3 Phase Electric

[blueST]

Not sure if this is best in here, or Home Mechanics, hopefully here!

I'm in the process of fitting out my garage/workshop. I've been offered a two post lift at a very reasonable price, but it's a three phase commercial one. Is it going to be practical to get this running at home? I've seen 3 phase converters for sale, but know what I'm looking at.

Something like this would be affordable but the warning in the description seems to suggest it's not suitable http://www.clarkeinternational.com/shop/product/de...

This item might be man enough, but these rotary ones are very expensive, and it would just be cheaper to buy a lift that's already single phase. http://www.clarkeinternational.com/shop/product/de...

So, first question, can anyone confirm whether the first item listed is indeed unsuitable? If it is unsuitable, are there any more cost effective alternatives to get the lift running? For example, is it possible to convert the lift from 3 phase to single phase easily?

If I can sort this out, it may help me out when I'm looking to buy a lathe too, as they are mostly 3 phase.

[blueST]

Just to add, I've also seen this item http://www.ebay.co.uk/itm/3-HP-DIGITAL-240V-to-415...

It's 3hp, and a bit cheaper than the Rotary one above. I dont know how many HPs the lift needs but ones that provide less HP are cheaper still.

[vdp1]

Why not just put a single phase motor on the lift. You can get some fairly meaty ones.

[blueST]

vdp1 said:

Why not just put a single phase motor on the lift. You can get some fairly meaty ones.

How easy is that? Will all the switchgear work? Is the rewiring straightforward? I actually used to buy and design around these motors but never had any involvment with the wiring side.

[GnuBee]

I've "converted" a lathe and a mill to single phase using digital inverters. You need to get a look at the motor rating plate and confirm whether it can be wired to 220V delta and if so you can use the cheaper digital inverters. This site has good information about choosing and the pros/cons of the various types http://www.drivesdirect.co.uk/how_to_choose.htm

I quickly decided against the "just bung a single phase motor in" because it's very rarely that simple - you could/will end up fabricating new mounting points.

For the potential lathe conversion I'd definitely suggest going down the digital inverter route - you'll end up with fully variable speed control.

[kimducati]

GnuBee said:

I've "converted" a lathe and a mill to single phase using digital inverters. You need to get a look at the motor rating plate and confirm whether it can be wired to 220V delta and if so you can use the cheaper digital inverters. This site has good information about choosing and the pros/cons of the various types http://www.drivesdirect.co.uk/how_to_choose.htm

I quickly decided against the "just bung a single phase motor in" because it's very rarely that simple - you could/will end up fabricating new mounting points.

For the potential lathe conversion I'd definitely suggest going down the digital inverter route - you'll end up with fully variable speed control.

Be very careful with your inverter selection if you do go down this route. I was involved in trying to get a similar setup working a few years ago and although the inverter was rated sufficient for the motor load, it was impossible to get it to restart if you stopped half way up, if you see what I mean. You had to go all the way down again and re start, the fraction of a second of 'slack' in the lifting jacks was enough to get the motor running. It didn't matter what you did with the inverter settings, it just wouldn't work. Eventually fitted a much higher rated inverter and it was OK.
IF it's possible, I'd swap the motor and rewire the starter, but be careful, single phase motors haven't got a lot of startup torque, you have to get the correct type for a high torque application. Contact a decent electric motor specialist with all of the details of your motor (mainly kW rating, speed & frame size) and they may well be able to supply a matching frame size motor in single phase. If the motor is the same frame size, it WILL fit onto the existing brackets, so no mods required there.
You'd probably need a new overload for the starter as well as possibly a coil, and it would need rewiring to suit the single phase supply - all easy enough stuff, if you know what you're doing, but DANGEROUS if you dont, so don't take chances.
hth

Kim

[blueST]

Thanks all, this is very interesting stuff. Although that last post is making me wonder if this is going to be worth the hassle, and wind up costing me more than just buying a brand new single phase lift.

Now the lift itself is likely to be very cheap, problem is I can't view it before I buy due to where it is. Getting any info about is not easy either, I'm buying indirectly off a friend of a friend, and none of those people have any idea about it, they just want it gone. I'm going to see if I can get someone to take a photo of the motor plate and go from there.

[kimducati]

It'll be worth it, as long as you get the ramp at the right price - factor in the likely cost of the conversion to single phase and do the maths. A new single phase ramp would be at least 2K, at least the last time I looked they were.
BTW I assume that you've got a thick enough concrete base slab to set the base on to - there's a lot of strain potentially going into the base. If you're not sure, a four post lift may be a better bet.

Kim

[blueST]

The lift itself should be under £400, but I've got to dismantle, transport etc. All I've seen is a photo and a measurement of the height? I had thought about the floor already, I've not done a test drill yet but it's on the list. Need to find out what thickness I need.

