Needs Pictures: 0
Picture(s) thanks: 0
Results 1 to 15 of 18
Thread: Electric motor experts
-
23rd Aug 2021, 08:32 PM #1Golden Member
- Join Date
- May 2020
- Location
- Willowbank QLD
- Posts
- 517
Electric motor experts
Hello all
Here is the situation. I have purchased a Kondia mill with a variable speed head (FV-1) The 3 phase motor is unserviceable. I have had some quotes and am looking at about $800+ to get this rewound and then I will still need a VFD to run it . These motors have a 25 mm diameter, 160 mm long shaft, so not off the shelf.
I have seen reasonable priced single phase motors for sale on gumtree. Is it possible to press the motor shaft out of one armature and press in a new shaft? This way I could make up a motor that would work. I would then have a 1.5 Kw single phase mill.
I have some other ideas but I thought I would rule them out one at a time.
PS If you have a Kondia mill motor dead or alive I may be interested.
Thanks
Steve
-
23rd Aug 2021, 09:27 PM #2Senior Member
- Join Date
- Jan 2012
- Location
- Melbourne
- Posts
- 149
I recall a discussion on another forum (probably Practical Machinist) about changing a motor shaft. The opinion was that it is doable, but with the warning that the laminations each have a slight burr which means that the shaft can only be pressed through in one direction. Other direction the burrs bite into the shaft and stop it moving.
Not sure how to decide which way!
-
23rd Aug 2021, 09:37 PM #3Most Valued Member
- Join Date
- Nov 2008
- Location
- North Brisbane. Qld. Australia
- Age
- 70
- Posts
- 1,511
-
24th Aug 2021, 12:18 PM #4Most Valued Member
- Join Date
- Sep 2010
- Location
- Lebrina
- Posts
- 1,910
I was under the (possibly incorrect) impression that Kondia FV-1's had 2Hp motors on the step pulley variant and 3Hp on the variable version, so you may be dropping 50% over stock.
I take it that the 3 phase motor is properly fried as in unrepairable? If possible, a repair may be the easiest option. If that's not an option, have you considered using another flange mount motor and extending the shaft? If properly done, I can't see too many dramas emanating from such a modification.
If using a single phase motor, you will need to change your switch gear so as to maintain the reversability of the motor, (not sure if a 3 phase with VFD has the inbuilt capability of not).
-
24th Aug 2021, 01:01 PM #5Member: Blue and white apron brigade
- Join Date
- Feb 2006
- Location
- Perth
- Posts
- 7,183
If its geared correctly you won't need the variable speed head so just replace it with a pulley directly driven from the motor pulley and then use the VFD to vary the speed.
You should be able to GET way with <$400 for a new motor and a VFD.
-
24th Aug 2021, 01:06 PM #6Senior Member
- Join Date
- Apr 2018
- Location
- Perth
- Posts
- 168
Agree with Karl. Buy a comparable flange mount 3 phase motor with say a 16mm shaft and machine a stub shaft to fit over the motor shaft. Could do same to a single phase motor if that is way you want to go but probable cheaper to go 3 phase if you have the supply.
-
24th Aug 2021, 06:11 PM #7Golden Member
- Join Date
- May 2020
- Location
- Willowbank QLD
- Posts
- 517
-
24th Aug 2021, 10:12 PM #8Most Valued Member
- Join Date
- Sep 2010
- Location
- Lebrina
- Posts
- 1,910
I'm not saying you're wrong as you generally have your ducks well and truly in a neat row, but would a VFD offer the required speed range? I don't know as I have never played with them, being lucky enough to have 3 phase at my disposal. Without engaging the back gear, my King Rich has a speed range from 500 to 3600 RPM which by my is a 7:1 ratio range. If I understand the theory correctly, without entering the realm of 2 speed motors, that would necessitate a frequency range from say 15Hz on the low side up to 100Hz on the high which I thought was outside the parameters where most electric motors would be happy and also present cooling issues.
-
24th Aug 2021, 10:31 PM #9Philomath in training
- Join Date
- Oct 2011
- Location
- Norwood-ish, Adelaide
- Age
- 59
- Posts
- 6,541
I worked in a place that made motors once, and the answer to whether you can press the shaft out is 'it depends...'
If it were mine I would get the motor repaired, keep the speed change and use a VFD for single to 3 phase conversion and perhaps minor speed adjustment. The range of speeds that you will likely need will far exceed the speed range you can get from a VFD by itself, so you will need some form of speed change on the machine anyway.
Michael
-
24th Aug 2021, 11:22 PM #10Member: Blue and white apron brigade
- Join Date
- Feb 2006
- Location
- Perth
- Posts
- 7,183
It depends on how long you run things for and under what load.
