[Ovmsdev] Leaf canbus

Wed May 7 07:16:37 HKT 2014

OVMS reports 0% SOC and sends out panicked low battery messages when it's
not getting a valid SOC message from the CAN bus. I get this when I screw up
the vehicle setting, which is set via the MODULE command. The first thing
I'd do is make sure the vehicle type is set correctly. You can see it from
the smartphone app on the Vehicle Info screen, look at the Car line. For my
set up I see:

Car: 2.6.5/TR/V2

This says the car is running firmware version 2.6.5, the car type is TR
(Tesla Roadster), and it's V2 hardware.

You can get the same info by texting MODULE? to the car, which returns the
VehicleID, VehicleType, Units (miles or km), and the notifications setting.

For the Leaf, you should see NL as the vehicle type.

Which CAN bus OVMS reads depends on how the cable is wired. I believe the
group consensus is that reading from the CAR CAN bus is the best strategy
since we know LeafSpy is able to get everything from the that bus.

The code in vehicle_nissanleaf.c that decodes data from message 0x5b3 looks
like it's trying to pull out the Gid values scaled down to work as a rough
SOC %, but it looks like the array offsets are off by one. Dividing by 3 is
a rough approximation to multiplying by 100 and dividing by 281 to get the
standard conversion from Gids to percent.

    case 0x5b3:
      // Rough and kludgy
      car_SOC = ((((int)can_databuffer[5]&0x01)<<1) +
((int)can_databuffer[6])) / 3;
      break;

Here's a sample message from our Leaf:

5B3 69 BE FF FF FC DD 53 0A

When I captured that message, I was reading 221 = 0xDD Gids. Both the Leaf
message decoder spreadsheet and the OVMS can_databuffer array start indexing
bytes at 0, so byte zero is 0x69, byte 1 is 0xBE, etc.  Using the Leaf
message decoder spreadsheet, I believe the Gids calculation is: take the low
bit of byte 4, shift left by 8 into 16 bits then add byte 5:

    (((int)0xFC&0x01)<<8) + 0xDD = 0xDD = 221.

So I think the code to extract Gids from CAR CAN message 0x5B3 is:

    (((int)can_databuffer[4]&0x01)<<8) + can_databuffer[5]

My thought is that the Gids value should be stored in car_idealrange. Like
Gids, the ideal range on the Roadster is an estimate of the state of charge
in absolute energy units. An ideal mile is 225.4 Wh; a Gid is 80 Wh. The UI
on the Smartphone app will have to change, or Gids will have to be scaled.

I propose this:

      car_idealrange = (((int)can_databuffer[4]&0x01)<<8) +
can_databuffer[5]; // raw Gids
      car_SOC = (car_idealrange * 100 + 140) / 281; // convert Gids to
percent

Optionally, we could do the same thing with Gids that Tesla did to compute
ideal miles. The EPA said the Roadster's range is 244 miles, so Tesla
equated that with the nominal full capacity of a new Roadster battery, and
thus the ideal miles was created. To do the same for the Leaf, take the EPA
rating of 84 miles (after Nissan eliminated the 80% charge to get rid of the
EPA's stupidity in taking the range to be the average of the 100% and 80%
charge levels). After using the raw gids to compute the SOC percent, convert
to EPA rated miles:

    car_idealrange = (car_idealrange * 84 + 140) / 281;

We can also get the SOH value out of message 0x5B3. According to the
spreadsheet, it's the top seven bits in byte one, so

   soh = can_databuffer[1] >> 1;

For my sample message above, that's 0xBE >> 1 = 0x5F = 95, which agrees with
the SOH reported by LeafSpy when I did that data capture.

BTW, SOH and Hx appear to be different, but perhaps related. I'm trying to
figure that out. I suspect SOH is just the Hx value rounded, but I have some
data from the Plug In America Leaf survey which contradicts that. The value
in message 0x5BE doesn't have enough bits to be the higher resolution Hx.

   Tom

On 5/6/14, 11:39 AM, "Nigel Jones" <nigel at cherrybyte.me.uk> wrote:

I have the OVMS module running in my car so found an hour tonight to start
looking through the source - sorry it's taking a while to catch up, so
forgive the newbie questions too......

One thing I noticed is that I'm getting a 0% state of charge indication, and
regular texts saying my battery is low (for testing I setup the sim with
unlimited texts.....). I see there was a commit last year which used some of
the data from the spreadsheet at

https://docs.google.com/spreadsheet/ccc?key=0An7gtcYL2Oy0dGRaSWl6VTV2eXBQMy1
ON2xZSzlMUXc#gid=0

which I found references from the nissan leaf forum discussion at
http://www.mynissanleaf.com/viewtopic.php?f=44&t=4131&start=340

If I'm not mistaken the OVMS currently reads the CAR CanBus ?

There's an indication in the spreadsheet that CAN message 0x5b3 contains SOC
information - but in fact the spreadsheet refers to it as SOH. I have a
leafDD and I think this is also known as the Hx figure -- ie it seems to
vary with battery age/capacity -- mine for example is down to around 82%,
but it is not current state of charge, so I don't think decoding that will
help?

GIDs are what I use in daily driving as they are absolute. The sheet
suggests that figure might be retrievable from this message, but then most
people would only see a % of 95% for example as life is lost? Is that's
what's wanted? I suspect not for the overall SOC figure.

I can't see much else decoded yet (I was looking for low hanging fruit!) on
the CAR canbus - instead most work was done on the EV canbus, including
looking at state of charge etc.

So the question comes how to bridge the data from that bus onto the CAR can.
There was reference to this previously on the list at

http://lists.teslaclub.hk/pipermail/ovmsdev/2013-October/001712.html

It would appear the way to get any of the EV can data is to actively request
the data. I can see examples of CAN data requests in the tesla module but
haven't yet figured how I might for example retrieve CAN msg 0x5bb for
example (it's one of the ones to try). I can also see the developers guide
p24 which refers to writing on the bus. I'm also wary of the need to be
careful in making active requests rather than the easier passive monitoring!
Can anyone point me to an example of how I might do this? I'd make that call
from the ticker functions? and then handle it in the poll right?

Apologies if this is all covered in the nissan leaf forum thread - I have 39
pages to read now...

Thanks
Nigel.
nigel at cherrybyte.me.uk

-- 
----
Nigel Jones 
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