Blower Motor Question
Blower Motor Question
(OP)
Hi,
I have question about DC blower motor in typical automobile air conditioner. Some circuit have variable resistor that used to adjust air flow from low to hi. I'm wonder if voltage across blower motor changed or current through motor changed to make air flow more or less when you change fan speed on panel control. My guess voltage stay same and current adjusted to make more or less air out. Thanks for help.
I have question about DC blower motor in typical automobile air conditioner. Some circuit have variable resistor that used to adjust air flow from low to hi. I'm wonder if voltage across blower motor changed or current through motor changed to make air flow more or less when you change fan speed on panel control. My guess voltage stay same and current adjusted to make more or less air out. Thanks for help.





RE: Blower Motor Question
RE: Blower Motor Question
R Chung
RE: Blower Motor Question
In that motor,
Eg=NKPhi
Ia = (Vt – Eg)/R = (Vt – NKPhi)/R
T = K Phi Ia = K Phi(Vt – NKPhi)/R
The T vs N curve is Straight Decreasing line with:
* Slope is – K^2 Phi^2 / Ra
* T intercept (max T) is KPhi Vt/ Ra
* N intercept (max speed) is Vt/ K Phi
There resistor may be in either the field or the armature circuit. Increasing resistance in either circuit should increase speed (of course assuming constant voltage applied to the winding/resistor combination). Although if there are resistors in both circuits than increasing both would increase speed until the point that motor stalled. If the field current is reduced too far the armature current will become excessive and burn up the armature.
RE: Blower Motor Question
When the resistors go bad ( they are wire wound and in the air flow of the blower to keep them cool. You can pull them out and see if they are bad ) you have high speed only on the fan.
The resistors are fairly easy to replace on most cars. GM has also designed the control switch marginally and that is much harder to get at.
RE: Blower Motor Question
The symbols in my equations are defined as
N= speed
T = Torque
Eg = Generated EMG (internal voltage)
Vt= terminal voltage
Phi = flux
K = conversion/constant
R=Ra = armature resistance
I = armature current
Rf = field resistance - I didn't mention this one but hopefully it's apparent that decreaseing the field resistance increases the field current which increases the flux proportionally.