Motor type for grain mill?
I am planning ahead for when I motorise a Diamant grain mill and I would appreciate some clarification on the two main Capacitor categories that are offered for the sort of motors we would commonly use.
I have narrowed my search down to (probably) 0.5HP single phase, 4 pole for the Diamant (they advise 0.5HP as a minimum) but have the choice of permanent capacitor or cap start/cap run and I don't know which is advised for grain mills.
I do know that the cap start/cap run motors can draw a high current at startup and I wondered how you deal with that current draw. Some 0.5HP motors were drawing more than a household 13A fuse at startup.
If it helps, I am in the UK so 240V 50Hz.
The next question will be reduction... the Diamant flywheel is 16" so I think the common 1500rpm motors would turn at 187rpm given a 2" on the motor and the 16" flywheel. Is that correct? I would prefer something in the range of 75-90rpm. How would you handle it? A gearbox or a second pair of pulleys?
First, this is a link for an arbor speed calculator, you can work out the size of the pulley on the motor here http://vintagemachinery.org/math/arborrpm.aspx. If you are going to use an induction motor in the US, the motor speed is either 1725 or 3600, since you say 1500, I assume you are in 50 hz territory. I am no motor expert, but according to this page, http://www.leeson.com/TechnicalInformation/sphase.html if you go with a permanent capacitor, you just need to be sure to start the mill empty, and run it to empty, you may have trouble if you start it with grain in the mill, or stop and try to restart when you haven't finished milling. Note that the same cautions apply to the universal motor impact mills, and that is why they say to start it empty, then add the berries. As to the surge, in the US, we normally have 15 amp circuits, but the fuse is designed to allow a surge when the motor starts without tripping, so long as the surge is not excessive.
Thank you for those links... especially the second one which was the overview of AC motor types and their intended use.
Given that information, I am likely to go for a cap start/cap run motor but may have to ask my electrician to discuss the startup current. I will want to have grain in the hopper, run it a little to check the grind then stop, adjust and resume and it sounds like a cap start/cap run motor is the way to go.
As for speed, yes I am in a 50Hz area so I am offered AC motors that are around 1500rpm. Unless I look at variable speed drive boxes, I will need to have either a (roughly) 2:1 reduction through a gearbox or a second pulley pair. I was looking at a 2" on the motor to a 6" on a spindle with a 3" leading to the 16" flywheel for a 94rpm speed.
Would you suggest an AC VFD, a 2:1 gearbox or second pulley pair?
Dan, if you can afford a variable frequency drive, that would be the way to go. It would let you run a 3 phase motor, which is usually much cheaper than a single phase motor. The problem, in my mind, with the two other options is that they would take up a lot of room.
I do like the sound of that... I have access to a qualified electrician after all.
It sounds like a dedicated circuit breaker located where I will be using the grinder, a VFD with a 3ph 0.5HP motor and a single belt to the Diamant is the "correct" way to go.
Thanks for the advice and I will be certain to post a review once it is all set up (some time in the autumn I think).
This might be a little off topic, but the people that make the Country Living grain mill have some ideas on motorizing their grain mill.
http://countrylivinggrainmills.com/motorized-grain-mill.html
You might have to change a few things for a Diamant, but it's doable.
Thank you for the pointer to the Country Living page on motorisation - I had not seen that page before.
I am still planning to use a VFD for the simplicity of only having a single belt but have come across a few issues during web searches that may be of interest to other folks planning to motorise...
First is pulley size - anything under a 2" pulley is considered pretty small and will have a risk of the belt slipping or wearing. One and a half inch pulleys are really about as small as you can go.
Secondly if using a VFD, you need to consider the motor HP that you need to do the job. Running a motor at half speed on a VFD results in (roughly) half the horsepower at the output. If a company specify 0.5HP at the flywheel, then you would need a 1HP motor if you were using a VFD to run it at half speed so that you still delivered the correct HP to the machine.
As I understand it, VFD-driven motors also have the additional benefit of fairly large energy savings. A good VFD only supplies the current the motor needs to do the job.
VFD is one solution to the problem of driving a mill and has a set of advantages (easier and more exact control over mill speed, simplicity of set up, etc) but also has drawbacks, namely higher cost.
Compared to the cost of the VFD and mill, the risk of belt slipping is fairly negligible. A friend of mine that fixes motors for a living showed me a pulley off a commercial refrigerator that's been running for 18 years and while it it definitely was worn it still worked. You've gotta remember that unless you're running a mill 24/7 I wouldn't worry about things like pulley or belt wear. Small pulleys are around $3 here and industrial belts under $15. Price is all relative.
My current set up uses a Country Living mill (purchased used) motorized similar to the link in my other post using a old furnace motor that I got at a garage sale. Not surprisingly it uses more power per unit of flour than my Wondermill impact mill, but I digress.
I'd be interested in how your set up works when completed.
It will be a while I am afraid. My house purchase fell through... or should I say my sale did so I am back to square one and waiting.
Once I have the full kitchen, I will talk to the electrician and joiner about parts and safety. Fortunately it is for home use, not commercial, but there are things I want to talk to them about like a power interrupt switch.
Given that I will be paying for a Diamant (albeit in the EU), I don't mind paying for a new motor and VFD.