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

All 3 values vary over time and can go up and down, especially weather related. It's pretty obvious here which you can correlate with the average temperature during the time when I recorded the values



From the start until 1/3/18 or so the BMS was learning the capacity of the new pack (cells were replaced by Cor, you can find the other thread about this). After that it seems to have switched algorithm and behaved a little differently afterwards. So far I have not seen any trend towards decreasing life, I try and keep the car charged <=80% all the time (set it up to default to 80% unless I override).

I am still stuck with 5 capacity bars, despite my now ~87% SOH. It looks like Dala found a way to at least visually change the capacity bars though, so presumably a Muxsan enabled car could show a re-calculated true SOH: https://secondlifestorage.com/showthread.php?tid=6308&pid=57641#pid57641

How far is your range? does the 5 bar capacity limit the range or power level (go to turtle).

nlspace said:

How far is your range? does the 5 bar capacity limit the range or power level (go to turtle).

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My battery now is a 2013 87% SOH battery. The cells were swapped from a salvage Leaf. Range now is 50-60 miles depending on outside temp, my commute is mostly freeway 60MPH. The car behaves like it should with a battery of this health, the only difference is the display still shows 5 bars.

Before the swap, battery was ~20-30 miles if you were careful. I don't think it limited power level/acceleration, but of course I wasn't doing much of that since every kWH was precious

Anybody have links or info about a burned leaaf which used an 18650 extender pack in the trunk--was it discussed on this forum? was it a forum member that did this?

Supposedly an access hole was drilled thru the pack cover to add the wiring and either something shorted or water got into the main pack and caused the car to catch.

I don't think it was posted here - at least not recently.

nlspace said:

Anybody have links or info about a burned leaaf which used an 18650 extender pack in the trunk--was it discussed on this forum? was it a forum member that did this?

Supposedly an access hole was drilled thru the pack cover to add the wiring and either something shorted or water got into the main pack and caused the car to catch.

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Yes, I remember reading that in MNL. But I can't find the original posting.

There are two postings that I've definitely seen in the past but cannot find now.

One was the one described here - somebody added an access hole and most likely water got in and caused the car to go up in flames.
Another was somebody who I don't remember even added extra capacity (but he might have), but definitely removed the top shell, put it back and probably also had water ingress. That car went up in flames during a fast charging session.

I've recounted these stories to other people, but recently wanted to show the original stories in a blog/vlog and can't find them anymore. If anybody has clues, there's now two people searching for these.

Found a couple of videos but no details. Looks to me that fire started where the added wires entered the pack (sharp edges slice insulation?), oem pack did not catch

https://youtu.be/2cIo95W-vfE 18650 extender pack fire

North Texas street fire, no details: https://youtu.be/8PUG-ldjD48

What is that burning mass on the ground (extender module?) Look at the intensity of the fire, and how far out the bottom edge of fire and smoke extends from the back seat window--what in the car could burn like that? i think this was an extender fire also--extender pack in the back seat and maybe in the front seat too. Backpack and laptop over in the grass?



Flower Mound TX

nlspace said:

Found a couple of videos but no details. Looks to me that fire started where the added wires entered the pack (sharp edges slice insulation?), oem pack did not catch

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Thanks for the finds.

In the case of the first video/stills, it looks to me that the extra wires included many thin wires. So it appears that they paralleled cells so that the original BMS would protect the added cells as well as the original cells. That saves the cost of an additional BMS, but I'm guessing more importantly it avoided the need to integrate the two BMSs.

If I'm right, that's 97 thin and unfused wires with complete battery potential between the end two wires, and anything from one to 95 cells worth between any other pair of wires. It's bad enough when the manufacturer does this with short wires professionally crimped and with industrial connectors all within the sealed battery shell, but to connect all those wires to a home made battery, regardless of the quality and care involved, is just begging for trouble to me.
I actually prefer the Mitsubishi iMiev cell top BMS design, to avoid all those unfused wires altogether.

Any clues as to whether they really did have many thin wires would be appreciated.

Also @mux, does your extender pack do this, or does it have its own BMS?