Under lighter loads most newer 4 pole motors can do 15 to 125 Hz without too many problems.
If you were to use a newish 3HP motor and a vector drive VFD you would then have 2 HP from about 20 to 120 Hz but if you were heavily loading for extended periods at low frequencies then a separate fan motor would be needed.
-
26th Aug 2021, 12:01 AM #11Most Valued Member
- Join Date
- Mar 2011
- Location
- Southern Flinders Ranges
- Posts
- 1,536
^ This
Gear for close to minimum required speed and use the VFD to accelerate the motor, this is generally much kinder on the motor than running it slow with low frequency. This will mean swapping pulleys at some point. Putting a 3kW motor on a machine and using so you only get 2kW out of it is just an exercise in wasting money both in initial outlay an ongoing running costs. Just because you can doesn’t mean you should.
-
26th Aug 2021, 01:42 AM #12Member: Blue and white apron brigade
- Join Date
- Feb 2006
- Location
- Perth
- Posts
- 7,183
Apart from things like compressors and fans, most machinery motors operate at well under their maximum power for most of their lives. Over a 10 year period the 30% purchase price difference (even less if a used motor is involved) between the price of a 2 and 3 kW motor and running costs, compared to what else is spent in things like tooling is trivial. It's not like were running a factory full of these things for 40 hours a week and 48 weeks of the year.
-
26th Aug 2021, 01:39 PM #13Golden Member
- Join Date
- May 2020
- Location
- Willowbank QLD
- Posts
- 517
Firstly a big thank you for all the information so far. It has certainly got me thinking about options.
I have never owned or used a mill of this size, and also have very limited experience with mills.
A couple of questions have come to mind. This mill appears to have a speed range of 60 to 4000 RPM.
For home use is lower than 60 or greater than 4000 rpm ever likely to be required?
Also the mill currently has a 1.5 Kw motor fitted. Is it likely that any more power is desirable for home use where production time is not a concern?
My plan is to decide what to do, do it once and do it right. I am not looking to do this cheaply, but I want to do this as economical as practical. This includes long term running and maintenance costs.
In some ways an off the shelf motor, pulley and belts make a lot of sense. Te other side of the coin is just keep to the original design intent.
Thanks
Steve
-
26th Aug 2021, 06:06 PM #14Most Valued Member
- Join Date
- Sep 2010
- Location
- Lebrina
- Posts
- 1,910
My choice would be rewinding the motor you have and using a VFD I think. Second choice would be to source a flange mount 3 phase motor, possibly a 3Hp unit and extend the shaft as required and then run a VFD.
Based on BobL's earlier post, I'm getting the impression that running on 240V from a VFD may only give 2/3rd of the rated power, (using a 3Hp motor for 2Hp output), which would make for quite an anaemic performance from the standard 1.5Kw motor if that were the case, giving weight to increasing the motor size as a viable option.
-
26th Aug 2021, 06:55 PM #15Philomath in training
- Join Date
- Oct 2011
- Location
- Norwood-ish, Adelaide
- Age
- 59
- Posts
- 6,541
In terms of cutting speeds, at one end 60rpm represents a 75mm HSS fly cutter on Cast Iron (probably also a useful speed if using a tapping head or larger hole saws), at the other 4000rpm is the speed that a drill in aluminium around 6mm could run at. I certainly would not be tempted to trim the bottom speed; if I had to I'd loose some at the top end, but would still want to keep at least 2000rpm, preferably 3000rpm.
Power is trickier. You could cut down on power if you needed to but for industrial class machined that is probably low anyway. (my mill, which is not big is around 3kW from memory) Depending on your belt/ pulley combinations, you may not even be getting that power at the spindle at low speed (which is where it is most needed). I would try to hang onto that power, because if you get into stainless steel for example, dropping your feed rate because you have not got the power at the rpm you need is one good way to ruin cutters, as for SS they need to bite.
Michael
Similar Threads
-
Three phase motor electric motor
By china eyes in forum METALWORK - Machinery, Equipment, MARKETReplies: 2Last Post: 5th Dec 2018, 04:02 AM -
3 ph electric motor
By eskimo in forum METALWORK - Machinery, Equipment, MARKETReplies: 19Last Post: 22nd Apr 2017, 11:35 AM -
Calling all electrical experts - DC motor conversion
By neevo in forum METALWORK GENERALReplies: 54Last Post: 8th Apr 2015, 07:26 PM -
electric motor fun
By morrisman in forum METALWORK GENERALReplies: 16Last Post: 30th Apr 2012, 06:17 PM -
Help with electric motor
By Woodlee in forum METALWORK GENERALReplies: 28Last Post: 26th Feb 2011, 11:14 PM