Blower Motor Control (out of the box thinking)... (1 Viewer)

[DanS HJ-45]

No problems with the stock blower motor switch, resistor, etc.... In fact, I don't want to effect that at all--I want that to continue working as always.

What I want to do is be able to turn on the blower motor, at a reduced power/speed from a completely different power source. And I want to use as little power doing so as possible, as this is something that will run when the engine is not running, but it will be running off of an auxiliary battery--likely for hours, and possibly days on end to keep the cab warm (there is also a Webasto coolant heater running at the same time, BTW).

So, I am planning on placing a large diode in the stock wiring, to isolate the power that I will supply to the blower motor--any issues with doing so?

And that leads me to the meat and potatoes of the question....

Is there more current draw associated with placing a fixed resistor inline with the power to (or from) the blower motor? If so, I guess I'd just as soon run the blower full blast if there's no reduction in power draw using a resistor. I also know I would have heat dissipation issues with a resistor like this, and would probably mount it on a framerail, or cut a hole and put it inside the ventilation ducting.

Or would it be easier to use a PWM DC Motor Speed Controller and relay to do this? RioRand Upgraded Adjustable DC Motor Speed PWM Controller 10V 12V 24V 30V Reversing Switch 120W: Amazon.com: Industrial & Scientific

Either are possibilities, and the Webasto will only control 1A as it is, which I believe means I will need a relay and other means of control either way (which isn't difficult for me to add at the moment).

Of course I know enough to be dangerous, but not enough to be good--so I'm asking here if anyone has any input. Especially EE types.... The Aux battery is a group 31, so it has a crap-ton of capacity, but I also want to conserve as much of that as I can when the blower motor is running. If I can keep the fan speed lower, then I should be able to sleep in the truck just fine when it's cold outside as well.

Dan

 

[Output Shaft]

I too did similar. But in my instance I wanted fresh air circulation inside the cab when I'm sleeping in it at night during a rain storm...with the windows rolled up by necessity.

The problem is the inefficiency of the blower fan.
The current draw for the slider switch on the HVAC panel is:

Low: 3.3 amp
Med: 5 amp
Med-hi: 7 amp
Hi 10 amp

All of those current draws are accomplished by resistors and low speed will kill most older batteries over night. And even if it doesn't kill the battery, that's a lot of amps to have to replace the next day if you're camping in a spot for a while.

The resistor for the fan is a combination resistor pack located in the air duct near the accelerator pedal. It's located inside the duct because it gets hot as hell when any of the slow speeds are chosen and needs air blowing over it to keep it cool.

As an experiment, I rewired my fan out in the boonies to run through a spare 55w halogen head lamp bulb as the resistor.

This brought the fan speed down approximately 1/2 from the normal low and the amp draw was about 1.5 amps.

Air circulation was enough to provide plenty of fresh air as I slept. Also the fan was whisper quiet at that speed. I also ended up with a dim light running all night due to the current running through the bulb.

So if you're comfortable with sucking that much juice out of a battery for a long, cold ass winter night, then yes, a bigger resistor will work. In fact, using the correct sizes lightbulb might be the best resistor.

[when I ran the fan through the 55W bulb, it was not wired through the slider switch too... Just straight from the battery and a fuse, then the bulb, then the fan]

But if you really want to save power, a separate dedicated 12V fan installed in the HVAC duct would be way more efficient.

I have since rewired my cabin fan through the normal slider switch and reistor pack, but have rewired its power source so that the fan will run while the key is in the ACC
position, but not the off position.

I wired it this way so that the ignition circuit does not have to be on (as it normally does) and so when I turn the key to OFF, the fan will turn off too ... so I don't accidentally leave the fan running when I leave the car.

 

[DanS HJ-45]

I too did similar. But in my instance I wanted fresh air circulation inside the cab when I'm sleeping in it at night during a rain storm...with the windows rolled up by necessity.

The problem is the inefficiency of the blower fan.
The current draw for the slider switch on the HVAC panel is:

Low: 3.3 amp
Med: 5 amp
Med-hi: 7 amp
Hi 10 amp

Very good info! Thanks!

As an experiment, I rewired my fan out in the boonies to run through a spare 55w halogen head lamp bulb as the resistor.

This brought the fan speed down approximately 1/2 from the normal low and the amp draw was about 1.5 amps.

Air circulation was enough to provide plenty of fresh air as I slept. Also the fan was whisper quiet at that speed. I also ended up with a dim light running all night due to the current running through the bulb.

I like this even more. I don't need much air circulation, just a little bit. And frankly the thing shouldn't end up running continuously for more than 30 minutes at a stretch, and after that it would be on and off as the temperature regulates. At least, I think that's how it would work.

So if you're comfortable with sucking that much juice out of a battery for a long, cold ass winter night, then yes, a bigger resistor will work. In fact, using the correct sizes lightbulb might be the best resistor.

[when I ran the fan through the 55W bulb, it was not wired through the slider switch too... Just straight from the battery and a fuse, then the bulb, then the fan]

I definitely want to reduce the juice it sucks down. This system is both for camping on really cold nights, but also so that I can set a timer and have my truck warmed up (cab and engine) when I am expecting to get home from work (I often am gone 4 days, and getting back to a really cold truck at midnight seriously brings the suck--I frostbit a thumb one night when the faux-lux wouldn't start) so it might be on for half a day or a bit more if I don't get back as scheduled.

But if you really want to save power, a separate dedicated 12V fan installed in the HVAC duct would be way more efficient.

I've thought about this. But I didn't see an obviously good place to mount one in the duct. I might have to look a bit harder...

I have since rewired my cabin fan through the normal slider switch and reistor pack, but have rewired its power source so that the fan will run while the key is in the ACC
position, but not the off position.

I wired it this way so that the ignition circuit does not have to be on (as it normally does) and so when I turn the key to OFF, the fan will turn off too ... so I don't accidentally leave the fan running when I leave the car.

This one will be running on a circuit controlled by the Webasto, which is on a hot battery bus, but only on when the Webasto is on. Naturally I will have some protections to shut down the Webasto unless it's winter and I really need it.

Dan

 

[DanS HJ-45]

Further thinking....

(pic stolen from other thread about blow motor--but it was about the resistor)

Think I could fit a fan in that square space between the factory blower motor and the heater core?

Anyone have one handy to measure? I will be able to measure mine in a couple of days. But just thinking here... I see some at 92x92mm (Just under 3 3/4" square) that should draw well under an Amp.

Dan

 

[OGBeno]

Further thinking....

(pic stolen from other thread about blow motor--but it was about the resistor)

Think I could fit a fan in that square space between the factory blower motor and the heater core?

Anyone have one handy to measure? I will be able to measure mine in a couple of days. But just thinking here... I see some at 92x92mm (Just under 3 3/4" square) that should draw well under an Amp.

Dan

I can measure in the AM since my entire HVAC system is on my kitchen table.

Rebuilt.

 

[DanS HJ-45]

I can measure in the AM since my entire HVAC system is on my kitchen table.

Rebuilt.

I appreciate it.

I'm finding more sizes and options...
AFB1212M DELTA PRODUCTS | Fans & Blowers

Dan

 

[DanS HJ-45]

Here's some measurements for future reference....

Sorry for the dirty/plastic calipers. . There's a lot of grinding that goes on around them.

Stay tuned for my plan....

Dan

 

[Output Shaft]

I'm interested in this.
Tuned in...