Start up current is something to be concerned about, I had trouble with a giant chop saw that would blow the 440V fuses on startup but that was fixed with slow blow fuses designed for that purpose. Since a shop vac doesnt blow a houshold fuse I think it will be alright and would only lead to a momentary heating of the controller, if at all. A better option than a dimmer switch might be a ceiling fan controller. Lowes says they are not interchangeable but doesnt elaborate.

http://www.lowes.com/cd_Install+Dimmers+and+Fan+Controls_834665761_

Fan contollers i found in a cursory search were rated to 1.6 amps or more. I would think thats enough for a mini shopvac.

I was actually planing on using a much simpler solution. I would like to use a low power vacuum cleaner and controlling the airflow by adjusting a hole in the tube going to the roaster. A bigger hole means less air has to be "taken from" the roaster. This way I can have the heatingelement on full power, and use only the airflow to controll the temperature.

In any case, as I understand its not so importen to have a temperature controll on +- 1 degree, instead I will focus on a even roast finished at a correct time.

Can't wait to get back to the university and start assembling! (:

Is this a better option?

It's 2 fans on 12V, 0.18 A.

Don't now how to control the airflow with this option..




It's only a basic prototype, as I hope you guys understood ;p

Tnx again for all the help!!

Something to consider. Drum roasters usually suck air thru the roaster so the roaster is under a slight vacuum not under pressure. Reason being they are not well sealed around the dump door or trier etc and so you will get some smoke leakage. This would count out using a VC motor. If you do use a vc blower a triac based controller (dimmer) is the ideal way of controlling it. 99% of VCs use a basic triac dimmer. Don't get thrown by the inductive load jargon. Universal motors are not an inductive load (least ways not enough to matter). Just make sure there is a good heat sink on the triac. I have made several 1 kw 230v dimmers to control VCs on air roasters.

Rob vL
NZ

deanelwood wrote:I would check wattages first - gut feeling is the current draw from a vacuum would fry a dimmer switch in a big puff of smoke almost instantly....

If it's an AC motor, you'll need a variac.

Vacuum cleaners all use triac based controllers, almost identical to a light dimmer. VCs have universal motors which do not rate as an inductive load. The wattage is the only issue. I have made several of these http://www.epanorama.net/documents/lights/lightdimmer.html#1kw230v
have used them for years with no problems.
Rob vL
NZ