25 or 100ohm rheostats?

[JFettig]

i almost bought some rheostats the other day, then i thought id check some sites... and i came up with a few diffrent things,
iv only seen and heard of people using 25 and 100 ohm rheostats and i dont know what ones to buy,
id like your input.
and how much of a diffrence is it from 25 - 100?


thnx

[Diggrr]

I used a 35 ohm 5 watt resistor on my Panflo 120mm L1A (quietest one). A 25 ohm resistor/rheostat wouldn't slow it down enough.

You'll want at least a 5 watt rating on the rheostat for a single large fan, 10 watt if you plan on adding more than one fan per rheo.

[Veland]

I've used a 20ohm 5W reo to control a standard 80mm fan. It would then go from 12V to about 8-9V So I wired a switch to get 7V and the reo could then reduce that to about 5V. I don't remeber the exacte numbers, it's a while ago..

[Hoot]

The more current a fan or combination of fans draw, the less resistance it will take to slow it (them) down. I have found that 25 ohm rheostats are more than adequate for speed control. If you use a rheostat with a single fan that draws a small amount of current, you may need more resistance and a 35, 50, or 100 Ohm rheostat will work fine. You can connect the two end taps of a 100 ohm to get a 50 ohm yield, with the center of the rotation representing the greatest resistance. Then, turning the shaft either side of center will result in higher speed. It also helps distribute the wattage over the entire resistive winding area. Many moderate to large metropolitan area have Electronic Surplus stores where you can rummage about and get nice, high wattage rheostats for pennies on the dollar. We are fortunate to have three of these in the Twin Cities area. Some have boxes full of new and pulled rheostats for very good prices.

73, Hoot

[el]

ne body know of a place near DC that has a surplus electronics outlet?

here is a link to the fanbus tutorial. http://www.fanbus.com/thelab/rheostat.htm

[JFettig]

thanx i can only find 25ohm rheostats at radioshack...is there any ware else that i can get them?

[el]

I like Jameco.com

[Hoot]

I went to the Electronics Surplus store today and picked some up that I will pass along at my cost. See add in Cooling Parts Classified or PM me.

73, Hoot