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93tracerwagon 11-30-2019 06:13 PM

More efficient HVAC fan for cars?
I no longer have the 93 tracer wagon... upgraded to a 99 Escort wagon with a swapped in zetec engine. I will soon have changed to all LED's for car lighting, except front turn signals so I can prevent hyperblinking. The last big power draw normally in use is the HVAC fan. I have already insulated all the panels below the window line front to rear with 1/2 duct insulation and will be doing the roof this next year, so my heating and cooling loads will probably be cut in half. Has anyone found a more efficient motor for using for the HVAC or some way to make the current motor more efficient to run? Any cheap ECM motors or more efficient speed controls so I could run the motor at low speeds efficiently?

I am also running a 25 % underdrive pulley. Gearing in the car however, keeps the revs up.

2000mc 11-30-2019 08:12 PM

I had linked to something about this before, but the images are gone... Assuming your car doesnít already have it, PWM speed control. At full speed it doesnít matter, at the lowest speed the amount of power drawn is small. IIRC I think when youíre running medium or low-medium with resistors you could be using 75-80% of the power of running full speed, and have half of it being used by the resistors. The percentage being wasted on low is greater, but the total draw is much less.
I donít think it would be worth it unless you get a junkyard PWM speed control with connector, and it used as many or more individual speed inputs as your current resistor.

93tracerwagon 11-30-2019 08:48 PM

I think I currently have 4 speeds. If I understand correctly , you are saying that the current low speed already is using much lower power than the higher speeds or is that only with the PWM control? I assumed that all speeds have resistors, so I also assumed power draw was always high.

oil pan 4 11-30-2019 09:31 PM

Full speed just runs straight electrical system power to the blower. But a pwm can make it a lot more efficient over a resistor.

93tracerwagon 11-30-2019 10:51 PM

I meant to say resistors on all the lower speeds. I am guessing the only time I'll need high is for defrosting. I bet low will be enough for heating even on below zero days once I finish the insulation.

2000mc 11-30-2019 11:09 PM

So if say you used the lowest (speed 1) primarily, the total draw is relatively low, and while pwm would gain a lot in terms of %, the total amperage, or wattage to be saved would be very small. The real gains to be had with pwm would be if you use speeds 2 or 3 commonly. If you only used speeds 1 and 4 it really wouldn’t matter whether you had pwm or not

redpoint5 12-01-2019 07:37 AM

That doesn't make sense. The highest efficiency gains to be had with PWM would be at the lowest settings and have diminishing returns the higher the "speed" (lower resistance) up until the "hi" setting, which is a straight connection to the battery.

JRMichler 12-01-2019 08:33 AM

I once measured the heater blower power draw in my truck:

In winter, I mostly leave the heater blower on the lowest speed, and the second lowest speed when the temperature is below zero Fahrenheit. A more efficient blower with LED lighting is tempting because it would have got me THAT close to a 40 MPG summer average....

2000mc 12-01-2019 12:33 PM


Originally Posted by redpoint5 (Post 612552)
That doesn't make sense. The highest efficiency gains to be had with PWM would be at the lowest settings and have diminishing returns the higher the "speed" (lower resistance) up until the "hi" setting, which is a straight connection to the battery.

It sounds counter intuitive on the surface, but a greater percentage of a smaller number wouldn’t necessarily be more than a smaller percentage of a greater number or vice versa. Jrmichler's blower doubled its draw from speed 1 to 2, so if the efficiency gains aren't double on low vs setting 2, you would be saving more power on setting 2 than 1.
I imagine this could also vary from vehicle to vehicle. I’m also regurgitating info i saw years ago I can’t see from some chart on Pulse-Width Modulated Fan Controllers for Automotive Applications | PowerGuru - Power Electronics Information Portal
But maybe you can with a different browser. But as I recall, it seemed like the squeeze wasn’t going to be worth the juice at the lowest setting

93tracerwagon 12-01-2019 02:16 PM

I was thinking that the resistors would keep the total power used pretty constant no matter what speed you're on , but that assumption is obviously not right. It looks like I will be saving quite a bit just by being able to run low almost all the time.

I understand what you are saying about the percentage savings being higher at low speed, but the power consumption is already so low it isn't really worth upgrading.

It looks like I am already at the knee in the cost effectiveness curve. I'll just replace the rest of the Instrument lights with LEDs and I'll be in good shape.

If I eventually get the AC working, that insulation should gain me some MPG in the summer too. The compressor and blower both will have a lot less work to do.

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