jkenny23
Posts: 74
Joined: Sat Aug 19, 2017 12:49 pm
Delivery Date: 19 Sep 2017
Leaf Number: 009318

Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Fri May 11, 2018 2:02 am

I just realized it may be a moot point for me, I had my degraded 2011 cells replaced with ones from a 2013 pack (same open can style as the one I purchased). Granted they didn't officially switch chemistry until 2015.

mux
Posts: 85
Joined: Sat Jan 13, 2018 3:52 am
Delivery Date: 13 Oct 2011
Leaf Number: 6177

Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Fri May 11, 2018 2:59 am

Great, in that case you have exactly the right cells :)

jkenny23
Posts: 74
Joined: Sat Aug 19, 2017 12:49 pm
Delivery Date: 19 Sep 2017
Leaf Number: 009318

Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Mon May 14, 2018 11:19 am

Finished a full discharge and charge test of the Leaf module (in 7.4V configuration) in parallel with 2s2p Boston Power Swing 5300 cells. The discharge test was done at the max power of my tester, 60W, which means current did vary as the battery voltage dropped. The charge was done at 5A, which is a bit lower than an L2 charge (~8.8A). I performed the charge termination at roughly the same level I've seen my car stop charging at, which is about ~1-2A in CV mode. Here's the discharge graph:

Image

So exactly as Mux found, the extender pack (in my case using LCO chemistry) delivers most of its energy toward the end of the discharge curve, which means it is providing a majority of the power towards the end as well.

Just between turtle and dead, the extender pack took the maximum proportion, about 58.1% of the total current, meaning it would have had to provide 159A, which is way more than the 26A rating of 2 Swing 5300 cells in parallel. Basically, this limits the minimum extender size to at least 12-13p, or ~17.3 kWH usable for this model of cell! Taking the calculation for a higher drain cell, the LG HE4 (which I should be getting samples of in the next day or two), the minimum extender size drops to 8p, or ~5.4 kWH usable.

Image

The charge curve is nearly the inverse, with some bumpier behavior at the start of the curve. In charging, the BP cells took a maximum of 52% of the charging current, which again would be an issue in DC fast charging, limiting the minimum pack size to 6p of the Boston Power cells, or 16p (~10.9 kWH usable) for the LG HE4 cells, in order to take the ~65A that would be coming from the charger.

Early conclusion from this data; it's better to go with hybrid or EV batteries that are already sized/designed to take such large charging/discharging powers, if using a cell chemistry other than LMO. Otherwise, you can use "standard" Li-Ion cells but you will be building a very large pack (at least 11 kWH sized), and we still have the SoC estimation problem to resolve.

RNM
Posts: 48
Joined: Mon Feb 29, 2016 10:11 am
Delivery Date: 05 Mar 2016
Leaf Number: 012707

Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Wed May 16, 2018 9:56 am

Thanks for sharing that, jkenny23!

Just one note: all 24 kWh batteries to date have the same chemistry, Cathode Active Material is LiMn2O4 (or LMO) with a pinch of LiNiO2.
The only upgrade in "Lizard" was the electrolyte.
(to know more, https://www.nec.com/en/global/techrep/j ... 120112.pdf )

LMO batteries have a distinctive discharge curve, with the knee bend at ~3.65V
Image

Good work, gentleman!

mux
Posts: 85
Joined: Sat Jan 13, 2018 3:52 am
Delivery Date: 13 Oct 2011
Leaf Number: 6177

Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Wed May 16, 2018 10:26 am

Alright, I was wrong then. Good to know, and I always wondered if I was imagining that little nickel hump on the discharge curve...

RNM
Posts: 48
Joined: Mon Feb 29, 2016 10:11 am
Delivery Date: 05 Mar 2016
Leaf Number: 012707

Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Wed May 16, 2018 11:55 am

Mux, how is that CAN translator coming?

jkenny23
Posts: 74
Joined: Sat Aug 19, 2017 12:49 pm
Delivery Date: 19 Sep 2017
Leaf Number: 009318

Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Wed May 16, 2018 6:20 pm

Now for the real extender pack (Hyundai PHEV modules)...

First test is a discharge test of the Leaf module in parallel with 2s (out of the 8s full pack) of the Hyundai PHEV module:

Image

This pack fares much better with the voltage curve of the Leaf, utilizing up to 95% of the "full" capacity from 4.11 to 3.0V by the time the Leaf reports dead (3.2V/cell). Still, just over a third of the capacity is delivered between VLBW and turtle. Also of concern, at peak, the Hyundai module provided 81% of the load current, meaning it will deliver up to ~72.9 kW peak, a bit higher than the pack's 68 kW max discharge spec.

And for charging:

Image

The extender takes a maximum of 68.1% of the input current, which is no concern since the pack is rated for 54 kW charging (more than CHAdeMO can even deliver in total to the Leaf).

Finally here's a "baseline" of the Leaf module by itself. Capacity is 42.15 AH from 4.11V to 3.2V (dead). With the Hyundai module in parallel, this number increased to 63.52 AH (+50.7% capacity).

Image

And here's a picture of the test setup in case anyone's interested:

Image

Currently I am running a test with all 3 in parallel (Boston Power Swing 5300 in 2s2p, Hyundai PHEV module, and Leaf Module) to see how easy it is to add capacity in smaller 18650 packs later once the initial ~10 kWH high power extender pack is installed.

mux
Posts: 85
Joined: Sat Jan 13, 2018 3:52 am
Delivery Date: 13 Oct 2011
Leaf Number: 6177

Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Wed May 16, 2018 10:03 pm

RNM wrote:Mux, how is that CAN translator coming?


Just got the boards in, now I 'just' have to program them. Expect an update at the end of may.

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