Just read that the ZPM guys are manipulating the pressure to the group by programmatically controlling AC power to the pump instead of using a traditional overpressure valve. Video going from high to low pressure. Looks like they're testing without a shower screen in place.

Actually this was a high to low flow... I find weird the rattle sound. I've used a little demo board from Korea for some time and it was very smooth. But I made a stupid mistake and burn it.

Carneiro,
The Korean board you are using has a board mounted fuse on it. It may only be this. You cannot reset this fuse but you can replace it with another type of fuse that IS replaceable. If you send me a picture of the board I can tell you what to check for.

The Korean board along with a wide variety of super automatic machine (also the breville dual boiler) use a method called phase control using a triac. (also phase chopping, phase firing, and a couple of other names). This method monitors the sinusoidal wave form the AC current and instead of turning on all of the time it make a small delay of time to turn on at the beginning of each cycle to reduce the average power to the vibe pump. The reduced average power causes the stroke to be shorter in the pump and lowers the pressure.


BillC

Hey, Bill.

Yes, I'm pretty sure it's the fuse, actually I've blew it I have to take some time to try a replacement. I was wondering it was phase control indeed, thanks for clarifying. Maybe ZPM is using some zero crossing SSR hence the rattle?

Márcio.

Phase control does not allow the use of Zero Crossing SSR. You would have to use a random fire SSR. A "Zero Crossing" SSR will only turn on at zero crossing (and off at zero crossing). Zero Crossing SSR are good for pulse control but pulse control has proven to be unsatisfactory for vibe pump control and coffee quality.

Billc

Yes, that's what I'm wondering, if they are using the wrong SSR at ZPM

Looks like they're getting close. They are almost ready to order the last board. THEN they can order that PRE-production board. THEN they can get the REAL board. THEN the machine will be obsolete... http://www.kickstarter.com/projects/zpm ... hine/posts

*edit "obsolete" is a bad choice. Point is, even with all the progress they're making, it's looking like a VERY long time is still left.

bostonbuzz wrote: THEN the machine will be obsolete...

obsolete? did i miss some new equipment news about a machine with their feature set at an extremely low price point?

Carneiro wrote:Actually this was a high to low flow... I find weird the rattle sound

They talk about switching the pump on for selected half cycles, although maybe that's just a bad explanation. A vibration pump works over a full cycle of the mains. During the positive voltage half cycle, the current builds up from zero to a maximum as the coil energises and pulls the piston back against a spring. During the negative voltage half cycle the current (gently) decays back to zero, allowing the spring to push the piston forward - pumping water. A diode is used to make sure the current varies between zero and the maximum, rather than just oscillating about zero. It's a very neat idea. If you were to interrupt the current flow at any stage then the piston is going to jump violently forward until resisted either by water pressure or the end stops - in this case, all the stored energy has to dissipated somehow.

The reason they indicate half cycles is because the diode in the pump restricts the current flow on one half cycle. The AC Current wave form for the pump is close to sinusoidal (because it is an inductor is is not exactly the same as the voltage wave form). During one of the half cycles, the current in the pump coil goes from zero to a maximum then back to zero. At the zero crossing the current the coil is zero so the magnetic energy is also zero. Then during the next half cycle (Opposite in sign to the first half cycle - i.e. first one positive and the second one negative) the diode restricts the flow of current so nothing happens in the coil.

What happens in the pump during the half cycle that the current flows.... the piston is pulled back. Then during the half cycle that current is restricted, the return spring in the pump pushes the piston forward. The following is an animation of the process.
There are several ways to control the power to the pump. The 2 used in espresso machine currently are "Phase Control" and "Zero Crossing Control". In Phase Control, the start time to turn on during this period varies. There is a delay to the turn on of the switch to control the pump. If the delay is zero then there is full power. As the delay increases the average power the pump receives is less (unfortunately this is not a linear relationship). In Zero Crossing control the pump is turned on for the complete half cycle. To control the power you can ski some of the half cycles. If you skip none then you have full power, if you skip every other one you have half power etc.

The disadvantage of the Zero Crossing Control, is that you change the frequency that that the piston moves in the pump. This causes unusual pressure fluctuations on the coffee cake and has unusual results.

In contrast, Phase control keeps the frequency of the piston the same but varies the distance it is pulled back.


BillC