Using single phase to run a 3 phase car lift.

[andyborris]

A local group have a large workshop with a 2 post car lift, which I can use for a very small fee (£25 a year!) , the only drawback is that it doesn't work !

However, it's only because it's a 3 phase motor and the workshop only has single. I've looked on-line and found "Made in China" Variable Frequency Drives, Like this

Anyone know about these? Do they work, are they reliable and how hard/easy to wire are they?

It's worth £70 to me to get it working.

Thanks

[dazcapri]

I'd ask Dez I'm sure he's answered that before

[vitesseefi]

That, or something like it should do the job. Just be aware that you may need to go up a size on the inverter relative to the motor in order to get enough starting current/torque. Inverter manufacturers discriminate between “variable torque”, which is things like centrifugal pumps and fans, where initial torque is v8 low but builds with rpm, or “constant torque” where torque is high from 0 rpm like compressors, PD pumps and (probably) hoists.

[Dez]

Don’t buy a cheap inverter and expect it to work. Even the expensive ones usually can’t push the figure they claim. I know a couple of people who have considerable sums with ‘brand name’ ones and been let down on performance. In the long run a new motor is nearly always a better investment.

Simply, you can’t break the laws of physics. You need to check what power the ramp requires to lift a given weight and work backwards from there- a ramp mechanism is just a mechanical torque multiplier, either by hydraulics or gears, so it has a ratio linked to the motor power output to give its weight rating.
Most domestic supplies can’t run a motor bigger than 4hp at startup load- startup is really important on a ramp as you’re instantly requiring full torque when lifting a loaded ramp.

For example, I have a 5 ton 4 poster than I can’t run on single phase as I need a 5.5hp motor. But I can downrate the ramp to 3.5t and it will work with a 4hp motor.

So start with the existing motor spec plate and work from there.

[andyborris]

Thanks chaps.

I'll investigate getting a new motor. Got to admit that I'm way out of my depth here!

[brachunky]

Nov 21, 2023 9:29:58 GMT andyborris said:

Thanks chaps.

I'll investigate getting a new motor. Got to admit that I'm way out of my depth here!

I'm in the exact same position as andyborris both as in skillset and a 3 phase motor dilemma!

Interestingly, I have had a conversation with two individual electricians (the one being a factory sparky) who both informed me that the 3 phase motor could be connected to run off a single phase. I don't know if this would affect the motors torque or speed as I imagine there would be some or other trade off.

[crockpot]

As Dez said 4hp is the limit. Also can it be wired in delta which is required for a single to three phase inverter.
Some of the Chinese inverters have been used by guys on the MIG welding forum. Worth a look as there is a good pool of knowledge on there about them. I can't comment on them as I use a Moeller inverter.

[slater]

A Chinese inverter will run it fine. Yeh they arnt great quality but they work. You just need one thats big enough for the job and supply it with the power required. Overspeccing will help offset the quality somewhat!

Switching to a single phase motor would work too but bare in mind it will need to be a motor big enough to do the job too so weigh up the costs.

I find single phases motors can be as faffy as VFDs tbh. Lots more to go wrong than a 3 phase.

[ejenner]

Is there a difference between direct drive motors and motors which are running a hydraulic pump? My hoists when I had my workshop all ran on single phase but were hydraulic pump systems rather than direct drive worm gear type.

[andyborris]

Nov 21, 2023 9:29:58 GMT andyborris said:

Thanks chaps.

I'll investigate getting a new motor. Got to admit that I'm way out of my depth here!

When I say "out of my depth here", you've lost me!

What's "wired in Delta" mean?

And how I can tell what size Chinese inverter I need and they seem to have a lot of connectors for wiring too!

[crockpot]

www.electronicshub.org/comparison-star-delta-connections/

To be blunt, if you don't know the difference between star and delta motor wiring and think inverters have lots of wires this may be a time to find someone local who can guide you and offer practical assistance. This is not a subject to be taken lightly, this stuff can kill.
If I've read it wrong then my apologies.

[homersimpson]

Nov 22, 2023 16:20:03 GMT andyborris said:

Nov 21, 2023 9:29:58 GMT andyborris said:

Thanks chaps.

I'll investigate getting a new motor. Got to admit that I'm way out of my depth here!

When I say "out of my depth here", you've lost me!

What's "wired in Delta" mean?

TAnd how I can tell what size Chinese inverter I need and they seem to have a lot of connectors for wiring too!

