Resistance tests:
The quality of a test resistor is its initial value and final value after
heated up during application. If doubt, consider well calibrated I-meter
and V-meter. The I-meter, in particular, should be a true current(i.e.
current-magnetic-displacement) type, instead of those cheepo I-meter which
is derivitive of a volt meter upon a current sensing resistor.
Battery internal resistance, or
(Effective Sries Resistance) is
best determined dynamically.
That is; ESR = (V2-V1)/(I2-I1),
with I2 at rated load and
I1 around 0.66*I2.
Where V1 and V2 are coincidence
with I1 and I2, respectively.
Motor internal resistance, or
(Motor, Resistance, stalled) is
best determined with
I-meter, V-meter and a dummy test resistance.
If dummy resistor shot temperature drift,
have one test observer assign to each meter.
The motor; Rm = (Vm)/(Ib-Is)
or = (Vm)/(Im)
Where; Vm is voltage across stalled motor by V-meter.
Ib is the battery current under Vm by I-meter.
Is is the predetermined solenoid current.
Im is the current into the stalled motor,
if I-meter is inseries to motor (+ve).
(To make things more complicated, Rm existed in two mode the static and
dynamic reisstance. They are differ in percentage. Static here refers to
stalled. The static brush resistance is differ from the electric-arc
resistance. The CD may void a static number for one traced to dynamic mode.
There was an article in NEW years back on dynamic Rm determination.
To make things even worse, the CD should ask for motor efficiency, without
that, we might as well just forget the whole deal for Rs and Rm.)
Regards,
YK Chan
Seattle area
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