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  1. #1

    Join Date
    Aug 2015
    Posts
    15
    Location
    British Columbia
    Mower
    CMM1200

    Added temperature guages to battery and motor (CMM1200) - see how hot it gets!

    I was curious to see how hot the battery and motor in my CMM1200 got. Since I installed the lithium ion battery, the motor works quite hard as the new battery is able to supply a much higher amperage than the old battery. The highest measured amperage was 133 for only a few seconds, and it rarely goes over 50 amps.

    After installing the temperature guages I mowed the lawn. The lawn was fairly thick and part of it was a little wet, so the mower did have to work hard today, although it has certainly worked a lot harder, it took about 20-25 minutes to mow. According to the coulomb counter, I used 6Ah mowing the lawn today which doesn't seem like a lot.


    Results:

    Starting temperature was 19○C (66○f) for both the battery and motor. About halfway through it had only risen to 21○C (70○f) for the motor and 19.5○C (67.1○f) for the battery. At the end of the mow, the battery's temperature was 22.6○C (72.7○f) and the motor's temperature was 34.7○C (94.5○f).

    I am rather impressed that the motor keeps relatively cool despite working so hard. I don't know at what temperature the motor will fail, but given that the wires feeding the motor current are right there, those wires will certainly start to melt at I would guess around 100 degrees Celsius as they don't feel like a silicone wire.

    I suspect that most of the measured rise in temperature of the battery is just heat convected from the motor. The battery's temperature did not rise until after the motor's temperature rose. The probe for measuring the battery temperature is attached to the middle of the battery, but only approximately 15 - 20 centimeters from the motor. The temperature probe for the motor is attached to the motor casing itself near the top of the motor, not far from the brushes.

    I have attached a couple of pictures. The temperature guage on the far right is for the motor, the guage just to the left of it is for the battery.

    Any questions or comments are welcome!

    20150911_125516-640x360.jpg20150911_125507-640x360.jpg
    Last edited by Filek; 09-12-2015 at 03:22 AM.

  2.  

  3. #2

    Join Date
    Aug 2015
    Posts
    15
    Location
    British Columbia
    Mower
    CMM1200

    Re: Added temperature guages to battery and motor - see how hot it gets!

    More results:

    Out of curiosity I checked the temperature several hours after I had finished mowing the lawn. The temperature of the motor was down several degrees to 30○C, but the battery's, temperature had gone up! It was 23○C, only up a little.

    This could be from the heat of the motor radiating to the battery, or even partly from the sun shining on the black case. It didn't seem out of the ordinary.

    A couple of hours later I checked the temperature again (it is now approximately 6 hours after mowing the lawn) and the motor's temperature is down as expected. It is 23○C which is similar to the ambient temperature. The battery's temperature however, is now 24.3○C! An hour later, the battery's temperature was back down to ambient temperature as well.

    Anyone have an idea what is happening to the battery post mowing? I mentioned in the first post that it discharged about 6Ah, it is a 30Ah capacity battery and I did not charge it after mowing.

    Part of the reason that I added the temperature guages to the CMM1200 was because I saw a lecture from Dalhousie university on lithium ion battery technology. One of the things they are researching is the different lithium battery chemistries and their heat tolerances. They found that the type of lithium battery that I used (LiMn2O4) is particularly sensitive to heat (much higher than encountered today) and capacity loss is accelerated when used in high heat.

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