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BMS and contactor box

Posted: Thu, 04 Sep 2014, 04:32
by coulomb
Graeme from Suzi Auto recently brought in a decent quantity of Leaf batteries from overseas. The supplier threw in for free some BMS units. These came in the form of an ECU (Electronic Control Unit) and what turned out to be a contactor box, connected by a common cable.

Weber and I have been investigating Leaf drive systems, so Graeme kindly asked if we'd like to take one and do a quick disassembly. How could we refuse?

The PCB inside the ECU-like box:


The connectors along the bottom all go to individual cells. So this is not a cell-top BMS, it's the other kind, where the management/monitoring happens away from the actual cells. As most readers of this forum will know, Leaf battery cells are packaged into 2S2P "cans" with three screw terminals. There is a nifty flexible orange plastic harness arrangement that screws to the cells, making the interconnections (from memory, maybe that's not right) but also the connections to the BMS.

The twelve chips all in a row in the bottom half of the board are ASICS (Application Specific Integrated Circuits, i.e. custom silicon) with the part number D15110. There isn't a manufacturer's logo that we could find. Each chip handles four cells. There are another 12 of these, with all the associated components, under the board. Here is a close-up of one such channel:


Note the four larger resistors (0805 size, about 2 mm x 1.25 mm, still pretty small), marked "431". These are 430 ohm resistors, and would appear to be the only possible bypass resistors. If so, these would have a maximum of about 4.3/430 = 0.01 A or 10 mA of bypass current. This is about a tenth of the current of the next lowest BMS bypass capability, so maybe they're not bypass resistors at all. If these are bypass resistors, bypass capability is extremely weak. Power dissipation would be around 43 mW; these resistors are generally rated at 125 mW with adequate heatsinking. So they are sized about right for taking around 4.3 V (the approximate potential of one Leaf cell near full charge).

Near the middle top of the board is a CPU, I believe it's a Renesas chip similar to the one in the VCM (Vehicle Control Module, the main ECU). Maybe that "pacman" symbol (sorry, not visible in these reduced-size photos) is the same as the one on the ASICs; the logos (if that's what they are) on the latter look more like dots. It's presumably the BMS master, and seems to also control the main and pre-charge contactors. That's what's in the second box, attached to the BMS box by a cable:


The two rectangular black boxes with the Panasonic labels are the main contactors (breaking the positive and negative ends of the pack, by the looks). The coloured wires go to a smaller contactor, which must be the pre-charge contactor. It is associated with a ~ 20 W resistor under the contactor unit. This unit oozes quality; all the quick-connect connectors have plastic boots; every place where battery (circa 400 V) potential exists in a small space has a substantial plastic barrier separating the terminals; the bus bars are a work of art, and so on.

So: will these battery monitoring (and possibly very weak management) units be usable by converters? Well, the contactor box is pretty neat, if your conversion doesn't need a heap of current. The BMS ECU... well, it's designed for a 96S (~ 365 V nominal) pack, and I don't think it would take too kindly to a bunch of cells being missing. However, if your pack had a multiple of 4 cells in series (i.e. an even number of cans), then you would not be using half a channel, so it may be possible to ignore or bypass the unused channels. The ASICs appear to communicate to each other digitally, and there are opto-couplers at end ends of the pack. There are more details, including a schematic, here: My Nissan Leaf article "BMS details" . So you could perhaps intercept the digital stream on its way to the BMS master, which you might be able to ignore, but then you'd have to figure out what the digital stream meant. That might be easier than trying to figure out the CAN bus packets that the vehicle normally uses to communicate with the BMS master. So: a fair bit of work.

BMS and contactor box

Posted: Thu, 04 Sep 2014, 16:46
by PlanB
Turbo3 has an Android app that shows which cells are in shunt via a Bluetooth CAN dongle. Doesn't make a whole lot of sense to me, often cells with a lower voltage are in shunt & ones with a higher voltage aren't.

BMS and contactor box

Posted: Fri, 05 Sep 2014, 06:27
by 7circle
Thanks for the inspection and links Coloumb.

His "sketch" of the board has a 0.1uF filtering the 4.7uH on the path the cell terminals. He has schematics for the Mid and Bottom pairs of ASICs.

The 0.1uF stumps my idea the ASIC may be using buck [oops should be boost] converter to step up the voltage across the 430R resistor using the 2 X 4.7uH inductors?

