[FIRST DRIVE] Leaf to VW Type 2 Campervan

[johu]

This all looks very familiar and typical Leaf BMS
"Flying Tools" and youtube runs 8 MEB modules with Leaf BMS and of course the SoC calculation is off. Leaf 40 kWh cells must be in the 110 Ah ball park while 60 kWh is more like 165 Ah. So SoC calculation is off by 2/3.
Same goes for the jumper wire. The BMS then measures cell voltage+voltage drop (or rise) over the wire.

[ianlighting]

This all looks very familiar and typical Leaf BMS
"Flying Tools" and youtube runs 8 MEB modules with Leaf BMS and of course the SoC calculation is off. Leaf 40 kWh cells must be in the 110 Ah ball park while 60 kWh is more like 165 Ah. So SoC calculation is off by 2/3.
Same goes for the jumper wire. The BMS then measures cell voltage+voltage drop (or rise) over the wire.

Thanks.

When I started this I decided using OEM parts would be a good policy as it meant no configuration (at least using my Resolve-EV VCU). But when it comes the BMS I can see now that maybe being able to tweak the parameters of a BMS to better match the battery box(es) you actually build could be an advantage. If I did this again, I’d give that a bit more thought.

What is unknown to me with the parts I have is what effect a low SOC has on the system. If I went down to a reported ‘zero’ on remaining capacity, does actually mean I have 30% still in the battery? And will it enforce a safety turtle mode because it believes I’m close to empty.

[johu]

If I went down to a reported ‘zero’ on remaining capacity, does actually mean I have 30% still in the battery? And will it enforce a safety turtle mode because it believes I’m close to empty.

I haven't gone there, so I don't know if it drops the discharge limit based just on voltage or also supposed SoC. One trick you can pull is pull over, cycle 12V supply to BMS. Then it will estimate SoC based on voltage and you're back up.
The Leaf experts will know whether you can program SoH>100% or greater AH in the first place.

[ianlighting]

I promise not to document every time I go to a public charger, I realise that could be one of the most tedious travelogues ever. But worth sharing that at Winchester InstaVolt today, they wanted to take my photo and give me a free charge! Think I got lucky because there looked to be a management tour going on of their new 40 charger facility so the marketing dept were up for something more interesting than a Tesla.

Anyway, was happy to chat but declined for the moment. But took her email and promised to go back once I’d passed DVLA checks, so all nice and legal. If anyone else in an interesting EV conversion wants to come along I’ll try to co-ordinate. Not imminent, got a few things to do, but let me know.

Anyway, back to business. Did 25 miles to Instavolt’s Chademo charger. Charged up to 75%, drove 80 miles, and parked up at home after lots of 50 - 60 mph driving with 9% / 10Ah remaining

On that basis, it would be 118 miles range with zero left.

But this is with my 40kWh BMS on a 60kWh battery. If (still to be confirmed I think) I could expect 30% more if it was a 60kWh BMS the range would be 150 miles. That’s more what I was hoping for.

The final LeafSpy (it’s zoomed in below, so looks worse than it is) once back home shows 3.60 for the lowest cell and 347V for the pack. I think I’m right in saying that I’d expect to see the low cells much lower than that on a close to empty battery. So gives me hope that my range can go closer to the 150 than 100. But whether that is possible with the current BMS is something I haven’t dared to push yet.

I know there are Leaf BMS reflashing efforts ongoing in another forum. But if I was confident a CANBridge might do the job, I’d probably be happy to go for that to avoid the risk of clumsy me bricking the BMS.

Go on, admit it, you do really want to see me parked at another charger

[ianlighting]

So CANbridge isn’t the answer. Investigating 62kWh BMS.

In other news, cable tidying…

1) Engine Bay now much nicer… (aaargh, upside down!)

2) VCU wiring up at the front. Getting there, still a bit to do on the driver controls part which are still a bit temporary.

