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Post by joanlluch on Oct 7, 2015 6:36:38 GMT
It is true that an inverter will give 3 phase power in the home but not , as far as I am aware , for 440 volt 3 phase motors as fitted for industrial use. Hi Abby, as Roger already implied, all 3 Phase motors are rated at two different voltages depending on how you connect them, Star or Delta. So a motor for use in Europe can be rated at 660/400V 50Hz or 400/230V 50Hz (In the UK voltages are slightly higher, but the concept is the same). As long as your motor is rated 400/230V, you can use it on your 220V mains (or 240 in the UK) with a 2 Phase inverter. Chances that you can use an inverter with your lathe at home are high because of this : - Only motors above 15Kw tend to be rated 660/400, your lathe will most probably have a motor rated 400/230 - Even if you had a 3 Phase current contract at home, the electric company would supply you 400V, not 660V, so there's no point anyway on having motors rated 660/400V. Thus common small motors are still rated 400/230V. - You can buy an inexpensive 2 Phase, 230V inverter, which will output 3 Phase 230V current. - You connect the input of your inverter to your 2 Phase, 230V home mains. - You connect the output of the inverter to your 400/230V 3 Phase rated motor by using a Delta configuration. [Note that I referred to the voltages common in continental Europe because I'm not sure about the exact figures in the UK for the highest ones, but the discussion is the same] I hope this is helpful and clarifies things.
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Post by joanlluch on Oct 7, 2015 6:48:27 GMT
You can get 440 Inverters but they are very expensive. I've got lucky with several 440V motors which turned out to be universal types that could have their internal connections swapped from Star to Delta so I could use them with a standard inverter Hi Roger, I would be highly surprised if the rating of common 3 Phase motors in the UK was not 440/240V. So I don't think you have been lucky, but you just found the most common thing.
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Post by Roger on Oct 7, 2015 7:08:26 GMT
You can get 440 Inverters but they are very expensive. I've got lucky with several 440V motors which turned out to be universal types that could have their internal connections swapped from Star to Delta so I could use them with a standard inverter Hi Roger, I would be highly surprised if the rating of common 3 Phase motors in the UK was not 440/240V. So I don't think you have been lucky, but you just found the most common thing. Hi Joan, The reason I think I was lucky, was because the motors are on my Jones & Shipman tool and cutter grinder which is very old. It would have been difficult to change the motors on that because the frame sizes are obsolete. Modern motors are more likely to be universal types, yet the one on my Mill was 415V only, and that's a much more modern machine. In that case I swapped the motor for a universal one a friend didn't need. With older equipment, it's just the luck of the draw as to whether you can use them with 220V 3-phase or not.
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Post by joanlluch on Oct 7, 2015 9:13:09 GMT
Hi Roger,
I understand frame sizes for old motors may not follow current standards so you may not be able to replace them, but in fact that's not the point.
So, I am confused about what you say about old motors and "universal" types. To my understanding, all 3 phase motors -old or new- can be wired as Star or Delta. In my Country -and everywhere in continental Europe- 3 Phase motors are either rated 400/660V or 230/400V. Some OLD motors are rated 380/600V or 220/380V but nothing happens if you connect them to 400V or to 230V with Delta configuration because their electric isolation is more than enough for that voltages. In fact they are rated to much higher voltages if you connect them as Star. I am aware that voltages in the UK are slightly higher for some reason, but I do not see why that makes a difference.
I mean it is totally safe to make a Delta connection to these motors, provided you never pass their rated current or overload them above their rated power. Please, can you clarify your post?. Particularly what's different from an OLD 3 Phase motor compared with a new one from the point of view of connections?
Thanks
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Post by ejparrott on Oct 7, 2015 9:20:21 GMT
Not that the voltage of motors has any bearing on the question that was originally posed
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abby
Statesman
Posts: 927
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Post by abby on Oct 7, 2015 11:22:41 GMT
Joanlluch I haven't the knowledge to argue with your explanation , however I have 2 lathes both of which I retro fitted with new 3 phase motors of around 0.5 hp. The original 3 phase motors had to be replaced because they could not be run from an inverter on domestic mains supply. This information was supplied by a manufacturer so I presume it was true. As an aside I have replaced my milling machine motor with a DC unit taken from a no longer used treadmill. Dan.
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Post by joanlluch on Oct 7, 2015 11:36:53 GMT
HI Dan. I am talking from my experience. So I don't know why your motors could not be run with an inverter. My understanding is that for a motor to be powered through an inverter the only requisite is that it is a 3 phase motor. In some cases the motor requires separate air cooling, specially if it is to be run at very slow speeds, but as far as I know this is the only requisite. Some motors intended to be used with inverters incorporate a temperature probe in them, but that's just an add on, not that any standard 3 phase motor couldn't be run with an inverter.
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Post by andyhigham on Oct 7, 2015 12:34:39 GMT
Some of the older small three phase motors connected the "star point" internally rather than bringing the wires to the terminal block. Therefore they could only be run on 400V
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Post by joanlluch on Oct 7, 2015 13:16:32 GMT
Some of the older small three phase motors connected the "star point" internally rather than bringing the wires to the terminal block. Therefore they could only be run on 400V Ok Andy, that clarifies it for me. I don't think this was ever the case in my country, but maybe I just have never looked at old enough motors, or they not were small enough.
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Post by ejparrott on Oct 7, 2015 21:49:20 GMT
PB102 doesn't care what voltage you use when you want to drill it.....
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jma1009
Elder Statesman
Posts: 5,901
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Post by jma1009 on Oct 7, 2015 21:57:57 GMT
Ed,
i agree entirely! this must rank as one of the most extreme 'off topic' discussions on this forum that does nothing to help Reg drill PB! use a sharp new drill with the lands backed as off for brass. it will cut cleanly and easily with no hassle or angst! you will get a nice constant spiral of swarf if you keep up the pressure. ok, reaming speed for brass and bronze, but not too slow a speed!
cheers, julian
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Post by springcrocus on Oct 7, 2015 22:39:35 GMT
If you sharpen the 240 volts slightly off-centre, then the hole will probably turn out to be inverted. And, to a chemist, Pb is Plumbum (lead) which is a crappy material for anything except ballast anyway!
Steve
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Post by andyhigham on Oct 18, 2015 19:57:59 GMT
I have just rough turned a spacer/thrust bearing for my BSA. 34mm dia PB102 drilled/bored 5/8", turned to 1 1/4" dia x 3/8 and 3/4" dia x 1 1/2". I centre drilled, drilled 6mm x 60mm then drilled 15mm. Tomorrow (when it cools down) I will take the final cut on the diameters and finish bore the inside. Then I will start on the second one
The lathe, Harrison M300, coped very well, no doubt a "model engineers" lathe would have struggled. The swarf and the part made some lovely colours.
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