The 0.1uF is only a small "stump" and the effeciency is not the goal.
So the chip could be using boost from the inductors to dissapate power into the circuit.

The choice of 6.2V zeners allows the flow of current in the top inductor feed the current through the reversed zener charging the cap in the above cell circuit. [6.2V is too low to allow this, would need 4.2V + 4.2V = 8.4V with this chemistry of cell.]

Similarly the negative side inductor can pull current via the reversed (-0.8V) zener from the cap on the cell bellow.

Coloumb photo show DA39 DA90(?) and L13 not fitted. [Not shown in schematic]
mmm... I haven't heard of DA .. could it be "dual" diode or just a FET.
They use TR for NPN transistors.
If the DAx's are fets or the like they could also play a part in the boost function with L13 too.

Might need to draw some colored lines on the schematic.

But not now...

[edits ... zeners voltage too low for cross channel current transfer. Unless the zener V-I curve shows that say 10V doesn't blow it. The ASIC may have internal clamping diodes to allow parallel path to zener reverse conduction. ]

BMS and contactor box

Posted: Fri, 05 Sep 2014, 18:03
by Johny
Ken, my take on the 4.7uH inductors is that they are only there for RFI and EMI suppression. I.E. 25W Taxi transceivers could play havoc with the cell balancers without RF suppression.
While we normally user ferrite beads and 100pF in Mobile radios (sometimes 1uH chokes), the 4.7uH may be to remove motor controller pulses as well.
I've been wrong before though...

BMS and contactor box

Posted: Fri, 05 Sep 2014, 20:41
by 7circle
Thanks Johnny
Trying to recover from the thought of a taxi stand with 10 taxis pulsing out 250W of EM. Image

I can see the need for filtering on the long connections to the batteries.

But somehow the circuit leads me to think there is more going on.
With each channel having 4 connections to the D15120-ASIC there are more possibilties than just the 430R as the shunt.

Will see if Coloumb or Turbo3 show up more info.

I was wondering if Turbo3's sketch was correct.

The cell to cell approach is old news but I don't see it in the the eBikes or EV's.

This chapter (4) Barsukov PDF on Cell Ballancing shows different techniques.

TI/BQ and LinearTech have high efficiency Cell-to-cell balancing chips.

Image 7 Cirkles of Tua

BMS and contactor box

Posted: Wed, 26 Nov 2014, 04:29
by bradleyk
do you know what the connectors are, i am trying to find one for my 12kw pack

BMS and contactor box

Posted: Wed, 26 Nov 2014, 13:32
by coulomb
7circle wrote: mmm... I haven't heard of DA .. could it be "dual" diode or just a FET.

On re-reading this, it occurs to me that DA may well stand for Diode Array.

The connectors seem like standard car ECU ones. I have no idea if they are available to individuals. There must be a hundred combinations of total number of pins, number of rows, retaining mechanism, and so on. Even so, I bet there are some sizes way more common than others, and you might be able to find some at a wreckers, complete with partial wiring loom. You'd need patience and luck, though...

BMS and contactor box

Posted: Wed, 26 Nov 2014, 13:38
by bradleyk
cheers, was hoping there might be a label or part number the socket. but, i think will just replace them with something else.

BMS and contactor box

Posted: Tue, 24 Mar 2015, 17:51
by jateureka
Does anyone have the circuit or any more information on the operation of the hall effect current sensor that's mounted on the contactor assembly?

BMS and contactor box

Posted: Wed, 25 Mar 2015, 03:40
by jateureka
The ev wiki says it is +/- 2.5V, but the mynissanleaf BMS article said he was reading 3.162V no load and 3.142V with 3A charge current. So 0.02V for 3A

BMS and contactor box

Posted: Wed, 25 Mar 2015, 13:26
by coulomb
jateureka wrote: The ev wiki says it is +/- 2.5V, but the mynissanleaf BMS article said he was reading 3.162V no load and 3.162V with 3A charge current.

That's still possible. The LEMs that I use at work have an output centred at 2.5 V, from a 5 V supply rail. So these measurements could be to ground, instead of the 2.5 V reference. It's also possible, but much less likely, that they have true differential outputs, so that +/- 2.5 V on two outputs can see +/- 5.0 V between the outputs.

Sorry, I have not looked at the specifications to see what type of outputs it has.

BMS and contactor box

Posted: Wed, 25 Mar 2015, 13:36
by coulomb
coulomb wrote: Sorry, I have not looked at the specifications to see what type of outputs it has.

