variable frequency drive conversions

[tonyfoale]

I just hooked up a cheapo vfd on my little mill. My understanding is that there is a loss of torque at lower rpm. At the moment I do not remember who posted it but recently there was a post about repowering a lathe (?) With a larger motor to have the necessary torque at lower speeds. With time I will find out for my self. What i have found out is the torque and rpm drops to neer zero at max frequency of 400 htz. I have been testing it with 40 to 80 htz and found this to work so far. This applies to my setup, I realize other setups may be different.
Eric
The mill is from 1950's and is 3 phase German made.

I suspect that being German made and being old that the motor is designed for 50 Hz. it is probably not wise to run it above about 50 Hz or maybe 60 Hz maximum. The VFD sounds like a modern one with a max frequency of 400 Hz. That frequency is for the high speed spindles that have become available over the past few years, and it is not for normal lathe/mill motors.

It sounds like your VFD is currently setup for a high speed spindle, if so then you need to re-programme it to a maximum frequency of 50 or 60 Hz or you will not get the best results. The voltage to frequency ratio will be way out if max freq is set to 400 Hz, the max voltage will be set to about 220/240 volts at 400 Hz, that means the voltage will be reduced to 27/30 volts at 50 Hz. If you set the VFD to a max freq of 50 Hz and max voltage to 240 v then you will have 8 times the torque.

In most cases it is probably safe to feed a 50 Hz motor with 400 Hz at the normal motor voltage as you have mentioned, the current will be low because of the motor inductance at that frequency, meaning that the torque will be low and with higher iron losses the torque will be too low to spin it up to the speed that would match the frequency. This seems to be what you have experienced.

On the other hand NEVER EVER run a 400 Hz high speed spindle on a VFD set to a max freq of 50/60 Hz. because at that frequency the spindle will be expecting a voltage of 27/30 v not 220/240 v. This will burn out your spindle motor quicker than you can reach the off switch once you see the smoke.

The post that you mention about using a big motor on a lathe is here http://www.homemadetools.net/forum/i...515#post135903

[Saltfever]

Thanks for the fast reply, Tony. My 2HP, 3ph lathe came with a new (at the time) RotoPhase converter and 5 HP motor. The lathe also has an antiquated mechanical, infinitely variable drive. Everything has been in storage for the past 30 years and not used. However, my understanding is that the old phase converters were quite noisy. Since I need to convert the lathe to single phase it would be nice to simplify the variable RPM drive. I was considering a VFD because it may be quieter and more efficient than the RotoPhase but also because it would simplify RPM changes. Your thoughts . . .

[tonyfoale]

Thanks for the fast reply, Tony. My 2HP, 3ph lathe came with a new (at the time) RotoPhase converter and 5 HP motor. The lathe also has an antiquated mechanical, infinitely variable drive. Everything has been in storage for the past 30 years and not used. However, my understanding is that the old phase converters were quite noisy. Since I need to convert the lathe to single phase it would be nice to simplify the variable RPM drive. I was considering a VFD because it may be quieter and more efficient than the RotoPhase but also because it would simplify RPM changes. Your thoughts . . .

My thoughts. Firstly, many VFDs are noisy, those have a cooling fan which makes a lot of noise and is on all the time. I cured an ABB VFD by substituting a quiet computer fan which still runs all the time. More recently I got a Huanyang VFD which was even louder, I changed that for a computer fan, the original was 24 V but the computer fan is 12 V, so I used a series resistor. This is a very easy modification. Only last night I accidentally came across a video by Mark Presling (he also inhabits this forum so he might chirp in) about silencing a Huanyang VFD. His approach was somewhat different. He added a simple 45 deg bimetallic temperature switch such that the fan only comes on when the temperature of the internal heat sink gets to 45 deg. This morning I ordered some thermal switches, I think that the ultimate solution is Mark's switching and a quieter fan.

