[TriEmbed] Coffee roaster

[Brian]

On 10/24/18 7:53 PM, Craig Cook via TriEmbed wrote (snipped):
> I have been using this 
> https://smile.amazon.com/gp/product/B00XK3ALS0/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 
> for the last 8 years roasting green beans.
> 
> It's discontinued.  I have one of these to replace it: 
> https://www.gopresto.com/product/presto-poplite-hot-air-corn-popper-04820https://smile.amazon.com/gp/product/B00006IUWA/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
> 
> Given that new information, would it change the proposed design?
> 

One thing we can't tell from those listings is whether the blower motor 
is 120 VAC or some DC motor.  I doubt you'll find that any way other 
than taking one apart.  Depending on what kind of motor is in there, you 
will have different limitations on how it can be powered:

- A shaded pole 120 VAC motor will respond fairly well to chopped AC, 
but DC will turn it into a brake.
- A universal motor (with windings for both armature and field) can be 
run from either AC or DC, but DC requires a lower voltage or external 
current limiting (an inductor's impedance increases with frequency, so 
DC through a coil will reach a higher steady-state current than AC at 
the same voltage).
- A permanent-magnet DC motor of course requires DC, which is easy to 
control with PWM.

Isn't engineering fun? :D

-B