Thread: Discussion Change sun 12 bladed 70mm
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Old Feb 03, 2013, 06:52 AM
PeterVRC is offline
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Australia, VIC, Melbourne
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hehe, I can see the logic in those processes.....

Today I attempted to balance an L2855....
It has a terrible noise... buzz sort of.... at a few RPM areas. It seems to be the bearings to me. No balancing attempts could reduce that..... so I gave up for now.

I then balanced the shaft/rotor/nut assemly statically - testing the rotor at various spots around the shaft adaptor too. It needed a few 'small chunks of fibre tape'. Enough to be measurable (I should have weighed the clump! DOH)

The I put the shaft adaptor onto the motor - an inrunner (not the lousy L2855!!) and checked it for running true - it looked perfect to me. It was already a nice snug fit on the shaft and testing by hand, and by Phone Accelerometer, the vibration was negligible.

I put the fan on and tested it by Phone Accelerometer.... it was "approx 10m/s/s".... I just rotate it approx 45deg for each test (very easy to do in situ), and within a few moves it passed through 3m/s/s... so after checking it getting larger again past that, I went back to that spot. That proved to be super smooth. Perfect.

I don't know what part the rotation actually 'matches up' to give optimal balance... probably a bit of a few areas. eg possible motor imbalance, or possible shaft adaptor on motor shaft 'error'.

So I grabbed another one and did all the same stuff.
7m/s/s at best, but that is still very smooth anyway. Its worst spot was about 12m/s/s, which was still not terrible by any means. So I would say anything 5m/s/s, or better, is a good result. Not a single 'buzz' etc at any RPM point.

But I can see that 3m/s/s is possible, so I will revisit the first one again tomorrow to pinpoint HOW to get it under 5m/s/s also.
After doing this process I doubt that NOT Static Balancing the rotor/shaft/nut could match the end result they got. The rotor would have been a dominant offset that probably would not have anything else to cancel out enough.

But I would have to do them again with NO balance weights in them, to see what that really did. Plus I wouldn't mind pulling out the weights and weighing them to see what amount it was that they needed. So I guess I will try that when I re-do the first one....
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