[Ovmsdev] Motor temp does not support negative numbers (car_tmotor)

[Thomas Bergo]

On  i-Miev the motor temperature is with a -40C offset from the car.

Highest motor temperature I have seen is ~50C on i-Miev.

Regards, Thomas

mandag 13. januar 2014 skrev Håkon Markussen følgende:

> I was not aware of the industry standard -40C offset, so thank you (all)
> for good inputs.
> The "problem" is hereby addressed :)
>
>
> @Kevin: Can you recall the highest motor temperature ever seen on the
> Roadster? Do you know is Model S has the same temperature characteristics
> as the Roadster?
>
> Br.
> Håkon
>
>
> 2014/1/13 Mastro Gippo <gipmad at gmail.com>
>
> Håkon, it is industry standard to apply an offset of -40C. We should do
> that instead of transforming it to signed, as Collin said. That would also
> be directly compatible to the CAN message from the twizy. Let's wait for
> Mark's opinion.
> Regards
> MG
>
>
> 2014/1/13 Håkon Markussen <hakon.markussen at gmail.com>
>
> The highest motor temperature I ever have seen on Think City is ~45 C.
> This is the offset for the cooling thermostat
>
> I cannot even imagine that other EV-motors should reach a temperature near
> 100C? Then the cooling system have to be out of order ... or ...?
>
> Anybody who knows the expected operation range of motor temp for Roadster,
> Leaf, iMiEV and Zwizy?
>
> Think City reports temperature in 8 bits - signed.
> When bit8 (msb) is set to "1" it means negative temperature, so when the
> motor temp actually is -1C , OVMS reports 255C. When motor temp is -11 Ovms
> reports 245C ,etc.
>
> I think that this problem might apply to all vehicles(?).
>
> Mark, do you have any suggestion for solution?
>
> Br.
> Håkon
>
>
> 2014/1/13 Collin Kidder <collink at kkmfg.com>
>
> I don't think you'd want to do that. 127 deg C really isn't that terribly
> hot and -128C is extremely cold. If it is necessary to retain use of an 8
> bit variable then the standard solution is to just offset the temperature
> stored by -40. That way you can read -40 to 215C which is a pretty
> reasonable range. Unfortunately, I fear such a change would necessitate
> many other changes in code. It might be better to expand to a signed 16 bit
> integer.
>
>
> On Mon, Jan 13, 2014 at 7:50 AM, Håkon Markussen <
> hakon.markussen at gmail.com> wrote:
>
> Hi (Mark).
>
> In ovms.h the motor temperature is defined as unsigned char (non-negative):
> extern unsigned char car_tmotor; // Tmotor
>
> Currently the weather is cold in Norway (-15 C) and I noticed that motor
> temp was 244C.
>
>
> Is it possible to update the car_tmotor to
> extern signed char car_tmotor; // Tmotor
>  in ovms.h?
>
> Best regards
> Håkon
>
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