Fig. 1 shows the circuit used previously for the BB motor testing.
CH1
o
|
------(-)battery(+)--o---SW----Motor----
| |
| LED 4.7 k ohms |
| ----|<|---R2-------------- |
| | | |
-----o-----------R1-----------o---------
| 0.0631 ohms |
o o
ground CH2
Fig. 1 - Initial Marinov BB motor test circuit.
This scope lead placement permitted measuring battery potential drop
due to the overall load.
The scope test leads are now as shown in Fig. 2, so as to obtain the
voltage drop across the motor itself on the scope Channel 1.
CH1
o
|
------(-)battery(+)--o---SW----Motor----
| |
| LED 4.7 k ohms |
| ----|<|---R2-------------- |
| | | |
-----o-----------R1-----------o---------
| 0.0631 ohms |
o o
CH2 Ground
Fig. 2 - Circuit for measuring BB motor voltage drop
Using the Fig. 2 circuit the motor moving and stopped runs were made
again, with a few minutes cooling time in between. See:
http://www.mtaonline.net/~hheffner/HullVAmotorRun.jpg
http://www.mtaonline.net/~hheffner/HullVAmotorStop.jpg
The traces indicate, upon current stabilization, a voltage drop
across the motor of about 2.1 V running, 0.7 V stopped, giving a back
emf of about 1.4 V. This is slightly off because current was
slightly higher in the stopped position, but it still establishes a
back emf, and thus the magnetic nature of the motor, as well as Lenz'
law at work.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
