Motors braking time

Many circular saws and other rotary machine actions continue rotating for some time after they are shut off. Electronic motor brakes can stop the rotary motion within 1 to 2 s after the power is off. 

Drive motors should be of the high-starting-torque type and selected for 1.33 times maximum rotational speed. For two- or three-diameter Idlns, the brake horsepower for the several diameters should be calculated separately and summed. Auxiliaiy drives should be provided to maintain shell rotation in the event of power failure. These are usually gasohne or diesel engines. 

I. A CMR motor therefore can be operated at higher outputs on short-time duties as shown in curve (d). The extent to which a CMR motor cun be over-rated to perform a particular short-time or intermittent duty is considered in the follow ing example. While evaluating the rating for such duties, the heat during start-up and during braking and their frequency of occurrence should be considered. 

Therefore the heat of the motor during plugging is three times that of during a normal start. Stator heat and thus the total motor heat is a function of the rotor heat (see also Section 2.7.1). Such a method is therefore not suitable for larger motors or for frequent brakings. 

Duty types. S, S, and. S5 as discussed in Chapter 3 are normally applicable to crane and hoist motors. For duty types S4 and 5. the duty cycle per unit time is greater than S, . The most important factor is the number of switching operations per hour. A temperature rise in the motor occurs during acceleration, braking and reversing. 

Ford s Think NEV came in two and four passenger models with a range of 30 miles. It had a 72 volt battery with a 5,000 watt DC motor. The charging time was 4 to 8 hours and it had regenerative braking with hydraulic drum brakes. The price range was 8,000 to 10,000. 

Bowl rotates too slowly Check that brake is released that bowl rotates freely that motor and electric equipment have no defects that friction pads of friction blocks have no defects. If worn out, change all pads at the same time. Wash oily pads with trichlorethylene or some other fat solvent and roughen up the friction surfaces with a coarse file. 

Heat load from motors. Use 2,545 times actual brake horsepower divided by the fractional motor efficiency (0.80 to 0.85) for all motors within the enclosure. This gives motor heat load in Btu/hr. 

Each singly driven motor vehicle not subject to the parking brake requirements of FMVSS Nos. 105 or 121 at the time of manufacture, and every combination of motor vehicles must be equipped with a parking brake system adequate to hold the vehicle or combination on any grade on which it is operated, under any condition of loading in which it is found on a public road (free of ice and snow). 

---