Thread: Am I mad

Originally Posted by Stustoys

Or did explain you wanted to run it on a VSD and needed it rewired for 240V?


Stuart

Stuffed if I know... For all we know the people welder talked to may not have even heard of running a motor on 240V three phase via a VFD...

You can come across people who have worked in a field their entire lives, but know stuff all about anything outside the common everyday things they do....

Just have to read some of those american forums to see that when they come across a to them non standard thread like 1/2" X 12 and it has them totally confused, because it is whitworth, but they have never heard of whitworth before, because it is not the norm...

Originally Posted by welder

it will be $400 to reword te motor

That's ridiculous.

I recently had a 25HP 3 phase star/delta motor rewound - and I *mean* rewound - all the copper pulled out, new windings, baked etc (it let the magic smoke out in a big way).

Cost me $1265 including GST.

PDW

My guess is that you are getting the "I really don't want to do this but if you're silly enough to pay it I will" quote.

From the rewinders point of view, when they do a complete rewind they know exactly what has gone into the motor and that there should be no waranty issues.
When you ask them to simply extract the common and wire it out delta, you are effectively asking them to warrant the windings of a motor whose history they have no visibility of.
If they work your motor, they have to consider that if, in a months time it smokes out, you might come knocking on their door to make a warranty claim against their workmanship even though the burn out might have nothing to do with them.
Then you might even go to the point of bagging them out to others if they deny your claim and so on an so forth.

Of course I'm not implying that you personally would do such a thing but this is something that they need to consider.
Long and the short of it is they need to factor the cost of this rework into the initial quote.
I would bet that if the rewinder knew you then the quote might be more in line with your expectations but as a walk in, this quote sounds perfectly reasonable to me.

FWIW you strike me a a fairly inteligent kid so I would say have a crack at the conversion yourself.
When you next go to TAFE go have a chat with an instructor from the electrical engineering dept and my bet is they will be willing to advise you on the process and will probably even test it for you afterwards.

Most important, and I can't stress this enough, if you do have a go yourself, get it tested by someone who knows what they are doing before you take it anywhere near power, dead lasts a long time.

Worst case scenario, you bugger it up and you're up for a $400 rewind,what have you got to loose?

Cheers,
Greg.

Why do they want to rewind the motor? I thought you just want them to find and externally terminate the star point? Is there soothing else wrong with the motor or did you ask the wrong question? I paid $100 for a particularly difficult motor once, but the guy apologised... I would have thought $50 was the going rate.
Try again asking for the right quote 'Splitting the star point and bringing out the three ends to connect the motor in Delta' that's all. 'How much for just that?'

Dear PDW,

What are you running with a 25hp motor?

Cheers,
Joe

p.s. Good score Andre!

Originally Posted by jmebgo

Dear PDW,

What are you running with a 25hp motor?

Hydrovane 120 cfm air compressor. I try to run it as little as possible but when I need it, I need it.

In case I haven't mentioned it for a while, I *hate* sand (garnet) blasting.

PDW

Hi Andre,

Just noticed your quote for motor re-wiring, so i dug this up:

HI,

Thanks for all the replies and advice. I picked up my motor today from Austins at Lidcombe. Cost $70 bucks and all good to go (not that I'd really know). Will now be looking for a suitable VSD.

Cheers Ben.

All I did was take the motor to them and explained in a not so convincing way what i wanted. Worked out cheaper than the phone quotes I originally got for a 1/2 hp 3phase motor.

Ben.

I am going to give it a try with the motor wired as is will see what happens

Well I have it wired up but the motor turn very slowly and I can't get the speed to change no matter what I do

What sort of VFD did you get?

Did you get my last PM?

Ew

Originally Posted by welder

Well I have it wired up but the motor turn very slowly and I can't get the speed to change no matter what I do

Hi Andre,

Need more information. Take pictures.

Ray

The vfd says the motor has 50hz and is going 2800rpm but in reality it's only turning at around 80 rpm

Hi Andre,

Wiring looks ok at first sight.

Disconnect any load from the motor and check that motor spins freely when not powered?
Check VFD current limit settings.

Ray

<Moderator please insert electrical safety warning here>

Hi Andre,

Do you have a multimeter that can measure 240 VAC? Next question, do you have or can you borrow an AC clamp meter?

If so, and you don't find anything mechanical wrong, the next step is to start the VFD, set it to 50.00 Hz and measure the phase voltages.
Be aware these are lethal voltages, and you must use proper insulated probes and take extreme care,

1) Measure Voltage between U and V terminals
2) Measure Voltage between U and W terminals
3 )Measure Voltage between V and W terminals

They should all be 200+ volts AC if not, power down and disconnect motor, then repeat test with motor disconnected If you aren't getting 200+ volts per phase there's a problem with the VFD.

Next if we have 200+ volts per phase, use the clamp meter and measure the motor current in each phase. The current should be close to the same in each phase.

Ray