gordontech Posted April 20, 2013 Share Posted April 20, 2013 Rigging theory is not my game but Im trying. Recently asked to think up ideas for a venue that has 6 trusses, all 4 half ton motors a piece wired to one channel of a motor controller. From what I have been told they are all three phase. The venue is powered from 3 generators. As these bars are coming down the 20m drop they are almost always not coming in straight Despite being regularly realigned. The reason I have been given by the installer is that the generators sometimes go out of sync which means the speed on one or two of them are different. Is this correct or codswallop? The solution (if this is the case) that I thought of was replacing them with single phase motors and splitting it so each generator has 2 bars on it which should mean all the motors are 'in sync' and the power is evenly split. This is a costly way for the hopefully end client to have this problem solved? Link to comment Share on other sites More sharing options...
Dmills Posted April 20, 2013 Share Posted April 20, 2013 If all the motors on any given truss are on the same generator the truss should come in straight, if not organise things so that they are.... The speed of a three phase induction motor is directly related to the frequency of the supply, so if all the motors for a given truss are on the same supply they should come in at the same speed (Might be worth checking the brakes are all setup the same however). If however the motors on a truss are powered from different generators then any speed differences between the generators will result in things going very wrong. Single phase motors will if anything make matters worse. It may be possible to set the generators up so they run as a phase synched set in which case all the generators will run at the same speed, but this depends on the generator sets having the facility. Regards, Dan. Link to comment Share on other sites More sharing options...
flypig Posted April 20, 2013 Share Posted April 20, 2013 Dan has hit the proverbial nail on the proverbial head. 1. Have all the motors serviced / checked so you know they are all running at the same speed.2. Check that each set of motors per truss are all powered from the same source (ie all 4 motors are powered from the same generator).3. Have the generators phased synced.4. Do not under any circumstances change the motors for single phase. Regards,Ian Hamilton. Link to comment Share on other sites More sharing options...
Roderick Posted April 20, 2013 Share Posted April 20, 2013 I will leave the motor questions to my learned friends, but there is one thing I don't understand; why is the venue run of generators? It sounds like a permanent installation in a permanent venue, why doesn't it have mains power? :unsure: Link to comment Share on other sites More sharing options...
trussmonkey Posted April 21, 2013 Share Posted April 21, 2013 a couple of things spring to mind. 1) are the trusses empty? if not what is the load distribution? if a truss is un evenly loaded the bit with the higher load can run slower due to increased load on the hoist. especially if they are all half tonne hoists and you are picking up quite a large weight. general rule of thumb is if you reach 75% of the hoists capacity then move up a size2)why on earth would you have 4 hoists wired to the same channel of a controller? forgive me but I have never heard of this. it means you can not adjust the position of the hoist relative to the others on the truss. 3)sounds like the reason given to you from the installer is utter rubbish.if all the hoists are wired to the same channel then they are not being split over generators. as they are on the same channel then they will operate the same . Link to comment Share on other sites More sharing options...
Seano Posted April 21, 2013 Share Posted April 21, 2013 ... all 4 half ton motors a piece wired to one channel of a motor controller. The reason I have been given by the installer is that the generators sometimes go out of sync which means the speed on one or two of them are different. Is this correct or codswallop? All four motors from a single motor controller channel is not good practice. But, given that this is the case, obviously the thing about the generators going out of sync obviously is codswallop. How can two motors be powered by two different generators, given that they're paralleled on the same channel of the same controller? You do *not* want single phase motors. They're just about acceptable if you have only single phase power and no other option, but three phase motors are smoother, quieter, more efficient and more reliable. What kind of motors are they, and how far out of step with each other are they getting? Unless its drastic, I would tend to suspect its happening because (dur!) they are four separate motors. They're not stepper motors and 20m is a long way. It's unrealistic to expect to run four induction motors for five minutes and have them all cover the exact same distance of travel. It's totally normal that they'd be an inch or two out after that distance of travel. Which is one of the reasons why you run one motor on each controller channel and re-level the truss when it gets to trim. (You can use a Disto, but the easiest quickest way to do this is with good old fashioned surveyor's tape measures - one per point.) If you want all four points perfectly in 'sync' at all times you'll need a new, more sophisticated and possibly very expensive, installation. You could either use a single motor to drive the whole truss (eg: a winch, with four ropes running on a single drum), or a computer controlled system involving variable speed hoists and feedback from positional sensors (eg: Kinesys) Alternatively, Link to comment Share on other sites More sharing options...
