jkenny23
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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Mon Apr 09, 2018 3:10 pm

Lylou2 wrote:Ok if I use f.eg. extra battery pack in baggage aprox 10kw/h, how does the charging/discharging gonna work? Or it deals in 2 batteries or its cannot be too 'heavy' for smaller battery?


The simplest and most efficient way of adding a range extender (which mux and others have attempted) is to add a second battery pack of 96 cells in series (~370V nominal, 412V max, 320V min) via tap off the main HV cable, through a second set of contactors controlled by the main contactor controls. Charging and discharging is done at the same time as the main battery pack, by necessity, since it is "directly" connected when the contactors are enabled during charging/discharging. For small extender packs (e.g. ~1-2kWH) then the cells should be able to handle effectively the full charge/discharge C rate that the main pack handles, as its contribution is very small. In the case of the 24kWH Leaf, ~5C discharge, ~2C quick charge (max, tapers quickly), and ~1.6C max regen charge. For larger battery packs, the overall charge/discharge rate will drop as the total capacity of the pack increases (since the charge/discharge limits stay the same). For 10kWH + 24kWH in your example, discharge will drop to 3.5C, quick charge to 1.4C. The other factor to consider is the extender HV cabling will need to handle nearly the same current as the main pack if using a different chemistry like mux found with the NCA cells; at the tail end of the discharge curve, the extender pack was taking nearly all the load (almost no usable capacity left in the main pack). This works out to ~2 or 3ga cabling.

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

Mon Apr 09, 2018 10:55 pm

And as your pack approaches a similar size to the main pack (e.g. in my car, where the extender even has a little bit more usable capacity than the main pack it seems), it has to be able to bear the full motor current. I've just this weekend driven around with a current sensor on the wires, and we got a very consistent ~150A maximum current from the extender pack at 80kW of motor power. That translates to about 56kW or 70% of the power coming from the extender. For that kind of current, I highly recommend going to 1ga wiring, not because the ampacity of 2-3ga doesn't work fine, but that you'll get warm wires under heavy load with thinner stuff. In my car, I opted for 70mm2 (00 gauge), which is clearly overkill but... well, overkill.

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

Tue Apr 10, 2018 12:20 am

jkenny23 wrote:Assuming money is no object, the best 18650 on the market is the LG MJ1 at 3500mAH.

Now I don't know if this always applies unless DC quick charging, but according to https://batterybro.com/blogs/18650-wholesale-battery-reviews/40773059-new-lg-mj1-18650-battery-review-3500mah you're supposed to let those particular cells rest for 10 minutes after quick charging before discharging and 20 minutes after quick discharging before charging.

I'm not sure how that might affect the performance of an EV battery made of these. Probably not much if it's a 75kWh battery.

Letting the MJ1 rest
Something worth noting if you are using the MJ1 for high-drain and fast charge (which most of you will probably take advantage of) is that LG Chem recommends that cells are to rest 10 minutes after charge and 20 minutes after discharge. Take note of this if you are doing cycle-life tests.


Also thanks mux and jkenny23 for all your input! Great info!
2013 SL 50,000 miles.
12 bars until 44,300 miles on June 2, 2017. :D
11 bars current. :)
The Nissan Leaf is the fourth best long distance car for highway driving. >>Best Long Distance Cars<<

Lylou2
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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Tue Apr 10, 2018 2:23 am

Thanks for correct answers ;+

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

Tue Apr 10, 2018 5:03 pm

Any ideas on auxiliary battery balancing?

For an example. Say I put together a bunch of individual 18650 cells together in series and parallel, not modules like mux did. Then it seems is either have to manually balance them from time to time or get a battery management system. But such a BMS can cost over $1,000 (US), as much as the cells on a small upgrade. Of course once you have the BMS you can keep adding and adding cells until you have a battery trailer or something.

