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

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Lylou2 said:
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.
 
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.
 
jkenny23 said:
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-...73059-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!
 
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?
 
IssacZachary said:
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.
 
jkenny23 said:
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.
 
jkenny23 said:
IssacZachary said:
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.
 
mux said:
jkenny23 said:
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=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F253504258964
 
IssacZachary said:
jkenny23 said:
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?

Well since I fried my first one, and it doesn't balance any less than a full 96s pack, I haven't really tried it yet. There's lots of detail on how it works here: http://www.mynissanleaf.com/viewtopic.php?f=8&t=17470&sid=d98368436de139bf1bf43fd75c110590

It has a 430 ohm shunt resistor, which means less than 10mA balancing current at max charge. I do have a 1.8kWH pack made of salvage cells, and a Chinese BMS with about 30mA balancing current, and it has been plugged in for about a week and is almost fully top balanced now. Each series component in the pack is within ~134mAH (0.38%) of balance across 14s (35AH total capacity). So you can assume with only 10mA balance current or less you need a pack within maybe 0.1% of capacity delta across the series sets of cells.

I have considered making an expansion board that could work with any of these type of balancers, and add a larger balancing current in parallel.
 
I made a colculation, the best option looks tu use space in baggage use 96s14p, 1344 cells, weight aprox 70kg, 14.3kw/h extra energy for 70/120 km, couse if connect 14p for discharge it can handle aprox 140A if it's ncr18650PF cells, so it's enought then you have stock battery instead. For charging its only 19A (1350mAh for 1 cell) and I got max 7,6kw/400v, (max 15kw for 2 batteries) the question is that it's possible use fast charging?
 
Lylou2 said:
I made a colculation, the best option looks tu use space in baggage use 96s14p, 1344 cells, weight aprox 70kg, 14.3kw/h extra energy for 70/120 km, couse if connect 14p for discharge it can handle aprox 140A if it's ncr18650PF cells, so it's enought then you have stock battery instead. For charging its only 19A (1350mAh for 1 cell) and I got max 7,6kw/400v, (max 15kw for 2 batteries) the question is that it's possible use fast charging?

If you assume the 120A of the quick charger is split proportionally across the Leaf + extender battery pack, you would be getting ~45A into the extender, or 3.2A per cell. This is double their recommendation (max 0.5C). I would recommend finding a cell that can at least handle 1C charge, that said, you will still be exceeding the spec for a little while at the start of the QC session; most 18650s do not allow charging above 1C rate.
 
I did another discharge test from 4.2 vs. 4.1V with a different cell (different chemistry too I believe), and the result it the same. This time from 4.11 instead of 4.125V, but at a lower discharge rate of 0.4C:

uLm5wGd.png
 
That looks a lot like either the same chemistry, or an NCA vs NMC. These two chemistries are very similar, with NCA a bit 'bumpier' than NMC.

The real differences are LMO/LCO vs NCA/NMC. Try getting one of those to see the impact of significant chemistry differences!
 
mux said:
That looks a lot like either the same chemistry, or an NCA vs NMC. These two chemistries are very similar, with NCA a bit 'bumpier' than NMC.

The real differences are LMO/LCO vs NCA/NMC. Try getting one of those to see the impact of significant chemistry differences!

Looks like you're right, I didn't realize the Panasonic cell is NCA chemistry (makes sense, it's similar to the battery they make for Tesla). The first cell, Sony VTC-5A is NMC chemistry. I ran the test on an older Sony LCO battery, I'll try an LGABD11865 today since that's one of the ones for sale at ~$170/kWH from alarmhookups and I believe is also LCO chemistry:

MsBuEqs.png
 
Ok the new ones I can buy from victpower.com f.eg. I was looking for NCR18650PF best option for me price unit is aprox 1,85e plius sending 100euros to Norway it's good price? Some versions for used ones with good condition?
 
Lylou2 said:
Ok the new ones I can buy from victpower.com f.eg. I was looking for NCR18650PF best option for me price unit is aprox 1,85e plius sending 100euros to Norway it's good price? Some versions for used ones with good condition?
I don't know much about dealing with Chinese companies. I've been tempted to buy some from similar companies. But it could be a good deal or a type of fraud.

I don't know if you can get them to send to Norway but https://eu.nkon.nl seems to have a good reputation in Europe for selling 18650's.
 
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