an aside, my own homebrew Lithium Sparrow QuickCharge consists of nothing more than simply adding a whole bunch of benchtop chargers and power supplies (both 120vac and 240vac) in parallel when needed to recharge quickly, with both timers and HV shutdown should I get distracted.

JoeS said:

The more significant issue I see with doing anything with the i-MiEV is to figure out how to either integrate with its existing BMU or else fool the BMU into thinking everything is ok and have a completely separate Battery Management System.

Click to expand...

I agree. I wouldn't be interested in spending $8K on a battery pack unless it came with a pretty foolproof BMU. If it didn't, I'd rather spend my $$$ on another OEM set from Mitsu

While the extended range would be nice, the most important thing would be protecting my investment

Don

Hi all,

The idea was to use the existing Bms in the imiev. I thought you would be able to build a lev50 replacement out of 18650 cells. If you can package it in the same form factor then it's drop in replacement.

I don't know what the maximum C rating is on these cells. I read that you could get 6 amps out of the cell no problem. With 30 cells that would be 180 amps which should be plenty.

This might be a good idea for single cell replacement also. That might be a good proof of concept for doing a complete battery.

Don.....

As far as the BMS handling the new cells, as long as the voltage range covers the car's voltage range, they should work. The i-MiEV charges the cells to 4.1 volts per cell, though I'm not sure where it bottoms out before shutting down. The new cells should have a very similar charge/discharge curve, and the voltage range for most lithium batteries is quite similar, so the car shouldn't see much of a difference between LEV50 cells and bricks of 18650's, except that the new cells can take on more energy. I would be interested to see how the car would handle having much more storage available and trying to access it.

As for replacing one or two LEV50's with 18650's, you may run into problems doing that. I would expect to see the same symptoms as having bad cells in an OEM pack. A total replacement, however, should work out OK, unless there's a secret kWh counter built-in.

I've read that continuous C ratings on prismatic LiFePO4 batteries is 3C, with a burst rating of 10C. 6 amps on the 18650's would be 2C, 30 cells in parallel is 180 amps as Don stated. So for the whole pack, 180 amps at 360 volts is 64.8 kW, more than plenty for the i-MiEV. Even at 330 volts, that's 59.4 kW, still more than the i-MiEV requires. The LEV50 cells hit 3C at full acceleration.

The battery pack would be increased from 50 Ah (16 kWh) to 93 Ah (29.8 kWh), for a range increase from 62 miles to 115 miles per charge.

Hey PV1

That's how I see it.

As for replacing one cell, the bms would see one large capacity cell on charging I would see the bms bringing this cell up to 4.1 volts.

On discharge this cell would have a higher voltage then the other one and would stand out n the readings. The bms would count amps as it discharges and make its usual decisions until it thinks the pack is at 10% then you turtle down to 5% then you stop. In reality only of the batteries would be about 50 % then you charge and repeat.

I could see problems if the bms sees a rogue battery with higher voltage but I suspect this will happen to all our cells as they age. Malm has a few low capacity cells and his bms deals with it bringing the capacity down to the weakest cell.

I could also see a problem if you did a complete replacement and the pack had a much higher capacity. The battery gauge might go to turtle and then stop even if there was 40% left on the cells. It would not be good if you could not use the whole cell.

I don't know if it would continue in turtle until one cell hit 2.75 volts. If so that would be a long turtle ride.....

It would be nice if the bms learned the capacity of the pack and rescaled the gauge.

I guess for this type of thing to work a little bms tweaking would be required to tell the bms the new amout of ah to count and scale the dash gauge to.

Don......

Would we be able to see anything with MUTIII? Be able to reprogram any of the modules?

That's one of the big things I wonder about this is how to get the car to access the expanded capacity of the new cells, unless that's what the turtle is for. I would imagine the car counts kWh to run the charge gauge and RR, but once it thinks the battery is "empty" (no bars and '---' RR), it will resort to turtle (a low power mode) and watch the voltage until one or more cells hits LVC. It should then be able to re-calibrate from the new empty point and have access to the full 29 kWh of available capacity.

I guess it'll take one of us actually doing it to find out if the i-MiEV functions like this. If the car won't use the full capacity of the new pack...well, someone has an awesome battery pack for backup power or off-grid solar.

I would bet that in a car so sophisticated that replacing the center brake light bulb with an LED causes an error and running with a spare tire a little smaller (or larger) than the one it replaces causes an error, we're going to find all sorts of errors when we try replacing the battery pack with something . . . . better

I suspect all sorts of things won't work correctly, from the BMS to the RR calculations to the Turtle . . . . heck, it might not even charge correctly. When/if Mitsu comes out with an all new 24Kwh battery pack a year or two from now, it likely won't be a drop-in replacement for our pack either, at least not without a significant reprogramming of the car's computer. The benefit of buying it from Mitsu though will be that their engineers will likely do the programming to make it all work correctly

That said, I LOVE surprises - When one of you gets a new 29Kwh pack installed and functioning properly, I'll be as elated as anyone here! . . . . I just suspect that there will be all sorts of snags to overcome before anyone gets there

Don

If that flooded Mitsubishi is still available, maybe we can crowd source the funding to give this a go. :lol:

PV1 said:

That's one of the big things I wonder about this is how to get the car to access the expanded capacity of the new cells, unless that's what the turtle is for. I would imagine the car counts kWh to run the charge gauge and RR, but once it thinks the battery is "empty" (no bars and '---' RR), it will resort to turtle (a low power mode) and watch the voltage until one or more cells hits LVC. It should then be able to re-calibrate from the new empty point and have access to the full 29 kWh of available capacity.