[ Edit : even when the contactors are off, these wires would be live 24/7. Even with the safety disconnect out, some pairs of wires would have up to 3/4 of the pack voltage between them, since the Leaf disconnect splits the battery 3/4 and 1/4. So it's never safe. Again, all if and only if I'm right about those wires. ]

coulomb said:

Any clues as to whether they really did have many thin wires would be appreciated.

Also @mux, does your extender pack do this, or does it have its own BMS?

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Scary indeed having that many small wires. Would be easy to fuse the main connection at the original cells, but that design is just bad news all around. My plan would be to interface my extender pack with a "real" Leaf BMS, just a second model which you can pick up surplus for around $100. Where else are you going to find a 96 channel high resolution ADC with isolation and balancing (as low as it is) for that price, crazy! Easy to tie to another Bluetooth OBDII for a graphical representation too. There's also a user on the DIY electric car forums Wolftronix who has done a full "brain transplant" on the Leaf BMS replicating all the original functions, to give another option.

I'll let Mux answer but from what I saw in his videos, the modules he's using are each containing their own balancing BMS which is standalone but can all be communicated with for more detail.

Our modules have cell-top BMSes (well, per module instead of per cell, but *very* similar to Yuasa) that communicate via galvanically isolated CAN. We also have contactors inside the battery box, so everything is completely galvanically isolated from each other, both on the comms and power side.

By the way, this is not something I should specify, this is absolutely necessary for any such system. The approach in the pics above is... well, I mean, I understand it from a prototyping perspective somewhat, this is done in the e-bike community, but it's not something you should do for more than a few test drives. 97 opportunities for something to go terribly wrong.

But to be fair, I don't know if that is what caused the issues. Battery fires generally happen only when overcharging or *generously* exceeding max cell temperatures. And even then, the (old Mn-based) Leaf cells endure 4.4V/cell and 75C apparently indefinitely. They are really, really good in that respect. Shorting them over those tiny wires is unlikely to cause any issues, even if you put, say, 100V excess on a cell, you'd just use those wires as a fuse.

mux said:

Our modules have cell-top BMSes ... so everything is completely galvanically isolated from each other, both on the comms and power side.

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I assumed so, but I'm glad to hear it confirmed.

But to be fair, I don't know if that is what caused the issues. ...even if you put, say, 100V excess on a cell, you'd just use those wires as a fuse.

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But those wires aren't designed as fuses, certainly not DC fuses. One failure mechanism I could see would be a short caused by those wires, the wires get very hot very fast but don't actually fuse immediately, insulation is melted, that starts more shorts and the glowing wires start a fire. Remember that DC arcs sustain at 1V per millimetre once started, so even if the wire fused, the arc could continue for perhaps 300 mm (a foot)!. That's why DC fuses have to be specially designed, with melting sand or other techniques to extinguish the arc.

I know the cells can bulge due to over-voltage, but I would think that a fire would cause the electrolyte to expand before and during catching fire, and that might look much the same as overcharged cells. Granted, a complete failure of the BMS is another possibility, and maybe the extra wires somehow compromised the original BMS.

One more possibility. Maybe the wiring was such that the added battery didn't share charge current very well, and maybe ended up with enough charge current to cause some of the added cells to over-voltage much earlier than the main cells did. The thin wires don't perfectly convey the voltage of the added cells. So an added cell might have been at say 4.5V when an original cell was still at 4.0V. The 0.5V difference was merely dropped across those thin wires. So the BMS saw no reason to cut back the charge current, and the fire stated in the added battery.

Response from the Flower Mound Fire Dept. concerning fire post on previous page:

There was nothing suspicious about this fire and it was not investigated by the Fire Marshal's office. The fire report does not indicate the presence of any external batteries. I cannot say for certain if these were present or not.

nlspace said:

Response from the Flower Mound Fire Dept. concerning fire post on previous page:

There was nothing suspicious about this fire and it was not investigated by the Fire Marshal's office. The fire report does not indicate the presence of any external batteries. I cannot say for certain if these were present or not.

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The particular fire shown in the video could have been anything - an exploding Galaxy Note 7, a dropped Zippo, a bottle of nail polish remover spilling into the 12V cabin electronics and igniting. The cabin upholstery and seats are dense enough to eventually cause that scale of fire, no need for an extender pack (and no evidence of such).