Running drilling machine motor in absence of 3 phase supply

The Meddings pillar drill which I have been working on is fitted with a 1/2hp Newman 3phase dual voltage motor. After some dismantling and
cleaning it is now wired for 3 phase delta operation rather than star.
However, I'm not sure of the best way to run it from a single phase supply. My memory of three phase theory suggests that a rotary phase converter is basically a 3 phase motor run on 2 legs with some auxilliary starting arangement (e.g. a single phase motor coupled to the shaft). Therefore I suppose one option is to obtain a large surplus 3 phase motor and use it in this way (but at the moment my only 3 phase motor is the one I am trying to run!) and the necessary collection of contactors for the starting arrangement are likely to be somewhat pricey.
Another possibility would be to buy a digital inverter drives, but there seem to be a lot of manufacturers and variables and the provision of additional speed control doesn't really seem that useful on a 5 speed pillar drill (although it would be very nice on my lathe!).
The simplest solution would be to replace the motor by a suitable single phase one of suitable power (e.g. 3/4hp).
Judging by other posts in the newsgroup it seems that the inverter drive method is quite common. Is there been a good introductory article on this approach? Google seems to throw up a lot of manufacturer's publicity, which while useful isn't exactly objective.
Alan
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Alan Bain wrote:

Alan,
Having a delta wired motor opens up all the possibilities 1) Static converter. fixed speed Connect L and neutral to two corners of the delta. Wire a 20uf 400 v motor run capacitor between live and the third corner. In parallel with the 20 uf arrange to switch temporarily a 50uf- 80uf or so 400v capacitor ( I like to use another motor run type here) with a heavy current push button.
Apply the power, push the button until the motor starts, let go when it does. Add all the usual no volt release and fuses. Job done
Capacitor values are approximate. 40uf per hp to run and about 3 x that for starting usually works.
2Inverter provides speed control from say 25% to 200% of motor speed.
Suitable ones can be had used from Ebay for around 50 or 100-150 new.
running much below 25% of rated speed can lead to over heating due to insufficient fan cooling and the motor power out is reduced when running significantly above rated speed. Most inverters give the essential NVR action so the inverter can be wired direct to a 13amp plug. If you have RCD fitted to your mains supplies, then some inverters can trip these.
If you don't need the speed control, then method 1 is simple and effective.
hth
Bob
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wrote:

Can be even simpler than that. Since drills normally start on no load and don't have an awful lot of inertia, you may be able to not bother with the start capacitor at all. Works for my little Jones&Shipman drill.
Mark Rand RTFM
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Mark Rand wrote:

Mark, I find the ability to start without a boost button depends on the belt setting. When I used this method on a 5 speed drill some years ago, it would not start on top speed (3000 rpm from 1425 motor) without boost. Also at that step up ratio, spinning the chuck did not help. Cold weather make the belt stiffer too. But it is horses for courses and the OP might find he can get away without the boost.
I now have a 4 speed (pole switching motor)on a big Pollard pillar drill and use a 1.5hp 2pole idler motor as part of a 415v rotary converter. Unloaded, this motor starts easily on the run capacitor.
Bob
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On Thu, 02 Apr 2009 20:56:35 +0100, Mark Rand

The start capacitor on my cheap old (single phase) bench drill died ages ago. On the rare occasion I need to use it when the Bridgport drill isn't available I give the chuck a quick spin by hand and away she goes.
Peter
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Yup, Do as said in the previous posts and stuff a capacitor out of a florry essence light across the spare phase. Works for me but then I'm of the old school of do it and try it, full speed ahead, 17 fried cats to the pound etc
John S.
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On Thu, 2 Apr 2009 14:08:37 -0700 (PDT), John S

But don't injure yourself by tripping over any discarded H&S inspectors.
Mark Rand RTFM
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No they are all in the suds tank on the old TOS.
I actually had a visit from H&S about 3 years ago. This lady stood at the door, introduced herself and asked if she could come in. I replied no as she had no hard hat, steel toe cap boots safety glasses and haz jacket.
Real reason was she was butt ugly and was frightening the dog............
John S.
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Should have took her picture and pinned it on the outside doors and gates then you wouldn`t need the dog either.
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[cut]
I'll give that a try; I've got some motor run capacitors from old HP hard disks (the sort which look like washing machines) lying around and they should be about the right value.
Thanks for the suggestion!
Alan
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On or around 02 Apr 2009 19:47:46 +0100 (BST), Alan Bain

Also the cheapest, unless you have the bits to make an inverter to hand. Buying any kind of new inverter/phase converter is more expensive than a suitable single-phase motor.
Bought a 2HP high-torque one for my lathe - it's a tad underpowered but I mostly only do light work in it. If I wanted it to perform more like original spec, I could've bought a 3HP or even 4HP, but they cost more.
--
Austin Shackles. www.ddol-las.net my opinions are just that
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Austin Shackles wrote:

I don't know about that - there have been several 0.5-1 HP inverter drives, new, on fleabay for less than 40 recently. I bought one for 19 a couple of weeks ago, one went for 29.99 a few days ago, and so on.
The electronics in an inverter are about the same as a medium-end PC psu, or a 12V-230V inverter - and these are widely available for 15-20-ish, new, manufacturers price.
There's no real reason apart from scarcity why they should cost more than 40 or so, and the usual 90-140 can't really be justified nowadays. Too many manufacturers can say: "Here's a better one for a third of that. How many you want?".
Reminds me of. many years ago, buying digital watches at 19p each in order to get the silver oxide batteries - I was throwing the watches away, thinking I was buying them as old/surplus stock (they weren't actually much good, though they did tell the time) and selling the batteries.
I asked for more, and they offered me a discount, 17p each - but I'd have to wait until they were manufactured!
Gobsmacked doesn't come into it
-- Peter Fairbrother

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On or around Fri, 03 Apr 2009 00:57:15 +0100, Peter Fairbrother

I guess it's easier for lower power requirements. When I was looking into it for around 3HP, they were pricey, new at least, compared with a single-phase motor.
Frankly, unless the motor is odd in some way which makes it hard to replace, I don't seem much point in paying to make 3-phase from single-phase, rather than paying for a single-phase motor. I guess if you had a lot of 3-phase kit, buying one fattish inverter would make sense.
The exception to this is if you want to use the inverter to make an electronic variable-speed machine at the same time, of course.
Was running the Student at 1200 (max speed) for quite a while this evening, and it gets the gearbox casing quite warm. I don't think I'll try making it run any faster...
--
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Alan Bain wrote:

1) buy inverter, they seem to be cheapish on fleabay right now. 2) fit 2-phase motor from lathe to drill 3) fit 3-phase motor from drill to lathe 4) connect inverter between mains plug and motor on lathe
-- Peter Fairbrother

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