Extractor motor cutting out.

[Oscarmonster]

I'm having a few problems with my extractor. It an old Thorne 12 frame jobby with a motor underneath. Shortly after I bought it 2nd hand the old friction drive wore out so I decided to replace this with gears and a speed control unit.
It's currently too fast so I may have to go back to the drawing board with the gearing.
The main problem is that the motor keeps cutting out, it seems to be the speed control unit that is doing this.
Anyone got any suggestions why it might be cutting out?

 

[badger65]

does it have a thermal cut off.

 

[oliver90owner]

How much too fast?

Could be going out on thermal overload if motor is running high power on slow speed. Could be triac falling below usable gate voltage. Could be anything, really. Need to know much more information on what changes have been made and the type of motor etc.

 

[Oscarmonster]

I suspect it has a thermal cut out, not sure.
The motor is a 1/4 HP Hoover Mark IV, max RPM 1450.
I have used the thorne 2.5/1 gears reducing max speed to 580 rpm.
I was hoping the speed controller would bring it down to a useable speed, I can't tell you what it's current min speed is, I just know it's too fast.

 

[Oscarmonster]

The speed controller is ebay item number 371008491168

 

[Gilberdyke John]

I'm having a few problems with my extractor. It an old Thorne 12 frame jobby with a motor underneath. Shortly after I bought it 2nd hand the old friction drive wore out so I decided to replace this with gears and a speed control unit.
It's currently too fast so I may have to go back to the drawing board with the gearing.
The main problem is that the motor keeps cutting out, it seems to be the speed control unit that is doing this.
Anyone got any suggestions why it might be cutting out?

If the motor is fan cooled any reduction in speed may result in very significant reduction in cooling effect and the motor thus overheating. I suggest your gearing should be based on motor full speed being matched to maximum operating separator speed with the reduction unit only used for soft starting and stopping.
First thing to check though is does the separator turn freely when loaded.

 

[Oscarmonster]

Thanks that makes sense. I will revisit the gearing. What max rpm should I aim for?
And yes everything spins freely

 

[oliver90owner]

Definite gearing mis-match.

You are about three times the maximum speed for the extractor. That will mean the motor is being operated at probably less than 10% of rated speed for slow extractor rpm, at the start of extraction.

Not surprising there is a problem or two!

I remember, about thirty five years ago, when an engineer doubled the diameter of an extraction screw (so about four times the effective cross sectional area) AND increased the pitch, so the screw needed to rotate at about one sixth, or eighth, of the original for the same output., while retaining the original drive train. When the error was pointed out, they added a reduction gearbox in front of the original - then promptly destroyed the original gearbox by considerably over-torquing it!

 

[Oscarmonster]

Might try pulleys and belt instead.

 

[beenovice]

I suspect it has a thermal cut out, not sure.
The motor is a 1/4 HP Hoover Mark IV, max RPM 1450.
I have used the thorne 2.5/1 gears reducing max speed to 580 rpm.
I was hoping the speed controller would bring it down to a useable speed, I can't tell you what it's current min speed is, I just know it's too fast.

If you have the "2.5" gear on the drive side and the "1" on the driven side, then surely this is going to speed the unit up. You need the smallest gear on the motor, and the largest on the driven side. This will then slow the unit down, and give more torque to the motor.

Make sure you have them this way round. You may also have a current trip inside the motor. If the load is too heavy for the motor it will trip as a safety measure. Improve mechanical advantage by going to a ratio larger than 1:2.5

 

[Oscarmonster]

Yes I have the gearing the correct way round. Would be about 3000rpm the other way!!!!

 

[alanf]

Thanks that makes sense. I will revisit the gearing. What max rpm should I aim for?

Some commercially built extractors quote ranges around 100 or 200 rpm. What is appropriate depends on the radius, the greater the distance the more the acceleration for the same rotation speed. For instance, 120 rpm at 30 cm radius is going to give nearly 5 g acceleration.

One consequence is that smaller radial extractors may be more likely to damage frames. To get the acceleration you want for the frame edge near the centre, the outer side can easily be getting double or more.

 

[Gilberdyke John]

Thanks that makes sense. I will revisit the gearing. What max rpm should I aim for?
And yes everything spins freely

The shaft speed of the separator should be available from the manufacturers but failing that someone with the same model might be able to help. Different cage diameters will likely be designed to rotate at different speeds so don't assume a different separator will be suitable to copy.

 

[Oscarmonster]

Tested my extractor with its new home made plywood pulley system this evening. Worked perfectly thankfully.