Smoking motor ML7

[jo1010]

Looks like windings are shot ...but in one direction only! Weird? Idk normally I see motors that either work or they dont, but this one runs fine in one direction, but is slow and starts to smoke in the other direction. Any ideas how that can happen?

(It's single phase GEC motor, drum type switch, T2 from switch had been disconnected by previous owner (left floating inside box too). Resistances are ok A1 A2 T1 but A2 /T2 and T1/T2 are both OL)

Not even sure I need reverse on this, so could run as is - but is this winding break the start of something bigger?

 

[Dcal]

What HP is that motor, I can't read the plate?
I might have something similar.

The one on the right came out of my Eagle grinder and is 1400rpm 1/3HP.
I replaced it with the one on the left.

If it's any use you can have it for the postage.

 

[Nederlands]

Is it running free?
Like bearings that only want to go one way (because lack of fresh grease)

I would take it appart to see what is happening

 

[martyr]

same problem caused by centrificial switch contacts stuck on keeping start windings on overheating them

 

[Guineafowl]

The problem is most likely in the drum switch.

If it spins one way fine, then it’s unlikely there’s a problem with the windings themselves.

 

[jo1010]

What HP is that motor, I can't read the plate?
I might have something similar.
The one on the right came out of my Eagle grinder and is 1400rpm 1/3HP.
I replaced it with the one on the left.

If it's any use you can have it for the postage.

Thanks! The Hp isn't even on the plate which is useful haha....the current is on there as 3.4A though...some ML7s seem to have 0.5hp ...this one might be less though as it's a bit older. I think 1/3hp might be slightly underpowered though .....

 

[jo1010]

Yep thanks guys...motor is fairly free in both directions ....I thought to strip and have a better look...switch contacts are a good call......and if that works out ok I'll bypass the drum switch and see what happens. Maybe even get rid of the drum switch all together idk...

 

[Dcal]

Thanks! The Hp isn't even on the plate which is useful haha....the current is on there as 3.4A though...some ML7s seem to have 0.5hp ...this one might be less though as it's a bit older. I think 1/3hp might be slightly underpowered though .....

Current on this one is 2.5 amp so too small.

 

[jo1010]

I'll have a better look over the weekend hopefully and post my findings. Thanks guys

 

[Turbo]

Sounds like a wiring issue because it is running fine in one direction.
To reverse a single phase motor you swap the wires over on either the start winding or the run winding but not both.
Thats what the drum switch does.
You can do the fwd/rev switching with a rotary switch.
Sounds like the previous owner has messed around with the wiring until they got it running without knowing what they were doing!

 

[Turbo]

I'll have a better look over the weekend hopefully and post my findings. Thanks guys

When you have the motor split use the opportunity to soak the felt wicks that oil the bronze motor bushings.

 

[arther dailey]

Yep thanks guys...motor is fairly free in both directions ....I thought to strip and have a better look...switch contacts are a good call......and if that works out ok I'll bypass the drum switch and see what happens. Maybe even get rid of the drum switch all together idk...

are you refering to the o/c (open circuit ) switch as drum switch ? if so it should be connected to start windings and as name suggests goes o/c when motor is up to speed , if it doesn t work and start windings are left in circuit they will burn out , if start windings are nt connected motor will humm and not have the power to spin up in most circumstances.

 

[brightspark]

1/3d hp was originaly fitted but a half is better the super 7 had a 3/4 fitted to run on the higher speed than the ml7

 

[jo1010]

are you refering to the o/c (open circuit ) switch as drum switch ? if so it should be connected to start windings and as name suggests goes o/c when motor is up to speed , if it doesn t work and start windings are left in circuit they will burn out , if start windings are nt connected motor will humm and not have the power to spin up in most circumstances.
.......
The drum switch is a dewhurst type with forward /reverse. The o/c I'm talking about is ohm testing the motor terminals...here

