Cheap VFD's

DoubleChevron

Real cars have hydraulics
Moderator
VIP Paid Subscriber
Fellow Frogger
Joined
May 8, 2000
Messages
18,897
Location
Ballarat,Vic,Aust.
Has anyone tried the cheap VFDs that are availabe these days to run 3phase machinary? This sure is a cheap way of using an old hoist/grinder/lathe/tyre changer/compressor/etc if you don't have 3phase!


seeya
Shane L.
 

COL

Alpine A110
VIP Paid Subscriber
1000+ Posts
Fellow Frogger
Joined
Mar 26, 2002
Messages
5,647
Location
kinimathatakinta Van Diemen's Land
I got this for my lathe


I have had it running on the bench hooked up to a Hercus 9 inch lathe 3 phase motor.

The motor that I have was originally connected in star configuration to run on 400 volts which I have converted to delta configuration to run on 230 volts.

I have yet to mount the motor on the lathe and run it under a load.
 

DoubleChevron

Real cars have hydraulics
Moderator
VIP Paid Subscriber
Fellow Frogger
Joined
May 8, 2000
Messages
18,897
Location
Ballarat,Vic,Aust.
Oh, I thought all electric motors could run in star or delta ... You probably need to run delta as you can't run across the phases to get 400volts .... ? Or am I confusing my 3phase power :clown:
 

COL

Alpine A110
VIP Paid Subscriber
1000+ Posts
Fellow Frogger
Joined
Mar 26, 2002
Messages
5,647
Location
kinimathatakinta Van Diemen's Land
Oh, I thought all electric motors could run in star or delta ... You probably need to run delta as you can't run across the phases to get 400volts .... ? Or am I confusing my 3phase power :clown:
Yes they can, you need to look on the name plate of the motor to see what it has been designed to do.

Some of the smaller 3 phase motors are designed to in star 400 volts or in delta 230 volts.

Some motors are easy to change from star to delta by changing links in the motor terminal box. In this case you will see if there is two links it will be in star configuration and if there is 3 links it will be in delta configuration.

There is usually a connection diagram under the lid of the motor termination box
 

bob

Well-known member
1000+ Posts
Fellow Frogger
Joined
May 30, 2001
Messages
2,992
Location
Skipton
hmmmm.... I wonder if these electronic marvels are like generators and inverters ? You need to pick one that's at least double the capacity of what's written on the engine plate - and likely proper sine wave as well to be kind to your motor.

Bob
 

seasink

Well-known member
1000+ Posts
Fellow Frogger
Joined
Jun 11, 2013
Messages
11,763
Location
Sydney
I just got a three phase connection when the house was new. I don't know current charges, it was quite economical then, certainly less than buying a conversion device.
 

schlitzaugen

Well-known member
VIP Paid Subscriber
1000+ Posts
Fellow Frogger
Joined
Nov 10, 2010
Messages
11,534
Location
loneliness capital of the world
They're a very convenient and cheap way to get three phase things working on single phase power.

But.

Depending on application, you may find moving to PWM brushless power is better. Prices have come down enough that you can buy a brushless motor and controller for pretty much the same or less money at similar power. I have considered the same thing for my lathe (currently running a single phase motor but a little bit gutless and no electronic speed control). A lot of people have done the three phase conversion in the past (the lathe could be bought with a three phase motor when new) but that was when VFDs were unheard of and so were brushless motors. Now it's a different story.

Brushless motors are in fact three phase motors but with a completely different control. A PWM controller can actually be bought as a kit as well I think Altronics and/or Jaycar sell some I have made one in the past and still use it. There's of course cheaper versions on the 'nets.
 

