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26th June 2012, 10:28 PM #16
No, the VFD must connect to the motor directly. Any attempt to break the current flow while the motor is spinning will destroy the output devices in the drive.
You can fit a forward stop reverse switch to the low voltage control inputs of the drive unit, but you won't get instantaneous response because the VFD ramps the variations moderately slowly and the motor/mechanical drive will have inertia to overcome.
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26th June 2012, 10:30 PM #17
I have found that out in my reading but all the discussion seems to be about running 3 phase when that supply is not available. That is what I am looking into. I will have to check the plate on the motor if I find one available to see if a phase converter is suitable.
Big Shed. As above.
Stuart. My lathe finds it a bit of a struggle to acheive full speed in top 2 gears. I have to slip the clutch. This is with a drop from 3hp 3 phase to 2hp single phase. Given the reduction in efficiency in single phase motors this may be in the same range as you mention.
Most of my info came from Drives Direct - Digital Phase Converters - How To Choose.
So after all the posts I have read about using a VFD / VSD etc to use 3 phase when only single phase is available, this method is very expensive and only a second last choice?
What is the difference between VFD and VSD then?
My best bet then is to see if the motor can be wired in a delta config and then run with a VSD with 240v output or buy a 3hp single phase motor. If buying a single phase motor I may also have to buy another switch which cost $200 for my lathe. Single phase switches tend to be of smaller capacity due to the higher voltage and 3 phases. This is one possible advantage of using a VSD. It seems the current price is about $145 for a 2.2kw unit. It also seems that this is suitable for a 2.2kw motor as one of the units I looked at had both a 2.2kw rating and was classed as suitable for a 2.2kw motor. This is one thing that concerned me with induction motors.
I have the possibility of another lathe lined up. Much better than mine. I am waiting on a decision. Two other people have expressed interest but have done nothing. It is about the same size but longer between centres. About 1000mm from end of tailstock tube to chuck jaws. I have seen a picture of one the same (except this one also had a DRO) and is listed as 1000mm centres. I believe that it is far far more accurate due to wear.
Of course I could always use the motor and switch from my lathe. Depends on a number of things.
DeanLast edited by Oldneweng; 26th June 2012 at 10:32 PM. Reason: Lack of editing
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26th June 2012, 10:35 PM #18
Sounds like you guys could answer a question for me as well.
I bought this 3-phase-240v-415-0.75kw-motor with the intention of mounting it on my mini woodlathe and will need to acquire an inverter for it and from looking at all the links you guys have posted and more searching on eBay, this raises my question.
Plenty of 1.5 and 2.2Kw inverters out there to buy but it seems 0.75kw are rare, so the question is, will a 1.5kw inverter run a 0.75kw motor without any problems?Cheers
DJ
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26th June 2012, 10:37 PM #19
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26th June 2012, 10:45 PM #20GOLD MEMBER
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Hi Dean,
You mean getting up to speed? Shouldnt be a problem for a VSD.
No No, 240V input- 240V output VSD/VFD is fine. Its the 240V input-415V output that is the " very expensive and only a second last choice"
Same thing, different name
It needs to be a dual voltage motor(which it most likely will be), but you have to have a look at the plate.
I would stay away from the 3hp single phase motor, the start up current may give you problems?? It would likely cost more and you dont get all the pluses of having VSD.
Stuart
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26th June 2012, 10:48 PM #21Senior Member
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26th June 2012, 10:51 PM #22GOLD MEMBER
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Other than possibly costing slightly more money, no problems. All my drives are 2.2kW.(you should of course set the parameters to suit the motor you are running though). I figured the money I would save by having some 2.2kw, some 1.5kW etc wouldnt be worth it as you can bet the day I need the big VSD is the day it blows up and I'd only have the small one.
Stuart
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26th June 2012, 10:56 PM #23
Cool, so bigger kw inverter is ok but I would imagine not vice versa, such as 2.2kw motor coupled to a 1.5kw inverter?
Cheers
DJ
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26th June 2012, 11:05 PM #24GOLD MEMBER
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Hi Trong ,
Thanks for the offer, but for some reason I thought they were only in Perth, I can duck down there myself.
I might get stoned for this but. No thats fine also, the VSD should be able to look after itself, of course you'll only get 1.5kW from your 2.2kW motor.(long term, they will allow *I think* 150% output for about a minute??)
Stuart
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26th June 2012, 11:07 PM #25
When I say
I believe that it is far far more accurate due to wear.
I am almost looking forward to having a VSD to play with seeing all the options I could have. I say almost as we have lots and lots of VSD's at work and they are great when they work but are a real PITA when they don't.
Issues with them. I have set up a big job and are just about to start when some twit tastes off another job with water straight into the front of the VSD at high volumn. They dont like swimming.
When they first started using them they had older style RCD switches installed which were not very compatable with VSD's. They tended to trip as soon as power was switched on. Had to call up the sparky and wait. Probably 3 other pumps also connected to the same circuit.
They have advantages. Wine hammer is closely related to water hammer and just as loud. Thru 3inch stainless lines it can be very loud. Slow ramp up by using VSD's has made this a thing of the past for the many presses which were the worst culprits. Also saves wear and tear on piping. Some pumps can run at up to 75hz. I did not know that this was just a setting until a repair to our centrifuge pump caused the pump to only do 50 hz. Called the sparky and he pushed a couple of buttons and back to 75hz.
Dean
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26th June 2012, 11:08 PM #26
Thanks Stu, you've been a big help
Will place an order for a 1.5kw inverter soonCheers
DJ
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26th June 2012, 11:16 PM #27You mean getting up to speed? Shouldnt be a problem for a VSD.
No No, 240V input- 240V output VSD/VFD is fine. Its the 240V input-415V output that is the " very expensive and only a second last choice"
Same thing, different name
It needs to be a dual voltage motor(which it most likely will be), but you have to have a look at the plate.
I would stay away from the 3hp single phase motor, the start up current may give you problems?? It would likely cost more and you dont get all the pluses of having VSD.
I don't think it is likely to cost more! I know it will cost more! All those plusses are looking better all the time.
Dean
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26th June 2012, 11:21 PM #281915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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26th June 2012, 11:54 PM #29.
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27th June 2012, 07:50 PM #30
Ok. Now I have a bit more info but I still have not received or gone looking for an answer to whether it is mine or not.
I maybe know why the lathe has not been snapped up already. I don't know how long it has been sitting where it is waiting for a buyer but it has started to go rusty on the bed and ther places so If I get it I want it to be soon. It is under cover but exposed to the north side so condensation is getting to it.
A plate on the rear of the lathe says the drive motor should be 7.5hp 3 phase. I don't know if the motor is original or not and I cannot see the motor plate enough to read it. I would have to move the lathe and remove a cover (4 screws) to clean the plate up to read it. I would suggest that nobody is willing to take on a lathe that big without 3 phase power until I came along.
It is a bit bigger than mine in swing over bed (220mm) and in gap (about 300). It has about 52mm spindle hole. Face plate is 400mm while mine is 340mm. Other than that the chucks are the same size. My lathe has 750rpm max, this one 2000rpm. I am guessing that is the main reason for the extra power.
I still think it is possible to run it off a VSD based on what I have read here recently provided I don't expect to use it to its full capacity and I set the max current on the VSD. I think it would do at least as much as my current lathe.
This lathe has a taper attachment on it with micrometer adjustment.
Suggestions please as I want to ask about it tommorrow. SWMBO has said just get it and we will sort the power out afterwards. As we are on a SWER system the only other options are moving or a generator.
Dean
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