Just for the record I didn't originate the dimmer controlled boost transformer idea, would have to search the SM List archives to jog the memory for giving credit where credit is due.
Can't speak to the longevity of the Radio Shack 2A transformer because when I built Frankie I sourced some 2A transformers from a local electronics surplus which while rated the same where about 50% beefier and cheaper. I can say that the dimmer and this transformer are still working just fine 4+ years and many hundreds of roasts later.
IIRC I wired the dimmer after the transformer boost but come to think of it, Phil is probably right would work fine before or after and might be safer placed before. But I'm not going to bother re-wiring Frankie, if it works don't fix it!
(edit)Also I'll add to Phil's comment. But not that you'll probably need a larger transformer to control heater, you absolutely would need a larger transformer and higher rated dimmer. This circuit is NOT for heater control! Tapping the 2A transformer leaves with roughly a 1A rated circuit, fine for fan control but way way under rated for any heater control. (Ok, I suppose you could design a 1A heater element roaster for maybe 0.5oz roast batches, who knows maybe even a full oz:-) I did some reserach prior to building Frankie and large enough transformer and dimmer for heater control would cost more and be bulkier overall than a variac.
Posted Fri Apr 20, 2007, 10:10am Subject: Low-cost Variac alternative for PopperyI fan speed boost (15V boost transformer)
Yeah, if your popper is 1,200 watts, that's 1.2KVA., a Poppery1 1,500w., 1.5KVA. I'm not going to talk about duty rate cycles & over duty rate cycles that are completely safe with a GOOD variac, there's lots of info in the archives here..
Posted Fri Apr 20, 2007, 10:15am Subject: Re: Low-cost Variac alternative for PopperyI fan speed boost
Hi Mike,
Good to see you back. I learn a lot from your posts.
Phil
mcKoffee Said:
Just for the record I didn't originate the dimmer controlled boost transformer idea, would have to search the SM List archives to jog the memory for giving credit where credit is due.
Can't speak to the longevity of the Radio Shack 2A transformer because when I built Frankie I sourced some 2A transformers from a local electronics surplus which while rated the same where about 50% beefier and cheaper. I can say that the dimmer and this transformer are still working just fine 4+ years and many hundreds of roasts later.
IIRC I wired the dimmer after the transformer boost but come to think of it, Phil is probably right would work fine before or after and might be safer placed before. But I'm not going to bother re-wiring Frankie, if it works don't fix it!
(edit)Also I'll add to Phil's comment. But not that you'll probably need a larger transformer to control heater, you absolutely would need a larger transformer and higher rated dimmer. This circuit is NOT for heater control! Tapping the 2A transformer leaves with roughly a 1A rated circuit, fine for fan control but way way under rated for any heater control. (Ok, I suppose you could design a 1A heater element roaster for maybe 0.5oz roast batches, who knows maybe even a full oz:-) I did some reserach prior to building Frankie and large enough transformer and dimmer for heater control would cost more and be bulkier overall than a variac.
Posted Fri Apr 20, 2007, 10:43am Subject: Re: Low-cost Variac alternative for PopperyI fan speed boost
Thanks Guys for the reply and help.
Craig A. Thank you for not overwhelming me with to much info. One of the great things about this site is the abundant of info that is so readily available when one desires to go searching for.
What ever machine you choose...Enjoy and have fun...Learn and share the experience.
WonderClown Senior Member Joined: 17 Apr 2007 Posts: 203 Location: NC, USA Expertise: I love coffee
Espresso: Gave away a Saeco Via Veneto... Grinder: Baratza Virtuoso, Zassenhaus Drip: Buchner funnel + vacuum... Roaster: WB Poppery I
Posted Sat Apr 21, 2007, 8:06am Subject: Re: Low-cost Variac alternative for PopperyI fan speed boost
Chocolate_Dog_Kona Said:
However, with the addition of a $6 fan dimmer, you get all the control you need over the fan. Through the dimmer, I measure up to 17v boost, and as low as 48v of buck (without load). This gives you a range of 72v-137v to control the fan speed if desired, and at the low end the fan is barely moving. I would say this set-up does just as good as any variac could.
Given that the Poppery I fan is an AC motor (not DC like most other poppers), how does the dimmer control the speed? Some types of AC motors are basically fixed speed, based on the line frequency (60Hz in North America), and varying the voltage will change their torque but not their speed. And if you use a normal light dimmer, you'll just chop off part of the waveform, which is find for dimming incandescent lights but bad for most types of motors. Do these cheap fan dimmers actually alter the voltage without altering the waveform, and does that actually change the speed of the Poppery I fan?
mcKoffee Senior Member Joined: 29 Dec 2001 Posts: 785 Location: Vancouver WA USA Expertise: I live coffee
Espresso: Bricoletta, Audrey, LM 3AV... Grinder: Mazzer Major,SJ, Rocky,... Vac Pot: Gold Royal Balance Drip: When it rains...Moka, FPs Roaster: USRC3k,CCR HT, Behmor, Cafe...
Posted Sat Apr 21, 2007, 8:58am Subject: Re: Low-cost Variac alternative for PopperyI fan speed boost
WonderClown Said:
Given that the Poppery I fan is an AC motor (not DC like most other poppers), how does the dimmer control the speed? Some types of AC motors are basically fixed speed, based on the line frequency (60Hz in North America), and varying the voltage will change their torque but not their speed. And if you use a normal light dimmer, you'll just chop off part of the waveform, which is find for dimming incandescent lights but bad for most types of motors. Do these cheap fan dimmers actually alter the voltage without altering the waveform, and does that actually change the speed of the Poppery I fan?
