My belt grinder has served me well, and for a hobbyist, it would be probably good enough. But since I am inching my way towards knife making not being just a hobby, I needed some significant improvement on it. And an opportunity luckily arose.
One of the good things about my previous employer was that there was an internal process for employees to get obsolete materials and equipment either cheaply or completely cost-free. I have used this opportunity quite often and got a lot out of it – I am well stocked in graphite and alluminium, I got precise analytic scales completely for free, and one of the last things I have managed to get was a variable frequency drive.
I was not able to haggle this one down to zero, it was a bit pricey even though used, and I also had to pay a bit to a professional electrician to connect it for me. I could get a new one for a bit cheaper if I capped it at the 1,5 kW that my motor has (this one can handle 5,5 kW) and took the cheapest one there is, but it was still a good deal even if it was not exactly a bargain.
And it works like a charm, even when I am not able to use anything more than the manual mode yet. Finally, I have the ability to change the speed of the motor as I need it, I can even reverse the rotation. I have tested it already and it is exactly what I hoped for- finally I can work wood without burning it and I can sharpen tools and have a bit more time before the edge starts overheating.
I hope it continues to work well – I have great plans for the future. Multiple grinding wheels, a polishing attachment and, maybe, even a lathe attachment. The belt grinder shall not rest!
It doesn’t hurt that the VFD has bigger power rating than your motor. I think it could last longer, as it will not run as hot as a smaller rated one (due to better cooling).
What do you mean by manual mode? Setting speed manually in V/f mode?
I can set manually the frequency on the keypad, and that is it. This drive can also be connected to PC and programmed from there, but I do not think that I will have any use for it, even if I were able to figure it out.
You could be right, but using vector control mode (it seem it’s “Real sensorless vector control” in Mitsubishi language) could produce less torque vibrations. I don’t know if there is some sort of parameter lock or simple mode on the VFD, according to the manual, it should be possible to change parameters using the keypad. At least for the sensorless vector control, but also otherwise, you should be able to set the motor ratings in parameters and perform the auto tuning function in order to get correct system parameters for the speed/angle estimator.
@Ice Swimmer, I have looked at the manual and found out that about 99% of it goes way over my head.
Charly @ 4
The manual is quite a mess, I agree.
*Also, I’m sorry that I didn’t read the manual well enough.* They state that the sensorless vector control could actually make more uneven rotation speed than voltage/frequency (V/f) control.
What I was thinking that with V/f control (which is actually just setting the output frequency and voltage to have a constant ratio, with no feedback control) the motor speed tends to oscillate for a while if there is a quick change in frequency reference or load. Of course, the grinding process itself will damp such oscillations.
I have changed the speed of my grinder exactly zero times. Or one, if you count changing it from zero to somethingorother.
In 4 years.
Take care of your hands.
Because I might have a nice open spot on my left hand where the belt grinder faithfully removed a few layers of skin.