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How effective are phase converters

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Richard Arwel Jones07/01/2018 14:08:18
2 forum posts

Hi all, I am new to the site but have been subscribed to the magazine for two years or so. I spent 8 years in engineering when I left school but made a change in career . I am still very interested in engineering and keen to expand my collection of engineering tools and machinery. Hope to do a lot more when I retire in a few years. In the meantime I am in the process of setting up the workshops and was wondering if anyone has any views/experience with the above. I have requested a quotation from the local electrical board but I am expecting a high quote but worth asking just in case anyway. Kind regards Richard

vintagengineer07/01/2018 16:06:54
avatar
468 forum posts
6 photos

I have a Transwave rotary inverter and other than being noisy it's very good.

Tim Stevens07/01/2018 16:46:41
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1049 forum posts

I have a Transwave Jaguar Inverter to power my lathe, and it seems to work perfectly. Quiet, except for sizzles on Radio 3. If you want to run everything you have on 3-phase, a rotary is better, but for a one-off machine (as I have) the Inverter is recommended.

Cheers, Tim

Spurry07/01/2018 16:47:41
162 forum posts
58 photos

Another vote for a Transwave rotary. The local electric company wanted circa £65K to supply 3 phase. I was a bit lucky in getting a 100A main fuse in place of the 63A. surprise

The inverter works very well, it is not load dependent as are the static ones. Have to agree that the only downside is the noise of the thing. I moved it to another room, so not quite so bad. Just turning the radio up a bit, helps though.

Pete

steamdave07/01/2018 16:57:42
413 forum posts
34 photos

Most machines can be powered by 1phase - 3phase Variable Frequency Drives (VFDs), with the VFD wired into the ring main, provided the motor power isn't above about 3h.p. I have 3 VFDs: 2 driving 3 h.p. motors are wired separately to high current circuits (30 amp breakers) and the 3rd with a 2 H.P. motor is connected to the normal ring main.

Cost of a VFD is not a lot, just have a look at eBay. One possible disadvantage of the VFD route is that you will need one VFD for each motor, but still probably cheaper than getting the local electrical board involved.

Dave
The Emerald Isle

Thor08/01/2018 05:44:40
1102 forum posts
31 photos

I too have a Transwave VFD powering my 290 lathe. It has worked well for five years, well worth the money I paid.

Thor

John Haine08/01/2018 08:54:42
2577 forum posts
133 photos

More than one post on various threads here talk about sharing inverter across several motors. And vfds can be had relatively cheaply on eBay. Time to bury the rotary converter imho.

Chris Evans 608/01/2018 09:51:55
1442 forum posts

I run my 3HP lathe from a Transwave static inverter and my 2HP Bridgeport mill from a cheap Chinese (£90) VFD.

One day I will get the motor off the lathe and see if the "Star Point" can be found to enable me to run from a VFD as I would like the feature of being able to slow the lathe down. Other than that the static inverter works OK, but for some reason the Bridgeport did not like running off it hence the VFD.

MalcB08/01/2018 10:00:34
251 forum posts
29 photos

One thing that does meed mentioning is that the Transwave Rotarys can also take up a lot of space in a workshop. If space is at an absolute premium then that may well be an important factor as you can get a compressor in a worksop in the space that a rotary will take for example. A VFD takes absolute minimum space.

Edited By MalcB on 08/01/2018 10:01:05

Spurry08/01/2018 10:26:09
162 forum posts
58 photos
Posted by John Haine on 08/01/2018 08:54:42:

More than one post on various threads here talk about sharing inverter across several motors. And vfds can be had relatively cheaply on eBay. Time to bury the rotary converter imho.

That's an interesting observation. Would a vfd supply allow the powered drawbar, machine light, and X drive motor to used without the main spindle motor rotating?

My machine (in gallery) was only available in a 3 phase version unfortunately. The pic shows the rotary next to the machine, before the noise became too intolerable.

Pete

SillyOldDuffer08/01/2018 11:32:43
4536 forum posts
971 photos
Posted by Spurry on 08/01/2018 10:26:09:
Posted by John Haine on 08/01/2018 08:54:42:

More than one post on various threads here talk about sharing inverter across several motors. And vfds can be had relatively cheaply on eBay. Time to bury the rotary converter imho.

That's an interesting observation. Would a vfd supply allow the powered drawbar, machine light, and X drive motor to used without the main spindle motor rotating?

My machine (in gallery) was only available in a 3 phase version unfortunately. The pic shows the rotary next to the machine, before the noise became too intolerable.

