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

[Håkon Markussen]

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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>>
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