But still, any more thoughts on this?
2013 SL 50,000 miles.
12 bars until 44,300 miles on June 2, 2017. :D
11 bars current. :)
The Nissan Leaf is the fourth best long distance car for highway driving. >>Best Long Distance Cars<<

jkenny23
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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Tue Apr 10, 2018 5:33 pm

IssacZachary wrote:Any ideas on auxiliary battery balancing?

For an example. Say I put together a bunch of individual 18650 cells together in series and parallel, not modules like mux did. Then it seems is either have to manually balance them from time to time or get a battery management system. But such a BMS can cost over $1,000 (US), as much as the cells on a small upgrade. Of course once you have the BMS you can keep adding and adding cells until you have a battery trailer or something.

But still, any more thoughts on this?


If you have a well balanced pack to start with you can use a second Leaf BMS on the extender pack. It will supposedly balance automatically when hooked up to a 96s pack. You can then of course use an obd2 reader and Leaf Spy to monitor. Leaf BMSs go for around $60-100 making it pretty much the cheapest option. The issue is the balance current is only ~10mA.

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

Tue Apr 10, 2018 6:17 pm

jkenny23 wrote:If you have a well balanced pack to start with you can use a second Leaf BMS on the extender pack. It will supposedly balance automatically when hooked up to a 96s pack. You can then of course use an obd2 reader and Leaf Spy to monitor. Leaf BMSs go for around $60-100 making it pretty much the cheapest option. The issue is the balance current is only ~10mA.

That's a great idea! Also with a smaller battery a smaller balance current is needed anyway. I imagine the balance circuit could be enhanced with transistors and resistors for more current.
2013 SL 50,000 miles.
12 bars until 44,300 miles on June 2, 2017. :D
11 bars current. :)
The Nissan Leaf is the fourth best long distance car for highway driving. >>Best Long Distance Cars<<

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

Tue Apr 10, 2018 11:46 pm

jkenny23 wrote:
IssacZachary wrote:Any ideas on auxiliary battery balancing?

For an example. Say I put together a bunch of individual 18650 cells together in series and parallel, not modules like mux did. Then it seems is either have to manually balance them from time to time or get a battery management system. But such a BMS can cost over $1,000 (US), as much as the cells on a small upgrade. Of course once you have the BMS you can keep adding and adding cells until you have a battery trailer or something.

But still, any more thoughts on this?


If you have a well balanced pack to start with you can use a second Leaf BMS on the extender pack. It will supposedly balance automatically when hooked up to a 96s pack. You can then of course use an obd2 reader and Leaf Spy to monitor. Leaf BMSs go for around $60-100 making it pretty much the cheapest option. The issue is the balance current is only ~10mA.


Wait, $60-100? Where?

It's pretty typical for balance current to be in the low mA. You don't need much more unless you're right at the end of cell life.

jkenny23
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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Wed Apr 11, 2018 11:39 am

mux wrote:
jkenny23 wrote:
If you have a well balanced pack to start with you can use a second Leaf BMS on the extender pack. It will supposedly balance automatically when hooked up to a 96s pack. You can then of course use an obd2 reader and Leaf Spy to monitor. Leaf BMSs go for around $60-100 making it pretty much the cheapest option. The issue is the balance current is only ~10mA.


Wait, $60-100? Where?

It's pretty typical for balance current to be in the low mA. You don't need much more unless you're right at the end of cell life.


In the US at least, here is where I bought mine. Had to buy a second one actually, fried one of the ASICs on the first after bad wiring...
https://rover.ebay.com/rover/0/0/0?mpre ... 3504258964

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

Wed Apr 11, 2018 2:48 pm

jkenny23 wrote:Had to buy a second one actually, fried one of the ASICs on the first after bad wiring...

Wow!

How well does it work as a balancer?
2013 SL 50,000 miles.
12 bars until 44,300 miles on June 2, 2017. :D
11 bars current. :)
The Nissan Leaf is the fourth best long distance car for highway driving. >>Best Long Distance Cars<<

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