Steady-state DC currents superimposed on AC power systems produce waveform distortion and 4th harmonics. This occurs as transformer and motor lamina becomes saturated at the crest of each alternate half-cycle. Multi-grounded neutral networks are subject to stray DC where electric railways...
Have others encountered difficulty with cracking of sintered ceramic magnets in fractional HP permanent magnet motors? Do these cracks grow with time, and can they produce loose chunks that will jam the armature?
The magnets in question are epoxy bonded to the inside of a heavy gage steel...
This thread relates to the issue presented in thread238-114844. Specifically, why would there be a discrepancy between the specified step-down vs. step-up voltage ratios? One manufacturer's specs indicate that the primary output voltage will be 15% low when the transformer is fed through its...
Concerning small, dry-type step-down transformers in the 1-10KVA range, manufacturer's specs indicate that output voltage is reduced by about 15% when used as a step-up transformer. Why would a transformer having a nominal 4:1 ratio produce only 408V under full load instead of 480V with 120V on...
Anyone care to speculate on the possibility that all this has something to do with automatic versus manual control of phase angle regulators scattered throughout the system?
A resistor having a value between 1-5x the coil resistance might be a good alternative to the diode snub.
Advantages: Quicker, more positive release of the solenoid; simple resistor less susceptible to sudden failure caused by surges; no tendancy to rectify stray AC energy.
Disadvantages...
Thanks to everyone for the many useful comments and suggestions. The WF motor in question is a simple series motor; armature polarity is transposed when reversal is required. The controller is a simple on/off contactor. The power supply is steady or full-wave DC.
Kt, aka Motor Torque...
Doug: Determining net energy consumption was not the primary objective, however, this may be exactly the type of ‘figure of merit’ I’m looking for. In this particular case, the appropriate units would watt-seconds. With an operating time of 3-8 seconds, values would probably fall within the...
I’m in search of a simple answer to a complex issue – an expression of the transfer function that describes conversion of amps to torque in a DC motor.
As background information, I am comparing the performance of two types of 1-HP DC motors that operate at a nominal 24 VDC. The wound field...
skogsgurra: An excellent refernce - thanks! The particular system involved is not nearly as sophisticated as a servo-controlled disc drive (i.e. it is controlled by simple contactors and limit switches). Anyone else with information or anecdotes related to a PM motor's capacitor-like behavior...
Oh no... I feel that five bucks slipping away. GusD: better make other plans for acquiring that new set of balls.
skogsgurra has two good points: first, the bridge rectifier tends to create a peak-holding circuit, and second, I've carelessly used power loss (I*I*R) instead of voltage drop...
Another interesting point. In this particular instance, the voltage rise is consistent among several different motors on differing circuits that are geographically separated by many miles or more. Nothing to pursue here.
Aside from one instance of a loose magnet jamming against te armature, I...
I have a five dollar bet with a co-worker on the correct answer to this question, so please give it your best!
Here’s the scenario: A small (about 1 HP) 120 VDC permanent magnet motor drives a reversible mechanism that imposes a varying mechanical load. The 120 VDC source is a simple...
Difficulty has been experienced with silver-impregnated carbon contacts exposed to silicon compounds outgassing from RTV sealent inside a relay's dust tight enclosure. The failure mechanism works like this: Minute arcing occurs each time the contact opens. Silicon present in this atmosphere...