[RoBe427]

Electric motors draw a very high starting current this is why you would need an inverter with a larger output than the motor data plate states. Three or four times more in some instances. Probably require C or D type circuit breakers as well.

[blueST]

For arguments sake then, say the lift motor(s) require 3kw what sort of inverter would be suitable? I don't know the exact spec of this lift but looking at others on the net, that seems like reasonable ball park figure.

3kw is about 4hp. From the info above I guess a 5hp inverter might not have enough power get the loaded motor started. A 7.5hp inverter is about £900 and thats before I've paid an electrician to connect it up. In this case the cost is getting dangerously close to the cost of buying a new single phase lift.

Maybe converting it to a single phase motor is more cost effective. But I'd have to get someone to rewire it, unless there's a clear guide somewhere on how to do it yourself.

Edited by blueST on Thursday 31st January 12:49

[RoBe427]

I think you will find they have a maximum constant load and a maximum intermittent load, so i would imagine you need something capable of handling the starting current of the motor as an intermittent load. You would need to check with the inverter manufacturer.

Think the inverter would go into alarm and shut down if operating above its rated output.

[kimducati]

RoBe427 said:

I think you will find they have a maximum constant load and a maximum intermittent load, so i would imagine you need something capable of handling the starting current of the motor as an intermittent load. You would need to check with the inverter manufacturer.

Think the inverter would go into alarm and shut down if operating above its rated output.

The problem with starting a motor under full load with an inverter in this application is that they are usually a 'soft start', not an instantaneous full voltage like a starter. This is great for a centrifugal pump or a lathe, these start at minimum power consumption, which builds up as the speed increases, but not for a car ramp which needs to overcome the break out torque of the jacks before the motor can turn at all. What happens is that the inverter powers the motor up to its rated maximum amps (and beyond for a limited period) but if this isn't sufficient to turn the motor under the strain of the jacks, the whole lot just sits there and hums.
btw the starting current of a single phase motor is mahoosive - a spike of something like 8 - 10 times the rated full load current of the motor iirc. A 3 phase motor direct on line starting current is something like 5 - 6 times flc and star-delta starting is 2.5 times flc. Having said that, a correctly specced inverter would allow for these spikes within the programming, the problem comes when your dealing with an application like this.

Kim

eta I doubt if the motor is more than 1.5 or 2.2 kW at the most.

Edited by kimducati on Thursday 31st January 17:41

[robseagul]

Just be carefull chap.i have removed lifts because they are dangerous and shouldn't be used .if it was me and I don't like to spend I would spend a little extra for a sound tested unit which will then give you good(safe) service..just a thought..r

[blueST]

robseagul said:

Just be carefull chap.i have removed lifts because they are dangerous and shouldn't be used .if it was me and I don't like to spend I would spend a little extra for a sound tested unit which will then give you good(safe) service..just a thought..r

I know the lift is not very old and should have been properly maintained, so I don't think there is much risk there.

The only concern I have is my abiltiy to get it functioning on the electrical side. It's going to take me a week or so now to get any info on the motor, so there wont be any progress on that front for a bit. I'm going to ring one of the inverter supplers tomorrow and just try and get some general advice.

[robseagul]

That's fair enough.i was just airing on the side of caution.i had my inverter from direct drives which I can vouch for.cheers.rob

[blueST]

robseagul said:

That's fair enough.i was just airing on the side of caution.i had my inverter from direct drives which I can vouch for.cheers.rob

It's a fair point A tonne and a half of Focus is not something you want coming down on your head.

It's Drives Direct I'm planning to ring tomorrow, good to know that someone else has dealt with them. I've noticed that their inverters can give up to 150% of max load for short bursts to help with starting. I'm also hoping that the lift has a dual voltage motor, as that will help bring down the cost of the inverter too.

[ch427]

i might be missing something here but isnt the lift hydraulically operated?
The motor shouldnt have a huge load on it and may not require any sort of inverter or soft start.

Edited by ch427 on Friday 1st February 16:09

[kimducati]

ch427 said:

i might be missing something here but isnt the lift hydraulically operated?
The motor shouldnt have a huge load on it and may not require any sort of inverter or soft start.

Edited by ch427 on Friday 1st February 16:09

They're usually operated by a threaded block running up & down a long threaded rod in each leg.
The inverter was to create a spoof 3 phase supply from the 1 phase which the op has available.

Kim

[Steve H]

I've got a three phase two post hydraulic ramp running on a converter and it's been going strong for about ten years now. I got the converter from Machine Mart for about £3-400 I think, not exactly the same as the stuff you've linked to but probably the equivalent thing.

If I were doing it now though I'd be looking at something like THIS, amazing value and pretty decent quality from the ones I've seen.