VFD -under volt at source fault

[Gareth Blackstock]

So would your calculations restrict replacing even a very low amp 3phase with a single phase? When I initially queried this forum last december with the prospect of replacing the motors, I received some positive feedback on replacing my low amp motors. I got the impression that if the 3phase motor is a low enough amp, then a single phase can safely cover it. The machine I have is not a heavy power consumption user, I am guessing the 3 phase motors are to ensure consistent running speed as the machine processes cine film, and any variation in speed will effect the final product.

At the moment the machine is running 240volt house mains on bare essential motors, without blowing fuses or dimming lights. I was planning on wiring up the remainder motors on a separate circuit with their own switches.

As I am not a business I have to explore work arounds. I have tried getting sparkies to attend and look over the machine but I am too far out of town, and it seems not many electricians come across VFDs to offer opinions.

This thread was my original, and lists the motor specs.

Adapting a 3 phase industrial machine to single phase

Hello, I am hoping this is in the correct forum. To start, I acquired a film processing machine that runs on 3 phase. Now before getting the machine I fully understood it's power requirements and the cost of getting 3 phase installed at my house. I figured as processors are mostly a few...

www.electriciansforums.net

 

[Darkwood]

I didn't design the machine but it clearly had a 7.5 Kw (10hp) motor fitted for its needs, unless you are utilising the machine for different purposes to its design which in turn reduce the load requirements then you will need the same torque output as before which will reflect the issues I expressed in previous post.
You are also drip feeding information to us which may be crucial to the advice we give, you now express that variants in speed has a detrimental effect on product, this would then indicate why a VSD has been used, it is likely if speed is so crucial the VSD control wiring maybe looking at a closed loop feedback system to ensure speed to maintain as loading on the motor varies throughout the process, if may also account for a larger motor been fitted than expected so load variants are easily dealt with by the motor without it passing it through as speed variants if it does not have closed loop system.
The type of questions I need to ask you simply won't have the understanding to answer with all respect and is also why electricians you call in are somewhat in the shade, this is electrical engineering type of knowhow and not your general sparky if you get me, the forum provides info only based on the info you provide, if you miss out info' you never considered to be relevant or simply didn't know then the answers the forum give may not be the correct ones for your enquiry.

 

[Darkwood]

I will note here, the link you provide to a previous discussion shows much smaller motors than the VSD you have bought, you can oversize a VSD and de-rate for the motor in programming it up but you will run into operational issues if the VSD is several orders bigger than the motor it covers, why have you got a 7.5Kw VSD?

I took that you were controlling a 7.5Kw motor with it which now reviewing your previous posted thread I question is the right drive at all.

 

[Gareth Blackstock]

You have not read my replies, I did not say the machine had a 7.5kw motor fitted, I said I had bought a 7.5kw VFD originally. I did not drip feed information, I was taking a guess that the electrical load of all the machine’s motors are quite low, perhaps the use of 3 phase was to ensure no detrimental effect was caused by power drop that would affect the final product. I never said the VFD was attached for this purpose.

I think you have read my replies too quickly or are putting 2 and 2 together and coming out with 5. I initially bought what I thought was the right powered VFD, and as it was reporting “under volt at source” I considered that my house supply was not offering enough amps, so I simply wired the machine to 240v with the intention of replacing the very small load 3 phase motors with single phase, and running other motors manually when needed.

I recently saw a higher powered VFD for sale locally and that’s why I posted the question, to get advice if the higher powered one would solve my initial under volt question.

I have provided as much info as I have been able to, as the machine has no identifying spec plate, which ever electrician worked on it last has left no details of anything. So I have had to try and work it out backwards, looking at the motors and tracing the wiring back to the controllers, panels, and switches. I have even contacted the people who built the machine, they also were unable to offer any paperwork, I have contacted businesses who use similar machines, no paperwork there either. So apologies if I have been light on the info, and apologies for being too simple to answer your questions, as it seems I will get this machine fully running without your immense help.

I will also note here, I have been repairing cine film cameras for a number of years, and frequently assist people with their repairs from across the globe, and it seems I understand better than you, that people who don’t work on cameras are ignorant of cine camera terminology…. And that’s o.k, that’s why they are asking me for help.

Don't bother responding, I won't return...

Thanks to the other members for helping.

 

[DPG]

Out of interest, what type of circuit is your outbuilding fed from?

Interesting that you repair cine equipment. Must be quite a niche market now that. Can you still get 8mm film processed these days?

 

[Darkwood]

@Gareth Blackstock
Please don't take my post as any kind of attack on your intellect, I made a very good point about these kinds of controls based on your response, IE if it is crucial to maintain a set speed then it may be likely run through a closed looped system, however with the lack of tolerance of the system to speed variations it is hard to give definitive advice, If I actually started to ask you these kinds of questions and you knew the answers I would expect you wouldn't actually need the forums help given your knowledge of such systems.

What made for more confusion and something we try to avoid members doing is multiple threads addressing the same exact issue from the same member, I was not aware of a previous thread until you later posted a link, you yourself have expressed local electricians are not savvy to VSD's and hence my further comment that these systems are more complex and the seeking of help from an electrical engineer who is present on site would be the better options.

Further more and not mentioned in this thread is machine safety and the regulations around that, you are attempting to alter to get a machine running without any real knowledge of the regulations around what you are doing or to that of the codes of practice in the use of VSD's, had I wandered across this thread earlier or your previous one I would have instantly messaged you and advised you get on site hands on guidance by a competent qualified person even if you wanted to do the work yourself, this kind of work shouldn't really be attempted as a DIYer through forum help, again it isn't what you tell us that is the issue, its what you might not realise is important info that could lead to unsafe advice been given.

We are happy for members to help out but we also have to raise concerns when we suspect that someone maybe out of their depth and safety concerns could arise from incorrect advice simply because of the lack of info provided.
No doubt this machine has moving parts, it is crucial that it is safe to use and you are aware of any safety issues that may be present if you got it working and whether its existing safety controls work or even exist.

Whether you respond back is your call but I hope you heed the advice that we normally would not consider this a DIY project that members help on given the inherent concerns of safety and what I will assume is your lack of knowledge of the local machinery control regulations I can only suggest you reflect on what you are attempting lacking such knowledge.