Posted Fri Aug 17, 2007, 4:50pm Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
Yes, I read the entire thread, but it is best to just read the results and skip the part(s) about what went on to get there. One reason I haven't opened up the Gaggia is we NEED espresso around here every morning. No drip, I have a french press but it sees very little use. A one week trip to the coast, and that machine packs nicely in the trunk. I can't and won't rip into it until I have another machine. The resistor mod is very easy, just an experiment, but it made a noticable improvement so it's still in there. Good luck with the impending installation.
Posted Thu Aug 23, 2007, 5:42pm Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
Ok, I got my Isomac Venus a few days ago and dialed in the pressure/volume by adjusting the voltage to the pump rather than the OPV. It works so well I thought I would update this thread for anyone else interested in trying this approach.
The Venus has a nice pressure gauge mounted on the front that is real handy for dialing in and monitoring your shots. I started by putting a measuring cup under the steam/hot water wand and turning on the hot water. I adjusted the steam knob to reach a pressure of 9 bar in the boiler. Shut off the pump. Now turn on the pump and time the volume of water delivered by the pump in 25 seconds at 9 bar. You guessed it, over 5 ounces, I didn't bother to even measure it.
So then I plugged the machine into the Variac (my kitchen outlet delivers 120Volts and no sag with load) Then I adjusted the voltage to 115 and repeated the test.... Then to 110volts, now I'm in the ballpark: almost 3 oz in 25 seconds at 9bar. (I figure to add extra that will be left in the puck and down the 3way valve.)
I verified the volume/pressure then by dialing in the grind/tamp to give me a 2oz double at 9 bar. At 120volts it was a gusher, at 110 volts was just over 2oz in 25 seconds at 8.5-9 bar. (including 6-8 seconds ramp up to pressure time)
For anyone that may happen to have 110volts at their outlet already, they would bring this machine home, plug it in and dial in a good shot with no problem. For 120 volts to get a 2 oz double would likely be around 11-12bar, packed hard and a super-fine grind.
Not wanting to leave the machine on a variac and running the heater at 110 instead of 120, I found the proper resistor value to drop the voltage to the pump to 110 (ok 111volts) was 16ohms. Installed the resistor and now I have a well behaved machine with respect to pressure/volume of the shot.
In some ways I think this may be a more forgiving approach to using the OPV (I left that set at 12bar) Take this example: you set the OPV at 9 bar, but your grind/tamp only gets you to 8.5 bar: result is no water is diverted to the OPV and you have a gusher/sink shot. 8.5 should otherwise produce a good shot. OR you have the OPV at 9 bar and get a grind/tamp that required 9.5 bar for good flow.... etc. (not having used the OPV method to control volume/pressure, I really don't know how this all works out...)
With the voltage adjusted vibe pump, it is forgiving, you may need to adjust the time and get a little more or less volume, but avoid a toss in the sink.
Now a true Geek'r would install a knob or switch to have the adjustment available on the fly for doubles, singles, ristrettos, etc. I most often pull only doubles so for now I'm really happy with how this approach has worked out. (I suspect the range of adjustment would only need to be from 105-115 volts or so, at least for this machine.)
Actually they would probably install a feedback controlled variable resistance, and an knob that could be used to dial in whatever pressure they felt like... even during the shot! Live pressure profiling!
Posted Mon Oct 8, 2007, 9:50am Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
A knob that would adjust pump voltage from around 100-115 volts would be real handy for lots of things. You could calibrate it for everything from low pressure singles to high pressure triples. You could stretch the ramp to pressure at the beginning of a shot and/or ramp down the end of the shot. A simple high power, limited range rheostat should do it. ( something like 0-25ohm 20-30watt)
JGG Senior Member Joined: 31 Mar 2006 Posts: 1,343 Location: Kentucky, US Expertise: I like coffee
Espresso: PID Silvia; PID Alexia Grinder: Mazzer Mini E (A), SJ; Rocky... Roaster: Hottop D w/PID; Thermometric...
Posted Mon Oct 8, 2007, 10:13am Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
Would something as simple as a lamp dimmer in the pump circuit work?
