Rancilio Rocky Resistor Value..?

#1: Post by **aauwen** » July 8th, 2014, 3:58 am

The start-up capacitor in my Rancilio opened up and let the magic smoke escape. I have replaced the capacitor, but want to verify the correct value of the resistor across the capacitor. Does anyone know the correct value..? (I checked with Rancilio... they don't know)

#2: Post by **Burner0000** » July 9th, 2014, 12:37 pm

aauwen wrote:The start-up capacitor in my Rancilio opened up and let the magic smoke escape. I have replaced the capacitor, but want to verify the correct value of the resistor across the capacitor. Does anyone know the correct value..? (I checked with Rancilio... they don't know)

I don't own nor have hand on with the Rocky but if your looking for the microfarad load it's 60 Microfarad 110V. Info from espressoparts.com

July 21st, 2014, 3:05 pm

Thank you for.the reply..! I found the capacitor, but haven't been able to find the correct value for the resistor that connects across it...

#4: Post by **ira** » July 21st, 2014, 6:32 pm

Just guessing, but it's likely just a bleed resistor. What wattage is it if you can tell from the size or how big is it?

How hard is it to get to?

Ira

#5: Post by **OldNuc** » July 21st, 2014, 7:27 pm

The resistor value is not trivial. The resistor-capacitor together determine the phase shift in the associated winding. Google will explain the function of that resistor and it is possible to take the capacitor value and approximate the correct resistor value from the readily available motor characteristic graphs. Unfortunately I do not have any links but I located it by googling for running capacitor size and the consequences of increasing or decreasing the capacitance on running current, winding temperature, and starting torque.

#6: Post by **civ** » July 21st, 2014, 7:57 pm

Hello:

aauwen wrote: ... haven't been able to find the correct value for the resistor that connects across it ...

I assume you have the resistor at hand.
So look at it with a magnifying glass and write down the band colours.

Then go here:
http://www.csgnetwork.com/resistcolcalc.html
... read the explanations and follow the instructions.

You should be able to get the right value from there.
WRT the wattage, get one the same (cylinder) size, that should more or less do it.

But the question is:
why do you want to replace the resistor?
ie: is it blown or open?

I'd use the same one, you can check how much it reads with a common multimeter.

Cheers,

CIV

#7: Post by **mauidoug** » January 5th, 2015, 9:15 pm

Mine is: Brown, Red, Orange, Gold. Therefore 12.0 Kohms. Mine measures 11.7 Kohm.
I hope that helps any interested parties.
Doug

#8: Post by **Marcelnl** » January 6th, 2015, 6:50 am

OldNuc wrote:The resistor value is not trivial. The resistor-capacitor together determine the phase shift in the associated winding. Google will explain the function of that resistor and it is possible to take the capacitor value and approximate the correct resistor value from the readily available motor characteristic graphs. Unfortunately I do not have any links but I located it by googling for running capacitor size and the consequences of increasing or decreasing the capacitance on running current, winding temperature, and starting torque.

For what it's worth...just noticed the OT is half a year old...

A phase correction For a tiny (as in low power) single phase motor like this? Would the resistor not just be there to ensure the capacitor bleeds off preventing a jolt should you ever touch both of the leads on the power plug?

Imo a cosine phi phase shift attenuator is something that is typically done by a bank of capacitors or perhaps a coil and only on larger three phase motors. Aside from that, I only intimeately know the combinations of resistor and capacitor and coils from working on audio stuff like loudspeaker frequency filters (mainly from trying to avoid them and their hoeeible phase shifts) but I could be wrong...

Just slap the resistor back in if you cant't measure its value or establish its conductance (if its magic smoke is also gone it would likely measure to have an infinite resistance), imo its most probable that the resistor is fine.

#9: Post by **OldNuc** » January 6th, 2015, 10:01 am

The phase shift is actually critical for the 1/2 - 2 hp motors and as the capacitor is isolated it is not primarily a bleed down resistor. The curves I mentioned clearly show the consequences of an improper resistor value particularly the affect on starting torque which is a big deal with a grinder full of lightly roasted beans.