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  1. #31
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    I know you don't want to get into this now but surely the safe state refers to the hoist rather than the VFD. It just means that the motor can fail but the hoist will not change position. The hoist cannot rely on the motor/VFD to maintain it's position. No different than the motor that is on there now. The VFD has nothing to do with the operation of the hoist. It is solely there to supply the correct voltage to the motor. The soft start/stop are just bonuses. External buttons can be connected to the VFD and the VFD key pad can be disabled. You can stick the VFD in a cupboard away from the hoist if you want. You never have to see it.
    I think a VFD with a 3 phase motor is still a good, reasonably inexpensive option. I've wired up a few car hoists and I don't recall any of them having huge motors. But then I didn't pay much attention to the mechanics of the hoist at the time. They may have been heavily geared.
    Built: a Bench,a Desk,an Archery Display,

    Those were the droids I was looking for.

  2. #32
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    Hi NCarcher,
    I don’t want to spend too much time on this aspect and it does come down to my own interpretation of the standards, and if I even want to try to keep the hoist compliant to as 1418.9. I’m pretty sure the words are along the line that the vfd or circuit has to be fail-safe as this was written in 1418.x which is actually the electrical standard for hoists/cranes etc. A screw post hoist frame is mechanically fail-safe because it goes nowhere if you remove the power, as you say. Hydraulic hoists are more common (and cheaper) and get away with smaller motors but require more mechanical safety features because they can fail catastrophically if there is a failure in the hydraulics.

    Did you wire your vfd’s to the input of the hoist and use all the original mechanical interlocks and buttons as intended, ie, the vfd output can get disconnected at full load? To do that you’d need to change the contactors and thermal overload to suit 240V (unless you were using a 415V vfd of course), so it’s a bit more expensive option than wiring direct to the motor. Until recently, I thought that could damage the vfd, if you disconnected the motor under load but I read someone who said its OK (on another application). I’d be interested to know if you had a system that broke power from the VFD as its driving and its been working for a long time.
    Anyway, I didn’t want to be a guinea pig. Also, my vfd makes a big point not to switch off power to the vfd if its driving a motor because that will cause damage to the vfd. The kill switch would have to remove power from the hoist to be compliant and I’d say the vfd is part of the hoist because it won’t hoist anything without it. There is also a requirement that if the mechanical interlock trips at the top or bottom of travel, (or if the chain is loose) that the hoist cannot be operated again until a reset button is pressed. All these things would make a vfd wired directly to a motor, a non compliant system in my opinion. When you go through the standards, there’s loads of things that make using a vfd difficult, again in my opinion. I’d recommend everyone not to believe me but to make their own decision on it if they have an interest.

  3. #33
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    Hi Kryn

    DSEL74 above mentioned it but I dont think he stressed it enough to you.

    A single phase Variable Frequency Drive (VFD), Variable Speed Drive (VSD) or just an Inverter drive as they could be called, will need to be connected to a 3phase delta wound motor. (a few can be connected to 415v Star but are not as common)

    Some motors are convertible within the terminal cover plate from star to delta and vice verca, but some are not without pulling them apart and reconnect as delta.

    So Ideally you need
    1.a single Ph to 240V 3 phase inverter drive, matched to the motor size ie HP or KW.
    2. A three ph motor 240v delta wound or a 415V star wound Which Can Be Converted to Delta.

    The Inverter drive could also have Vector control ( torque booster for you) if required.

    and we are only in Adelaide if you need help.......not even a packed lunch away.

  4. #34
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    Quote Originally Posted by BobL View Post
    If the correct breakers are installed they should easily be able to cope with this

    Here's an example of some breaker curves.
    A C type breaker can hold continuity for 7 times its rated current for up to 4 seconds before tripping out.
    At 4 times its rating it can hold continuity for over 10 seconds.

    So a 32A C type breaker should hold 128A for up to 4 seconds, which should cope with start up loads from large motors.

    Attachment 366597
    Commonly called Motor Start circuit breakers and are a good idea for motors without overload protection.

  5. #35
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    Hi sossity,
    The standard AS 1418.1 is a broad based standard to cover cranes, winches and hoists so as such has a lot in it that is not relevant to a car hoist.
    In a circuit where you want to put contactors to open circuit a drive they normally go line side. I attach a simple circuit I have drawn to show how I would configure your application to meet what AS1418.1 and AS4024.1501 standards, the Safety Control Category is at Category 3 type circuit.

