Dust extractor start fault

[Krysstel]

Just taken delivery of a new dust extractor which unfortunately doesn’t work !
As we have not got to the bottom of why or who’s to blame I won’t throw the supplier under the bus as yet although the pictures may give the game away for those in the know 

The extractor has a 3kW (4hp) motor which is running (or rather not !) on a 230V single phase supply through a 16A Type-C circuit breaker.
I am no electrician but as I understand it the motor is in fact 3-phase but the start and run capacitors in the junction box mounted on the motor itself allow it to be run on single phase.

And so the symptoms.
The motor takes what I feel is far too long to come up to speed and before it reaches full speed the motor protection breaker in the control box trips out and cuts the power. This happens 99 times out of 100 although once or twice it has managed to stay running continuously without a trip (this fact may be significant ?)
The motor protection is set at 14A which appears to be correct given 3kW at 230V.As a test I tried adjusting it up to approx. 18A but then the 16A circuit breaker in the fuse box tripped instead.
I have measured the current being pulled by the motor on startup and this is initially at around 45A dropping to approx. 25A when it trips out.
I havn’t yet tested whether the capacitors are faulty as that would entail cutting the wires and I don’t want to do this until the supplies gives me the go ahead to do this.

Can anyone help or suggest what the fault could be ? Is there any likelihood the problem can be the fact that I only have a 16A supply ? Should it have been 20A for instance.

I should add that I am located in Norway (expat Brit) and logistically this is a nightmare for all involved as simply returning the whole machine is going to be extremely difficult, and expensive.
I am becoming increasingly desperate and so far the supplier has been very sympathetic but of little practical help

Lot of pictures attached

Mark

 

[CHJ]

You have checked the current draw, but have you checked the actual working voltage at the machine on switch on?

If you have too much voltage drop due to the supply wiring resistance the power available despite the high current may not be sufficient. (cable sizes)

I suggest the system is not speeding up quickly enough to provide sufficient Back EMF from the motor to counteract the inrush current.

 

[Krysstel]

You have checked the current draw, but have you checked the actual working voltage at the machine on switch on?

If you have too much voltage drop due to the supply wiring resistance the power available despite the high current may not be sufficient. (cable sizes)

I suggest the system is not speeding up quickly enough to provide sufficient Back EMF from the motor to counteract the inrush current.

Thanks for the prompt reply. You may be onto something here and you're actually the second person who has suggested this.
So increasing the cable size to 4mm2 and changing the circuit breaker to 20A maybe the solution ?

Mark

 

[ManowarDave]

Hi Mark,

If you are going to change the breaker, get a D type. These are specifically designed for high inrush applications such as motors. They are rated at 10 to 15 times the trip current for inrush.

Dave

 

[Krysstel]

Hi Mark,

If you are going to change the breaker, get a D type. These are specifically designed for high inrush applications such as motors. They are rated at 10 to 15 times the trip current for inrush.

Dave

I'm going to just try uping the cable to 4mm2 first and see if I get anywhere with that. After that I think a D-type 16A. And if that's not enough a new, separate 20A D-type circuit specifically for the extractor.

Mark

 

[Inspector]

One thing you might try is to block the duct to the DC when you turn it on. That will keep the impeller from doing any work, lowering the load on the motor allowing it to spin up faster. Once to speed open the duct up some. It seems counter intuitive but when the impeller is not moving air it isn't doing much work, lower amperage. With wide open ducting it is working the hardest, highest amperage. It isn't a cure but it will confirm if it is drawing too much current on startup.

Pete
PS. I'm no electrician either.

 

[Krysstel]

One thing you might try is to block the duct to the DC when you turn it on. That will keep the impeller from doing any work, lowering the load on the motor allowing it to spin up faster. Once to speed open the duct up some. It seems counter intuitive but when the impeller is not moving air it isn't doing much work, lower amperage. With wide open ducting it is working the hardest, highest amperage. It isn't a cure but it will confirm if it is drawing too much current on startup.

Pete
PS. I'm no electrician either.

Thanks for the suggestion Pete. It worked !!
At least I got the motor to start and run continuously with this method and it continued to run when I opened the blastgates. However it still trips out if any load is put on the motor during startup.

This morning I received some feedback from the manufacturer. They suggest turning the thermal protection relay up to 17A (from 14A) and changing the circuit breaker to 25A. In my (non electrician) opinion this seems like a dangerous solution. The motor should only draw around 13.3A (as is stated on the label on the motor). Surely turning up the protection relay and running off a bigger breaker is just a bodge and a way of disguising what I believe is a more serious underlying problem ?

