Thread: Variable speed hoist

Being lazy I wanted a electric crane, but wasnt happy with the way the cranes electric ones I have seen start and stop. So I figured I'd get a 415V 3 phase crane and put up with derating it a little and run it on a 240V VSD. Well what nice people the crane makers are, they bought the star point out for me. I've had it running in Star with the brake removed. The input wires are labeled W1, U1, V1, the star point is W2, U2, V2. Can I pair and "1" with any "2"(other than itself)? or is there a certain order they should be in? Another motor I have is set up W1 - V2, U1 - W2, V1 - U2. Maybe I should just copy that.
The brake solenoid works on 240V but I havent tried it any lower than that.(not sure what to do abut it yet. I'll have to test it to see what its actually for.

Seems to work very well, starts and stops very softly as you'd expect. I'll get it loaded up tomorrow and see how it goes.(and pretty up the wiring )

Hope it doees work because it would be a major pain to get it running on 3 phase again.
Stuart

Just use a multimeter to confirm both ends of each of the three coils and then connect them in delta.
Joe

Hi Stuart,

If it's wrong, it wll just run backwards, and you will have created an anti-gravity machine...

Swap any two windings to restore normality to the universe...

Regards
Ray

Hi Stustoys,
I have attached a pdf on Motor Terminal Markings as well as some data on a Leroy Somer Brake Motor that you may find useful.

Regards,
Keith_W

Thanks guys. Strangely the motor runs much faster in Delta. I've not seen this before on motors I've changed.(maybe I don't have the VSD set correctly)
Worked out the brake is needed(not very surprising really), I just didn't have enough load on it yesterday to make it free wheel.
The motor will turn with the brake on, but even for me that's a little rough. I wired the brake across two phases but even at full speed it doesn't pull all the way in. So things aren't going to be as simple as it was looking in the beginning.

Nothing special in the other end Joe.

Stuart

Stuart, just a thought (way of of my area of expertise):
what if you put a diode ir even a bridge rectifier in line with the brake solenoid?
Firstly that would increase the voltage applied and secondly it would provide a fixed direction magnetic flux field. My instinct tells me that a magnetic force which doesn't have to reverse 100 time a second could be stronger than one that does....
Joe

PS: many thanks or an enjoyable hour in your workshop and your company this afternoon! and for the presents!

Hi Joe,
Sounds like a plan. I'll have to see if I have a bridge/diodes with high enough V, current shouldn't be a problem. If the brake drags a little on start and stop I don't think I'd let that worry me. I'll just have to check what the minimum Hz is that fully closes the solenoid.

I've had a thought about the motor running slow in star. I think it might be something to do with the brake, it needs very little pressure to work and as the hoist was on its side the brake may have been on a little. Not that it matters, to fast is a problem easily fixed.

Was good to catch up. Now I have a little more shed space lol

Stuart

Originally Posted by jhovel

Stuart, just a thought (way of of my area of expertise):
what if you put a diode ir even a bridge rectifier in line with the brake solenoid?
Firstly that would increase the voltage applied and secondly it would provide a fixed direction magnetic flux field. My instinct tells me that a magnetic force which doesn't have to reverse 100 time a second could be stronger than one that does....

Joe if I understand what you are saying, the bridge rectifier should marginally drop the voltage, but only by about 0.6 V, however a DC voltage will allow a much higher current, because the solenoid has inductance as a major part of its impedance. The impedance of an inductor rises with frequency, so if you insert a diode bridge, you will have pulsating ripple, but a predominant DC current, which will also likely saturate the inductance, and IIRC, when that happens, the impedance drops dramatically, and you will most likely burn out the solenoid in the absence of any current limiting. I may be mistaken, but I would hesitate to make that mod without the advice of someone who knows whats what.
Stuart it sounds like a great project. With most electric cranes these days, there is no gentle acceleration up to speed and a gentle decelleration to stop at the end. It could be incorporated I would have thought with inverter drives, but I have not seen it except in the older cranes with DC traction motors, and for big heavy loads they were the cats whiskers, they could lift off very gently, and place down a 30 tonne load as gently as a feather.
To try to achieve the same effect with the usual controls you have to keep dabbing the down button (say) as you set the load down. The problem with heavy loads, when the brake comes off, the load comes down and hits hard because the brake takes a finite time to activate, and the load is momentarily in a semi out of control mode till the brake comes on again and halts the now fairly quick descent of the load. I wish you well with your project, and look forward to hearing of your solutions
Rob.

Rob,
as I said, this is way out of my area of actual knowledge.
Thanks for some of the insights.
I actually thought the voltage would go UP with a bridge rectifier not down (my experience). However, the issue with current limiting and inductance evade my understanding.... so Stuart, please look further into it before trying it - unless you can measure the current that is meant to go through the coil (e.g. on your 415V VFD) and then check that it doesn't go any higher on 240V fed DC. checking the pemperature is probably a good idea in any case - given that the brake may be off (solenoid on) for lengthy periods while you are lifting a load up high.
In any case, don't do anything to harm this piece of good gear on the mere basis of my 'gut feelings'!
Cheers,
Joe

Originally Posted by Ropetangler

impedance, inductor, saturate the inductance,

I remember why I hate AC now .

