Hard start 3 phase motor

[SomeoneSomewhere]

Yes, there are electrical issues.. that #14 wire being used as a current-limiter or even "fuse" ....at the top of the list.



That said, I suspect you ALSO have mechanical issues.

Cumulative wear... damage.. lube fail... distortion under load? Something that is causing binding when heavily loaded, such that the actual "present-day, REAL capacity", not the "as new, CLAIMED" capacity .... is being overly stressed mayhap?

"Heavier load" is exactly what it says it is, but there should otherwise not be THAT 'dramatic' a difference between initial lift, and resumed lift.

IF... it needs new parts... or is over-stressed, in general?

A whole 'nuther lift could indeed be cheaper and faster than the cost of f**k-around time and money with this one..

Dig deeper, first, into the source of the difference..

2CW

I suspect that 'initial lift' is lifting only the weight of the actual lift, and picks up the vehicle while already moving - there will be 100mm or so of travel where the load increases as the weight transfers from the vehicle's suspension and tires onto the lift arms. As long as full load torque (actually breakdown torque) exceeds the load torque, the motor will be fine.

Trying to start the lift while already elevated means that the motor means that the motor needs to supply adequate starting/pull-up torque to move the car. Single phase induction motors, including three-phase motors fed via phase generators, are notoriously worse at providing starting torque compared to full load torque.

 

[Froneck]

Looking at your 5HP lift motor, does it have a brake on it? It will look like a small motor attached to a standard 5HP motor. It will have an electrical connection to remove the brake when powered, if you do have a brake mounted of any other brake be sure it is wired to single phase line voltage and not connected to RPC created leg!
The situation that the motor will not start when attempting to use down makes me think there is a brake activated.

 

[SomeoneSomewhere]

For-sure!

It's actually a nachural tasking for a Dee Cee motor, if not hydro-holics... air-over, or 'straight' AIR.

How did I know we'd get that comment from you! But yeah. Three phase DoL probably is fine too as long as you have a nice stiff supply, given the manufacturer used that originally.

By straight air do you mean a pneumatic motor driving the shaft, or an actual pneumatic cylinder? The former would work (albeit inefficiently); the latter seems... bouncy.

 

[Froneck]

I agree AC motors have a limited starting torque but I have 2 friends that have lift that uses screw to lift. One is about 5 years old purchased new and works great, other works in a shop that also has one and is quite old. Both have single phase motors and I've seen 3/4 ton full size Pick-up trucks on them, work with no problems!
I've seen my friend put transmissions and some motors in cars by lowering them onto the replacement and when stopped there is no over travel, I'm sure there is some but it's not very much so there must be a brake someplace! It is very possible the break is not being released due to low voltage!
A rule of thumb with all RPC use is to be sure all single phase devises used on the line be connected to the direct single phase line and use the created phase for only devices that require the additional phase.
It may not be the problem here but it is something that should be checked!

 

[johansen]

Definitely mechanical issues. Not sure how fast a normal lift is, but 1 HP can life a 5500 pound car, one foot in 10 seconds.

Acme thread is over 50% friction, so 1 foot in 25 seconds minimum.

Then another 10% for mechanical friction between motor and screw.

1 foot in 30 seconds per hp. You have 5hp, it's not getting to the screw.

 

[Froneck]

Mechanical issues point to a brake not working though it could be something else. Up and down force required is different. For example when cranking my mill table up it requires a bit of force but down I can simply put one finger next to the handle and easily move it down. The problem the OP has is when the lift moves a car up it will not restart to move it down or up. Last week I fished a job for my customer that purchased Baldor 3 phase motors that came with 7/8" shaft, I was told 5/8" shaft size was availble but not for 18 weeks. So I was told to turn-down and key 3 new motors that were complete with brakes. The brake was released my a coil that is in the same configuration of an electrical contactor but does not pull contacts close, it's attached to the brake release lever. As most know it takes more energy to energize a contactor than is required to keep it closed. In addition it may take more effort to release a brake holding a load than without a load. I'm thinking it's possible a brake can't operate as it should when voltage is lowered due to loading. Fixing that problem if it exists may not fix the up but should allow down to work.
As I mentioned I would start by determining if there is a brake and if it is powered by the single phase 2 wires of the 3 supply wires.

