Endo Senior Member Joined: 26 Jun 2008 Posts: 804 Location: , location, location. Expertise: I love coffee
Espresso: machine is < important than... Grinder: !
Posted Fri Sep 7, 2012, 5:55pm Subject: Watt the F#%$#?
I ran my Quest roaster for the first time today and got some VERY strange results.
I did the warmup to 190C and dropped in 150g of beans. The fan was set to 4 (minimum) and I turned the amps to 7.5 amps as specified in the manual, but the roast never got beyond 175C BT (or ET), and never hit 1C, even after 19 minutes.
Funny thing is, the amp meter on the Quest and on my Kill-a-watt both read 7.5 amps as per the Quest manual. The Kill-a-watt also read 119V (which should give me about 900W I figure). But for some strange reason, it only reads 560W on the Kill-a-watt? WTF? This kind explains the slow roast....but whats going on? I'm sure my volts are 119 roughly. Could the amps be wrong on both the Quest meter AND the kill-a-watt? Why is my Kill-a-watt not calculating watts correctly (A x V = W).. right?
Just to check, I plugged the kill-a-watt into my toaster oven. It gave me 119V x 13.1A = 1550W. Perfect. Repeated again on the Quest. STILL, the watts read way too low. Now I'm really confused.
Could the kill-a-watt be providing watts RMS, but only when used with my Quest???? (RMS is about 65% and would explain the reading but not the slow roast time).
It must be something silly and obvious, but I'm totally baffled. Help me electrical guys!
Posted Sun Sep 9, 2012, 9:07pm Subject: Re: Watt the F#%$#?
Hi Endo,
In an AC circuit: power = Voltage X Current X Cosine (phase angle). In a purely resistive circuit the current and voltage are in phase (0 degrees) hence the power factor ( Cosine of the phase angle) is unity.
Your Kill A Watt will read VA as well as Watts. There is a button which toggles between Watts and VA. There is also a button which toggles between Hz and PF (power factor). At least that is so if you have the same model Kill A Watt as mine. The number you get for Watts should be the product of the reading for VA and the PF.
Phil
Endo Said:
I ran my Quest roaster for the first time today and got some VERY strange results.
I did the warmup to 190C and dropped in 150g of beans. The fan was set to 4 (minimum) and I turned the amps to 7.5 amps as specified in the manual, but the roast never got beyond 175C BT (or ET), and never hit 1C, even after 19 minutes.
Funny thing is, the amp meter on the Quest and on my Kill-a-watt both read 7.5 amps as per the Quest manual. The Kill-a-watt also read 119V (which should give me about 900W I figure). But for some strange reason, it only reads 560W on the Kill-a-watt? WTF? This kind explains the slow roast....but whats going on? I'm sure my volts are 119 roughly. Could the amps be wrong on both the Quest meter AND the kill-a-watt? Why is my Kill-a-watt not calculating watts correctly (A x V = W).. right?
Just to check, I plugged the kill-a-watt into my toaster oven. It gave me 119V x 13.1A = 1550W. Perfect. Repeated again on the Quest. STILL, the watts read way too low. Now I'm really confused.
Could the kill-a-watt be providing watts RMS, but only when used with my Quest???? (RMS is about 65% and would explain the reading but not the slow roast time).
It must be something silly and obvious, but I'm totally baffled. Help me electrical guys!
In an AC circuit: power = Voltage X Current X Cosine (phase angle). In a purely resistive circuit the current and voltage are in phase (0 degrees) hence the power factor ( Cosine of the phase angle) is unity.
Your Kill A Watt will read VA as well as Watts. There is a button which toggles between Watts and VA. There is also a button which toggles between Hz and PF (power factor). At least that is so if you have the same model Kill A Watt as mine. The number you get for Watts should be the product of the reading for VA and the PF.
Thanks Phil. I'll try again with the kill-a-watt with this new understanding.
By the way, I got an answer back from Molly at Quest. She said she talked to the designer Mr.Yen and he said he now uses 2 different heating elements ( though they look identical to me). The element on the left ( bean side) is a higher power heater and glows bright orange. The heater on the right is lower power element that will look only red in comparison. She said they used to use the dark red type on both sides on earlier Quest models. So basically, my Quest is fine and I only need to crank up the amps to 9A or so to work as designed. (Not 7.5A as stated clearly in the manual).
This is the first I heard of this. Does it make sense? It seems quite odd I would need to go to much higher amps than other folks to get hot enough. It also seems a little weird to have so uneven heat ( though I do understand the bean side needs more heat due to the thermal mass of the beans on that side).
I am not very familiar with the Quest roaster, in fact all I know about it is what I found from an Internet search this morning.
I am a bit puzzled at the low PF you are seeing with your Kill-O-Watt. The motors and electronics are a trivial part of the load in most home roasters so the power factor should be near unity. I don't know how the Quest controls the heater current. I am guessing that it uses phase control (triac) control as opposed to a variable transformer (Variac) for cost (and weight) reasons. The phase control approach gives a lot of distortion to the current. The Kil-O-Watt may not have the processising speed to accurately calculate the power at low duty cycles. I have an 800 Watt heater in my roaster and the Kill-O-Watt calls it about 800 Watts at full power but I have not checked through the entire range. I use a Harbor Frieght Router speed control which is a triac type.
My guess is that you may be getting a good bit of power into your roast heaters but the air flow is excessive so that it is wasting too much heat.
Phil
Endo Said:
Thanks Phil. I'll try again with the kill-a-watt with this new understanding.
By the way, I got an answer back from Molly at Quest. She said she talked to the designer Mr.Yen and he said he now uses 2 different heating elements ( though they look identical to me). The element on the left ( bean side) is a higher power heater and glows bright orange. The heater on the right is lower power element that will look only red in comparison. She said they used to use the dark red type on both sides on earlier Quest models. So basically, my Quest is fine and I only need to crank up the amps to 9A or so to work as designed. (Not 7.5A as stated clearly in the manual).
This is the first I heard of this. Does it make sense? It seems quite odd I would need to go to much higher amps than other folks to get hot enough. It also seems a little weird to have so uneven heat ( though I do understand the bean side needs more heat due to the thermal mass of the beans on that side).
As you guessed, I was reading Watts rather than VA. I pushed the button a second time and the VA value came up. I also looked at the PF reading which was 0.62. It varied quite a bit as I played with the power knob.
All seems good now. I cranked the roaster up to the max rating of 1050W (8.75A x 120V) and got a very nice city roast in about 15 minutes.
I suppose I should have read the kill-a-watt instructions more closely! Thanks for your help.
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