Coffee Beans Kurochamame

for Dripbags, Coffeemakers and hand-brewing

Swapped to magnetic tripping?

For the magnetic swiches are 30 years old and out of production.  It is taking such a long time to inquire the specifications  for alternate.   I decided to dismantle the magnetic switches and found out the reason why they trip so frequently.   

The ratings of the thermal swiches seemed so strange to me.   Left switch set at 1.3A connected to a 200W moter.   Second set at 4.2A is dedicated to a 40W moter.  Third set at 1.3A driving a 40W moter.    It seems like this machine was originally aseembled  by mistake at factory and the switches had misplaced.  The second switch at center had to be assembled to left and the left one to middle.    I have been wondering why the magnetic switch didn't trip when the drum rocked.   No wonder that the ampear rating was too high as 4.2A for a belt driven 40W moter . 

I also found out why all switches trip with such a small shock like start of the starring moter.  The wiring were not properly done to aviod close stroke of surge noise between the switches.   They omit the terminal block to share a circuit breaker.  This created common impedance for the magnetic switches to over react.    I am going to find a serge block to avoid this.

ie) Later, it turned out that it is more likely that the connection to the moters were miswired at factory default.   I connected to the inverters one by one so that It can't be me who made mistake.     I imagine Fuji must have had many troubles at the early stage of transferrng production to china.

This time I replaced the main short curcuit breaker from 20A to 10A.

With the high rating it never really worked at desired timing but functioned as just a snap power switch.

Note for the Correct Wiring (original ratings/Current)

U1/V1 to Drum moter which is most important not to stop.  40W/inverter driven 100W highest freq. =99.99hz※.

U2/V2 to Cooling/exhaust Fan moter which is essentical to roast. 200W/inverter driven 400W highest freq.=132hz※.

U3/V3 to stirring moter less likely to overload but best to stop when it is met by human finger/hand interruption. 40W/40W.


※With inverters the start rush current is less than 50% and low enough to be powered via those old magnetic switches.

The beans dance in the drum to reduce inertia of the whole rotating body when it starts to rotate and the belt slips so that the load to the moter is very low even at the highest frequency.  

The rating for the fan moter is 2.0A but it is easily driven by the inverter and the current to the moter is 60-70% less, 2.5A or so at 100V input of the inverter with max. freq.


Those old Mitsubishi magnetic switches are intact and good enough to use for a while.