 

[Gpzmax]

Hi Gpzmax.
I think you would do best using your 15HP Ronk with proper valuing of the capacitors and transformer taps. The
autotransformer method is by far superior to the Idler type RPC for high torque starting. With starting capacitor values
(in microfarids) if too low it will not allow the motor to start and when too high the amps are excessive for no gain.
The manufacturers name was Add-A-Phase before it was RONK.
And please let us know when you get this sorted out and your hoist working.

Jim

Jim,
thanks. I had already found and downloaded the most current information on the static converter from the RONK website. I got this converter for FREE, but it had sat outside for over a year. It does seem to function, but since I was not able to get it to do what I wanted I decided to go with building a Rotary converter. This is all for fun and learning. I am in to the lift and all of this for less than $400.00. Lot's of free or cannibalized parts.

 

[Gpzmax]

there is a whole lot wrong going on here.
1 the motor is not getting 230V idling. so there is one problem (power caps or motor is dead)
2 the lift is drawing down the power below useable, driving up the amps and thus will fry the motor (too small of wire or converter?)
3 why are you bothering using this old style hoist. they make new modern ones, single phase hydraulic that take almost no power...(used hoists can be had for $1500) cheaper then converting and fixing all this )

I got the lift for less than $400.0. I enjoy learning new things. For my day job I am a business analyst and ERP programmer. I could get a different lift, but I got most all of the other equipment for free. So This is mostly all for me to learn new things. My garage/shop was built in the '60s. With some help from electrician friends I learned and re-wired it form a 80 amp service to 200 amp. I also remodeled our home that was built in 1885. Completely gutted and then dug a 9' basement under the original and the addition. We quadrupled the size. I rewired and replumbed everything. All up to code. So, yes I enjoy learning new things.

 

[Gpzmax]

Yes, there are electrical issues.. that #14 wire being used as a current-limiter or even "fuse" ....at the top of the list.



That said, I suspect you ALSO have mechanical issues.

Cumulative wear... damage.. lube fail... distortion under load? Something that is causing binding when heavily loaded, such that the actual "present-day, REAL capacity", not the "as new, CLAIMED" capacity .... is being overly stressed mayhap?

"Heavier load" is exactly what it says it is, but there should otherwise not be THAT 'dramatic' a difference between initial lift, and resumed lift.

IF... it needs new parts... or is over-stressed, in general?

A whole 'nuther lift could indeed be cheaper and faster than the cost of f**k-around time and money with this one..

Dig deeper, first, into the source of the difference..

2CW

I'll check out the 'mechanics' of the lift today. I got this thing for super cheap. Less than $400. The other components were free. So this is mostly an experiment in learning etc. No frustration, just opportunity to learn and grow.

 

[Tony Quiring]

I keep seeing SPC at places.

Do not use one of those, you loose 1/3 of your nameplate power.

Our 7.5 L&S has SPC and on a cold day does not go full speed as oil in gear head too thick.

You need RPC with wiring and capacity overhead to supply a multiple of running current to work.

Sent from my SM-G781V using Tapatalk

 

[JST]

Yeah, this is an electrical subforum, but this surely does seem to have a mechanical issue. It's not all electrical.

Your 77A etc is NOT a "real" operating current.... that is a stalled motor current, basically what is known as "locked rotor" current. You should never see that for more than a fraction of a second at start.

Since you DO see that, there is something very different about the friction of the system with no weight, vs with a vehicle.

So, what is different here? The load. Yes, obvious. But it IS the problem.

I do not believe the issue is that the mass of the vehicle is too much to lift. Screws, if lubed, are very good at lifting things.

I would be looking hard at the connection of the arms to the screw. If the vehicle weight on one or more of the arms causes the nut to get cocked, or the arm to get cocked, the friction could go WAY up. Bad lube could cause an issue. a bad bearing at the bottom of the screw could cause an issue.

Possibly it is all or several of the above, or another issue that is caused by weight on the arms.

Since it does work when it starts at no load, even though you end up hoisting a vehicle, there may be some factor that depends on the arms setting with a load on them.

Our old friend "stick-slip" may be the issue, the lube may be wrong and get pressed out when the screw sets for a bit with a load on it. Maybe using way lube, or a different oil/grease is needed.

Do you know what lube is recommended? Are you using that? Can the arms get cocked under load enough to cause added friction?

You probably need to solve the mechanical issues before you have any idea if the motor and RPC can make it work (and it probably can).