    Keith.Hoist Circuit.jpg

  6. #36
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    Hi Keith,

    Thanks for going to the trouble but sorry, I still don't agree your circuit meets the requirements of 1418.9 (the standard for vehicle hoists) which says "Electrical equipment and controls incorporated in vehicle hoists shall comply with the requirements for electrical equipment and controls given in AS 1418.1."
    However, I'm sure most of hoists converted to use vfd will use the circuit you show, without the logic even, because most people don't know or care about type approval. I make no claims on the validity of my opinion or on overall safety. In my opinion there are technicalities which can't be met meet simply, on hoists which are converted to use a vfd. AS 1418.1 is a 179 page document, it would take a long time to argue over it and we still wouldn't agree. If I retain the control system exactly as it is without introducing a vfd, then there is no argument - it has been type approved already. I actually bought a vfd intending to do exactly what you suggest, but after reading the vfd manual and the standards, I bought a single phase motor and have retained exactly the same control circuit features as original, something I couldn't do if I used the vfd.

  7. #37
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    Hi sossity,
    I don't want to get into a argument with you over this, you don't agree with what I have said that's fine.
    BUT.... I have over 25yr's experience in designing safety circuits for Australian Industry and have involvement with Standards Australia, WorkCover and been part of the Safe Design Project as administrated by the Federal Government, and as such do have a very good understanding of Regulations and Australian Standards.
    To end this I hope you find a suitable solution to your application.
    Keith.

  8. #38
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    Hi Keith,
    I don't think this is about safety at all, what worries me is the approval as detailed on the hoist plate. I'm certain in Europe you can't change the design at all without having the whole thing approved again. Everyone talks about that when people do modifications to their cars etc. I notice here that for cars, people bolt or weld on all sorts of non approved things they have made but in UK everyone knows that voids your insurance. Are the rules in Australia not so bad? I confess to not knowing Australian laws. I can't get past thinking it comes down more to what a lawyer says than an engineer because that is who will saying your life insurance is void.

    Your experience is certainly relevant and I'd genuinely like to know more.
    If I do go ahead and use a vfd, what is your take on this,
    AS / NZS 1418.9:1996
    2.11 ELECTRICA L EQUIPMENT AND CONTROLS
    Electrical equipment and controls incorporated in vehicle hoists shall comply with the requirements for electrical equipment and controls given in AS 1418.1.

    from 1418.1

    Section 8 Electrical equipment and controls
    8.7 CONTROLLERS
    8.7.4 Electronic control
    Each electronic control circuit shall be designed and installed so that it complies with the
    following requirements:
    (a) The system shall be fail-safe.

    APPENDIX C
    FAILURE TO SAFETY (FAIL-SAFE SYSTEMS)
    (Informative)
    C1 GENERAL
    It is self evident that a single component cannot fail-safe. To satisfy the concept of failure to safety, a single component is replaced by a system of components or by re-configuring the whole so that the failure of the component will be inconsequential.

    A vfd could lock up while driving a motor for example. I don't think any unintended movement of the hoist could be considered inconsequential, that is the whole vibe of 1418.9. Surely you would need a watchdog circuit (capable of disconnecting the vfd) to monitor the button positions to make sure the vfd is not driving when it shouldn't, and also vfd phase, because I think 1418.9 says the buttons can't make the hoist go the wrong way.

    It would be good to hear your take on failsafe and the whole type approval thing after changing the design once approval was granted.

  9. #39
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    Hi sossity,
    As you said the standard AS/NZS 1418.9:1996 is the specificpart of the 1418 series of standards that defines the requirements for VehicleHoists and in part 2.11 where the type of hoist uses electrical equipment itrefers to AS 1418.1 – 2002.
    AS 1418.1 - 2002Cranes, hoists and winches - General requirements is a broad basedstandard that covers all types of cranes, hoists and winches. When reading thisstandard you need to use the parts of the standard that would be relevant tothe electrical control of the Hoist in question.
    You have asked me to give my thoughts on specific parts ofthe standards, this is my thoughts;
    We are looking at various control methods of raising andlowering the hoist being
    a.Standard three phase control, here the controlcomes standard with the hoist and no modifications needed. Not an option inyour application as you don’t have three phase.
    b.Replacement of three phase motor with a singlephase motor and use much of the existing control wiring. A lot has been alreadysaid on this in the postings and there is some torque problems as has beenstated.
    c.Use the original three phase arrangement and inserta drive to allow the use of single phase supply to run the three phase motor.
    For option C you have raised issues in using this method as whetherit would be failsafe as outlined in section AS 1418.1 section 8.7 and in particular8.7.4. That particular part of section 8.7 is referring to custom orproprietary electronic control circuit that has been designed by the cranemanufacturer where it is used to control the crane. This is where the design andlayout of components of that circuit needs to be such that a single fault cannotlead to the failure of the control, that’s where the term failsafe comes intoit. The whole of section 8.7 is referring to several different types of methodsof control trying to account for existing and emerging technologies.
    You have raised concerns that a Drive could fail ormalfunction or send the Hoist in the wrong direction. A fault like that couldhappen but highly unlikely as drives have demonstrated a high degree ofintegrity in their design and have been used very successfully in industry fora long time. If you look where a drive has failed in industry it has mainlybeen where it was not configured or used in keeping with the recommendations ofthe drive manufacturer. The type of drive also has a bearing, a drive that hasthe STO type design (safe torque output) could be used and the control systemdesigned so that feature is employed each time the drive is used to raise andlower the hoist.
    In conclusion a hoist has locking recommendations etc. to beused when using the hoist and this is also outlined in the standard for vehiclehoists. Raising and lowering of the hoist is done away from the hoist where theoperator has full view of the area to see if there is any danger to themselvesand other people.
    Legislation states that people conducting a business orundertaking PCBU are to do what is reasonably practicable to ensure the safetyof people in the workplace, and explanation of this is attached in a pdf, thisis what the lawyers will use.
    http://www.safeworkaustralia.gov.au/...racticable.pdf
    Keith.