[T1Terry]

IMG_8468.jpeg


Decided for my next test that if I was going to burn somewhere down with a battery fire I’d rather do the Shell garage than the local hotel (dear lawyers, this is just a poor taste joke and not a statement of intent).

All went ok.

I’ve moved on from focussing on my weak cell 55 as he doesn’t seem to be much of a problem. Still a slacker, but nothing serious.

All the attention now is cell 67. As mentioned this is the first cell of module 11 on a 2meter HV extension and the first of 30 cell tap extensions.

Just to be sure, Ive remade the BMS connections to all the cells in module 11. Rechecked the HV for a tight connection and retested around the block and then on to the Shell.

So this is what I get to watch when Chademo charging. Playing chicken with battery cell!
IMG_1404.png

That 99mV can bounce around of course, think up to 150 at one point.

I called it quits at 85% SOC and with cell 67 reaching about 4.08. That’s an upper limit I’m happy with. I’d prefer not to experiment with that cell hitting 4.10 and higher, although happy to hear anyone’s thoughts on safe voltages for a leaf 60kWh battery cell.
Edit - this is only a rapid charging problem as far as I know so far. Should I have the need, I ought to be able to go higher on my home 2kW charging.

Battery temp got up to 26.5deg

Chademo charging started at 30-something kW, but then was down in the 20s. Did about 30minutes.

IMG_8481.jpeg


Once I was done charging cell 67 rejoins the rest of the pack. Then 15 min drive home and final LeafSpy when at rest.

IMG_1408.png

Is the voltage on that high cell being measured at the cell or at the end of a series link joining the last module to the module with the high voltage when charging? In other words, measuring between cell 67 @4.065v and cells 68 and 69 that are both low at around 3.985v. The cell average voltage at that point was 3.99v.

I'm thinking the high reading is being exaggerated because of additional resistance between the negative on the high cell and the negative on the next cell that is using to get used to get voltage reading across cell 67 and this affecting the voltage reading of cell 68 and 69 ......

This can generally be verified if the voltage drops on the high cell when the charging stops, yet rises on the next two cells, then drops even more if a load is applied and the next two cells rise further ......

Not sure if any of that made sense, it did in my head when I was writing it, but not so sure reading back after posting it

T1 Terry

[ianlighting]

Is the voltage on that high cell being measured at the cell or at the end of a series link joining the last module to the module with the high voltage when charging? In other words, measuring between cell 67 @4.065v and cells 68 and 69 that are both low at around 3.985v. The cell average voltage at that point was 3.99v.

I'm thinking the high reading is being exaggerated because of additional resistance between the negative on the high cell and the negative on the next cell that is using to get used to get voltage reading across cell 67 and this affecting the voltage reading of cell 68 and 69 ......

This can generally be verified if the voltage drops on the high cell when the charging stops, yet rises on the next two cells, then drops even more if a load is applied and the next two cells rise further ......

Not sure if any of that made sense, it did in my head when I was writing it, but not so sure reading back after posting it

T1 Terry

The main conclusion I reached is that there isn’t much I can do about it apart from monitor it to make sure it doesn’t peak too high.

Since that post, I’ve done another drive of 80 miles, often at 60 mph. And done an AC charge from a low SOC back up to 90%. None of this causes that situation. It’s only a Chademo charge that will stress things and display those peaks on each module, with that module 11 being the worst. As long as I know the potential risk area, that’s the main thing. There’s nothing I can do about the HV or cell tap cable lengths, and I’ve remade the module 11 connections to be absolutely sure. I can set a max charge limit to 85% which should keep it within safe limits based on what I’ve seen so far. Most of the time that’s going to be plenty to get back from wherever I’ve been.

I’m not testing Chademo again until I have my 60kWh BMS (in the post), since the way results are displayed on LeafSpy should adjust a little, so that will need to be how I benchmark behaviour for the future.

[Bratitude]

The main conclusion I reached is that there isn’t much I can do about it apart from monitor it to make sure it doesn’t peak too high.