I guess it'll take one of us actually doing it to find out if the i-MiEV functions like this. If the car won't use the full capacity of the new pack...well, someone has an awesome battery pack for backup power or off-grid solar.

Click to expand...

I see it very easy. I think is just easy as this: Add the entire complete modules, with their electronics. Then just connect them. Then just replace in the software the number 16 kWh by 29 kWh. The car will then know that every 5% bar will correspond to something like 1,5 kWh and turtle will only be there when it has only 2,9 kWh. We all know that there are Peugeot Ion of 14,5 kWh - they show all the 16 bars. The diference is that they know that 100% SoC is 14,5 kWh.

I´m sure it will not recalibrate by himself so easily. It knows that tomorow it could have 10% less capacity because temperatures had go down 20ºC or something like that. So, it will not do that for one day to the other.

For me, I don't see a reason why it should be dificult to add 8, 16 or 24 more cells, Peugeot did it, taking 8. My car did it, 16 bars (Turtle - 10%, 2% ---, 5%, 5%, 6%, 6%, 6%, 5%, 5%, 5%, 5%, 5%, 5%, 5%, 5%, 5%, 7%, 8% SoC), all perfect. I mean exactly all perfect. All by himself (i think). How this is possible, well, one miracle happened, in the first days of March, it recalculated his capacity to 12,75 kWh. In february, I had a 16 kWh i-MiEV but i could stop with the car showing something like 14,5% SoC. Now, well, I just keep going until it gets to 0,0%.

3 years (exactly), something like 63.500 km, 15º C medium ambient temperature, and an 12,75 kWh i-MiEV - Believe it or not. I'm sure about what i'm telling you. The canary keeps singing.

MLucas said:

If that flooded Mitsubishi is still available, maybe we can crowd source the funding to give this a go. :lol:

Click to expand...

That sounds like a neat idea. How much to build a cell?

Malm said:

I see it very easy. I think is just easy as this: Add the entire complete modules, with their electronics. Then just connect them. Then just replace in the software the number 16 kWh by 29 kWh.....For me, I don't see a reason why it should be dificult to add 8, 16 or 24 more cells, Peugeot did it, taking 8. ...

Click to expand...

I'm assuming you're talking about adding these cells in series, boosting system voltage (what's it's upper limit?)? In any case, you have some significant repackaging and rewiring to do and, assuming you've got a balancing circuit on each cell, how do you now integrate the individual cell monitoring into the system, not to mention how exactly do you do the software mods? Not trivial, IMO, unless you have access to the Mitsu design team.

Malm said:

... How this is possible, well, one miracle happened, in the first days of March, it recalculated his capacity to 12,75 kWh. In february, I had a 16 kWh i-MiEV but i could stop with the car showing something like 14,5% SoC. Now, well, I just keep going until it gets to 0,0%.

Click to expand...

Malm, that's interesting - you're saying the software did a recalculation and established 12.75kWh as your new capacity? How did you figure this out and where/how did you get this new vs. old capacity reading?

I know that is not has simple as i said, but peugeot did in fact made them of 14,5.

Ok. I think assuming that it was of 16 kWh when new is consensual. I remember to charge, two years ago, something like 16,6 kWh from the charger, with some SoC in the battery. So I assume it taked, maximum, 16 kWh in the battery. Each bar of 5% used exactly 0,8 kWh from the battery. But now, every bar of 5% uses something like 0,64 kWh. I see it in Canion, I use now 6,4 kWh (more or less), and one bar of 5% goes away. And now I do clearly less km with each bar as compared with february. But in february, I could see two bars going away or stop with 14,5% SoC because one cell reached 2,75 V. Now I stop with 0,0% of SoC and my worst cell is far away from 2,75 V. Now, from 0% to 100%, I will use from the charger 14,6 kWh (in february I remenber to use regularly more then 15 kWh).

Now I will show things that you never saw, made by Malm and its portuguese I-MiEV. I know that getting the car so low is not good (sorry for that ). Well, this time, with 0,0% SoC I was far from getting to one cell 2,75 V. But that happened with 14,5% of SoC. I think getting to 0,0% SoC this time was not so bad.

Driving an I-MiEV with 0,5% SoC is possible. Not try this, that will only be possible with a perfect new I-MiEV, or with mine (for now, your time will came, some day).

https://www.youtube.com/watch?v=PkWW5w2e4XU

So, when it hit 0% SoC, did it come out of READY? I noticed at .5% you could move around with READY lit, but at the end the READY light was off.

PV1 said:

So, when it hit 0% SoC, did it come out of READY? I noticed at .5% you could move around with READY lit, but at the end the READY light was off.

Click to expand...

Yes, with 0.0 SoC, no more Ready. It assumes that it is tottaly empty (but it wasn't, 3,25 V for the weakest cell, not 2,75). In the exact moment that it hit 0,0 SoC, Ready go away.

Well that puts a wrench in the plans.

Maybe it'll work the other way. Run the i-MiEV down to turtle, install the new pack discharged, and charge it with the i-MiEV. Maybe during the recalibration is when the kWh counter is largely ignored.