  10. #40
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    Hi Keith,
    As an aside, a screw post hoist has no physical safety locking mechanism because unlike hydraulics, it is inherently safe when at rest. It’s the big advantage of that type of hoist as you can move it up and down just a few mm as you need, where I think hydraulic ones have to be lowered into physical locks at certain positions. There really is a requirement for the control circuit to be unable to malfunction and I even have concerns about those button wires you take to the vfd wearing through and shorting out causing the hoist to move. The original electro mechanical control system is really bullet proof and I can’t see how it could fail in any way
    I think you are agreeing that AS 1418.9 says the control system shall be failsafe, but your linked document says that safe work Australia allows businesses to take risks if they are small risks and so instead of failsafe, very reliable is OK. I had been under the impression that AS standards were a legal requirement but I just found out that’s not necessarily the case. It depends on whether the government has created legislation to make it a legal requirement. I couldn’t see anything to say if AS1418.9 is covered by legislation or not.
    That may get me out of conforming to AS1418.9 but what about type approval? https://www.safework.sa.gov.au/uploa...cle_hoists.pdf
    Vehicle hoists must have valid design registration numbers issued by a work health and safety authority in Australia. If in doubt, you must contact the supplier. It is illegal to operate a vehicle hoist without a valid design registration number.
    This is basically what I was saying about type approval which all countries have some form of. My hoist was approved and has a different design registration number for each state. If you change the design of the control circuit in such a major way as introducing electronics into it as well as running cables where they were not intended to be, don’t you need to get it inspected and get a new design registration number?

  11. #41
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by sossity View Post
    Hi Keith,
    As an aside, a screw post hoist has no physical safety locking mechanism because unlike hydraulics, it is inherently safe when at rest. It’s the big advantage of that type of hoist as you can move it up and down just a few mm as you need, where I think hydraulic ones have to be lowered into physical locks at certain positions. There really is a requirement for the control circuit to be unable to malfunction and I even have concerns about those button wires you take to the vfd wearing through and shorting out causing the hoist to move.
    This won't solve the compliance problem but a physical switch that isolates the VFD from the motor is easy to install.
    Then the VFD and any switching circuits can short/open all the likes and the motor just won't start.
    Of course both switches and wiring can fail but then so can the one in the original hoist.

    This is sort of what I have to switch between two 3P grinders
    The topmost black switch inside the transparent box switches between the two grinders, the centre switch position of which is a complete disconnect of both grinder motors.
    To access the switch the transparent cover has to be opened and a microswitch on the door stops the VFD and throws a relay in the box under the VFD.
    The VFD wont start a motor until the black switch in not in the middle position, the red/green switch is manually triggered to reset the relay and the toggle switch on the box under the VFD is its "start" position
    The toggle switch is the normal start/stop switch used when working on the same grinder.

    When the black switch is in the middle position the other switches and the VFD can do anything they like but nothing will happen because there's not physical connection to any motor.
    If you try to start the VFD it will report an error.


    Xover2.jpg

  12. #42
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    If a piece of equipment must have a design registration number for it to be legally used/operated then you can pretty well assume that one of the requirements will be that it conforms to or exceeds the appropriate standard(s). Without getting into the specifics of the discussion, if you modify an item away from a standard and something happens, there is a whole heap of trouble that can come your way.
    Standards are usually not written to be prescriptive but rather set out what characteristics or performance is expected from an item covered by it. So a standard will generally not say 'use widget X' but instead have a performance requirement that effectively requires the use of widget X to achieve.

