Thread: Variable speed hoist

Originally Posted by Stustoys

Hi Rob,

Thats it.


I'm talking about much much slower than that.(or at least testing, what I end up with we'll have to wait and see)
With a load of over 27kgs and the brake "off", the load is lowered by lifting slowly enough that the motor slips backwards against the VSD(if that makes sense). I'll try some lowering tests at higher "down" speeds and see if I get any locking.


Stuart

O.K. Stuart, I stand corrected then, I would not have thought that the motor would slip backwards against the VFD, even at low frequencies, as long as they were not so low that you lost stability of control. IIRC I have read somewhere the simpler VFDs work well down to around 25 - 30 Hz, and the vector types work down to 3 - 5 Hz, and in my mind I had thought that 30 Hz would give a pretty gentle deceleration or acceleration of the load, bearing in mind the final ratio of the gearing, and the fact that it works satisfactorily for most users at 50 Hz.
Do you have a vector drive you can try, that would let you set the low speeds much lower, and I suspect that it would be much harder for the motor to "slip" against it, than it might against a simple V/Hz inverter. I have not studied inverters all that much, but I imagine that there must be torque curves vs frequency published which should provide you with a fair idea of your chances of success. It is obviously more difficult than I thought it would be that's for sure. Cheers,
Rob.

Some numbers before I forget them

With an 80kg load the motor needs to be lifting at 15Hz to hold the load with the brake off. It loses about 3mm on start up, of course timing is everything I have the ramp set on 4 seconds*. While the load is 80kgs(on bathroom scales) it creeps, so I must be a little over its limit. I'll have to leave it now until I get the brake working with the VSD. Maybe all thats needed is a momentary switch to hold the brake "on" while the VSD gets up to speed in case you ever backed yourself into a cover where load was within 3mm of being down and you've stopped. But how often is that likely to happen?

Some of the time just being able to switch the brake "off" would allow you to lower the load fairly slowly. Of course you need more then 27kgs.

Stuart

*Since I wrote this I changed the ramp to 2 seconds and things not surprisingly improved but its hard to tell. For all I know even on 415V 3 phase the load may go down a little on start up?

As I understand it, simpler drives lose torque as the Hz gets lower, Vector drives dont lose as much.
30Hz isnt all that gentle, this thing moves! (I could get 25Hz effect by doubling the chain)
A vector drive might be part of the answer but I dont have one.
What I'm after is something that can do inches a minute not meters.

Also there is stopping. I have it set on coasting stop. A short ramp might be good for slow speeds(depending on how the brake ends up being set up), but that could be an issue are higher speeds. Although if you are lowering very slowly its likely the weight will be off the hoist before you stop anyway.

Will have to wait and see.

Stuart

Originally Posted by Stustoys

As I understand it, simpler drives lose torque as the Hz gets lower, Vector drives dont lose as much.
30Hz isnt all that gentle, this thing moves! (I could get 25Hz effect by doubling the chain)
A vector drive might be part of the answer but I dont have one.
What I'm after is something that can do inches a minute not meters.

Worm or planetary gearbox driven by your electrical motor. Also gives you torque multiplication rather than subtraction.

Sounds to me like you're indulging in the 'I have a hammer to hand so everything needs to be a nail just because I have a hammer....'.

What problem are you trying to solve? Raising/lowering a load at slow speed under fine control, or trying to see what is possible with a VFD and a box of other electrical components? If it's the latter, fine, go for your life. I'm kind of planning on the same thing for my boat when experience tells me to just use hydraulics.

PDW

Yes it could be done with gearing......... then I dont have high speed.(though I could double the chain and run try running the motor at 100Hz) As yet I dont see that I need more torque.

In this case I bought the hammer to see if it is a cheap mod that can be done to other larger hammers.

The former with the later.

Stuart

Originally Posted by Stustoys

Yes it could be done with gearing......... then I dont have high speed.(though I could double the chain and run try running the motor at 100Hz) As yet I dont see that I need more torque.

No but you said you wanted inches per minute, now you say that you also want high speed. Just what is your SOR for this device?

You simply are not going to get that speed range without gearing or some type of expensive control system - big DC motors and controls for example. You've already found the lower Hz limit of your existing setup and the speed is too great, plus (IIRC without reading back) you're still getting some sag. Since you can't go slower, you either have to increase motor torque by increasing size/HP to get more at a lower Hz, or go to gearing. There's no free lunch.

