How do I get an analog out to control a blower motor?

conjur · 06-20-2008, 12:23 AM

I've been reading data sheets for weeks now... I can get an analog out, at 1ma, but how to I "amplify" that to control a blower motor? I don't even really know how much amperage the motor takes... right now, the "stock" system uses a resistor box; and I'd prefer use a pic, to control it on a scalar level.

Anyone have any more information other than "google op-amps"? lol

I'm not really an electronics engineer, but I play one on TV. Seriously... I have a good grasp on how most things work, but without having the stuff infront of me, I can't really make sence of half of the numbers in the datasheets.

peace
Mike

EDIT1: btw, what I'm looking at now, is the IRFP250NPBF http://www.irf.com/product-info/data...a/irfp250n.pdf ... it "seems" like it would work. but again, I'm no electronics engineer. According to the Datasheet, it says that the source drain peaks at 1ma, and the emitter constant drain can be 30A, with a peak of 120A...

Chairboy · 06-20-2008, 12:33 AM

Easy plug & play answer: Get a serial servo controller and use it to run an RC speed control. Those are what electric RC cars and trucks use to power their drive motors. $20-$30 for the serial servo interface, and the same maybe for speed control.

conjur · 06-20-2008, 12:59 AM

Not sure if those RC speed controllers can handle 30 amps..

for (HIGH) speed, the blower runs P=220W, V=12v, R=0.65ohms, I=18.33A

Chairboy · 06-20-2008, 01:36 AM

Plenty of them can handle that load. I googles "30amp speed control 12v" and found lots of matches. Just let your browser do the walking.

Chairboy · 06-20-2008, 01:39 AM

You know.... It might be cheaper to get, instead of a speed controller, a servo. Attach it to the old controls behind the dash and make it "turn" the knob.

h3rk · 06-20-2008, 03:41 AM

Quote: Originally Posted by Chairboy

You know.... It might be cheaper to get, instead of a speed controller, a servo. Attach it to the old controls behind the dash and make it "turn" the knob.

That's a viable answer, but I know it wasn't your first choice. It's a bit of a weak link, to have an electromechanical interface in the middle there.

If you have a low amp 0-12V signal (or even 0-5V), you could use a power transistor (commonly found in Hondas, comes with a big heatsink, and doesn't require PWM input). Heatsink should go in airstream, just like a blower resistor.

WuNgUn · 06-20-2008, 08:35 AM

This is what I've been thinking about using...
http://www.hobbyengineering.com/H2338.html
But I'm not sure how I'd interface it with the PC just yet.

Chairboy · 06-20-2008, 08:41 AM

The HB-25 can't be controlled by a servo interface out of the box, unfortunately. It needs 5 ms delays between pulses and only expects to receive instruction when there's a change, instead of a constant PWM stream like RC servo interfaces provide. You could use some of Parallax's sample code to rough together a control for this through your analog output, but it'd be a little work.

JC-S60 · 06-20-2008, 08:50 AM

And using an electronic (solid state) speed controller for RC cars/boats? That would eliminate the mechanical part and still listen to servo controls...

Good luck!

WuNgUn · 06-20-2008, 08:54 AM

Quote: Originally Posted by JC-S60

And using an electronic (solid state) speed controller for RC cars/boats? That would eliminate the mechanical part and still listen to servo controls...

Good luck!

Now why didn't I think of that!?
They don't seem rugged enough to handle the current though...probably because they spend most the the time at full power?

Chairboy · 06-20-2008, 09:48 AM

Yaarrgh! That was my first suggestion!

When choosing a speed controller, they'll specify temporary and constant load. The limitation is cooling, if you make sure it's well cooled you should be in good shape.

WuNgUn · 06-20-2008, 09:51 AM

Quote: Originally Posted by Chairboy

Yaarrgh! That was my first suggestion!

When choosing a speed controller, they'll specify temporary and constant load. The limitation is cooling, if you make sure it's well cooled you should be in good shape.

I imagine swapping out the tiny heatsink for a old CPU heatsink, then putting it in the air stream should make everything alright...

Nice...now I should be able to do my whole HVAC with just a Phidget 4-servo controller.

Chairboy · 06-20-2008, 10:00 AM

The reason servo controllers have been on my brain lately is because I've been thinking of the possibilities it provides for motorizing various little doors and cabinets in the cabin of the car. A control panel with a Trunk Monkey or 'Ejection Seat' button it that raises out of the console dramatically....

WuNgUn · 06-20-2008, 10:04 AM

lol @ dramatically....
You luxury car guys!!

Would you even need servo control to 'pop' something open? Just a digital out to a relay/solenoid would work I'd think...

Looking at some of the 'cheaper' ESC, they come with a one piece heatsink...should be easy to swap.
I'm sure I could do the hardware on this, but as far as working it from Centrafuse, I'm a total retard...

Chairboy · 06-20-2008, 10:08 AM

A relay/solenoid would make it pop out indeed. But a servo means you get the full effect of it slowly rising out like something you'd see in a movie villain's lair. If you're going to do something, you've got to do it with style.

Most of the ESCs I've bought (I have 3 or 4 I think) have been a small PCB wrapped in a piece of heatshrink tubing. For the loads you're thinking, one with a big heatsink would be necessary for sure. The robot crowd needs beefy speed controllers, you might be able to find something cheap through ze google.