Motor analyzer
#31
Joined: Jul 2010
Posts: 2,741
Agreed. Stator variance is far easier to keep consistent than rotor variance. You'd need a hugely defective stator to increase the current by 50%. The two components with the highest variance are the rotor or sensor board. The latter can actually be checked by an analyser.
Stator resistance can vary HEAPS out of the factory. Easy to see 1milliohm per phase (tab to collector) between two samples.
Rotors I have found to be much closer out of the same batch. Typically it’s 25gauss or so variance.
25 gauss is around 1.5% typically, 1milliohm is more like 5% on a 17.5 - and as said, the latter is more common to see.
Sensors vary a heap too - but you can “tune” around it.
#32
not in my experience. I’ve tested the individual components (stator, rotor and timing board) of motors of 2 reputable brands for well over 100 “identical” samples of both groups when brand new and then for a very high portion of them, as used units as well.
Stator resistance can vary HEAPS out of the factory. Easy to see 1milliohm per phase (tab to collector) between two samples.
Rotors I have found to be much closer out of the same batch. Typically it’s 25gauss or so variance.
25 gauss is around 1.5% typically, 1milliohm is more like 5% on a 17.5 - and as said, the latter is more common to see.
Sensors vary a heap too - but you can “tune” around it.
Stator resistance can vary HEAPS out of the factory. Easy to see 1milliohm per phase (tab to collector) between two samples.
Rotors I have found to be much closer out of the same batch. Typically it’s 25gauss or so variance.
25 gauss is around 1.5% typically, 1milliohm is more like 5% on a 17.5 - and as said, the latter is more common to see.
Sensors vary a heap too - but you can “tune” around it.
#34
Joined: Mar 2011
Posts: 6,410
From: Austin,TX
I just got off the phone with Ron Schuur of Schuur Speed and he said there is no way two brand new motors would pull those different amps because of the slight manufacturing differences between rotors. He said the only explanation is that the stator in the one pulling less amps has a lower internal resistance. He stated the motor pulling less amps is the better motor. I trust what he says as he literally sets up locked timing motor batches for spec classes at big races.
If you want his phone number I'm sure he'd love to talk to you about it.
If you want his phone number I'm sure he'd love to talk to you about it.
I mentioned above that I would go with the motor which offered the closest gap between the timing across all 3 phases which can be measured with the analyzer, that's the motor I would pick regardless of the amp draw. The closer the gap on timing is the motor with better shim setup and will theoretically offer the best efficiency/power ratio.



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