12 volt Fan help needed

[L W]

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.

 

[CWatters]

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?





"L W" <LotsaWatts@webtv.net> wrote in message
news:6416-3FD1876B-145@storefull-2237.public.lawson.webtv.net...

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.

 

[Mark]

"L W" <LotsaWatts@webtv.net> wrote in message
news:6416-3FD1876B-145@storefull-2237.public.lawson.webtv.net...

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.

Make the tubes twice their diameter, or cut some holes with a sliding collar

to get the required pressure.

 

[Jerry Greenberg]

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:<6416-3FD1876B-145@storefull-2237.public.lawson.webtv.net>...

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.