The first big mistake, but still on track.

Wednesday, November 3rd, 2010

Things seemed to be going a little too smoothly, until I blew up a temperature controller. For future reference you cannot wire a device designed for 240 V across 415 V. It will explode. We wired our control panel to have a three-phase electric power supply so we could run the motors and the controls from the same supply inside the panel. If it is wired this way we can also cut the power to everything in the control panel at the same time for maintenance purposes. Only the motors run off of three-phase supply, the controls run off of a single-phase supply, but you can get single-phase power from the three-phase supply. Without getting too complicated, to get the single-phase supply for the controls you take one lead from the control to one of the three phases and the other lead from the control you run to a neutral, which gives you 240 V. Now what I did was run one lead from the control to one of the three phases and then ran the other lead to another one of the three phases, which gives you 415 V. If you are keeping score at home that is almost twice the voltage the control is supposed to have and in this case, as you can see from the photos, it led to an explosion.  We looked for a control here but the ones that I bought in the U.S. are $250 more expensive here and take 3-4 weeks to arrive. In light of this what I decided to do is to rewire the control panel so that everything runs off of the inlet-air controller (a fun morning project) and get a simple temperature-indicator for the bean temperature since we still have the thermocouple from the original sensor. My clients aren’t interested in the bean hi-limit temperature cutoff function at the moment as they are used to manually ending the roast, so the temperature indicator will work for them. After I re-wired the panel and tested it, everything else is working perfectly. So they still have the control on the inlet air flow-speed, on the inlet air temperature and the high-limit safety control on the inlet-air temperature (all from the control panel) so the missing control will not affect the quality or safety of their roasts. They will just lose a portion of the functionality of the roaster, which is more of a convenience, for a short time. Before I leave here I will label all the wires that the new control will require and when I get back to the U.S. I will mail the control back here and then they can wire it up.  Tomorrow the gas company comes to make the final connections. Since I was able to run the panel off of the one control and all the other controls are working, we will be able to run the first batch through sometime in the afternoon.

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