There is another source of noise which generally afflicts some older motors. The PWM carrier frequency of VFDs ranges from around 2 kHz to over 10 kHz. Some motors will make a noise at that frequency which can be quite annoying. My ABB VFD drives a very old 1950s 5 hp motor on a shock dyno and there is no audible noise, I have not checked the carrier frequency. The Huanyang drives a 5 hp modern motor on my mill and there is no noise that I hear. The default frequency on that is 7 kHz but that is programmable up and down. However, if I use the Huanyang with the newly fitted 1990s motor on my lathe it whines. I made what is called a dV/dt filter to put between the motor and VFD which has cured it. In his video Mark mentions the same problem which he fixed by programming the carrier frequency to be higher. This is a very common "fix" but a word of warning. In general terms a higher carrier frequency is good for the motor but bad for the VFD because the IGBTs inside (electronic switches) generate more heat due to the increased switching.

About swapping the mechanical variable speed for a VFD, that should be fine unless you need to do heavy work at low speed, I have commented on this in earlier posts. Like my recent lathe motor change it looks like your lathe motor has gone from 2 hp to 5 hp which will be a big help.

About replacing the rotary converter with a VFD, I would not hesitate. the rotary converter will have a 3 ph motor inside which might be useful to power something else.

PS. here is a link to Mark's video https://www.youtube.com/watch?reload=9&v=x882vvX_L7Y

PPS. I will make post soon about making the dV/dt filter and generally filtering VFD/motor combinations.

[DIYSwede]

-Thanks Tony - especially for the link to Mark's channel!
Cheers!
Johan
When is "soon" - as in the PPS?

[tonyfoale]

-Thanks Tony - .............When is "soon" - as in the PPS?

A bit longer than "very soon".

[tonyfoale]

-Thanks Tony -.......When is "soon" - as in the PPS?

Posting it right now, give me 10 minutes.

[Saltfever]

. . . About swapping the mechanical variable speed for a VFD, that should be fine unless you need to do heavy work at low speed, I have commented on this in earlier posts.

Yes, thanks . . . I understand that lower motor RPM = lower torque.

Like my recent lathe motor change it looks like your lathe motor has gone from 2 hp to 5 hp which will be a big help.

Sorry, my post was confusing and not clear. My RotoPhase (RP) has a 5 hp motor as part of the package. My lathe is still a 3 phase, 2 HP motor which I need to convert to 1 phase service.

If you note, the data plate indicates the RP sucks up 4 amps just at idle, no load! I was seeking quieter operation, higher efficiency, electronically variable RPM, and no loss of torque. I thought solid-state electronics could do that but I will loose torque and still have Hi Freq noise (about the same as the RP). Torque is important for my work so I may as well stay with the RP and the lathe's variable speed drive. I'm also considering buying a 3 HP, single Phase motor to make up for the HP loss when going from 3 phase to single phase.

[suther51]

So try 3 to succeed in posting.......
Thanks Tonyfoale for the information.
I currently have the max hz set at 100 or 80. I will.lower it, will.gave to try some settings and see what seems best under load, 60 or 50 max. Thanks again for the info. Hats off to all who post hard won knowledge to help others. The manual that came with the vfd is so incomplete it hurts my head. Status quo I understand for Chinese vfd's. I was real nervous for the first try ( some arrive doa I have heard) but all seems ok so far.

As a aside, the vfd's fan is thermally switched. I will see if i can post the "brand", many some pics if i have time to figure out how to post pics again.
Eric

[suther51]

https://rover.ebay.com/rover/0/0/0?m...2F283047413319

In the listing I do not see a brand name, will have to look at the manual.
Eric

[tonyfoale]

https://rover.ebay.com/rover/0/0/0?m...2F283047413319

In the listing I do not see a brand name, will have to look at the manual.
Eric

That looks like a Huanyang copy. The widespread consensus is that the Huanyang brand is the best of the Chinese offerings and as a result there are many copies (chinese copying chinese) some of which are reportedly missing several features as well as reliability. I hope that yours is not in that class.
That is only hearsay and I have no first hand knowledge of this. I have a German ABB which has worked fine since 2007 and a Huanyang which has worked fine since 2014. Neither have given any problems.