....T1 is the bottom terminal. I think T1 and T2 are the run terminals, and start is A1 and A2. T2 has continuity to A1 and A2, but T1 is open circuit to every terminal. I haven't even bothered testing the dewhurst switch (yet) but I've got a NVR switch to go on it anyway

 

[jo1010]

@brightspark
....I'm thinking a 0.5hp 3 phase motor would also be nice - I've got a vfd waiting, but I'll see what happens with the current one first

 

[Turbo]

are you refering to the o/c (open circuit ) switch as drum switch ? if so it should be connected to start windings and as name suggests goes o/c when motor is up to speed , if it doesn t work and start windings are left in circuit they will burn out , if start windings are nt connected motor will humm and not have the power to spin up in most circumstances.
.......
The drum switch is a dewhurst type with forward /reverse. The o/c I'm talking about is ohm testing the motor terminals...here
View attachment 503179
....T1 is the bottom terminal. I think T1 and T2 are the run terminals, and start is A1 and A2. T2 has continuity to A1 and A2, but T1 is open circuit to every terminal. I haven't even bothered testing the dewhurst switch (yet) but I've got a NVR switch to go on it anyway

I think there is a cenrifugal switch on that motor and the connections for that are on the back of that brown panel.
You can't test the windings or connections properly without getting access to that switch - ie take off the motor end housing.
Will also give you a chance to inspect the windings to see how cooked they are!

 

[jo1010]

...
Will also give you a chance to inspect the windings to see how cooked they are!

Yep, I'm expecting something crispy behind there I think ...

 

[Guineafowl]

T1 is the bottom terminal. I think T1 and T2 are the run terminals, and start is A1 and A2. T2 has continuity to A1 and A2, but T1 is open circuit to every terminal

It’s normally the other way around - A1/A2 run, T1/T2 start. Either way, the start winding should have higher resistance, assuming it’s a split-phase motor.

I don’t think T2 should have continuity to anything other than T1 - for a reversing motor you need access to each winding separately. T1 open circuit is certainly a problem - either an open centrifugal switch or broken wire.

 

[jo1010]

Well, motor is not so bad inside ....once I'd cleared out all the swarf and the accumulated greasy dirt that was plastered over the stator.....
Anyway the windings check out ok at 4 and 12 ohms, and centrifugal switch is ok. My surprise was that T1 (which had previously been connected to the dewhurst switch by the seller) does nada nothing - it's just a terminal that doesn't connect to the motor leads - presumably for additional functions that this motor doesn't have. So I need to check all the drum switch wiring next - and I can see an immediate problem ...there are 3 terminals to connect to on the board but 4 wires from the drum switch, so one terminal must be common?
Here's what I have so far....
Photo 1. Original view of the sellers wiring:

...slightly hard to see so terminals from top down are T2 A1 A2 T1
Photo 2. With motor stripped the connection board is clearer.....
Photo 3. The reverse of the board showing the centrifugal switch in the start circuit, yellow wire and blue wire go to start winding and the points terminal is A2. ......back to the face of the board the run winding is the black and red wires currently going to T1 ....and A2.
Photo 4. I can't find any wiring details for the motor..there's just the terminal cover talking about reversing rotation (last pic)....and especially not the dewhurst switch......i haven't a clue how that switch should be wired atm. Any ideas ?

 

[jo1010]

It’s normally the other way around - A1/A2 run, T1/T2 start. Either way, the start winding should have higher resistance, assuming it’s a split-phase motor.

I don’t think T2 should have continuity to anything other than T1 - for a reversing motor you need access to each winding separately. T1 open circuit is certainly a problem - either an open centrifugal switch or broken wire.

On this one it looks like A1 (the blue wire in my pics) is the start winding (going to the smaller winding in the motor - 12 ohm) and black and red leads are the run winding (4 ohm) going to T2 and seller chose to put the red lead to A2 - but that seems questionable? It's getting late and my brain hurts now haha.
As I found today T1 is just an empty stud on the board (or could it be a common stud to link 2 of my 4 switch wires idk)