I've been working with a universal motor that I've removed from a vacuum cleaner. I'm trying to get it to spin at 16,000 RPM, while under load. It's hooked up to the house's AC main line, and I'm trying to reduce limitations, in terms of how much current is allowed to flow through the motor. So, I have it hooked up to an electrical wall outlet whose circuit breaker allows 30 amps of current to flow, before tripping, rather than the typical 20. Despite doing this, the motor still tends to shut off, once it draws about 21 to 23 amps of current.

What's weird is that the house circuit breaker never really trips. I know this, because, although the motor shuts down, other appliances, on the same circuit, continue to work. Only the motor shuts off.

Upon closer inspection of one of the stationary coils of the motor, there appears to, potentially, be some sort of circuit element, like a resistor, or diode, that's grafted inline with the coil. Has anyone ever seen anything like this? Could it be what's causing the motor to shut down, once more than 20 amps starts flowing through the wires?

This is the first time that I've started toying with a universal motor. My hope is that someone, with more experience, may have an idea of what this little inline device may be. Are current-limiting circuit elements known to exist inside of some universal motors?

Thanks for your attention. Any hunches or insight, is greatly appreciated.

 

Hi,
A motor can be protected by a Thermal cut out or self resettable over current switch.
E
https://www.google.com/search?client=firefox-b-d&q=PTC+cut+off

https://www.google.com/search?clien...RHpAG8QtKgLegQIEBAB&biw=1448&bih=767&dpr=1.09

https://www.google.com/search?clien...WoQALEQtKgLegQIFxAB&biw=1448&bih=767&dpr=1.09

 

I've been working with a universal motor that I've removed from a vacuum cleaner. I'm trying to get it to spin at 16,000 RPM, while under load. It's hooked up to the house's AC main line, and I'm trying to reduce limitations, in terms of how much current is allowed to flow through the motor.

I agree, it does sound like a thermal fuse/cut-out, A Universal (series field motor) operates in a run away condition, IOW with no load, the RPM increases to maximum rpm and minimum current.
If you load it, the RPM reduces drastically, with current dependent on load,
16000rpm with high load may be asking too much to get both at the same time.

 

It's likely that the motor will rapidly overheat if you try to run it at a higher current then the built-in current limiter allows, since the winding resistive losses are proportional to the square of the current..

 

But to me 16,000rpm and under load may not be possible, depending what the load is, Vacuums usually max out at 20,krpm's.
All depends on the nature of the load imposed on the motor?
A ;little more info on details of the project may help?

 

Hi,
A motor can be protected by a Thermal cut out or self resettable over current switch.
E
https://www.google.com/search?client=firefox-b-d&q=PTC+cut+off

https://www.google.com/search?clien...RHpAG8QtKgLegQIEBAB&biw=1448&bih=767&dpr=1.09

https://www.google.com/search?clien...WoQALEQtKgLegQIFxAB&biw=1448&bih=767&dpr=1.09

Thanks for the helpful information.

 

But to me 16,000rpm and under load may not be possible, depending what the load is, Vacuums usually max out at 20,krpm's.
All depends on the nature of the load imposed on the motor?
A ;little more info on details of the project may help?

At this point, my intent is to attempt to lessen the load.

The motor is being used to turn a vertical shaft, which has a diameter of 2 inches. The shaft spins a plastic disc, that is 11 inches in diameter, and about 1/16 of an inch thick. I'm using air bushings to support the shaft. However, the shaft isn't one piece. The air bushings require a tight tolerance on the shaft. So, the portions of the shaft that come into contact with the two air bushings, are made of stainless steel. The rest of the shaft is made of plastic; joined to the steel sections with plastic inserts and plastic shaft collars.

Because the whole shaft isn't one solid piece, it tends to vibrate and wobble a lot. At this point, it seems to have topped out at a speed of about 8500 RPM.

When I try it with a single, hollow, stainless steel shaft, my hope is that it'll perform a lot better. However, because I need to double the speed, I've already started wondering about needing to find a faster motor. My hope is to stick with brushed motors, since brushless motors have turned out to become quite a challenge.

Vacuum cleaners seem to be the best source for fast, brushed motors, that I can think of. Blenders have smaller motors; allowing vacuum cleaners to out-perform them with greater torque and power.

If you, or anyone, may have a better idea of a source for faster brushed motors, I'd be glad to hear about it.

Thanks for your input.

 

It's likely that the motor will rapidly overheat if you try to run it at a higher current then the built-in current limiter allows, since the winding resistive losses are proportional to the square of the current..

You're probably right. Which is why, for now, I'm choosing to keep the current limiter, while trying to lessen the load on the motor.

Thanks for your insight.

 

I was asked to "look at"the motor for a very high speed leaf vacuum, which was lighting up the whole plastic housing. The label claimed 15,000 RPM, and certainly the motor did scream at a very high pitch. The "lighting up" was caused by commutator arcing spreading completely around the commutator, producing a very bright green glow from the ionized copper vapor. UNdoubtedly this was made a bit worse because one segment has raised up a small amount, and is playing hobb with the two carbon brushes.
My point being that in general, high speed failures of rotary mechanisms are both very rapid and rather destructive. A very graphic example can be seen in the damage done by a breaking apart clutch mechanism in a dragster, where the broken segments would pass thru the bell housing , the floor, and the drivers leg, on their way out. And that was usually at less than 10,000 RPM.Current dragsters in NHRA events have the driver in a different location so that is no longer able to injure the driver. Things still fail but the driver is able to walk away with both feet still intact.
A vacuum cleaner motor failing will not be on that scale, but even commutator fragments can do a fair amount of damage. And the pieces of an 11 inch plastic disc could be very damaging at high speed.