ira wrote:If it doesn't warm up in 15 minutes, it's not likely going to ever warm up. But you need to test it at the frequency (RPM) extremes you will use while roasting.

Good point.. it would be fun to try and grind a whole pound at once at a low speed as a "load test".. I do still have the hopper.. maybe I'll do that and donate it to the work coffee bin.

bgnome wrote:Love the Sama back there!

Thanks!! It's a sweetheart with brand new piston seals now

bgnome wrote:As much as I love a good VFD mod, I've gotta ask where you got your piston seals? Did you import them or did you substitute?

Not to get too far off base, but I got them from lamacchinadelcaffe.com(very easy and quick shipping from the motherland) sold as Ponte Vecchio parts but they work just the same.

Here's some more details from that-

No more Sama Drama

I'm not sure what seals my machine had originally.. they were softer and different color than what I got from Italy.. however one of the POs of my my machine installed the top seal backwards!

Wanted to say- so far so good still- here is a little video showing how it sounds!

Looks good! No issues with stalling even at the lower speed? With my VFD I was able to hook up a switch and program the VFD for either high speed or low speed depending on the switch position. That, with a ramp up and ramp down over a second or two made for nice smooth running and speed changes.
It is encouraging to see your results! Thank you!

ira wrote:Depending on the motor it may become very inefficient and get hot at frequencies far from it's design frequency. But other than that, there is no issue with using a VFD.

So is it that a full 3-phase motor can just do a wider range of frequencies (like all the way down to 2Hz or so) whilst a single phase motor can relatively safely vary around the designed frequency of say 50Hz, but gets very inefficient and loses power at frequencies lower than 10Hz for example? I'm just plucking a number from thin air here... I would also assume the windings etc won't be spec'd for higher speed like a three phase motor might be, so taking it significantly higher could also be risky. On top of all of that there is the cooling factor if the motor has an impeller, but three phase motors are usually actively cooled if expected to run at slow speeds, so that's universal...

Motors can be designed for a fixed frequency or for a wide frequency range. If the motor is just designed for a fixed frequency it may overheat if run far off it's design frequency. Since most of us run the motors far under their design limits we'll never see a problem, but trying to grind continuously might turn up a problem.

ira wrote:Motors can be designed for a fixed frequency or for a wide frequency range. If the motor is just designed for a fixed frequency it may overheat if run far off it's design frequency. Since most of us run the motors far under their design limits we'll never see a problem, but trying to grind continuously might turn up a problem.

You are correct that I am operating this outside it's original design. I am guessing and taking the risk that by running it in a lighter duty cycle by single dosing I won't overload the motor. It's a bit of a calculated risk as you can infer grinding slower takes less energy. I will keep an eye on temps but so far so good!

A true 3ph motor would be best, but both 1ph ane 3ph motors use a shaft mounted fan, in an extreme case using a separate cooling fan would be needed.

jannus wrote:Looks good! No issues with stalling even at the lower speed? With my VFD I was able to hook up a switch and program the VFD for either high speed or low speed depending on the switch position. That, with a ramp up and ramp down over a second or two made for nice smooth running and speed changes.
It is encouraging to see your results! Thank you!

Thanks! I got excited and realigned my burrs.. only to find it would stall on light roasts at 30hz! I adjusted the torque compensation setting and now it is good again, however that was a pretty interesting experience to see how burr alignment effects motor load

I have been grinding at 1200rpm mostly as that sounds the smoothest with the least clumping.

Unless you decide to grind a pound or more at one setting, I would not worry about overheating.