Hi Jim;
In the past there where a lot of plants running 600 volt AC systems. You don't see plants implemented that way much any more.
The reasoning is the same as the reason to go from 220 to 440, you cut copper usage because the same power can be handled by lighter gage wire. I'm not up on why industry standardized on 440-480 in the US, but maybe we will see a return. A big factor is likely the versatility of motors capable of being wired 240 or 480 in the field.
I'm actually surprised at how small and versatile 3 Phase drives have become. One of the first drives i worked on was from PTI, later A&B. They where huge just to drive a small motor. Back then they where also simple basically a clock generator driving a ring counter with a little extra thrown in. These days the drives have more capability and options than the average guy can manage to employee.
By the way the above should not scare people off. Todays drives are very easy to use.
There is one other advantage I seldom see mentioned in these threads. VFD can provide you with soft starts. That is instead of starting the motor across the line and throwing all that torque into a machine, you can instead ramp the motor up to speed. This is easier on old machines and can be an advantage for the machinist too.
I don't want to sound like a VFD salesman but it has only been the last couple of years that these controllers have become reasonable for the small shop or home hobby shop. Five years ago such drives would have been dismissed (rightfully so) based on cost alone. Today you can buy a very good drive for a couple of hundred that may have cost thousands five years or so ago. When looking at used machinery one should always study the trade offs of various retro fit stradegys, in many cases a VFD is a wise choice.
In this case the 575 volt motor is a bummer if it can't be easily rewired for 240. If that is the case I'd still look at the feasabilty of a new 3 Phase motor and VFD.
David A Frantz
websterindustro@mac.com
Sent from my iPhone.
On Sep 9, 2010, at 12:28 PM, Jim Ash <ashcan@earthlink.net> wrote:
> Good point. Actually, my suggestion applies to any of the ways to get 3-phase into your shop; you just open up a window of opportunity that others frequently neglect.
>
> My motor theory is weak but IIRC, rotatary converters aren't terribly efficient. In my particular home shop with comparatively infrequent use, I don't care that much.
>
> I've never heard of a 575v motor, but then I'm not really a power electronics guy. Is this possible that the 575v is peak-to-peak, and it's really 408v rms (does the square root of 2 difference for sinusoids apply to 3-phase)?
>
> As others have said there are gobs of advantages to a VFD if you can afford the bite. The ones I saw at Cabin Fever had a mind-knumbing array of software-driven options, but I don't recall if 575v output was one of them.
>
> Jim Ash
>
>
> -----Original Message-----
> From: Ron Thompson
> Sent: Sep 9, 2010 8:26 AM
> To: gingery_machines@yahoogroups.com
> Subject: Re: [gingery_machines] Repowering lathe
>
>
>
>
>
> I agree, BUT. As nice as VFDs are, they are expensive. Cheaper options
> would be to build a rotary phase converter or buy or build a static
> converter.
>
> I built a rotary years ago, they aren't that hard. Plenty of good info
> around free on the web. I had to sell it when I moved, just too much
> weight in the trailer along with everything else. I now use a static
> converter with good results. I use one converter on two machines.
>
> On 9/9/2010 8:08 AM, Jim Ash wrote:
>>
>> What he said.
>>
>> Also - Having a VFD opens up possibilities for you that others avoid.
>> Lots of folks won't give a piece of 3-phase equipment a second look
>> because it's 3-phase. This attitude has caused lots of really nice
>> equipment to sell for somewhere between scrap and get-it-out-of-here
>> prices. Bad for the 3-phase phobic; good for you.
>>
>> In a one-man shop, size your VFD for the largest piece of equipment
>> you plan to run on it.
>>
>> Jim Ash
>>
>> -----Original Message-----
>> From: CNC 6-axis Designs
>> Sent: Sep 10, 2010 7:24 AM
>> To: gingery_machines@yahoogroups.com
>> <mailto:gingery_machines%40yahoogroups.com>
>> Subject: Re: [gingery_machines] Repowering lathe
>>
>> The smaller motor will work, but DONT DO IT!
>>
>> For less money, you can get a VFD that makes the 3-phase from whatever
>> you have (110, 220, 50 hz, 60 hz etc.).
>> The model is the Hitachi 2xx, 2.2 kW size. About 400$. (I have one on my
>> Bridgeportr M-head spindle on my shop-built milling machine).
>>
>> The 3-phase motor is VASTLY superior to a ANY single phase solution
>> apart from indexed servo spindle (which I also have).
>>
>> If you buy the smaller motor you then ideally need a speed control for
>> it, which is extremely useful on a lathe. At least a contactor (you need
>> one for lathe use) and that will be 50-100$ on its own.
>> To get the VFD, go to automation direct, drives warehouse, etc.
>>
>> Look for one that eats 220 (if you have it) and outputs the 575v.
>> The docs are good, and will get you going.
>> There are a lot of very useful things in a VFD that only exist in VFDs
>> (and servos) you simply cannot get any other way. Included in the same
>> price.
>> Dynamic braking, holdng, soft start, ramps, PID loops, safety features,
>> forward and reverse, WITH automatic safety features, overload overheat
>> protection etc etc.
>> All of the above are included in the Hitachi I used, and all work on my
>> CNC milling machine, with about 5 control wires and 2 days setup time in
>> the VFD.
>>
>> Safety is important. VFDs come with all the safety features as standard,
>> things like not getting the spindle to run at last (full) speed in an
>> error, overload, overheat, power-out situation.
>> VFD driven 3-phase motors also give a much better surface finish, when
>> you have a good heavy lathe behind them (I do).
>>
>> My lathe is currently running with an original factory 1.5 kW industrial
>> motor, and I am swapping it for a servo (indexed) spindle.
>> I am now fixing the swarf guards on the mill, to face mill the mounts
>> (30 mm steel flat bar F114), to permanently install the servo motor
>> mount on the lathe.
>>
>>> I have been lurking for several years and have cast the gingery bed in
>>> aluminium but then stalled. Have cast a few other objects as I
>>> needed them but have always wanted to play with a lathe since taking a
>>> metal working class at school back in the 1970's.
>>> I just lucked out and ended up with a Harrison 300 metal lathe which
>>> has a 3-phase 575volt 3Hp motor driving the spindle. I need to convert
>>> to a single phase motor. A 3hp motor with the same frame size will
>>> cost about $600.00 but I found a 2hp motor for about half that. The
>>> question is-Will a 2 Hp motor give an adequate level of performance
>>> for home/ hobby use considering that the lathe has a spindle gear
>>> range of about 48rpm up to 2400rpm? The lathe is a 61/2inch (13 inch)
>>> by 24 inch size.
>>> I have absolutely no experience running a lathe but I suspect the
>>> smaller motor will work but will limit the size of cut I can take. Is
>>> that correct?
>>> Thanks for any input.
>>> Cliff Swan
>>>
>>
>> [Non-text portions of this message have been removed]
>>
>>
>
> --
>
> Ron Thompson
> On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA
>
> Sometimes you just gotta do what makes you smile.<GRIN>
>
> http://www.plansandprojects.com My hobby pages are here:
> http://www.plansandprojects.com/My%20Machines/
>
> Visit the castinghobby FAQ:
> http://castinghobbyfaq.bareboogerhost.com/
>
> [Non-text portions of this message have been removed]
>
>
>
>
>
> ------------------------------------
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