Three phase supplies are wired in two ways, star or delta, star is basically three lives and a neutral whereas delta is just three lives and no neutral.  Any three phase load that is balanced (has the same current on each phase) does not require the neutral and motors generally fall into this category.  In star the current on each phase is lower but so is the output (torque) of the motor and in delta the current per phase is higher and so is the output of the motor. 

It used to be quite common to start bigger motors in star and then switch them to delta (star delta starter) to reduce the inrush current when first started, the downside of this is the motor power output is lower initally which might not work on ramp.  This of course has nothing to do with using the motor on a single phase supply.

A motor that can be wired in either star or delta will generally have six terminals and links inside on some of the terminals that change it from star to delta.

If you use an inverter then as above get one thats going to be a little bigger than you need, also bear in mind that if the motor needs a 16A three phase supply it will need a supply of at lease 48A (nearest probably being a 63A circuit breaker) to provide the same power at single phase.

I fitted some inverters to some reasonably large portable extraction fan systems at work as they were three phase and only single phase sockets were available, I recall we had an issue where the control system on the extraction unit was linked between one phase and neutral and this didn't work correctly as one of the phases that the inverter created was effectivly 0V and we therefore had to swap the phases along one for it to work (i.e. 1 became 2, 2 became 3 and 3 became 1).

One thing to know about three phase motors is that if you reverse any two of the phases the motor runs backwards, its amazing the number of electricians I meet that don't know this.

[homersimpson]

This was the one we used but interestingly it mentions that its not suitable for car hoists due to the inrush current so perhaps time to get a new single phase motor instead:-

www.machinemart.co.uk/p/pc-60-5-5hp-phase-converter/

[ivanhoew]

if using a single phase motor , you could down gear the ramp , it'll be slower but work with a lower output motor .

[vitesseefi]

Andy,

We could really do with a pic of the existing motor nameplate. This will give us the power rating, number of poles, supply voltage options etc. We can also work out its running and starting torque ratings.

If it’s sat there unwired then a pic inside the terminal box would help too.

We could also do with knowing whether the hoist is hydraulic. jack-screws or whatever.

The real point about star and delta in this context is that 3 phase motors can be wound/wired either for 3 x 400v, or 3 x 240v. Many of the better ones can actually be swapped from one to the other by repositioning links in the terminal box.

The important thing from your point of view is that it must be 240v capable. An inverter can make more phases, but it can’t make more voltage.

Single phase motors….. in my world of pumps at least are always bad news, usually used by farmers in dank places connected to dodgy rural mains by several hundred metres of damp string (or caravan extension cables) so all kinds of start problems due to bolt drop. Anyhow, the ones with decent start torque are the capacitor-start, capacitor-run ones. These are not the cheap ones.

[kevins]

I converted my 4 poster 15 years ago by fitting a similary rated single phase motor and contactor, but since then we have aslo converted a couple of 3 phase wood working machines (5hp planer and a 1/2 horsepower band saw) both work fine with a chinese inverter, we did choose one well above the rating of the motors though, for these machines the inverters are great becasue they give you variable speed as well.

[andyborris]

Thanks everyone.

I think I'm in well over my head here, so unless I can find a sensibly priced single phase motor that'll fit (and live with a slower running lift), I'm going to step away from it.

The lift is in a huge polytunnel and there's carpet on the floor, so I'll be warm and dry, it's just the knees (and everything else!) that slow me down!

Of course I'm assuming that a single phase motor is relatively easy to wire?

[kevins]

aside from matching the mounting flange and shaft size the only issue is if like my Tecalamet one and the motor is switched by a contactor or relay which is rated for 415V, you will need to swap it out for a 240V one, it was easy enough to find a 240V version of the same part on ebay though.

If you go the inverter route it wasn't too bad but as most of them put out 3 phase 240V you do need to convert the 415V motor from star to delta (usually just a matter of swapping connections in the junction box on the side of the motor)

[carat 3.6]

Forgive me for asking but are you sure the workshop doesn't have three phase? Most do even if the board isnt.

[andyborris]

Thanks for everyone's help and advice.

Unfortunately, I've run into politics and I'm no longer going to be involved.

It was a nice dream, while it lasted, but because we're new in the village we have no wish to "step on toes" or "take sides".

So I'll quietly forget it.

Thanks again everyone for your advice and time.