Like Rob I've had some exposure to 'real world' cranes where equipment had to be lowered or raised from a surface moving in 3 dimensions while the crane was also moving somewhat independently in 3 dimensions. Those cranes are seriously expensive. Your problem is a lot simpler but that doesn't mean that it's easily solved.

Even hydraulics have their limits. We once had an oceanographic winch installed that in practice had nothing like its rated pull as installed. We found this out *after* spooling out 1.5km of 12mm cable with over $100K of equipment on the end. Getting it all back aboard was not fun. Worked fine with only 400m of cable out which is what we did when we tested the damn thing in the Derwent before going to deep ocean.....

PDW

Bad thread name maybe. "Variable speed hoist"* may have been better. Want I want is everything, from full speed to hover, its yet to be seen just what I will end up with.

I have the speed range, its the starting that is currently the issue(and then only if you above 27kgs. At full load you need to have stopped where sagging about 3mm would be a problem), though the shorter ramp time seems to have improved that. If I can get the VSD to control the brake and if that control can be done with "Set freq reached", then I think it will be all good. I'll have to wait and see on that one until I get it wired up. I may even leave the brake on for very slow movement.. I'll see. Another option is the up and down switches are two stage, I could wire the brake to the second stage so it stays on until the button is presses right down.

As I said earlier I cant recall how much "real" cranes sag(if any). Though I do recall that they bounce that far when you take your finger off the button.

Stuart

*Ok now that just looks silly now that the threads name is "Variable speed hoist". I got up this morning and thought I was losing it and had to go back through my emails to be sure it had been "slow speed hoist" . Thank you Mr Mod

Originally Posted by Stustoys

As I understand it, simpler drives lose torque as the Hz gets lower, Vector drives dont lose as much.
30Hz isnt all that gentle, this thing moves! (I could get 25Hz effect by doubling the chain)
A vector drive might be part of the answer but I dont have one.
What I'm after is something that can do inches a minute not meters.

Stuart

Hi Stuart.

While a vector drive with a shaft encoder would be the ultimate solution you may be able to achive a suitable outcome with you existing drive. It seems as if the VSD may be configured for a variable torque aplication eg a fan or centrifugal pump. In this mode the available torque from the motor is greatly reduced as the speed is lowered.

For hoisting use you always need the same torque regardless of the speed ie constant torque mode.

Most modern drives can be setup in either configuration or somewere in between.

If you have a manual there may be parameters which will increase the volts/Hz ratio at lower speed to achieve this.

John

Hi John,
Thanks, I'd forgotten about those settings. I'll have a go at them when I get the brake set up, though I havent had a lot of luck with those setting on my other VSD....... but that doesnt mean much lol

Stuart

Success!!!!!!!! or at least I can see the light at the end of the tunnel*.
I've gone from Up/Down buttons with a pot for speed control to a Run button with the pot controlling both FWD(up)/REV(down) and speed.
Finally worked out the terminal switching(or at least enough so I can get the VSD to do what I want it to do) so the brake .
Time to make a new pendant, clean up the wiring and mount the VSD.

I hope the only thing left to decide whether the brake should be set to come of when the VSD gets a run command or when the VSD gets to it set Freq. Set freq is good except if you change the speed to fast the brake comes on until the VSD is back at speed. Not sure its a huge deal either way.

One last problem is the travel limit switch. The way is was set up it would inhibit running in one direction but allow it in the reverse direction at both ends of the chain. depending on the switches in the hoist I think I can sort it with one extra DPST button.

Stuart

* hope its not another train

Well its ungly but it works.
Sorted the over travel problem without having to add another switch, so all thats left is the small matter of cleaning up the wiring and mounting the VSD.

Stuart

Well its pretty much finished. Though the controls aren't.

174meg video (on its side, with crappy lighting... sorry but you'll get the idea) This is a full 80kg load. It will hoover cant get much slower than that
vsh - YouTube

I have a 10 turn pot on it ATM which seems to work ok.

There is an issue below about 2hz, the motor cant hold the load so it starts to freewheel. Playing with settings should fix that(fingers crossed).

The only thing I really don't like and cant see a away around is if you lose a speed pot wire or the pot goes south, the VSD either goes to full speed up or full speed down.................

Stuart

Noticed something in the old wiring, it appears the primary of the transformer was wired to earth. (maybe that's it was for sale?) strange as it appears to be 415V.