PWM blower motor control

[CowboyBilly9Mile]

Duncan, this should be right up you alley.........

I'm doing some planning on an upcoming EATC mod and the system I'm using is from an Expedition/Navigator. These use a PWM unit for the blower and it, along with the blower motor, is located inside the cabin, on the passenger side on the right and above their right foot and next to the cowl. On the PWM unit are three for four cooling fins and they make up one side one side of the unit. No fan forced cooling, just convection.

I'm running into available space problems if I try to use this same location but I do believe this can be resolved by mounting the unit inside the dash behind the center panel. There's space for air movement in there, it's not stuffed with electronics. So now comes concern #1, heat. Currently my blower circuit is 40A on #10 wire and I expect the PWM unit will use the same, plus more wire ( on more #10 wire, that's on the table for now). So, do these PWM units generate a whole lot of heat?

*I could run a bench test, but I just don't happen to have a suitable power supply to do so.

EDIT: If needed, I can take a pic and post.

 

[DNFXDLI]

Typically they create minimal heat...as compared to a triac/SCR or other type of chopper circuit...depends on the duty cycle and load.

For the most part (in my experience) the MOSFET's need to be kept cool as from what I can remember from my EET schooling, they are a positive temp coefficient...so as temp increases, resistance increases which will result in lower currents passed...a nice circle with a load.

An easy way, without going through a bunch of calculations having to know loads/duty cycles etc. would be to get an inexpensive 12v brushless fan and use a thermodisc on the heatsink.....thermodisks are pretty reliable and avoid the BS of a relay/thermistor circuit.

 

[fatherdoug]

Pardon my ignorance, but what is a PWM? Enquiring minds want to know.

 

[DNFXDLI]

Pardon my ignorance, but what is a PWM? Enquiring minds want to know.

Pulse Width Modulation

Think VFD Doug

 

[fatherdoug]

Pulse Width Modulation

Think VFD Doug

Thank you. I understand VFD.

 

[CowboyBilly9Mile]

Typically they create minimal heat...as compared to a triac/SCR or other type of chopper circuit...depends on the duty cycle and load.

That's was about my expectation since it's really just a "rapid firing" switch.

For the most part (in my experience) the MOSFET's need to be kept cool as from what I can remember from my EET schooling, they are a positive temp coefficient...so as temp increases, resistance increases which will result in lower currents passed...a nice circle with a load.

Hmm......cool is sort of a relative term as I have no idea what environment temp range the unit was designed for. But honestly, even with a black dash parked in the sun on a hot day, after a period of driving with AC on, it's just gotta be "sort of" steady state in there at, say, 75 - 85*F. At least, I'd like to think so....

An easy way, without going through a bunch of calculations having to know loads/duty cycles etc. would be to get an inexpensive 12v brushless fan and use a thermodisc on the heatsink.....thermodisks are pretty reliable and avoid the BS of a relay/thermistor circuit.

Calcs? I'm not really sure how to run any numbers on the thing. Lost me on the rest. In the vehicle, the EATC unit will control fan speed automatically, unless the driver over rides that.

 

[DNFXDLI]

Calculations that will figure out load/heat dissipation....and what I was referring to was to simply mount a thermodisk to the exposed heatsink that would turn on a fan once a set temperature was reached...100F would work as an example

http://www.mouser.com/Search/Refine.aspx?Keyword=therm-o-disc

Controlling a small fan..

https://www.parts-express.com/imc-m...-12-vdc-60mm-x-25mm-cooling-fan-008a--259-147

 

[CowboyBilly9Mile]

Hmmmm.........A fan crossed my mind earlier but I so badly want to just use a "canned" solution rather than have to engineer one. I honestly just have to wonder how significant the airflow is in the upper foot area of the dash area VS inside a dash itself.

*I have learned why Explorers didn't use the PWM unit for the blower on their EATC systems, lol! Which BTW, using those components is an option, but I really don't want to use that EATC head unit. It has one function on the panel that is great for an SUV, but lame for a pickup. That is...."Rear Fan".

 

[DNFXDLI]

Sorry Bill, I didn't realize you just wanted straight plug and play...I don't know what to tell you without knowing the load, rating of pwm etc.

 

[CowboyBilly9Mile]

I've got the plug and play unit, it's a cooling concern based on location.

 

[CowboyBilly9Mile]

Duncan (or?), question.

Under what condition would a PWM unit operate at it's highest temperature, when the output is 100% (ie, functioning like straight through wiring) or when it's reduced to it's lowest design level?

 

[DNFXDLI]

Typically when it is reduced.

 

[CowboyBilly9Mile]

Typically when it is reduced.

To the maximum that the device will reduce it to? Midway? Me asks because, I have an idea how to test and determine operating temp, and to some extent, what the upper tend temp might be.

 

[DNFXDLI]

To the maximum that the device will reduce it to? Midway? Me asks because, I have an idea how to test and determine operating temp, and to some extent, what the upper tend temp might be.

Typically in general...how do you like that , lowest setting should produce the most heat...but it could vary depending on the particular design...sorry I'm not more help.

 

[CowboyBilly9Mile]

Duncan (or?), question.

Under what condition would a PWM unit operate at it's highest temperature, when the output is 100% (ie, functioning like straight through wiring) or when it's reduced to it's lowest design level?

Typically when it is reduced.

Bench testing yesterday as proven this to be true.

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To the maximum that the device will reduce it to? Midway? Me asks because, I have an idea how to test and determine operating temp, and to some extent, what the upper tend temp might be.

Typically in general...how do you like that , lowest setting should produce the most heat...but it could vary depending on the particular design........

Again, bench testing yesterday demonstrated that the lowest fan speed (and PWM output) and 2/3 of max fan speed (and PWM output, ie, fan ~ lo lo med low) have about the same effect on heat generated by the PWM unit which is the most heat. The temp increase is also somewhat rapid under these operating conditions.

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...sorry I'm not more help.

I wouldn't be so sure of that bud.