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

[Kevin Sharpe ZCW]

Hi Håkon,

No, I don't know the highest temperature for the Roadster but someone with access to the server logs might be able to tell us.

The Model S is liquid cooled and Roadster air so no direct correlation.

Keep up the good work!

Kevin Sharpe | Founder & Trustee | Zero Carbon World, a UK Registered Charity

From: Håkon Markussen <hakon.markussen at gmail.com<mailto:hakon.markussen at gmail.com>>
Reply-To: OVMS Developers <ovmsdev at lists.teslaclub.hk<mailto:ovmsdev at lists.teslaclub.hk>>
Date: Monday, 13 January 2014 14:31
To: OVMS Developers <ovmsdev at lists.teslaclub.hk<mailto:ovmsdev at lists.teslaclub.hk>>
Subject: Re: [Ovmsdev] Motor temp does not support negative numbers (car_tmotor)

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<mailto: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<mailto: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<mailto: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<mailto: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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