All EMD radiator cooling fans since the change to electric fans after the FT are three phase AC motors that are powered by the companion alternator mounted to the main generator or alternator. The 48" AC fans, introduced mid-production on the GP9 IIRC, run at nominally 2 times engine speed. So at 900 rpm engine speed, the fans are running at about 1,770 rpm, twice engine speed minus the slip of the AC motor. The companion alternator puts out about 200 volts at 120 Hz at 900 engine rpm so the motor is designed for that source.
In 1980, EMD introduced the Q-fan accross the domestic model line in order to comply with the reduction in loco wayside noise required by EPA regulations and enforced by an FRA regulation. The prior fans had the motor supported on radial struts from the fan frame that were on the inlet side of the fan. This caused a siren effect that has been described in this thread. The Q-fan inverted the fan construction so that the motor support struts are located on the discharge side of the fan, which eliminates the siren effect and makes the fan noise more of a white noise. The Q-fan has 12 spots equally spaced on the fan hub where blades can be bolted but the motor is only powerful enough to handle 9 blades so no fans with more than 9 blades are used. EMD has made fans as low as 4 blades and uses as many blades as are required for a particular application, so unless you look, you don't know for sure how many blades will be on a particular loco model. HEP cooling systems use fans powered by the 480 VAC 60 Hz HEP supply so have special wound motors to handle that power supply.
Since the SD60, EMD fan motors have been wound to have two speeds, full and one-half so they can be operated at slow speed to reduce fan power and more tightly regulate cooling water temperature.
The SD70ACe/M-2 introduced a new design fan that is 54" diameter so that only two are needed on a 4,300 HP loco. But the design is similar to the Q-fan with the motor on the discharge side. These fans also operate at a slower speed, 1,500 rpm full and about 1,000 rpm low speed to better optimize fuel economy.
All dynamic brake fans use a DC motor powered by tapping the grids, so as noted earlier, the DB fans spin proportional to grid power and also affected by air density. At altitude, the DB fan speed increases due the lesser air density. The DB fans can run up to about 2,000-2,100 rpm and are constructed with the DC motor on the inlet side so there are struts in close proximity to the blades that generate the siren sound. The larger fan used on radial grids, starting with the SD50, is 54" in diameter so the tip speed is higher making that even worse. A primary reason the DB was located in the rear of the SD80/90MAC and 70ACe/M-2 was to move the noisy fan away from the cab.
The exception to the DC dynamic brake fan is the DE/DM30AC locos for LIRR - those units use a 48" AC Q-fan to ventilate the grids in order to minimize noise on the platform as the train enters a station. Two of the same fans are used as cooling fans on those units and are powered off of the HEP system so they just have two discrete speeds, ~900 and ~1,800 rpm regardless of engine speed.
Dave
In 1980, EMD introduced the Q-fan accross the domestic model line in order to comply with the reduction in loco wayside noise required by EPA regulations and enforced by an FRA regulation. The prior fans had the motor supported on radial struts from the fan frame that were on the inlet side of the fan. This caused a siren effect that has been described in this thread. The Q-fan inverted the fan construction so that the motor support struts are located on the discharge side of the fan, which eliminates the siren effect and makes the fan noise more of a white noise. The Q-fan has 12 spots equally spaced on the fan hub where blades can be bolted but the motor is only powerful enough to handle 9 blades so no fans with more than 9 blades are used. EMD has made fans as low as 4 blades and uses as many blades as are required for a particular application, so unless you look, you don't know for sure how many blades will be on a particular loco model. HEP cooling systems use fans powered by the 480 VAC 60 Hz HEP supply so have special wound motors to handle that power supply.
Since the SD60, EMD fan motors have been wound to have two speeds, full and one-half so they can be operated at slow speed to reduce fan power and more tightly regulate cooling water temperature.
The SD70ACe/M-2 introduced a new design fan that is 54" diameter so that only two are needed on a 4,300 HP loco. But the design is similar to the Q-fan with the motor on the discharge side. These fans also operate at a slower speed, 1,500 rpm full and about 1,000 rpm low speed to better optimize fuel economy.
All dynamic brake fans use a DC motor powered by tapping the grids, so as noted earlier, the DB fans spin proportional to grid power and also affected by air density. At altitude, the DB fan speed increases due the lesser air density. The DB fans can run up to about 2,000-2,100 rpm and are constructed with the DC motor on the inlet side so there are struts in close proximity to the blades that generate the siren sound. The larger fan used on radial grids, starting with the SD50, is 54" in diameter so the tip speed is higher making that even worse. A primary reason the DB was located in the rear of the SD80/90MAC and 70ACe/M-2 was to move the noisy fan away from the cab.
The exception to the DC dynamic brake fan is the DE/DM30AC locos for LIRR - those units use a 48" AC Q-fan to ventilate the grids in order to minimize noise on the platform as the train enters a station. Two of the same fans are used as cooling fans on those units and are powered off of the HEP system so they just have two discrete speeds, ~900 and ~1,800 rpm regardless of engine speed.
Dave
