3 Phase to single phase

jddevel · Feb 27, 2023

Hi, As a DIYer I`ve quite a bit of wiring up domestic house single phase experience but no 3 phase experience. So I have been offered a two post car lift which currently operates of off a 3 phase supply. I have a brand new single phase 3hp motor which I believe will run the lift but I assume I will need to alter the current operating switch. Advice please. I realise I could buy an inverter and use the existing set-up but my existing single phase motor will just be wasted.

brianmoooore · Feb 27, 2023

If you change the 3ph motor for 1 ph you will need to uprate the contactor and its overload relay. The existing contactor might just have the current switching capacity to be suitable for the new motor's load, although unlikely, and will probably have a 400V coil anyway. The new contactor will need a 230 volt coil
I've had a 3ph ramp running on single phase for over a decade now. The motor was a dual voltage type, so the links were changed from 400V to 230, and with a change of contactor and the addition of a run capacitor, a start capacitor and a current operated switch, i'ts operated faultlessly - last used about three hours ago to change a set of brake pads.

jddevel · Mar 2, 2023

Having decided on a second hand 2 post lift it being 3 phase and my only having a single phase supply I now need pointing to a £ phase converter. The current motor is a Hofmann 3KW running a mechanical screw type lift Holman 2.5 ton lift. I`m purely a classic car enthusiast so it will not be "over worked". Once a suitable converter has been purchased I will get a qualified guy in to sort it.

brianmoooore said:
If you change the 3ph motor for 1 ph you will need to uprate the contactor and its overload relay. The existing contactor might just have the current switching capacity to be suitable for the new motor's load, although unlikely, and will probably have a 400V coil anyway. The new contactor will need a 230 volt coil
I've had a 3ph ramp running on single phase for over a decade now. The motor was a dual voltage type, so the links were changed from 400V to 230, and with a change of contactor and the addition of a run capacitor, a start capacitor and a current operated switch, i'ts operated faultlessly - last used about three hours ago to change a set of brake pads.

Hi Brian, Have decided to look into getting a VFD to run it and asking for advice on which one. Cheers

brianmoooore · Mar 2, 2023

Funnily enough, about two months ago, I decided it was time to bring a 4kW 3Ph air compressor that I have, into use, since the smaller one I've been using is beginning to fail, and bought a VFD to attempt to run it.
This compressor was bought cheap a few years ago, and has stood back in the corner of the workshop, unused, ever since.
So far, my attempts have failed, so I'm maybe not the person to ask. It's a cheap Chinese thing, with all singing and dancing functions, 99% of which I don't need.
There was a thread started on here a couple of days ago about setting up AFDs, but so far, it doesn't seem to have 'taken off'. Maybe post there, and give it a 'prod'.
Note that most AFDs are just phase creators, and not voltage changers, so your three phase motor will need to be one that can be changed (by links in the terminal box) to run on 230V 3Ph as well as 400V 3Ph..

jddevel · Mar 7, 2023

brianmoooore said:
Funnily enough, about two months ago, I decided it was time to bring a 4kW 3Ph air compressor that I have, into use, since the smaller one I've been using is beginning to fail, and bought a VFD to attempt to run it.
This compressor was bought cheap a few years ago, and has stood back in the corner of the workshop, unused, ever since.
So far, my attempts have failed, so I'm maybe not the person to ask. It's a cheap Chinese thing, with all singing and dancing functions, 99% of which I don't need.
There was a thread started on here a couple of days ago about setting up AFDs, but so far, it doesn't seem to have 'taken off'. Maybe post there, and give it a 'prod'.
Note that most AFDs are just phase creators, and not voltage changers, so your three phase motor will need to be one that can be changed (by links in the terminal box) to run on 230V 3Ph as well as 400V 3Ph..

What I`ve in mind is a Transwave converter. Model number STC5. Existing motor is a 3KW 3 phase. The STC5 is rated at a maximum of about 8-9A per phase.

brianmoooore · Mar 7, 2023

That will do the job, but a bit OTT at £1000 or so for DIY use. Surely it would be cheaper to change the motor for single phase?
My conversion was entirely built using bits from the scrap pile, but even if I'd used all new, it would only have been around £100.

mainline · Mar 9, 2023

jddevel said:
What I`ve in mind is a Transwave converter. Model number STC5. Existing motor is a 3KW 3 phase. The STC5 is rated at a maximum of about 8-9A per phase.

You can buy a 4 ton 2 post ramp brand new for £1200 ish.

It would be cheaper and more reliable to convert the ramp to single phase.

InTheHighlands · Mar 12, 2023

I've a bit of experience as a user of 3 phase converters.

As Brian & Mainline say, you'd probably be better off swapping to a single phase motor - and I wonder if you might be able to downsize the motor, if you find a slower running one ie 1400rpm v 3,000 rpm, if the 3 phase motor is 3,000? As it's a hobby car lift, probably not really an issue if it's slow?

Back to 3 phase converters...... One reason for going that route could be if you see yourself buying other 3 phase machinery - lathe, mill, compressor etc. In which case the cost is spread wider - and 3 phase machinery can be a pretty attractive buy. If this appears attractive, I'd strongly recommend looking at the (more expensive) range of rotary converters that Transwave make as they are much more flexible regarding differing loads. Transwave's website is pretty informative - and they are v helpful if you call them up. Rotary converters appear regularly on Ebay.

One word of warning - they need a decent supply, otherwise will stall on starting. Again Transwave's website has information. I've just put in 100m of 16mm SWA to our barn to run one of their 5kw rotary converters. As a backup, I've also put in a 3 phase SWA supply so, if it struggles to start, I can have the converter in the house & run 3 phase out to the barn.

Good luck!