Aftermarket iMiEV battery upgrade project

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jonescg
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Aftermarket iMiEV battery upgrade project

Post by jonescg » Sat, 07 Apr 2018, 13:52

I bought about 800 of these three-hexagon cell holders for 18650 cells. More than enough to put some 4-cell and 8-cell battery packs together as replacements for the iMiEV battery packs.
20180407_134158.jpg
20180407_134158.jpg (358.05 KiB) Viewed 368 times
This layout gives a 23-parallel arrangement, so if you assume a reliable 3 Ah per cell, that's about 23 kWh for a complete battery 88s23p (or 2024 cells).

The cells are well shorter than the original LEV50 cells, so that gives room for a cooling plate top and bottom, as well as cell pick-ups for the OEM battery management system.

I'll start compiling ideas here for making a drop-in replacement for the iMiEV.
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Peter C in Canberra
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Re: Aftermarket iMiEV battery upgrade project

Post by Peter C in Canberra » Fri, 13 Apr 2018, 11:18

It seems to me that a key question is, What would the unmodified BMS do if it suddenly finds the battery capacity had increased? I could imagine that it might simply observe the voltage rise is slower and more than 16kWh have gone in but keep going with charging and quickly learn and recalibrate on the new larger capacity. Alternatively, something in its programming might insist that more than 16kWh does not compute. Has anyone done the experiment of hooking a bit of extra capacity in parallel with each original cell and charging to see what happens?
Daihatsu charade conversion 2009-18, demo iMiEV 2013-present, used Holden Volt 2018-present, on the ACT's 100%-renewable-by-2020 electricity.

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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg » Fri, 13 Apr 2018, 13:14

I don't know to be honest. I think there is a 're-learning' process involved, and the SOC would surely be a combination of coulomb counting as well as monitoring cell voltages. At least the capacity increase would only be 45% more than the original, so it's not too far off.

My bigger concern is the difficulty of getting thicker conductors to adequately share the loads of so many cells. Based on my current layout the series connections (nickel strips) are only able to handle at best about 45 amps without significant temperature rise. I guess you can thicken them up with soldered copper or something. Otherwise it's a case of devising something like Tesla's system where the bus plate has access to the cell tops via a thin fuse wire, but the total current is easily covered by the thicker plate. This makes axially cooling the cells a bit tougher though...
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Peter C in Canberra
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Re: Aftermarket iMiEV battery upgrade project

Post by Peter C in Canberra » Fri, 13 Apr 2018, 13:44

At the moment, the prismatic cells are cooled by just having air blown past, I think, air-conditioner chilled air if on a fast charger. It seems to me that the hexagonal array would be more porous to air flow than single solid rectangular blocks and might be better cooled without any special effort.

Why thin nickel plate, what about a thicker copper plate?
Daihatsu charade conversion 2009-18, demo iMiEV 2013-present, used Holden Volt 2018-present, on the ACT's 100%-renewable-by-2020 electricity.

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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg » Fri, 13 Apr 2018, 14:42

Peter C in Canberra wrote:
Fri, 13 Apr 2018, 13:44
At the moment, the prismatic cells are cooled by just having air blown past, I think, air-conditioner chilled air if on a fast charger. It seems to me that the hexagonal array would be more porous to air flow than single solid rectangular blocks and might be better cooled without any special effort.
True, but there is room for a cooling plate top and bottom, so if it's not too complicated I will try for that approach. Otherwise air cooling might be sufficient.
Peter C in Canberra wrote:
Fri, 13 Apr 2018, 13:44
Why thin nickel plate, what about a thicker copper plate?
The issue is connecting the cell terminals to said copper plate. Copper won't spot weld because it absorbs heat so well. Tesla uses ultrasonic wire bonding of fuse wire between the nickel plates aluminium bus plate and the nickel plated steel can. I'm not that well resourced, but spotwelders are common.

You can solder to the cells too, but the risk of damaging the cells is higher.
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Peter C in Canberra
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Re: Aftermarket iMiEV battery upgrade project

Post by Peter C in Canberra » Fri, 13 Apr 2018, 14:51

What about cells with threaded terminals and a copper plate with just an array of holes? [Lots of screws to do up and retighten and potential to come loose, I guess]
Daihatsu charade conversion 2009-18, demo iMiEV 2013-present, used Holden Volt 2018-present, on the ACT's 100%-renewable-by-2020 electricity.

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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg » Fri, 13 Apr 2018, 15:27

I don't know of any 18650 cells with such features unfortunately.
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Re: Aftermarket iMiEV battery upgrade project

Post by Adverse Effects » Fri, 13 Apr 2018, 18:58

this is how you get them to handle more amps

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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg » Fri, 13 Apr 2018, 19:21

Yeah, I'm thinking of something like that - basically a copper interconnect between the series connections, but soldering is my best option there. It makes for a less conductive thermal path for axial cooling plates, but it might be good enough.
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Re: Aftermarket iMiEV battery upgrade project

Post by majorphill » Sat, 05 May 2018, 08:31

Chris

If you need any 5x4 holders similar to those you've shown above or are interested in seeing a completed module somewhat similar to Peter Mathews as shown above, give me a shout.

Phil

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