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
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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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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?
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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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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?
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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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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]
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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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Re: Aftermarket iMiEV battery upgrade project

Post by DkubusEV » Thu, 26 Jul 2018, 14:49

great thread, im following along for the ride. looking forward to seeing how this goes. im fairly keen on perhaps making a larger capacity battery for my project imiev one day.

cheers guys.
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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg » Thu, 26 Jul 2018, 15:21

I concluded that the Samsung SDI prismatic cells are a better fit than thousands of 18650 cells. You can fit almost 47 kWh into an iMiEV with similar weight and volume. Similar price too.
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Re: Aftermarket iMiEV battery upgrade project

Post by praxidice » Thu, 26 Jul 2018, 20:12

47kw would be wonderful if there was a way to hack the firmware

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Re: Aftermarket iMiEV battery upgrade project

Post by offgridQLD » Sun, 29 Jul 2018, 10:48

Lets say you have a 80kw battery and your told it will loose 20% of it's capacity in 10 years. Most people would be reasonably happy with that. Though when you look at it from a different perspective it may not represent great value.

Lets say you purchased a 20kwh battery and that lost 20% of it's capacity after 10 years. You give up 2kwh and now have a 18kwh battery. The 80kwh battery looses 20kwh and is now a 60kwh battery. As you can see with the 80kwh battery you loos the equivalent capacity of the entire 20kwh battery.


Given calendar life (use it or loose it) is a real thing with a Ev lithium battery. Why buy more capacity than you need. Purchasing a 20kwh battery and replacing it four times over 40 years could be a better option.

So I'm thinking you might be able to fit 47kwh of Samsung prismatic cells in the Imiev for the same cost and weight as the 16kwh bank. Perhaps a 23.5kwh at 1/2 the weight and 1/2 cost.....Now you have my attention.

I guess the reality is the Panasonic cells are only manufactured in a few AH sizes. Is it 60ah and 94ah ? . This would determine the few available KWH configurations

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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg » Sun, 29 Jul 2018, 11:35

They do make a 72 Ah prismatic too. It would be cheaper and would fit quite easily inside the iMiEV. A 20 kWh iMiEV is actually quite reasonable considering they were never exactly a highway cruiser...
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Re: Aftermarket iMiEV battery upgrade project

Post by offgridQLD » Sun, 29 Jul 2018, 11:55

Are the cells available to purchase in Au?

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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg » Sun, 29 Jul 2018, 11:56

Damien Butcher in Canberra has brought a few in, but it's Liyuan (aka Jack Zhang) in China who sells them. MOQ is 200 cells I think.
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Re: Aftermarket iMiEV battery upgrade project

Post by mikedufty » Sun, 29 Jul 2018, 15:44

jonescg wrote:
Sun, 29 Jul 2018, 11:35
A 20 kWh iMiEV is actually quite reasonable considering they were never exactly a highway cruiser...
I'd be much more interested in a cheap 20kwh i-miEv than an expensive 47kwh one. We rarely do more than 50km/day. Most of the longer trips we use the ICE for also require more space, comfort and ground clearance than the i-MiEV has anyway.

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Re: Aftermarket iMiEV battery upgrade project

Post by nuggetgalore » Sun, 29 Jul 2018, 20:25

mikedufty wrote:
Sun, 29 Jul 2018, 15:44
jonescg wrote:
Sun, 29 Jul 2018, 11:35
A 20 kWh iMiEV is actually quite reasonable considering they were never exactly a highway cruiser...
I'd be much more interested in a cheap 20kwh i-miEv than an expensive 47kwh one. We rarely do more than 50km/day. Most of the longer trips we use the ICE for also require more space, comfort and ground clearance than the i-MiEV has anyway.
I'd be much more interested in a cheap 20kwh i-miEv than an expensive 47kwh one

Yes, about twice the 70% of the original 16KWh (ie 20KWh). That is really all that is practcally needed for an iMiEV. I have my doubts about the cheap though.
Any guess how cheap?
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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg » Sun, 29 Jul 2018, 21:34

I think I read $135 each for the 72 Ah cells. These measure 95 mm high, 148 mm long and 39 mm thick and weigh 1.35 kg each.
23 kWh in an iMiEV is entirely viable.
$12k in cells.
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Re: Aftermarket iMiEV battery upgrade project

Post by offgridQLD » Tue, 31 Jul 2018, 09:15

$135 US or AU?

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Re: Aftermarket iMiEV battery upgrade project

Post by offgridQLD » Tue, 31 Jul 2018, 09:24

I think sticking with a cell that's close to 50ah would be best as the BMU would be happy in its capacity calculations. The Imiev range is fine with stock capacity. If modern spec lithium was a few KG less weight than stock at the same capacity.... great!.

if price - AH was the same as the 72ah cells then $8,000 88 cell 50ah replacement is better value.

That said the stock cells are very good given they are discharged up to 3c and charged at up to 3c. they have proven to be very reliable cells over time.

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Re: Aftermarket iMiEV battery upgrade project

Post by jonescg » Tue, 31 Jul 2018, 10:12

Aussie dollars for these, but only if you're buying 200 or more. Otherwise it might be a bit (but not a lot) more.
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Re: Aftermarket iMiEV battery upgrade project

Post by carnut1100 » Tue, 31 Jul 2018, 14:57

Personally I would love an imiev that can do 300km plus...but I do rather a lot of driving too.

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Re: Aftermarket iMiEV battery upgrade project

Post by T1 Terry » Wed, 01 Aug 2018, 12:19

carnut1100 wrote:
Tue, 31 Jul 2018, 14:57
Personally I would love an imiev that can do 300km plus...but I do rather a lot of driving too.
That got my attention :lol: Is it really possible to build an iMiEV that could handle 300km round trip with the Adelaide Hills added into the drive? Not interested in having to leave the vehicle anywhere to recharge while in the city because it would be a stock collection trip combined with the wife's addition to shopping so multiple stops for short periods that would not coincide with an available charge point. So charge before leaving Mannum and recharge when it gets home are the only real options. Otherwise it's back to extending the range of the Prius on battery only while still having the ICE there as a back up.

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