3hp motor problems

[arther dailey]

good job !!

 

[Sausage]

The plate says uF R 45 which translates to 45 uF run capacitor

Nice one! I am learning...

 

[Sausage]

Poop. (or whatever language will pass here)

Dug out my manual for my fluke meter and yes i had to press an extra button to get it on the farad scale. The cap measures 45.8 (discharged and disconnected).

Sooo, i'm thinking the windings are likely shot now, so is that due to me not drying it enough or an underlying problem that fried the 1st cap?

Will strip the motor later when my headache eases off.

 

[arther dailey]

Strip it down, if it isnt obvious by sight or smell check the windings to earth with a megger tester if you can borrow one,it may still be cap, we tested them by charging with a megger then dis charging by shorting terminals,if you get a weak spark its duff,if you get a crisp crack its good, yes their will be others who disagree with this method, but I can tell you now it is the only way to check a cap under load that is 100% reliable.we honestly tested thousands like it as customers wouldnt appreciate a rewind firm sending back a overhauled mtr that didnt work.Arther

 

[arther dailey]

I find it depends on age - I've a few 'recent' motors that have a single cap always in circuit and a few older ones that have a single cap and a centrifugal switch.

Extrapolated from the large sample of single phase single cap motors in my shed, I'm going to say it's 50/50

Its all down to starting torque/work load required wether it permanent capacitor or not,dependant on machine its designed to run, cap start with o/c switch is generally up to 3/4 hp, mostly after that the larger ones have to be permanant cap so start winding stays in to give it the extra power when running,you will find also some fitted with twin capacitors,varying value,one to start and other switches in on run mode.as with welders there is only so much power you can sqeeze out of single phase.
the motor in question here is a nice piece of kit.Arther

 

[Sausage]

Stripped and tested for resistance. There is moisture on the inside of the rear end cap and a small amount on the front one.

Resistance figures are:

Blue - Red 1.3 ohm
Blue - Brown 1.4 ohm
Red - Brown 1.0 ohm

Any lead to earth screw on casing = 7.2 M ohm.

Pics: (you can see the tide mark)

Not sure i can get away with this in the oven, so any other suggestions for drying this out? I have a griddle or a fan heater.

 

[dobbslc]

I know you names sausage but frying on a griddle it would be a bad idea!
I reckon an hour lightly heated by a fan heater whilst gently turning would do it.

 

[Sausage]

Make that a commercial grade griddle and a laser thermometer, but yes i think i will roll out the fan heater instead.

 

[arther dailey]

fan heater, let it blow threw the open core,horizontal, try putting a bit of tin or similar on top of motor , and possibly at the other end couple inches clear so as to slow but not stop air flow,overhanging on top to slow down the heat loss ,but make sure air flows otherwise you will blow/burn heater.after four or five hours reverse and cook other end, you might find as it warms condensation will appear from the laminations,which shows its damp. we used to stove for minimum 8 hours. cant tell if those are good readings need a megger really.
If when finished it tests ok see where rust in inside case behind windings,get a small brush and paint with red oxide, same with end plates,obviously not the registers.also warm and dry rotor and end plates.
Windings look good but that can be deceptive, just see how readings improve as it dries,shame you cant get hold of a megger.Arther
ps sand rust of centre of rotor...

 

[windingroads]

That's an induction motor, drying that solid rotating part is not really necessary as there is no wires in it.
Its the windings that need dried, and to me they look heartened, as suggested a megger would be the job.
You can test your Capacitor by charging it for up to 4 seconds, that will give you enough time to throw a switch with a household light bulb across the cap, with the feed to the cap disconnected, it should light good and bright like normal, not completely definitive but it gives on an idea if the cap has enough oomph.

 

[Sausage]

Thanks, i have had it on hot for 2 hours about 10 inches from the fan changing ends and then medium for a couple of hours and just now switched it onto cold air. Now reading your reply I will do it some more and do the rotor too.

The windings got to maybe 60 - 70c using mk1 finger to test it with.

 

[windingroads]

you could run a 500 to 1000 watt electric fire in series with the windings, that will warm up the windings, you could also
measure the current flowing through them, at a 1000 watts it should be about half the current of the motor when running.
I used to do this do dry out big generators, the heat of the fire or if you use large lights should also be directed at the windings, not too close as slow drying / warming is better.
If you do this, test between where you feed the windings and the motor casing for power, there should be none, also if your windings
start to smoke as you draw for example 500 watts through them then they are arcing somehow and it will be clear that they are done.
If you care to try this use a fuse and a trip, and keep clear until you test for shorts first.

 

[Sausage]

Can i do something similar with dc instead as that is well outside my comfort zone?

 

[windingroads]

You sure can, but to produce enough DC to heat things up will give you quite a lift too, the trips in the house will save you with AC, but as you seem to be heating it up now anyway why stop, DC is more dangerous than AC given the same voltage.
You also have to use a DC device to draw the current, a bulb of fire will do this fine, but DC will heat your fire element or bulb more than they are rated for.
I have looked at your images again, and I would not depend on those windings, they look
heated, and even looks like drips of solder on top of them in a place or two, the insulators are also melted in places, none of this suggests anything other than a rewind or new motor, or even better a wee engine sitting on to make it portable.

 

[rtbcomp]

DC and AC RMS have the same heating effect.

A coil has less "resistance" to DC than AC because the inductance acts on AC, but not DC. You will get the same heating effect though as the inductance of a coil doesn't produce heat, just the resistance component does, (neglecting heat produced by eddy currents).

 

[arther dailey]

Well I only rewound motors every week for 18 years what would I know ! one of the larger ones being the turbo alternator on HMS Hermes!! the windings look good,but may be internal shorts or shorts to earth, the slight glistening you can see is the resin where dipped.you wont see any solder as joints are brazed or silver soldered.
yes the rotor is solid but watch the sweat come out of it as you warm it up,and strangley water and electrics dont seem compatable, anyways I think I will step out of this because to many cooks spoil the broth . good luck ,hope it works out for you. I will keep my fingers crossed. Arther

 

[windingroads]

Well I only rewound motors every week for 18 years what would I know ! one of the larger ones being the turbo alternator on HMS Hermes!! the windings look good,but may be internal shorts or shorts to earth, the slight glistening you can see is the resin where dipped.you wont see any solder as joints are brazed or silver soldered.
yes the rotor is solid but watch the sweat come out of it as you warm it up,and strangley water and electrics dont seem compatable, anyways I think I will step out of this because to many cooks spoil the broth . good luck ,hope it works out for you. I will keep my fingers crossed. Arther

arther is right, I never dipped windings so mistook what could be dry lacquer or whatever they use for solder, seen plenty of solder though laying in the back of over heated burned out generators.
I said there really is no need to heat the rotor, never said not to dry it, which would be the obvious thing to do.

 

[Sausage]

Figures after my dying efforts from yesterday and another hour or so on hot today, are (back at room temp):

Any lead to earth = OL

The other figures havent changed all that much.

Motor starts and runs now but is slow (maybe half speed) and noisy and if left to struggle will trip the overload switch (with no pulley no belt) after maybe 10 seconds. Cap reads exactly the same 45.8uf and the resistances are the same after running it.

 

[Sausage]

OK update: have bought a Megger insulation tester and tested it just now:

Any lead to earth = >1000 M ohms on 250v or 500v (yes it is putting out those volts as tested with my fluke)

So the windings should be good I would think and I need to try another cap.