IIRC, dimmers use phase control to reduce the voltage/power. I can't think of any reason a vibe pump would complain about not getting clean sine wave input.
crgwbr Senior Member Joined: 8 Oct 2007 Posts: 40 Location: PA Expertise: I love coffee
Espresso: Heavily Modded Krups XP2010 Grinder: Turkish Hand Mill Drip: French Press Roaster: Popcorn Popper
Posted Mon Oct 8, 2007, 12:54pm Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
I hate to complicate things for you, but just using a dial resistor to adjust voltage will not work. The pump in an espresso machine pulls quite a bit of current (Amps). Trying to run that much power through a resistor means that the resistor will be dissipating a lot o power as heat. The only way to get around this, is instead of using a resistor to limit the amount of power getting to the pump, you must use PWM or Pulse Width Modulation. It involves switching the power to a motor on and off very rapidly. For example, to reduce 120 volts to 100 volts, 83% of the duty cycle would be on and the other 17% would be off. If the duty cycle of the PWM controller was 1 mS long, that would mean a pulse of power lasting 0.00083 seconds followed by a 0.00017 second gap of no power going to the pump. This would then keep repeating, 1000 times per second until you told it to stop. This method of management is much more efficient than using a resistor, and not all that expensive if you know what your doing.
"Better to be a geek than an idiot." "To go forward, you must backup." "Programmers are tools for converting Espresso into code."
Posted Mon Oct 8, 2007, 2:03pm Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
My Isomac Venus pump is only 55 watts. Dropping voltage from 120 to 110 is less than 10%, or 5.5 watts dissipated in the resistor. I'm using 2 33ohm 10 watt resistors in parallel to get this voltage drop. I haven't bothered to put a knob on the machine, or looked into the appropriate rheostat for the job.
JGG Senior Member Joined: 31 Mar 2006 Posts: 1,343 Location: Kentucky, US Expertise: I like coffee
Espresso: PID Silvia; PID Alexia Grinder: Mazzer Mini E (A), SJ; Rocky... Roaster: Hottop D w/PID; Thermometric...
Posted Mon Oct 8, 2007, 2:11pm Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
crgwbr Said:
I hate to complicate things for you, but just using a dial resistor to adjust voltage will not work. The pump in an espresso machine pulls quite a bit of current (Amps). Trying to run that much power through a resistor means that the resistor will be dissipating a lot o power as heat. The only way to get around this, is instead of using a resistor to limit the amount of power getting to the pump, you must use PWM or Pulse Width Modulation. It involves switching the power to a motor on and off very rapidly. For example, to reduce 120 volts to 100 volts, 83% of the duty cycle would be on and the other 17% would be off. If the duty cycle of the PWM controller was 1 mS long, that would mean a pulse of power lasting 0.00083 seconds followed by a 0.00017 second gap of no power going to the pump. This would then keep repeating, 1000 times per second until you told it to stop. This method of management is much more efficient than using a resistor, and not all that expensive if you know what your doing.
Most of these vibe pumps are around 40W, so they should be drawing less than 1/2 amp. The 16 ohm resistor that Frost installed would need to dissipate less than 5W, so that seems like a workable solution to me.
I am curious about the dimmer idea, though, to avoid even these moderate power dissipation needs, and to allow adjustments to be made more easily. I think a dimmer will maintain the basic AC frequency of 60 Hz, but uses phase control to add just a little "off" time between waves to reduce the average power. So unless the pump is really sensitive to the shape of the pulse, seems like it oughta work.
I wish somebody would try it on their pump ;-]
Jim
[EDIT - sorry for the repetition. I didn't see Frost's reply.]
Posted Mon Oct 8, 2007, 2:52pm Subject: Re: Is anyone using voltage to control Vibe pump pressure instead of OPV?
I know there is a diode in the pump curcuit that may complicate things a bit. I don't know much about the behavior of these pumps outside of a limited voltage range. That's one reason I used a simple resistor. I would also suggest for anyone experimenting with this approach that the useful adjustment range is at least 90 volts or above. You don't need to adjust to 50 volts for example. I don't think the pump will work at all ( or at least not useful pressure for espresso) at such low voltages. Best to design the adjustment for precise control from around 100 volts up.... If you feel the need for a knob to tweek. I have my machine dialed in just fine with a fixed resistor. Doubles are around 9 bar, singles at around 10.5. I run mostly doubles.
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