electric motor guru needed

[Deano]

hello all

i have finially got my lathe and mill running this last weekend.

i have found i have an issue with the mill. at this stage i only have 1 invertor so used the same invertor to get both items running.

both the lathe and mill use a 3hp motor, the motors are originally a 415v 3phase motors and if you connect to delta then you are able to run them in 220v 3 phase, the lathe motor is a brand new cmg motor that i have connected in delta to run off the invertor. this seems to work a treat with the motor rated at 8 odd amps and with the gearbox in high gear the motor is drawing 5.6 odd amps according to the dig readout on the invertor.

now with this combination working great on the lathe i transfer it to the mill. the motor is the original 3hp 2phase motor that had to have the delta winding brought out to the terminal box but that is a very basic job. with this done i am able to run the motor on 220v 3phase. after hooking the invertor up to it i turned the motor on and away it goes runs great drawing about 3 amps with no load but when i try to vary the speed with the variable speed pullies the variable speed belt tightens up and loads the motor slightly. when this is done the motor starts to drop lots in rpm. my limited knowledge in motors tells me that the motor should draw more amps as the load increases. this does not happen. the motor just keeps pulling 3 odd amps and if i keep winding the variable speed knob it would eventually stall.
the motor guy says the motor is not a problem.
the invertor guy says the invertor is not a problem.
i tend to argree with the invertor guy cause the invertor works great on the lathe. i then decided to hook up the motor wires from the mill to the lathe. so that way the mill electrics are running the lathe motor. as you would expect the motor draws about 4 amps and seems to run great so that being said there is no problem with the electrics in the mill.

i spoke to 2 different motor rewinders and they both say it would be very doubtful that the motor would be a problem. one of the guys has done this mod for the local king rich mill agent for this exact conversion and they had great success. the only different thing from there conversion to mine is that they used a different invertor. the main reason for that is they have an account with the other mob.

checked the windings with a multimeter and they all returned to 0 resistance.

any ideas as to why the mill motor wont make any power?

[Redmohawk]

Mate you need to use a lower setting on the multi meter to read the resistance of the motor it shouldnt be 0 ohms maybe 1 or 2 (not sure how low it should be but i can check for you) but deffintily not 0 if it is that low you have a problem. I'm assuming your using a phase change inverter to change single phase to 3 phase 240v with the delta wind to improve power of the motor.

I'd be looking to make sure when they/you? re wired the mill motor that you got the windings the right way around, as it will prob run ok with out a load on it but as soon as you put a load on it , the motor will have trouble sustaining power and drop in rpms. Sorry it's all a bit vauge my 3 phase motor theory is so long ago I've forgotten it all. About the most I remeber is reverse two conections on 3 phase to reverse rotation and the difference between delta and Y lol.

I do have a mate in the rewinding business I'll drop in and have a chat this arvo and ask for you.

[Deano]

cheers mate. yes using a single phase in 220v 3 phase out.

will check again with multi meter but both motors return to 0 restitance

[Redmohawk]

Sorry for the delay mate took a bit to track done the guru. Need more input is the next problem lol

From what I read in your info so far and info from guru, looks like its probably your Mills electrics causing the problem. Inverter guy should have told you inverter should only be used direct to motor definitly no contactors between motor and inverter (as the sparks etc can distroy your inverter and no warenty there ) the mill electrics may be messing with the inverters operation , guru sujests driving mill motor direct from inverter to see if it runs it ok to iron out if its the mill elecrics for a start. If this is the case (likley) then there are prob ways around the mills electrics but the motor will have to be direct controled from inverter. Might be easyer to swap mills electrics to be able to control 240 volt single phase so power goes though mill electrics the to inverter and direct to motor , pain in the ass for lathe as well I bet but prob only option.

Guru sez motor is prob fine on mill as faults like phase backwards or burnt out etc would draw more current , other thing pointing to mill electrics is when you run lathe through mill electrics the current should have remained the same as when it was direct to the lathe or gone up , not down to 4 amps! Other possablilty is mill is just drawing more power than the inverter can throw at it happly and inverter is going into current protection mode (but less likley as they usally just stop)

[Redmohawk]

The other thing is (and not taking the piss here) is it possable the mill has an Issue ? Ie are the pulleys alley ? if so might be warn into a U shape belt slip ???? instead of motor rpm dropping ? just a random thought.

[livewire]

'Sniff' test the mill motor.
Smell of death is unmistakable.
Burnt varnish.
Brushes?

[Deano]

ok will have to explain a bit better.

the mill motor is powered directly from the invertor. the contactor is only used to 'contact' the 24v forward/reverse control wires. when i use the mill electrics to power the lathe motor it works great draws 5.6amps at full rpm.

don't think the electrics on the mill are an issue at all. the invertor gets its power from the master switch before the the power goes into the contactor. the contactors take care of the switching of the invertor not the power to the invertor.

when i power the mill motor it draws 3 amps. and no more. with no load, pullies are fine they are cast and in good shape. can tell mill motor is dropping in rpm as it gets to a stage that i can nearly count the revolutions.

my only saving grace is if the wires for delta and star have been paired incorrectly but my motor guy says the motor would just not run at all.

motor does not smell at all. no brushes. motor ran fine when i went and looked at it befre buying it.

will be pulling the motor off this weekend to send to another motor rewinder next week for a second opinion.

