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  • Author Author: colporteur
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Blog 6: Now for some initial data

colporteur

With the python library, misaz shared in his blog post, I can continue with my challenge testing.  My initial tests of the sensor are using the locomotive on the bench. I have been using 3VDC, 5VDC and 12VDC to set some expectations before moving to the rail tests.

I still try and follow the process my electronics lab college instructor tried to instill in us 40 years ago. Have some idea of what the measurement should be, before you go poking around with testing equipment making measurements. I had no success getting current measurements using my Fluke VOM so I only have what the sensor is providing.

The python script generates a current & voltage reading every five seconds. The initial voltage applied to the locomotive motor is 5VDC, then changes (highlite) to 3VDC and then to 12VDC.

image

My question to the sharper electronic knives in the drawer than me is, do the current values look reasonable?

The current reading moves between.05 to .09, the average, throwing out the negative values in the calculation, is .06. I was expecting higher current values at the higher voltages. What I interpret from the current reading is a motor that is an active load where the resistance changes to ensure a steady current. That doesn't seem correct?

The motor speed does change with a change in the voltage.

I confess there is a lot of rust and dust accumulated on my electronic theory. Part of my motivation for doing these challenges is to refresh my knowledge. I would appreciate any feedback members have to offer before proceeding with further testing. What do you see in the values so far?

Parents

  • The readings seem to make sense, although timing of conversions and filtering may affect results.  If you multiply voltage times current you will get an idea of the power consumed in each state. If the load is more or less constant (no load except friction), the speed will be proportional to power. Back EMF of the motor, which is proportional to speed will reduce the effective applied voltage, which tends to reduce current through the motor.

Comment

  • The readings seem to make sense, although timing of conversions and filtering may affect results.  If you multiply voltage times current you will get an idea of the power consumed in each state. If the load is more or less constant (no load except friction), the speed will be proportional to power. Back EMF of the motor, which is proportional to speed will reduce the effective applied voltage, which tends to reduce current through the motor.

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  • in reply to dougw

    I would like to better understand your explanation.

    With much help from the sharper knives, I have scripts that contain reading that are more stable.

    image

    I pulled the following readings and did some ohms law calculations. Well, truth be known I let some website do it for me so that it was presentable.

    There is a power difference between each load voltage as you suggested. What confuses me is the change in resistance. In my mind, the copper wire windings should have a constant resistance. Varying the voltage across that resistance would produce different currents. I'm wondering if I am mixing impedance and resistance. Yes, there is a constant resistance but that is not the only variable in play. There is inductance and capacitance along with the resistance.

    I have tried measuring the resistance of the motor with little success. The value reads 1 ohm and I know I'm not putting 12amps through this little motor.

    I have a disconnect in my theory at some point. I went digital in my career and motor theory took a back stage. The only time I got involved with them was by replacing them.