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

Håkon Markussen hakon.markussen at gmail.com
Mon Jan 13 22:13:34 HKT 2014

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?


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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>> OvmsDev at lists.teslaclub.hk
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