His statement is if the measurement it self is in correct, not that the cell it self is too high

[ianlighting]

His statement is if the measurement it self is in correct, not that the cell it self is too high

His point is interesting. But there is no way to verify since it’s the BMS that reports this data and it’s only seen during a fast Chademo charge.

Even if the BMS is not reporting accurate voltage due to the wiring changes I’ve done compared to OEM original, I still have to behave as though they are ‘real’. Because any safety measures the BMS might take to protect a cell, module or pack, due to a cell that has overly high voltage, are going to be real. I’m speculating on the BMS behaviour, but if the BMS decided to shut down to prevent a cell reaching too high a voltage for example, it doesn’t matter if the cell is actually at a normal level if it was tested separately. All that matters is what the BMS thinks.

So that means charging up to 100% on AC (only tested up to 90% so far) is fine, and 85% on Chademo, keeps cell 67 within a safety margin.

It’s a bonus if cell 67 is actually not peaking in the way the BMS reports.

[Bratitude]

If the bms is not reading correctly, going to do the incorrect function. A safe response is predicated on if the data collected is data that accurately represents the real world. If that model is wrong… it’s not “safe”

What the bms reads and what the cells actually read might be different… you’re going to need to verify that…..in which u can. You just need to have an external meter on those cells and run a test. If the numbers are the same between your meter and bms then it’s good to go

[ianlighting]

If the bms is not reading correctly, going to do the incorrect function. A safe response is predicated on if the data collected is data that accurately represents the real world. If that model is wrong… it’s not “safe”

What the bms reads and what the cells actually read might be different… you’re going to need to verify that…..in which u can. You just need to have an external meter on those cells and run a test. If the numbers are the same between your meter and bms then it’s good to go

I do agree that accurate data in = valid response out.

But I also have to deal with the real world and make a judgement on what I consider to be high risk. Breaking into the HV cell taps in a such a way that fast charging can carry on, but also extending wires to allow a multimeter to read the live charging voltage introduces risk. That might be ok at home. But doing this in a public charging place with people wandering around, I’m not comfortable with that. Too much potential for distraction or mistakes.

I will get back to Chademo testing when the 62kWh BMS arrives - just been delayed a week. So I can think again based on results I see with what I hope will be the final, long term BMS. If I think it’s worth the risk at that point I can do as you suggest.

[tom91]

Have you figured out where the offending cell is?

Does it also sag under heavy loads? If so it could be an extended cable.

[ianlighting]

Have you figured out where the offending cell is?

Does it also sag under heavy loads? If so it could be an extended cable.

Yes, I know where it is. And yes it is at the start of a module on an extended main HV cable. I’m sure that’s the reason.

It also has extended cell tap wires, but then so do 29 other cells. So the unique thing is the main HV.

Under AC charging it’s fine. Not noticeable during driving.

I haven’t noticed a drop under heavy acceleration, but I probably need to repeat tests with particular focus on that next.

[tom91]

So yea the HV cable will be the change. As you are measuring including volt drop (during discharge) and volt increase during charging.

Specially since during charging its a steady current for a while so it will be picked up better by the BMS.

[ianlighting]

So yea the HV cable will be the change. As you are measuring including volt drop (during discharge) and volt increase during charging.

Specially since during charging its a steady current for a while so it will be picked up better by the BMS.

Unless an expert specially called out what I was doing as particularly dangerous, i am not planning to change the setup, just monitor and manage it.

But I am interested to understand how non-OEM BMSs deal with this scenario. Do they let you configure cable size and resistance so that cell tap monitoring and balancing takes this into account? On a cell by cell basis?

[tom91]

It is not dangerous, as long as the connections are fine, you can just throw faults/derate more quickly.

Do they let you configure cable size and resistance so that cell tap monitoring and balancing takes this into account? On a cell by cell basis?

Yes a lot feature "busbar compensation"