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Laptop charger to run fan?
tag1260
Hi,

New guy here with questions.

Modifying my hot air popper (Popcorn Pumper) and while I have my heaters figured out I am having trouble with the fan.

I know it's a 18v DC motor but am unable to source the right transformer locally and reasonably but have read about using a laptop charger to run the fan. Now, is this a possibility? and where would you place a potentiometer to control speed? Would you just use a dimmer switch to control 120v input ? Or place a pot on the DC side?

Thanks
 
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JitterzZ
Welcome
Until someone with direct knowledge weighs in, these links may be of some help:
"I took the diode bridge out and wired an IBM laptop charger that outputs 16 volts DC directly to the fan motor" https://www.reddi..._roasting/
https://www.home-...11841.html
https://www.engad...e-roaster/
https://www.instr...offee-roa/
Edited by JitterzZ on 04/15/2019 5:02 PM
 
renatoa
Not a pot, but a DC PWM dimmer:

https://www.ebay....2667035967
 
tag1260
Thanks everyone. With your help I might have it figured out. For some reason though, I cannot get the laptop charger to work. However, I found an old computer power pack that does. it's only 15 volt but for now it will have to work until I get a more powerful one.

When you sent the PWM speed control link, I realized that I actually had one of those in my stash for another project.

Cobbled it all together and it's running perfectly!!!!

Now to roast some beans later today!!!!

Thanks again
 
tag1260
burned up that speed control somehow. Using a 24v 15a power supply . Don't know if that would do it or not but back to the drawing board. Or maybe just buy a Fresh Roast hot air roaster.
 
Monarda
I used a laptop charger for the step-down transformer and it works fine. BUT, I have yet to re-wire to the DC side of the diode bridge for speed control. So, my question is, just how important is it to control fan speed? I'll be posting again in the roasting section- I can control the heat profile perfectly, but I am getting rather flavorless roasts- I think I am baking. Does controlling air flow speed really effect the roast if I am getting even roasts and good temperature profiles (including controlling the RoR profile)?
 
Wiz Kalita
When I first built my roaster I used an L298N circuit for PWM control. This is a problem with higher power motors because there's a 2V power drop in the driver, and at high currents that gives a lot of heating. Burned out a few of those cheap boards before I got a different controller. But for my purposes, always running at full power is ok. You need enough airflow to have good agitation, but not so much that you can't reach the right temperature, but I have a chimney and a chaff filter that put me in that sweet spot.
 
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