 

[SomeoneSomewhere]

Note that while the legs supplied by the mains are seeing 70A+ (likely consistent with what LRA would be on a 3~ utility supply), the generated leg is seeing a substantial voltage drop and only supplying 30A. The RPC is clearly unable to keep up with the current the motor wants.

With symmetric supplies to a three-phase motor, they often use reduced voltage starting. With reduced voltage, phase voltage is proportional to phase current, and starting torque is generally proportional to the square of the current. Half current, quarter starting torque.

Given that a single-phasing motor with full current on two legs but nothing on the third develops no starting torque, I think it's reasonable to estimate that this roughly applies to the lowest current leg. In other words, because this motor is only being supplied less than half of its starting current on the generated leg, it is developing less than a quarter of rated/intended starting torque.

 

[JST]

That is a reasonable estimate.

However, it does not seem as if it is reasonable for the lift to be designed so that it requires every possible amp of current to get itself started, especially when lowering. Normally, one would design the thing to have quite a bit of margin to take care of the heaviest rated load, as well as variations in voltage, wear, and lubrication.

There was a comment that it would not even start when lowering.

" If there is no load, the motor will spin up and lift. IF I stop it and try to lift or lower it the motor will not get up to speed."

If so, that is obviously much more significant, since it takes the weight of the car out of the picture as far as needing power. Lowering is generally far less difficult if the parts are mechanically free.


We are not given the percentage of full load that the "car" represents. It would make a huge difference in the responses if the "car" is known to be half the maximum load, vs being at or even above the maximum load. There are VW bugs, and there are 1960's Lincolns, etc.

Most lifts have more than one column. Often there are two, and the two sides are linked so as to lift together.

How sure are you that the lift has all it's original parts? Could it be that the drive was changed to lift a lighter load faster? That would certainly change the start torque needed.

Did you see it lift a load successfully when you bought it?

As mentioned earlier, it might be possible to change a pulley (if it has any) to give you a slower lift, but more start torque. While that does not address the reasons why you need such perfect conditions for the thing to start, it could make it "work".

I would still be worried about the reasons for hard starting.

While acme and square threads will usually not back-drive, there still might be a mechanical lock, similar to an elevator safety, that disengages when the screw takes a load. You might have to lift slightly, then lower. If that does not disengage correctly under load, there is a direct problem that could stop it working.

There are other reasons why friction might increase with load. Lubrication, wear allowing the arms to cock and jam, gearbox issues causing jamming under load, etc, etc.

Before running off after electrical problems, mechanical issues have to be eliminated.

For instance, can you turn the motor by hand (using a lever) when it will not start? You should not need a lot of torque, since the motor would not be expected to have a lot of torque even with a perfect 3 phase supply, unless it is one of the less common "design C" or "design D" types. A standard "Design B" motor might have less start torque than it has when operating at normal speed.


As for the static phase converter, it is unsuited to this use. As you found out, they work best for one particular load, and are really intended for use with loads that are constant, like pumps, fans, etc.

 

[Just a Sparky]

Skipped.

Swap the three phase motor for a single phase motor. Use manufacturer's catalog to select a capacitor-start motor with high locked-rotor torque and pull-up torque characteristics. Often these can be spotted visually by a larger termination box on the side of the motor (to house more capacitors), as opposed to the usual small, form-fitting stamped shrouds on the tops of most motors which house only one or two caps.

Phase converters and high starting-torque loads don't play nice with one another.

Don't have to buy new if on a budget - find the motor you want in the catalog, then check Ebay, etc.

Alternatively if it's a hydraulic lift then just swap the whole power pack.

 

[SomeoneSomewhere]

Arguably, my 1/4 torque estimate was an overestimate. It's drawing 30A locked currently, and we see 77A on the mains legs. Those legs are already experiencing moderate voltage drop - real starting current with a stiff 230V supply could be >90A. So we could be seeing 1/3 starting current, and 1/9th starting torque. Manufacturers often size motors with requirements on the supply volt drop - that's not just for continuous duty; it also ensures that the volt drop under starting conditions is not more than say 15%.

I can't find the post, but I think we saw some comments about it working with lighter vehicles? Can we get a few pictures of the lift nameplate, motor nameplate, motor setup, and what kind of load you're trying to run it at?

If there's a chain drive involved somewhere, simplest fix is going to be a different size cog.