[Hagarr]

Hey Deano what does the inverter conversion cost you?

I've just moved in to a new house/shed and I am currently getting a price to upgrade the 3 phase power for my equipment.

[Redmohawk]

Yeah mate , passed on info to guru he sez prob a burnt winding or a dodgie conection inside the motor, but sez its seems strange as it should be using more current if that was the case, sez time to pull it off yep and have it looked at. If it needs to be rewound prob cheaper to buy a 240 single and use it instead.

[Deano]

it is a special motor mate. not that easy to replace or i would have done that from the start. have a output shaft that is about 120mm longer than standard and an odd flange bolt pattern. major works needed if i have to put on a universal motor.

invertors are about 300-400 a few connectors a bit of wire and time and that is it. i alse brourght a fancy enclosure for the invertor that was another 100

the lathe needed a new 3hp 3phase foot mount motor so add another 250 to the above price to convert the lathe.

also forgot had to buy new single phase coolant pumps. another 109 per pump.

the thing about putting 3phase on is the fact that when i move house next i will have to put 3phase on again. they think roughly 4-5k for me to put it on. the equipment is worth more on single phase anyway

[Redmohawk]

Yeah I feel your pain mate been there in the past not with motors but welders (bigger issues lol) now I stick to small and 240 lol

Could you not nock up something with the lathe to adapt a universal for the mill? adaptor plate and drive shaft arrangment? Or have the guts of the motor replaces (just keep the housing and rotor and have a new field assembly fitted , you could prob do most of it yourself with assistance from a motor rewinder)

[Deano]

yes i could make a universal motor fit but i don't want to if i can avoid it. it would be a easier job to do if i had a mill going to pitch out the holes etc.

see what the next week holds. i may be making a new motor fit if the motor is stuffed

[Deano]

well the plot thickens.

i just got back from the rewinders and he pulled my motor apart and tested it.

guess what ---- it tests out perfect. we had it running on 220v 3 phase and when you turn it on while holding the motor on the bench there was a 'kick' when starting as the motor wanted to spin around its rotor.

the rewinder said the rotor was good. it tested up fine.

the only thing it can be now is that the vacon invertor is not compatible with the motor.

so frustrating

got a couple of things to double check but am not that hopefull. next is to buy the WEG brand invertor that the other guys are using with great sucess and cross my fingers

[Redmohawk]

Bummer mate lol but I guess theres no hassle with rewinding/fitting a different motor.

[Deano]

no but still got to get this fucker to work

[Deano]

i think i found the problem.

and guess what

it was not the invertor or the motor.

you will laugh at this one.

after getting the motor tested i went home and had a good think about what was going on. i returned to basics would you say. i connected the motor up to he invertor and electrics of the lathe and ran it on the floor. i got a welding glove and shoved my hand in the between the cone pullies to load the motor up. it pulled 6 amps. all looking good at this stage.
then i installed the motor back on the mill.
i pulled the covers off the side of the head so i could look in and see what the pullies were doing when i turned the motor on and played with the variable speed dial.

i started the motor again off the lathe invertor and electrics and wound the handle and once again the motor only pulled 3amps and as the rpm of the dial increased the rpm was decreasing. - you can see where this is heading cant you.

i then pulled the fan cover off the motor so i could gauge just how much the motor was slowing down. when winding the speed up the rpm were dropping like made until i could just about count the rpm of the spindle when the dial indicated 4200rpm. i then stood on a chair to check out the fan speed and what do you no the motor is still flying around at what looks like full speed.

by this stage i was in shock . i had this awful thourght that i had gone through all this stuffing around all because someone had pulled apart the variable speed dial and put it together back to front so when you wound on more rpm the dial showed the rpm increasing but infact it was actually going the wrong way.

i had a little look behind the adjuster and noticed hte piece of chain that wrapped around the shaft was wrapping to the right so i pulled it apart adn changed it to wrap to the left put it together and what do you no as you wind the handle the speed goes up matching the speed indicator.

so after all that there was never a problem with the motor or the invertor the problem was that i was watching the speed indicator dial increase in rpm but hearing and seeing the spindle drop in rpm after just having a quick look at what was going on came to the conclusion that the motor was causing hte problem. if i had have taken a little more time to look further i probably would have found it but hey it now works. now i can start making swarf.

thanks to all that assisted with my problem sorry to send you on a wild goose chase.

[Redmohawk]

Hahahahahahahhahahahahaha now all you have to do is find the wanker who put it together backwards and run him through the mill lol