DoubleChevron

Real cars have hydraulics
Moderator
VIP Paid Subscriber
Fellow Frogger
Joined
May 8, 2000
Messages
18,897
Location
Ballarat,Vic,Aust.
I'm not sure what the brushless ones are. The phase converters I've seen in the past have involved actually powering another motor to generate the extra phases. I have done this in the past to run a 3phase grinder. i hooked up another 3phase motor as a phase converter. The 3phase motor is growly but still runs (you would need huge 3phase amperage as you are running the extra motor in the phase converter as well). I thinking if you found a cheap hoist that is 3phase, the electronic controller above would be a very cheap way to get it working.
 

schlitzaugen

Well-known member
VIP Paid Subscriber
1000+ Posts
Fellow Frogger
Joined
Nov 10, 2010
Messages
11,534
Location
loneliness capital of the world
Sorry. My mistake.

What I meant was that you can leave the single phase power alone and swap the three phase motor with a brushless motor and drive that with a PWM (pulse width modulated) controller. These are often sold as a bundle for whatever application you care to think of and it's simpler and possibly cheaper than a VFD. Functionality is the same but you don't need three phase power. There may however be applications that don't really lend themselves to this option.

The brushless motor is in fact a three phase motor but driven differently. To compare the two options with a VFD you "make" the three phase power (same deal - pulse width modulation mimicking three phase power) to accommodate the motor, with brushless you change the motor to accommodate the existing power.
 

COL

Alpine A110
VIP Paid Subscriber
1000+ Posts
Fellow Frogger
Joined
Mar 26, 2002
Messages
5,647
Location
kinimathatakinta Van Diemen's Land
I'm not sure what the brushless ones are. The phase converters I've seen in the past have involved actually powering another motor to generate the extra phases. I have done this in the past to run a 3phase grinder. i hooked up another 3phase motor as a phase converter. The 3phase motor is growly but still runs (you would need huge 3phase amperage as you are running the extra motor in the phase converter as well). I thinking if you found a cheap hoist that is 3phase, the electronic controller above would be a very cheap way to get it working.
Those old style phase converters are from last century, are big and bulky and not very efficient.

The electronic phase converters are small, efficient and programmable to your needs and because they are made in China are very cheap.

Your plan to buy a 3 phase hoist and power it with a phase converter sounds great to me, the only thing you will need to do is look on the name plate of the motor for its size in Kw/HP and what configuration it is connected in star or delta. if it is in star you will need to change it to delta to get full power from the motor. You will also need to make sure that the VFD you choose can power that size motor.
 

bob

Well-known member
1000+ Posts
Fellow Frogger
Joined
May 30, 2001
Messages
2,992
Location
Skipton
how big is hoist motor ? Chinese 240V motors are pretty reasonably priced these days - $250 will probably get you 3HP.

Bob
 

DoubleChevron

Real cars have hydraulics
Moderator
VIP Paid Subscriber
Fellow Frogger
Joined
May 8, 2000
Messages
18,897
Location
Ballarat,Vic,Aust.
Yes they are but you will need a much larger single phase motor that what the 3 phase motor is.

Most hoists will be flange mount onto the pump too. Its probably not a simple task to repower as you would need the right shaft legth, shaft size and flange mount.

I was looking around, if its a hydraulic (not screw type) hoist you can buy entire pump assemblies. this would be a better way than trying to repower the existing pump most likely.


I don't actually own a hoist ... or a shed to put one one :rolleyes: ...but I reckon next time a spot a cheap 4poster I'm going to grab it!
 

jaahn

Well-known member
VIP Paid Subscriber
1000+ Posts
Fellow Frogger
Joined
Nov 5, 2010
Messages
3,577
Location
Newcastle
Hi
Quite some years ago I used a VFD for some lab uses to achieve variable speed for some smaller 3PH motors. They were not cheap chinese type s but budget aussies bought types. They worked OK and also had the advantage that 240V power points allowed for greater portability than 3Ph points.:)
The motors powered high pressure hydraulic pumps and having variable speed meant we got variable delivery to achieve variable speed of the high force rams for close control. Worked well for the planned testing programs and almost no silly complicated computerised control needed. ;)
For those that want variable speed for the motor there are possible motor cooling and over current supply to be aware of in extreme uses. But reducing the voltage might improve the PF and improve the problems.
Jaahn .
 
Top