Many people have been varying their AC fan motor speed for many years with these light dimmers. Is the motor getting a perfect sine wave? Who cares! It works, and keeps right on working hundreds and hundreds of roasts later.
Posted Sat Apr 21, 2007, 9:29am Subject: Re: Low-cost Variac alternative for PopperyI fan speed boost
The motor in a Poppery 1 is a series wound universal motor. These are series wound DC brush motors where the field core is laminated and other design parameters are chosen to permit them to operate on AC. This type of motor works well with phase control dimmers. Variable speed corded tools typically use these motors.
Most true AC motors are squirrel cage induction motors. These motors run at nearly syncnonous speed minus the slip speed. The slip speed increases with increasing torque. Phase control dimmers can be used with varing sucess. The phase control will reduce the available torque which in turn increases slip speed. Slip speed vs. torque varies with rotor design so that is why the results vary. In any case phase controlled induction motors can only be used on loads where the required torque increases monotonically with speed. Fans and blowers are such loads.
Phil
WonderClown Said:
Given that the Poppery I fan is an AC motor (not DC like most other poppers), how does the dimmer control the speed? Some types of AC motors are basically fixed speed, based on the line frequency (60Hz in North America), and varying the voltage will change their torque but not their speed. And if you use a normal light dimmer, you'll just chop off part of the waveform, which is find for dimming incandescent lights but bad for most types of motors. Do these cheap fan dimmers actually alter the voltage without altering the waveform, and does that actually change the speed of the Poppery I fan?
Many people have been varying their AC fan motor speed for many years with these light dimmers. Is the motor getting a perfect sine wave? Who cares! It works, and keeps right on working hundreds and hundreds of roasts later.
Well, that's useful information. Explains a lot. So yeah, I can see how a triac dimmer would work fine here, though I do think it's advisable to get a control designed for fans, as an incandescent dimmer might not have a good enough snubber to deal with the highly inductive load.
mcKoffee Senior Member Joined: 29 Dec 2001 Posts: 785 Location: Vancouver WA USA Expertise: I live coffee
Espresso: Bricoletta, Audrey, LM 3AV... Grinder: Mazzer Major,SJ, Rocky,... Vac Pot: Gold Royal Balance Drip: When it rains...Moka, FPs Roaster: USRC3k,CCR HT, Behmor, Cafe...
Posted Sat Apr 21, 2007, 11:08am Subject: Re: Low-cost Variac alternative for PopperyI fan speed boost
PJK Said:
The motor in a Poppery 1 is a series wound universal motor. These are series wound DC brush motors where the field core is laminated and other design parameters are chosen to permit them to operate on AC. This type of motor works well with phase control dimmers. Variable speed corded tools typically use these motors.
Most true AC motors are squirrel cage induction motors. These motors run at nearly syncnonous speed minus the slip speed. The slip speed increases with increasing torque. Phase control dimmers can be used with varing sucess. The phase control will reduce the available torque which in turn increases slip speed. Slip speed vs. torque varies with rotor design so that is why the results vary. In any case phase controlled induction motors can only be used on loads where the required torque increases monotonically with speed. Fans and blowers are such loads.
Phil, thanks for the why it works, interesting to know. And in truth I'd heard the explanation before but didn't feel competent to attempt to explain it. I only knew both from personal experience and that of others that it does work. Somewhat like I don't quite really know the specifics of why gravity works and can't explain it, but know it most certainly does!:-)
mcKoffee Senior Member Joined: 29 Dec 2001 Posts: 785 Location: Vancouver WA USA Expertise: I live coffee
Espresso: Bricoletta, Audrey, LM 3AV... Grinder: Mazzer Major,SJ, Rocky,... Vac Pot: Gold Royal Balance Drip: When it rains...Moka, FPs Roaster: USRC3k,CCR HT, Behmor, Cafe...
Posted Sat Apr 21, 2007, 12:52pm Subject: Re: Low-cost Variac alternative for PopperyI fan speed boost
WonderClown Said:
... So yeah, I can see how a triac dimmer would work fine here, though I do think it's advisable to get a control designed for fans, as an incandescent dimmer might not have a good enough snubber to deal with the highly inductive load.
I seem to recall also trying a ceiling fan controller but IIRC it resulted in a lower maximum voltage, having higher voltage loss through it. But it's been over 4 years since I've built one of these circuits so not 100% positive on that. In addition to the original one I built that was passed on to another home roaster after building Frankie, also built a couple more fan controllers for other home roasters back then. To the best of my knowledge they're all still working and I know with 100% certainty mine is still working (I'll say it again) 4+ years later, many hundreds of roasts later. Or at least it still worked last time I used Frankie which was 3 days ago for 4 back to back 227gr=1/2# greens batches. (3 SOs and an espresso straight shot blend, 227gr batches because while can do larger batches I like greens to come out even when they run out.). So while some light dimmers might not have a good enough snubber to deal with the highly inductive load, observed evidence highly suggests the one's I've purchased from Home Depot and Lowes will and do in fact work.
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