re-setting the blower motor

[mans]

The blower motor of the ventilation system is one of the power hogs in my car.

on setting #1 its like 2.5 amps,
#2 its like 3.5 and by the time u get to the higher #'s its sucking like 7-8 amps.

the higher settings are almost never used, and very often I don't need the full power of setting #1, all i'd need is a tiny bit of power ..just enough to bring the heat into the car and 1 amp would do this...


i'd like to have 2-3 settings that are inbetween the factory "off" position and the factory #1 position, and the same for between the factory 1 position and the factory 2 position.

I'd rather leave the existing motor in place, and perform this mod by replacing the electricity controller/switch that goes to the motor, and the knob.


I'm wondering what the best way to do this is....
I'm sure it wont take me long to locate the factory motor controller, but what would I put in it's place?

I'm having some brain fog as to whether this should be done with a pwm or a voltage adjuster of some sort....

if anyone can shed some clarity as to the best way to do this I'd be very appreciative...

[SentraSE-R]

You probably want something like this. That one's a bit pricey, but you can find plenty of other choices, like this one at half the price.

[straight5]

I don't see what car you're talking about, but wouldn't a different resistor work? That is what the manufacturers use for different speeds.

[RobbMeeX]

Just add a blower resistor inline in addition to the standard one.

[mans]

Originally Posted by RobbMeeX

Just add a blower resistor inline in addition to the standard one.

what size resistor would I use? how many ohms?

the motor sucks about 7 amps when on full power, I'd like to cut that in half

[SentraSE-R]

The trouble with adding resistors to control fan speeds is you still waste essentially the same amount of power at low speed + resistors as you do at high speed sans resistors. Adding the rheostat or resistors, you won't save any significant amount of power.

[mort]

Originally Posted by mans

what size resistor would I use? how many ohms?

the motor sucks about 7 amps when on full power, I'd like to cut that in half

Hi Mans,
If you assume about 14 volts and you know 7 amps, then the motor looks like a
2 ohm resistor, using 100 watts. If you add a 2 ohm resistor in series with the motor then the total resistance looks like 4 ohms and at 14 volts the current will be 3.5 amps. the total power will be 50 watts half through the motor and half through the resistor. So the resistor needs to be rated more than 25 watts. The motor will run a little slower than 1/4th as fast as full speed.

Power = Volts X Amps
Ohms = Volts / Amps

But you said you wanted just a little bit of air flow. Some fan motors will run at much lower speeds than they can start at. You need to start on a higher setting then lower the speed. If you want to run a lower speed than the speed you said used 1 amp, say you want to try 1/2 amp. If the voltage is 14 volts and the current through the motor is 1 amp then the total resistance is 14 ohms. The motor resistance is 2 ohms, so the resistor used is 12 ohms. To go to 1/2 amp the total resistance will be 14 volts / .5 amps = 28 ohms. so you need to add a 14 ohm resistor. The power coming out of the resistor is 3.5 watts.

-mort

[Daox]

Is an extra 1.5A really going to make it or break it? Seems insignificant in the grand scheme of things IMO.

[mans]

Originally Posted by SentraSE-R

The trouble with adding resistors to control fan speeds is you still waste essentially the same amount of power at low speed + resistors as you do at high speed sans resistors. Adding the rheostat or resistors, you won't save any significant amount of power.

I was concerned about this...
An electrical engineer is telling me resistors work by wasting off the extra electricity into heat.
if thats the case the motor would use 7 amps regardless of the control knob setting, as at full power none would be wasted to heat, and the lower you go the more is turned into heat...

but when u put an ammeter to the car you will see that power draw DOES go down when u turn down the control knob.

This difference between what I find in actuality and what the electrical engineer tells me is confusing.
can anyone shed some light on this one?

[SentraSE-R]

Originally Posted by mans

I was concerned about this...
An electrical engineer is telling me resistors work by wasting off the extra electricity into heat.
if thats the case the motor would use 7 amps regardless of the control knob setting, as at full power none would be wasted to heat, and the lower you go the more is turned into heat...

but when u put an ammeter to the car you will see that power draw DOES go down when u turn down the control knob.

This difference between what I find in actuality and what the electrical engineer tells me is confusing.
can anyone shed some light on this one?

It's all there in Mort's post #7. The power consumed (wattage) remains the same, but the amperage through the fan motor drops to half if the resistance in the circuit doubles by your adding resistors.