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Dead Centrifuge

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Dead Centrifuge

Postby centrifugemurderer » Mon Jan 19, 2009 12:12 am

Hi everyone,

My microcentrifuge has gone on the fritz. I was spinning some cells down _at_ 2000rpm when, in the middle of the cycle, I heard the centrifuge began to speed up. The display showed the speed going up to ~11000rpm before the centrifuge suddenly died. There was a strong smell halfway between burnt rubber and burnt motherboard. The thing came with a spare fuse, but when this was replaced, it immediately revved up and died all over again.

It's been sent in for repairs, but could any of you diagnose the problem? I'm hoping to free myself from culpability here. There were (gasp!) five eppendorf tubes in the microcentrifuge at the time, two on one side and three on the other. I've been told that this imbalance - or at least, the accumulated stress of such malfeasance over the two weeks that I've been using this machine - is why the thing broke. It should be added that the machine was not shaking like an unbalanced centrifuge (and yes, I've seen and heard unbalanced centrifuges before) at the time. Another person has told me that the inner lid should have been on the centrifuge. I use the lid to minimize noise, but according to this person the second lid is necessary to maintain some sort of vacuum. (Why?) I have been using microcentrifuges for three years with these same practices and have never killed one (or been reprimanded) before.

Are these really the causes of the machine's demise? What could cause a tabletop microcentrifuge to fry this way while spinning at 2000rpm?
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Postby mith » Mon Jan 19, 2009 1:35 am

speeding up means there's something wrong with the speed control no?
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Re: Dead Centrifuge

Postby MichaelXY » Mon Jan 19, 2009 4:47 am

Most well designed units won't run with the lid open ( Safety reasons) Vacuum theory sounds silly. And again good units shut off when an imbalance occurs. Like Mith said, this sounds like a failure beyond your control as in speed control went kaput...
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Postby canalon » Sat Jan 24, 2009 3:19 pm

Yes, your centrifuge was not balanced.
And yes the accumulated stress on the rotor can cause the centrifuge to break. This stress wil depend on the importance of the imbalance and the speed at which the centrifuge is running.
And in the case of a small tabletop centrifuge, the imbalance is just noticed by a slightly louder noise that is immediately recognizable. However I guess it would be drowned in the "wind sound" if you run it without the plastic cover.
So I can say that you are groslly negligent, but I cannot prove that you are guilty of the murder of this centrifuge.

To answer some of you other concerns:
- There is no vacuum in a tabletop centrifuge, the plastic lid is used to reduce noise and to prevent the dissemination of aerosols created in the centrifuge in the room. You can notice a strong wind behind the centrifuge where the air is quickly expelled while running. If your tubes are contaminated or not closed some liquid can be aerosolized and blown into the room. Now depending on what you are spnning, it can be a problem (spores of B. anthracis) or not (rat cells in PBS). But it is usually considered safer to avoid spreading unknown in the air shared in the lab.

-I do not know waht model of centrifuge you were using, bu there is no reason NOT to balance your tubes. Most centrifuges have a rotor with 24 spaces. In those you can balance everything but 1 and 23 tubes without the addition of counterweight. Balancing 2 tubes is easy, balancing three just as well but instead the tubes must be located at the 3 angles of an equilateral triangle (so for a 24 tubes rotor, in the locations numbered N, N+8 and N+16 as in 1,9,17). Combining your tubes in groups of 3 and 2 allow all numbers between 2 and 22 to be balanced:
2=2
3=3
4=2x2
5=2+3
6=3x2=2x3
7=2x2 + 3
8=4x2
9=3x3
10=2x3 + 2x2
11=3 + 4x2
12=4x3
all the other configuration can be deduced from those replacing the tubes by the holes...
Patrick

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)
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