Mark

 

[sunnybob]

I would try the increased thermal overload value first. Youve proved its the start up current thats the problem.
But I'm not so keen on upping the circuit breaker to that much over rated.

 

[CHJ]

Equipement Thermal overload protects the motor.

Supply Circuit Breaker is there to protect the supply wiring from overheating and should be rated no bigger than the maximum continuous current rating of the supply wiring to protect the wiring from a short circuit or excessive running load.

 

[Inspector]

As I see it the thermal protection hasn't tripped to this point with repeated attempts to start the motor so I wouldn't touch it. Your circuit breaker at the box is tripping because starting is taking too long and the breaker doesn't like it. Now if the wires feeding the motor are big enough you could try a slower breaker, one that takes a little longer to trip during the starting surge. If the new breaker still trips and the wiring is large enough you could try to use a bigger breaker. Both of the suggestions should not be attempted if the wires are not big enough to handle the surge during the starts. You should discuss this with an electrician. If he deems the wires too small for slower or bigger breakers you will either need to pull larger ones....

.... or see if you can get a 3 phase motor that fits and use a variable frequency drive (VFD) to change your 220V single phase to 220V three phase. The VFD can be programmed to ramp up the power slowly, limiting the current so the existing breaker doesn't trip. It also has the benefit over single phase of being able to start and stop the motor as much as you like. A single phase motor should not be started much more than a half dozen times per hour because it can't dissipate the heat that builds up during starting. Another benefit is being able to run the motor at 60 cycles giving you 20% more airflow, like the ones sold here.

The motor / VFD option is offered as a solution of replacing the wires with bigger. They both have a cost and nuisance factor, ripping into walls vs changing the motor etc. You have to decide. My VFD for my 5hp cyclone was about $170US and once the shipping from China and taxes were done it came to about $350Can to my door. You would need a slightly smaller VFD.

Pete

 

[Krysstel]

I would try the increased thermal overload value first. Youve proved its the start up current thats the problem.
But I'm not so keen on upping the circuit breaker to that much over rated.

Would this not potentially reduce the life of the motor by allowing it to overload before tripping out ? I am not keen on this as a permanent solution.

Mark

 

[Krysstel]

Equipement Thermal overload protects the motor.

Supply Circuit Breaker is there to protect the supply wiring from overheating and should be rated no bigger than the maximum continuous current rating of the supply wiring to protect the wiring from a short circuit or excessive running load.

If I go down the route of increasing the supply circuit breaker rating I will definately at the samer time increase the cross sectional area of the associated wiring.

Mark

 

[Krysstel]

As I see it the thermal protection hasn't tripped to this point with repeated attempts to start the motor so I wouldn't touch it. Your circuit breaker at the box is tripping because starting is taking too long and the breaker doesn't like it.
Pete

It's the thermal protection that trips all the time.
The circuit breaker at the fuse box has never tripped.

Mark

 

[CHJ]

I would seriously go back to your original status of checking out the adequacy of your supply wiring and any resultant power loss on start up surge due to cable resistance.

Did you measure for voltage drop? at the machine.

Your electrician may be able to prove a point by running a temporary cable in Parallel with the existing wiring to increase its current handling rating.

There is also a possibility ( although remote) that the supply to your distribution outlet may not be maintaining its voltage on surge.

 

[Krysstel]

I would seriously go back to your original status of checking out the adequacy of your supply wiring and any resultant power loss on start up surge due to cable resistance.

Did you measure for voltage drop? at the machine.

Your electrician may be able to prove a point by running a temporary cable in Parallel with the existing wiring to increase its current handling rating.

There is also a possibility ( although remote) that the supply to your distribution outlet may not be maintaining its voltage on surge.

I have measured the voltage drop as; start = 232V, at trip = 212V.
This is with the thermal protection at the factory adjusted 14A.
At start the motor draws 45A and 25A when it trips out.

When I this weekend got the extractor to run by blocking the air intake to reduce the load on the motor I measured the current as around 5A once it was running continuously.

Mark

 

[Inspector]

It's the thermal protection that trips all the time.
The circuit breaker at the fuse box has never tripped.
Mark

Sorry I misunderstood and thought the circuit breaker was tripping.

Do you have any other circuits closer to the panel you could try it on? Never mind if you have already tried.

Pete

 

[Myfordman]

A 20v drop during starting says the supply cable is inadequate (either too long or too thin or both) for the job. The voltage drop means starting takes longer and that is causing the thermal overload to trip.

 

[Krysstel]

Hopefully we have reached a conclusion.
Scott & Sargeant are sending me a new motor + start and run capacitors

Mark