Will a VFD output single phase?

[vladdy]

Dumb question to some maybe, but I never did much with VFD's..
anyways, VFD in question is a Delta B series 3-5 hp rated, I know I can input single phase , but never tried output as single phase...
Motor that I would like to run on output end is a Baldor 3 hp single phase on an old Gisholt converted turret lathe..
be nice to have a choice of more than six speeds...
tia..

[Al_The_Man]

The ability to control a single phase motor with a VFD is prone to stall at the lower speeds, the only type that I know of has been Capacitor-run motors, Motor that are capacitor start only, suffer from the problem above.
IOW I would put a three phase motor on if you really want Variable speed drive.
In any case, you may have to search a bit to find a VFD that even attempts to run a 1ph motor.
Al.

[vladdy]

when you say 'stall' is that below an approximate speed percentage, power draw , or??
I was basically looking to get [hopefully] +15 / -35 % on rated speed..

..

[Al_The_Man]

I have never used one but have read reports of dismal performance, apparently if base speed is reduced only marginally and a load is placed on the motor it can fall out of run.
I would think that the absence of any but one or two products that can be found for this type of motor speaks to the popularity and success.
Also, the majority of 1 ph motors used in MT spindles etc, use capacitor start motors, If you were to use one of these motors, with the reduction of RPM, the start windings would come into operation again, and I believe these are not continuous rated.
Al.

[vladdy]

ok..I know the motor on there has start windings, so I 'assume' capacitor start, definitely would not want it to drop down to the point where those start winding cut in again, from previous experience I know that shortens the life span quite drastically [ they warm up quite noticably in less than 30 seconds]...
I was hoping that around a 35% reduction in speed would still keep the starter plate flipped out...maybe, don't really know for sure when they cut back in normally,
so at this point, as far as I can tell, is to look around for a three phase motor of equivalent capacity, failing that, the VFD will go up for grabs on ebay I imagine..
I have no three phase machinery [except for air conditioner at another building], so not sure how much time I want to spend, but it would be nice to have more variable speed ranges on this old lathe..most of the time it runs around 500-700 rpm with fairly aggressive cuts.. basically 'rough' work..trimming down flywheels or cutting the weld out of driveshafts and such..
the Delta VFD was fairly cheap as the plant was updating some of the conveyors, and I rescued it from the scrap bin...it's value ws directly comparable to it's weight...

thanks

[in2steam]

AL is correct if you were to drop a cap start, or cap start-run( two caps) motor down to start winding(around 60% of nameplate rpm) you would both fry the motor but more then likley the drive also. The currrent draw would go through the roof, torque would be unstable and things would get hot fi they don't explode first. Similiar would happen with any motor that has a start winding cutout switch, be mechincal(most) or electrical. I have run permanant split capcitor motors with mitsbushi drives(with the hopes of using it on a taig), the preformance was less the stellar, not even worth the while to do. There are some purpose built single phase drives poping up now but again they are being used on fans primarily, and thats were PSC's work the best. Best to go with either DC or 3 phase AC, the psc route is pretty much a waste.

chris

[handlewanker]

Hi all, one thing must be realised and that is the reason that single phase motors were/are so popular is because they can be driven directly from the mains.
The only problem is they don't like to slow down , for the reasaons already stated.
Now there are TONS of 3ph motors out there that no-one looks at because to have 3ph in the home is going big time.
These 3ph motors usually go for A$50 for a 1hp job and up to A$150 for 3 hp.
You can drive these motors from the 240volt mains, probabvly 110volt as well, I don't know, we don't have 110V in OZ, if you have a VFD that converts 1ph to 3ph.
I recently bought a 1 HP VFD brand new, on Ebay, for A$250, to drive my bandsaw, which means that the motor can be controlled from 15% to 200% of it's rated speed without having to change belts on pulleys.
You just have to make sure not to load it too much at the lower speeds or it will overheat due to loss of fan speed.
To overcome this I belted the motor down to give a primary reduction of 1:8 and this lets the motor still run fast enough while the final output speed is as low as required.
The beauty of a VFD is that you can get ramp up and down and dynamic braking and also jogging.
The other way is to make a rotary phase converter, using a 3ph idler motor rated above the HP of the motor you're going to drive.
You don't get speed control, but you do get a lot of cheap motors available.
I'm going to use the latter method for my Bridgeport mill, as it's cheap and the mill's got adequate speed control already.
There's a big market for oil filled run capacitors, in the 400volt 10 - 20 Uf range, that are used for this purpose,and to buy them new probably cost more than the motor, so when you come across any at junk sales or scrap yards, you grab them.
Start capacitors are only used for a second or two to get the motor up to speed, and are in the range of 400volt 100-150 UF and are much cheaper and easier to get hold of.
Ian.

[in2steam]

Theres a secondary market for the oil filled caps?
Seems to me that my disposal department seems to think that they are next to nuclear waste here, can't ship, can't get ride of them, again thats in a blown condition also.
Then again I use, large ones, in 15-20 mic range across the primary of a ballast transformer.
chris

[vladdy]

I did a bit of checking today to see what was available for 3ph motors [again from the fellows doing the updates at the milling plant here, and there's nothing left under 5hp, so the VFD update on the lathe will have to wait a bit..
There apparantly were a few in the 2 to 3 hp range, but as there is no industrial recycling depot in this area, they went to get melted down as scrap..oh well..the scrap yard already had them trucked out to Winnipeg with the loads last week,
but I did manage to scrounge some load cell display units, a gallon pail of AB switches, a half dozen older slo-syn [appx 34 size] steppers, for less than $10 so it's definitely not a total loss...
I'll put the VFD on the shelf 'just in case'..I may never use it, but someone else might make use of it later on.
The old gisholt will stay a six speed for a while, but I'm used to it, so it's not like I'm 'missing' anything at this point..

thanks

[alipavsky]

Originally Posted by vladdy I'll put the VFD on the shelf 'just in case'..I may never use it, but someone else might make use of it later on.

