How to speed up a motor

[mackconsult]

I bought this centrifuge on ebay a few weeks back. When the rotor is not attached to the shaft the tachometer will wind all the way up to about 9k rpms. With the bowl on and WVO going into the centrifuge I only get about 4.5k rpm's.

I put this pdf together that describes the electrical system of the centrifuge. Couple of questions that hope people on the forum could help me with.

1) what are the items with ?'s on them?

2) is there a way that I can speed this thing up?

 

[jraef]

Well, if there are brushes on the motor, it's either a DC motor with the AC-DC rectification on-board, or what's called a "Universal" AC motor. Either way you can't easily make the motor go faster than it is designed to go, and if you do, it will be at the expense of torque, so you will not be able to load it the same anyway if you do. Why do you need it to go faster?

By the way, just because the dial goes higher than 4.5kRPM does NOT mean that the centrifuge was designed to do so. I have a Toyota Corolla that has an old analog spedometer that reads 160MPH, but I would NOT drive it that fast! Running it at 2X speed, even if you changed the motor, may result in serious risk of it coming apart at high speed, which could kill someone.


"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[mackconsult]

I appreciate your concerns. These centrifuges are designed to spin a star pattern with medical tubes in them. By speeding up the motor my WVO would be filtered quicker. I doubt that upping the speed would be a problem due to the design of other centrifuges I have seen. I am a mechanical engineer and would not propose something that would be dangerous. If I can squeeze out a couple thousand rpm that is what I would be looking for. The casting at the base is super heavy duty, more so than any of the centrifuges I have looked at.

 

[itsmoked]

Just the word "cast" in a sentence with, "more thousands of RPM", gives me the willies. I had a cast flywheel fail next to my feet when I sped it up "a few thousand more RPM". It was a disaster. I wouldn't consider it unless you could run it twice as fast(4k more) as you desire to go and have in NOT fail.

And the energy in a bullet? Nothing compared to the energy pumped into a spinning mass over a substantial period of time.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mackconsult]

The "BASE" is a heavy casting. The rotor bowl is much smaller, machined aluminum. Just had the shaft aligned by a electric motor shop to with in .001" run out. So there is no vibrations that occur through the whole speed realm.

 

[mackconsult]

Is no one going to answer the original question ....

 

[mackconsult]

By the way just for clarity here .... the centrifuge bowl that is aluminum is the only part the spins, and it only weighs about 2 lbs. The cast base that the motor is integrated in weighs about 35 lbs.

 

[jraef]

Electrically, we have no idea what that motor is. Your description makes it appear that it is not a common product.
If it's a DC motor, speed is regulated by the voltage applied to the armature and the strength of the field. As the field weakens, the speed will increase until the motor destroys itself. But at the same time, the torque will drop as well. If you apply a load to it, the motor will respond by increasing current but will at the same time slow down. But there are a lot of variations on this theme and several ways to make a motor work for you. We have no idea what that centrifuge mfr used to make it work, so there is no way to tell you what to do to change it.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

Let me Google that for you!!

http://www.blockscientific.com/centrifuges/iec-hns-centrifuge.htm

IEC HNS centrifuge, with its unique features, represents the perfect solution for work in the areas of industry and research, and in clinics and hospitals. Some of the standard features of IEC HNS are covered tabletop rotor, adjustable speed, speed meter, brake button, on/off switch, rugged steel guard bowl and cover, variable speed control, and timer. The maximum speed/force is 8450rpm/6200xG and the maximum loading capacity is 1L (4 x 250ml).

http://eurtonelectric.com/catalog/motors/damon_iec_hns

Sure looks like a standard motor armature for either a universal motor or a DC motor.
Looks like you are good for over 8K RPM.
BUT It may be wise to check the calibration of the tach before doing anything else.
Then, with a calibrated tach, check the current the motor is drawing (or the line current in). If this is at or close to 2.5 amps, that's all you can get.
Your reading of 42 Volts to ground is meaningless. Check the voltage from brush to brush, both AC and DC.
The red things are probably capacitors. The other thing is a rectifier (maybe an SCR if there is another tab that is hidden in the picture.)
The "brake is probably the tach generator. Braking is more likely effected internally by letting the motor regenerate and then loading it by wasting energy in the resistors.
Whoever had this before most likely turned every adjustment in sight trying to fix it.
CHECK THE TACH BEFORE DOING ANYTHING ELSE. IT MAY EASILY HAVE ENOUGH ERROR TO BE DANGEROUS.



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[mackconsult]

Okay, thank bill. I am planning on getting a strobe first before doing anything to verify the rpms.

 

[mikekilroy]

knowledge is power...... information can add to knowledge....

it is free to call the mfgr and ask them some stuff, like what is the motor type & ratings... The worst they can do is say no.

Sure sounds like it is worth a phone call.

 

[mackconsult]

I am calling today to get mfg information.