Hello: Kid has me building a "snow-machine" for a school play, it will blow white confetti out of several pvc tubes, However......... it is about twice as strong as we need for a realistic effect, we used a standard 2 terminal 12 volt auto heater/defroster blower fan, Any ideas what size resistor paralelled in the hot lead might cut the power/speed to about half??? Thank you & Happy Holidays!!! J.
A resistor will probably dissipate a lot of heat. Here are two other ways to do it that avoid the problem..
1) Try a 6V battery if you can find one.or
2) If the motor has a rating label that gives you the wattage (eg 100W) try connecting car headlamp or other bulbs with a similar rating in series with the motor. Bulbs of the right size are likely to be easier to get than resistors and you might even have spares in your car. The bulb will get hot so you need to take car. Mount it in the airflow?
Make the tubes twice their diameter, or cut some holes with a sliding collar to get the required pressure.
The resistor will have to be a very high wattage one, and it is connected in SERIES, not parallel to drop the current through the motor. The value of the resistor would be hard to calculate, because the torque of the motor would be reduced, and the mechanical load may not be constant all the time.
You need to lower the voltage, not put a series resistor. See if you can get a varible supply, or see if you can have a 6 Volt source for it. This should drop the speed.
Or use an AC fan. These mostly all come with a speed control. You can get a big floor fan, and just throw the confetti in front of it. In the TV studio we use about 6 to 10 of these fans when we do the stage shows that need confetti. We get a bunch of people to throw the stuff in front of the fans, and it goes all over the place! If we want to have the look of snow, we throw the white stuff from up in the lighting grid.
In the black and white days when I was starting out, when we wanted the look of snow, we used to use cornflakes. It was funny. The stage hands were eating the cornflakes while throwing them down to the floor to make the snow. Occasionaly the people on the set would grab some and start eating them when they were off camera. With colour TV, and the quality of TV today, cornflakes would not look very good for snow. For large flakes we used to use popcorn. The actors were sweating under the hot lights in the studio, because they had to be dressed like out in the winter.
Yea... I am getting on in years.
Jerry Greenberg
-- LotsaWatts@webtv.net (L W) wrote in message news:... > Hello: > Kid has me building a "snow-machine" for a school play, it will blow > white confetti out of several pvc tubes, However......... it is about > twice as strong as we need for a realistic effect, we used a standard 2 > terminal 12 volt auto heater/defroster blower fan, Any ideas what size > resistor paralelled in the hot lead might cut the power/speed to about > half??? > Thank you & Happy Holidays!!! > J.
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