Are you saying you might be willing to part with your VFD? I need a single-phase VFD for a small (3A) motor.

[in2steam]

I hope you know a majority of single phase motors cannot be run on a VFD, only ones without a switch(either mechincal or solid state), which about 99.9% of those are permanet split capcitor, which are pretty bad doing anything esp if it only draws 3 amps. They also at that power level tend run hot as it is, and some PSC motors don't run on VFD's anyway(my mitsubushi VFD manual states that they may not run at all) as they eliminate the capcitor.
chris

[handlewanker]

Hi all, one of the problems with single phase motors is the HP to physical size factor.
The duty cycle of the motor will give you the run time for it.
For instance, if you check on the electric specs plate on the motor and it states continuous run, you can be safe in thinking that it can be used at it's stated HP capacity to run a machine all day long, but if the plate states int. or intermittent run, then you have a whole different ball game.
Here we have a motor, that rated at 3/4 Hp, will for a short time, usually 1/4 hour or less, act like a 3/4 HP motor, but soon gets too hot to use.
You can pump in the amps to get the wattage out of a small motor package but in the end the current drawn has got to go somewhere and that is in the form of heat.
I use to see 1/3 HP motors from washing machines driving small lathes on the home workshop circuit.
They work fine up to a point, as most of the work is cut and try, with the lathe being switched off for longer than it runs as the operator battles with the mysteries of turning etc.
Which brings me to another point, not mentioned before by anyone, and that is the number of start cycles per hour for single phase motors, usually about 4 or 5, after that the start windings just add to the miseries as the whole motor gets hotter and hotter.
You just can't get the heat away quick enough, and as it follows an exponential curve, with every switch on cycle, you get that familiar smell of hot insulation.
I was told once that the "modern" single phase motors have insulation that is designed to run hot to improve the insulation properties, crap!
Incidently if you do come across a 1 ph motor that won't start but only gives a loud humming sound, then 10 to 1 it's the start windings or centrifugal switch that has gone west.
It's also vital to test for a short to the frame of the motor.
NEVER touch a motor frame when it's running, unless you want a nasty surprise with a shorted out winding.
Also NEVER run a motor without an earth connection.
Last but not least, before running a motor test it with a meter to see if you have a high resistance between the live input wire and the frame.
If the resistance is low then ten to one you will blow something at start up.
If you do get a start problem, it doesn't mean the motor is dead.
If you isolate the start windings by disconnecting them from the switch plate, then the motor can be used by wrapping a cord round the shaft and giving it a pull.
The old familiar phrase "Don't try this at home" would probably fit in here.
As soon as the cord is free the motor is switched on and if you get enough revs with the " cord starter" it will run, and quite happily too, in any direction, as it is the start windings that determines the direction the motor will run in.
Some 1 ph motors can't be reversed, due to inaccesibility of the wiring connections etc, but for the majority it's only necessary to swap over the start winding connections to effect reversal.
I once bought a practically new 3/4 hp motor with the centrifugal switch burnt to a crisp.
It was a 2,800 rpm job from a circular saw, and I paid about 1 pound back in 1975 from a scrap yard in UK.
I cleaned out the innards of the motor and reinsulated the wiring connections.
The centrifugal switch was on a Tufnol board that had burnt out and was totally unrepairable, so I just brought the two start winding wires out and connected them to a momentary contact switch that was used to get the motor going. One quick press for a split second and the motor was up and going.
Later I rewired the input connections and added a relay with a time delay, to effect the start up requirements.
By adding a relay to the start circuit in place of the start switch meant that if the motor was overloaded it could even stall, and as there was no centrifugal switch present to switch the start windings back in with speed drop, no catastrophic burn down can happen.
This also works to reclaim a motor if the start windings are actually burned out.
I use a 1 HP motor on my Colchester Bantam lathe, but to avoid switching the thing on and off all the time, I added an electric clutch from a car's airconditioner.
Now the motor runs continuously, with the electric clutch being switched on and off for as many times as you want, and never gets hot.
The bonus is that the clutch gives a softer start, as opposed to the jerk when a motor is switched on, even without a load.
The clutch is designed to be switched on and off continuously, and only consumes 2 amps at 12 volts DC, so a battery charger of 4 amps output will power it quite well.
It is activated with an ordinary car type toggle switch, mounted in a conveniant position on the headstock, rated at 12 volt 4 amps, and fused accordingly.
I'm adding an electric brake as well, so that when the clutch is deactivated the brake will come on for a second or two to stop the lathe quicker, very necessary when your'e using a turret lathe on short run cycles, and beats having a foot type mechanical switch.
I think I'd be right in saying that all of the Chinese and other foreign import lathes have motors that are connected directly to the drive train and so get switched on and off all the time as required.
They're designed to do this, but I dislike the thump in the drive train when the motor starts up.
An electric clutch and brake here would not add too much to the cost, but would extend the usefullness a hundredfold.
Ian.