Pete

I did some web research on this recently - basically reading VFD manuals. With my usual efficiency I've lost the notes but the gist was:

  • A couple of manuals explicitly saying "don't''
  • Most manuals fail to say anything about sharing one way or the other, but the wiring instructions all show only one motor attached
  • The few manuals that explicitly said sharing is allowed were all for big VFDs, several kW. When you get to the very large units used for Hospital emergency power etc they all do it.

I don't think you can generalise, there are lots of different VFDs about especially at the cheap end. I guess what's going on is that small VFDs are normally used one-per-motor. Dare I suggest that designers don't expect small inexpensive VFD's to support sharing? The electronics may cope, or they may not.

When only a few machines need 3-phase, it's straightforward to fit one VFD per motor and only a cheapskate enthusiastic cost-cutter would want to share. However, in a larger workshop, it soon becomes far more convenient to plug existing kit into a shared VFD behaving just like an ordinary 3-phase supply. I think that's why big VFDs do support sharing. They aren't cheap though.

The risk of sharing a VFD inappropriately is that it either won't work properly or goes pop, not that it's dangerous. Being careful with money myself, I'd be inclined to try sharing a small VFD if I owned a mix of older kit. My gut feel is there's a good chance of success and people have done it. I'd be ready to write-off the cost if it went wrong though. No whinging about poor quality, delicate electronics, or money wasted after you chose to walk on the wild side!

Dave

larry Phelan08/01/2018 12:32:12
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544 forum posts
17 photos

Hi Spurry,

Looks like your lathe is on wheels,is this correct?

larry Phelan08/01/2018 12:47:10
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544 forum posts
17 photos

To answer the question,"Are they effective" ? The answer must be yes. Are they expensive ? That depends on how much it would to get a 3 phase supply [unless it passes by your door,dont even ask !]

It,s a case of,how long is a piece of string ?. If you have a number of machines to operate,a good sized converter is the way to go,just set it up and forget about plugging in this and unplugging that,and messing around trying to balance loads. I have a 10HP unit and I just switch on whatever I need to use,sometimes two or more,if I have over to visit.

Buy a fair sized unit and I doubt if you will regret it.

Good luck.

Larry.

larry Phelan08/01/2018 12:49:00
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544 forum posts
17 photos

Should read if I have a friend over to visit !

Old age is a curse !!

ega08/01/2018 13:00:02
1216 forum posts
101 photos

SillyOldDuffer:

VFD sharing: when I converted my S7 with the Newton Tesla "turnkey" package they were happy to sell me a second 3ph motor to replace the 1ph motor on my mill/drill. These stand next to each other with the control box accessible to both and unplugging one and plugging in the other is the work of seconds.

This arrangement has worked well for me for several years

Rod Renshaw08/01/2018 16:23:24
45 forum posts

Hi all

VFDs are the way to go, the variable frequency aspect is enough to make them more useful than earlier types of converter.

The ability to vary the speed of the cut at the twist of a knob is a huge time and irritation saver - it almost eliminates the need to shift belts or gears, and it can be done even during the cut to improve the finish and eliminate chatter.

I used one VFD for both lathe and mill back in the day when VFDs were much more expensive. I used plugs and sockets to "switch" between machines and I did not hurry the changeover. I think this helped to reduce any chance of damage by voltage spikes and I had no problems. Worked OK in a one-man amateur shop where it typically takes much longer to tool up the "new" machine and transfer the workpiece than change the plugs.

Rod

vintagengineer08/01/2018 17:21:54
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468 forum posts
6 photos

Will they run a 3 phase mma and tig welder?

 

 

Posted by John Haine on 08/01/2018 08:54:42:

More than one post on various threads here talk about sharing inverter across several motors. And vfds can be had relatively cheaply on eBay. Time to bury the rotary converter imho.

 

Edited By vintagengineer on 08/01/2018 17:24:05

Roger Williams 208/01/2018 17:34:41
331 forum posts
1 photos

John Haine, with all due respect, burying the RPC is really not an option if you have a Hardinge HLVH with a dual speed motor, unless you really know what you are doing with VFD's !!. Unless you can afford 3 phase in your workshop.

Mark Rand08/01/2018 20:19:23
729 forum posts

My HLV (no -H), Beaver VBRP, J&S 1400 grinder are quite happy running individually and together off a single VFD with DOL starting. Of course, it is a larger one. Look out for Danfoss ones on fleabay, they do nice kit

Haven't bothered with the welder, most will run happily off single phase even if they need 415V.

Ray Sub08/01/2018 20:27:05
5 forum posts

I run a SMP Digi phase 7.5 hp rotary converter, can run as many machines together as I wish plus welder. It is enclosed in its own unit so in my opinion quiet enough and not at all intrusive.

Only drawback is initial cost, otherwise very happy with it, run a ring main and draw off as many machines as you want within its capacity, simples!

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