The centrifuge is designed to cut out if an out-of-balance occurs. First, check that the buckets are evenly balanced, the maximum allowed is generally about 5g.
Remove the buckets if it is a swing out rotor and run the centrifuge with just the rotor in place. If the centrifuge now runs smoothly weigh the buckets to ensure they are of equal weight. Often the inserts/cushions get mixed up during cleaning, thus making the overall bucket weights uneven.
Buckets, at times, do not swing out correctly during the run due to dirt or dried grease on the trunnion pins that the bucket sits on. Clean and lubricate trunnions and bucket slots.
Check that with the buckets on the rotor they swing up to the horizontal position freely, then try the same with tubes in place. This is because the tubes may be too long and may be catching on the rotor.
The imbalance detector may be too sensitive. All centrifuges in general will cut out at about 500 to 1000 rpm to prevent damage to the machine if an out of balance is detected. The set up of the imbalance detector will require an engineer.
Often users operate the centrifuge without performing a pre-cool. The motor in the centrifuge generates heat and the cooling comes from the rotor bowl. It is unrealistic to start a centrifuge at ambient temperature and run it at full speed and expect the refrigerator to pull the temperature down to say 3 degrees on a 10 minute run.
We advise you to run the centrifuge with no samples in the rotor at the required temperature at a low speed such as 800 rpm for 15 minutes to allow the bowl and rotor to get to the set temperature. Then put samples in and run as normal.
After use, all refrigerated centrifuges should be left with the lid open to allow the frost on the inside of the bowl to evaporate. If the lid is shut after use, the frost melts and remains in the bowl, this can cause corrosion and is the main reason for damage to the top bearings in the motor or drive assembly. This can be a costly operator error, always leave the lid open.
Sometimes the out-of-balance switch jams in transit. Try to move the motor and rotor about. Just by this action, the out-of-balance switch will reset itself and the problem is resolved.