Originally Posted by Ropetangler

To try to achieve the same effect with the usual controls you have to keep ..................

Hi Rob,
I was thinking along these lines and a dragging brake on start and stop may turn out to be a good thing. I know I cant use "coasting stop" as of course the brake comes straight on and I'm back the the sudden stop(though likely you'd slow it down with the speed pot normally). I'll have a play with ramp times with a load on the hoist to see what the shortest ramp I can use is.

I had a good go at pulling a building down with "dabbing" the button. I was lifting about 2.2t and had the control box on the load, pressed the down button, load goes down switch opens, load stops with a bounce, closes switch, load goes down, opens switch. repeat at the freq the building is bouncing at... things really started to rattle around very quickly.(I guess there would be a "dont rest the contorl box on the load" rule somewhere)

Stuart

Hi Joe,
*As I understand it* AC voltages are normally giving in RMS. To get the peak voltage, RMSV x 1.414, so 240VRMS becomes 339Vpeak. So the number has gone up but its the same thing.... if that makes sense? Roughly, there is likely more to it but that about as deep as I go(and I may even have it completely wrong).
I'd thought about measuring current but I've no idea how AC current of a coil relates to its DC current carrying.
And to think 24 hours ago it was looking like I'd be finished by now lol

Stuart

Hello Stu,
My limited understanding of the windings in AC solenoids, contactors etc. is that they are a centre tapped winding, and that one side of the AC supply will go to the centre tap and the other side will connect to both outer ends of the coil which are paired together, so that there is always one half of the AC cycle holding the coil in. Not sure what the effect of a diode in the circuit would be, but it may create two opposing DC fields in the coil. Guess there is one way to find out, so put a light fuse in the line and proceed with caution. Just my thoughts, Combustor.

Originally Posted by jhovel

Rob,
as I said, this is way out of my area of actual knowledge.
Thanks for some of the insights.
I actually thought the voltage would go UP with a bridge rectifier not down (my experience).
Cheers,
Joe

Joe the voltage will rise higher if the output of the bridge rectifier is fed into a capacitor. As Stuart has said, AC voltage waveforms normally have their voltages expressed as RMS volts, which is the DC voltage which would have the same effect in a purely resistant load. For a sinusoidal waveform the RMS voltage is 0.707 of the peak voltage above or below 0V. In other words, half the peak to peak voltage X 0.707.
When a capacitor is charged by the output of a bridge rectifier, it will charge to the peak voltage, which is 1.4 X the RMS voltage (√2) X RMS.
There is a small voltage drop of around 0.7V per conducting diode, in a normal bridge rectifier there are 4 diodes, but only 2 conduct at any one time. the first pair conduct on the +ve half cycle and the other pair conduct on the -ve half cycle. This is much more significant at low voltages , but is less significant in power circuits. Clear as mud I dare say. Regards,
Rob.

Originally Posted by Combustor

Hello Stu,
My limited understanding of the windings in AC solenoids, contactors etc. is that they are a centre tapped winding, and that one side of the AC supply will go to the centre tap and the other side will connect to both outer ends of the coil which are paired together, so that there is always one half of the AC cycle holding the coil in. Not sure what the effect of a diode in the circuit would be, but it may create two opposing DC fields in the coil. Guess there is one way to find out, so put a light fuse in the line and proceed with caution. Just my thoughts, Combustor.

That does not sound right to me Combustor, you would just have 2coils in parallel. When the voltage went through the zero point, both windings would have the same 0 volts across them.
This is not my field of expertise, and I may well be wrong, now where is RayG when you ant him?

Originally Posted by Stustoys

I remember why I hate AC now .


Hi Rob,
I was thinking along these lines and a dragging brake on start and stop may turn out to be a good thing. I know I cant use "coasting stop" as of course the brake comes straight on and I'm back the the sudden stop(though likely you'd slow it down with the speed pot normally). I'll have a play with ramp times with a load on the hoist to see what the shortest ramp I can use is.

I had a good go at pulling a building down with "dabbing" the button. I was lifting about 2.2t and had the control box on the load, pressed the down button, load goes down switch opens, load stops with a bounce, closes switch, load goes down, opens switch. repeat at the freq the building is bouncing at... things really started to rattle around very quickly.(I guess there would be a "dont rest the contorl box on the load" rule somewhere)

Stuart

Hi Stuart, that is an intriguing problem, you want slow ramp up and ramp down times, with the brake only activating when the motor has power cut, and releasing when power is applied. A relay with n.o. contacts to release the brake should do it as long as it still worked satisfactorily at the lowest frequency your inverter runs. It would be better if there was an output available which was active only when power was being output to the motor, say +5v or +12v, which would remove the frequency variation from the equation. I don't know enough about inverters to know if there is any such output available.
On the matter of resonance, it is indeed a powerful force, now Stuart I hope that you weren't riding that load of 2.2t were you
Cheers,
Rob.