    The idea of 'fail safe' is exactly that - if an item fails it must revert to a safe condition. This may be through multiple redundancies, significant over design of key components, mechanical interlocks, devices to remove/ deplete stored energy and so on. I have even worked in factories where there are written procedures on how automatic work cells are 'made safe' before anyone is allowed to enter (so robots are electrically isolated, counterweights are secured, pneumatics are exhausted (or locked) and any other steps to ensure that if a control system failed in either an on or off condition, nothing unexpected would happen), and written evidence is required to show a responsible person has done this.

    In this particular case, if the VFD failed either in the on or off state would the hoist
    • stay in a safe condition, or would it
    • drive up/down in an uncontrolled manner, or would it
    • collapse/ settle into a lower energy state that has potential to endanger life or property?


    This is why cable and hydraulic hoists have mechanical travel locks - so if a cable breaks or a line springs a leak, the platform will not descend without being arrested. As you have noticed, a screw hoist will self lock and so does not need those devices. When wiring E-stops, hard switching is preferred (required?) because when they go open all electrics have power cut, whether that is because the E-stop is tripped or a connection has broken. If you ran travel limit switches through a VFD, could you guarantee that the hoist would stop at the limit switch, or could a hardware or software issue cause a malfunction?
    I suspect that if you said to a regulator that you wanted to use a VFD on a hoist their approval would be conditional having a set of independent switches, such that power would be cut to the drive motor on reaching travel limits or an E-stop trip, regardless of what the drive may do. That is, you are not reliant on the software or electronics in the drive to provide a safe system.

    Michael

  13. #43
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    Quote Originally Posted by BobL View Post
    This won't solve the compliance problem but a physical switch that isolates the VFD from the motor is easy to install.
    Hi BobL,
    I like that and I’d definitely put a switch in as you say. It would make it very safe, the hoist just can’t move anywhere unless you drive the post.

    They do take the failsafe side of the hoist quite seriously though. The nut which runs on the screw post, is also failsafe. The load is taken on a brass nut, which has 6~9mm gap then a steel nut below it. The steel nut takes no load and is just along for the ride unless the brass nut fails. On my hoist, the brass nut was worn to a ridiculous amount, completely unsafe, but the steel nut is still like brand new with zero wear. You must check the gap every day and measure how much wear has occurred and replace the brass nut when required.

    I know you said it wouldn't help with compliance and I like the idea as it stands, but just for completeness I'll mention the standard has words to the effect that the design of the switch must be such that every effort has been put into making the switch unable to fail. It also specifically says it should not be possible for it to weld together for instance. I remember thinking how can you make sure of that? You could make it unlikely but impossible is something else.
    Quote Originally Posted by Michael G View Post
    In this particular case, if the VFD failed either in the on or off state would the hoist

    • stay in a safe condition, or would it
    • drive up/down in an uncontrolled manner, or would it
    • collapse/ settle into a lower energy state that has potential to endanger life
    Hi Michael G
    If the motor drive fails in the off state, then there is no risk to anyone. The hoist goes nowhere and can be wound down manually quite easily.
    The vfd could fail on, which would drive the hoist uncontrolled. I felt that could not be considered inconsequential. Even if you are at the switches, what if there was a transmission jack under the vehicle, it could tip the car in seconds.
    The interlock switches as standard do indeed carry the current for the motor making the interlock a good safe guard to the end stop. Although it would be quite dangerous to have the hoist drive too far at the end, the standard says something like it should be designed to handle such an accident without collapsing to the ground. I think it might say it is ok for the hoist to be damaged but not to the extent that it collapses but I am relying on my memory for that.
    It sounds like you are thinking the same as I was Michael, and that to modify at all will make it illegal. I kept all the interlocks the same and could argue the control system is the same design but I did rewire for single phase.
    The interlocks on mine were burst and I couldn’t find the same type of switch anywhere so I substituted a higher spec lever switch. I had to modify the mount (drilled another hole in the mounting plate) I’d say changing the switch was inconsequential, but is it still illegal because it was not what was approved? I wonder if there is any legislation which covers what a modification is as against maintenance.

  14. #44
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    I doubt that replacing the switch would be considered illegal as such - the important thing is that it is there and functions as the designer (and standard) intends. The standard would not be concerned with the transmission jack possibility as that should be covered by your own hazard assessment. It would however be concerned with the idea of the hoist driving up or down and no way to stop it.

    Michael

  15. #45
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    Sossity, to prevent any chance of the VFD operating as a result of wire/switch damage etc, having a 2 button operation where one of the switches is normally open and cuts the DCM wire and the other one is the up or down button as required. A normally closed emergency stop type switch, also cutting the DCM wire will act as a lock switch. No external switches will operate while the DCM wire is cut.

    These will not prevent any issues internal to the VFD, but will prevent any external problem from causing the hoist to move.

    Dean

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