ronnie_b Senior Member Joined: 7 May 2005 Posts: 289 Location: New Jersey Expertise: I love coffee
Grinder: Bodum Antigua Drip: Melitta pour over Roaster: PID'd P1
Posted Sun Mar 2, 2008, 6:33am Subject: Re: Low-cost Variac alternative for PopperyI fan speed boost
tom957 Said:
I'm resurrecting this post with a semi-related question ;)
My current dilemma is that I live in an old building with crappy voltage. I'm doing the heatgun/bread machine combo, and it's taking a bit long (around 17 min for FC+) to roast even a half-pound. My heatgun is 1500W/12A. For the electricity noob, I would say, "Variac". After seeing the link on this thread to the boosters at Surplus Center, the lower cost is definitely a consideration.
I checked out that circuit and would love if someone could help explain it to me. I have never seen a transformer wired like that. It looks like it is wired to somehow give it self feedback. Why is it wired like this instead of how you would normally wire a transformer. I googled and checked my textbooks but have not been able to find any info on this method of wiring a transformer.
Chocolate_Dog_Kona Senior Member Joined: 21 Jun 2005 Posts: 143 Location: Over a mile high, CO Expertise: I live coffee
Espresso: SD3C PID Rancilio Silvia! Grinder: Solis Maestro Plus Vac Pot: Bodum Press Pot Drip: Mr. Coffee Roaster: Boosted Poppery I
Posted Tue Mar 4, 2008, 3:26pm Subject: Re: Low-cost Variac alternative for PopperyI fan speed boost
Basically, the Franken transformer is wired to provide its boost to the AC voltage. I see what you are saying about self-feedback. I do think that is basically what it is doing. Remember this is an AC circuit, not DC, so things are a bit different in that respect. I can't provide any further insight without pulling my old textbooks out.
The one thing I never figured out myself (and never got around to checking) was whether the transformer was boosting one half of the AC sine wave (resulting in something similar to a DC offset), or whether it added half its output to both halves of the sine wave (+/- about 12v).
I didn't really care, as I abandoned that idea after buring up my first Rat Shack transformer. The surplus center transformer works EXTREMELY well. I am surprised to see they still have so many in stock! (almost a year later)
As another data point, I have moved since initially starting this thread. I am still roasting a green bean load of about 220g. In my new house in CO (built in '79), the voltage tends to run on the high side at about 125v on average. I have measured as high as 128v so far. Also, the voltage at the Poppery doesn't sag anywhere near as much under load as it did in my house in TX (built in '01). This is probably due to the fact that the outlet I'm using during my roasting now is only about 10 feet from the breaker box, where it was probably at least 50 - 75 feet before. However, the combination of those two things has had an unexpected result.
My biggest problem now is my Poppery works too well!!! The added voltage to both the heater and the fan is producing fast roasts (7-9 minutes), and I still need to make a longer chimney to keep the beans from flying out of the roaster near the end of the roast. I have been using 200 feet of extension cord to drop the voltage in order to lengthen the roasts a bit, but I can still roast coffee on my back porch when it is only 15 degrees F! I couldn't do that before! I'm not going to complain though, because with a longer chimney I will eventually be able to roast more beans (a tough situation to be in, I know ;-0).
ronnie_b Senior Member Joined: 7 May 2005 Posts: 289 Location: New Jersey Expertise: I love coffee
Grinder: Bodum Antigua Drip: Melitta pour over Roaster: PID'd P1
Posted Tue Mar 4, 2008, 4:55pm Subject: Re: Low-cost Variac alternative for PopperyI fan speed boost
Evazan Said:
I checked out that circuit and would love if someone could help explain it to me. I have never seen a transformer wired like that. It looks like it is wired to somehow give it self feedback. Why is it wired like this instead of how you would normally wire a transformer. I googled and checked my textbooks but have not been able to find any info on this method of wiring a transformer.
No offense to the guy who did the Frankenformer circuit but DON'T do it. I blew out the Radio Shack transformers using that circuit.(their new transformers are from China and they suck) I can't explain the circuit, but the output from the transformer is added to the input voltage. I originally thought it was a mistake but it works. I highly recommend the booster transformer from the Surplus Center. It is fool proof. I have 2 in series boosting the voltage to my P1 fan and have no problems whatsoever.
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