gordontech Posted April 23, 2013 Author Share Posted April 23, 2013 They are something like chainmaster 2000, and look very like a "if Carlsberg did motors..." kind of deal. The installer who is undoubtedly an utter nipple said they was not enough power on one generator so I believe the 3 phase motors are run from 3 different generators at one phase a piece. The motors when dropped would range from the truss being from 2inches out of line to around 1ft. This is why its concerning me as the weight loading (give or take) is fairly even. Cheers chaps I will feed this back to the boss man Link to comment Share on other sites More sharing options...
david.elsbury Posted April 23, 2013 Share Posted April 23, 2013 No offence, but I think you are seriously out of your depth here.Way too many unanswered questions...- It's a venue. Why is it on generator power?- If they are 3 phase motors, like you said in your original post, they couldn't be run at "one phase a piece".- If they are 3 phase motors, then there is no way they can be wired to seperate power sources if they are on one channel of a motor controller. Time to get in a "man who can"? :)David Link to comment Share on other sites More sharing options...
MarkPAman Posted April 23, 2013 Share Posted April 23, 2013 ..............not enough power on one generator so I believe the 3 phase motors are run from 3 different generators at one phase a piece. No. Just not possible. I think you need to get someone who knows about these things to take a look. <E2A - Far too slow - that's what happens when the phone rings! At least we said the same thing> Link to comment Share on other sites More sharing options...
Brian Posted April 23, 2013 Share Posted April 23, 2013 ...I believe the 3 phase motors are run from 3 different generators at one phase a piece. Eh? I read this that there are 3 generators, each of which has one of its phases connected to one phase of the motors! Which can't be right. As David said, get in a man who knows their electrics. And by that I don't mean your average run-of-the-mill sparkie. Link to comment Share on other sites More sharing options...
Seano Posted April 23, 2013 Share Posted April 23, 2013 ... not enough power on one generator so I believe the 3 phase motors are run from 3 different generators at one phase a piece. That makes no sense at all. :huh: The motors when dropped would range from the truss being from 2inches out of line to around 1ft. This is why its concerning me as the weight loading (give or take) is fairly even. Two inches out of line is completely normal and to be expected, one foot is a bit beyond the upper bounds of "normal" but doesn't necessarily indicate a fault. It's a bell-curve innit. It isn't a powered flying system and no matter what you do you're not going to get more accurate than a couple of inches as long as you're using four separate motors without positional encoders. The truss needs to be levelled each and every time it's brought in/taken out, which is not a problem but does require training/competence and obviously requires a motor controller used in accordance with the manufacturer's instructions (ie: one motor per channel). I hope the mechanical/rigging side of this installation is more sound than the electrical side appears to be. Link to comment Share on other sites More sharing options...
Peter F Posted April 23, 2013 Share Posted April 23, 2013 Could you please ask your installer what happens if one of the four motors jams? Cheers, Peter Link to comment Share on other sites More sharing options...
Giles Favell Posted April 23, 2013 Share Posted April 23, 2013 Is this a recent installation? Seano is right about the motors. A 'normal' chain hoist will never run at exactly the same rate as another. If that is required, a 'synchronous' system must be specified, complete with encoders, control,etc., which is MUCH more expensive. When buying sets of chain hoists it is even important to specify that the chain on all the motors comes from the same batch in order to minimise the run-out. The last thing to remember, is that a bar or truss with multiple motors on it and an equally distributed load, will in all likelyhood have the motors carrying UNEQUAL loads - ie, some motors will be more loaded up than others. With a 4 motor pick up, you may typically find that the centre motors ar carrying more than the outside motors - unless someone has worked it out and distributed the load properly. Lastly, presuming it is a comparatively recent installation, there must be a reliable, safe way of working it, or it is not it for purpose. Check the O&M manual for a start. Link to comment Share on other sites More sharing options...
Roderick Posted April 23, 2013 Share Posted April 23, 2013 This is getting weirder by the post! Let's try to make some sense of this.GT, could you please answer the following questions:1 - Brand and model of the motors. Maybe post a picture of one?2 - Explain the '3 generators' in what appears to be a venue. Maybe post a picture of one?3 - Explain the controller set-up. http://www.cre8asiteforums.com/forums/style_emoticons/others/popcorn.gif Link to comment Share on other sites More sharing options...
kerry davies Posted April 24, 2013 Share Posted April 24, 2013 Gordon, have you escalated your concerns to the "responsible persons"? If not may I recommend you do so right away? I won't comment on motors or rigging but if the power is anything like described it needs checking out by a competent person ASAP. Tell the bosses and tell them that this retired safety geezer recommends it is not used until these things are sorted properly. Having told us all of this problem you are now the man holding the baby, pass it on/upwards. Quick as! Link to comment Share on other sites More sharing options...
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