All I can see on the Wiki page is this:

" * Ground
* Signal (0~ 5 V, 2.5 V at 0 current)
* 5 V supply"

So I'd say that they are single outputs, centred on 2.5 V, and the quoted measurements were with respect to ground. So subtract 2.5 V from those measurements to get a value proportional to current.

BMS and contactor box

Posted: Sun, 05 Apr 2015, 19:44
by reecho
Hows this for a good use of surplus Leaf cells....

Integrated with SMA Sunny Island too.....


BMS and contactor box

Posted: Mon, 06 Apr 2015, 14:17
by coulomb
Very interesting. Is that yours, Reecho, or just spotted somewhere?

I also see a photo of another cabinet with Nissan Leaf cells; is that part of the same system? (On photobucket, clicking on the image in your post) .

BMS and contactor box

Posted: Tue, 07 Apr 2015, 06:22
by reecho
no not mine just off the inter webs...

BMS and contactor box

Posted: Tue, 07 Apr 2015, 14:31
by coulomb
reecho wrote: no not mine just off the inter webs...

Ah. So I should have been less lazy and done a Google image search.

[ Edit: the other image yielded a much better page in English: ]

Ok, so I did that now, and unfortunately the main page seems to be in Norwegian:

Faktisk produsert solenergi

Google Translate translation:

Actually produced solar

I note that Google seem to have translated the Norwegian currency, the Norwegian Krone, into Euro dollars and Euro cents. Today, the Krone was equivalent to AU$0.17.

It seems to be 30 kWh (perhaps expanded to some 35 kWh later), 48 V. I'd like to know how he overcame the problem of 50 V not dividing nicely by 7.8 V nominal Leaf modules. Weber and I may use Leaf Modules in a monolith solar system soon, and I think the plan was to use 6.5 modules in series (wasting one pair of cells in each set of 7 modules).

[ Edit: it seems he just uses 7 modules in series. This would be 14 x 4.2 = 58.8 V if fully charged. This would be the equivalent of 4 14.7 V lead acid batteries in series. ]

BMS and contactor box

Posted: Tue, 07 Apr 2015, 20:46
by Richo
I like how it nicely fits in a 19" rack - and wheels to boot!

BMS and contactor box

Posted: Wed, 08 Apr 2015, 00:49
by offgridQLD
"This would be 14 x 4.2 = 58.8 V if fully charged"

Thats not to bad if using components designed for 48v flooded lead acid chemistry that can be 60 volt + during EQ charging. Especially if you conservatively charge the leaf cells at less than 4.2v.


BMS and contactor box

Posted: Thu, 31 Mar 2016, 14:49
by coulomb
User WolfTronix over at DiyElectriccar seems to be doing well reverse engineering the BMS's CAN bus protocol. Now he's aiming to replace the processor with one of his own, but with a JTAG / programming connector. It's an interesting idea: ... post751202

He's using a 75 pin PIC chip to replace the original 100-pin microcontroller. Why a PIC chip? (Weber hates them, for example.) Well, presumably you don't need a lot of CPU horsepower, but more particularly this PIC chip seems to have a feature whereby almost any pin can be configured to become almost any function that the chip supports. (There are a few exceptions of course; I assume that power, ground, and probably programming pins would be among the exceptions.)

So for the most part, he's just brought each original 100-pin signal to the nearest PIC pin, thus minimising the number of vias and crossovers, and making the PCB simple, and this practical to route when it's so small.

I have doubts that he will be able to merely paste the PCB on with a hot air gun, so I'm keen to hear how this progresses. It would be interesting if this technique, or some variant of it, is able to progress the art of re-purposing OEM equipment like this.

BMS and contactor box

Posted: Fri, 01 Apr 2016, 01:35
by 4Springs
Wow, that is some plan!
It does seem ambitious to get all 100 connections soldered on in that manner. Will be interesting to see how he goes. Please keep us updated!

BMS and contactor box

Posted: Sat, 30 Jul 2016, 20:01
by KiegKhan
I read Tesla has made a lot of their tech open source, it would be awesome if one of the manufacturers made their battery tech available for converters, it would be a whole new area for them and would not impact their regular sales as converters are going to do it anyway.
If Nissan battery systems were available to use in conversions it would also add to the value of the Nissan components.
Unfortunately, I don't think any of the companies are truly visionary, except maybe Tesla. So many potentials available you would think they would be jumping at the chance to become a real dominant force rather than just another "me too".