STIR PLATE FAN

the various techneques used to power a fan..i am using PWM just like servos but here is explainations.

Home Designed Stir Plates
Home built magnetic stirplates can be loosely lumped into three categories, LM317 regulator based, Rheostat base and model Train Transformer based. And although all three designs work, we discovered through experimentation that each suffers from one or more basic design flaw.

LM317 Voltage Regulator Based

These designs use a LM317 voltage regulator to vary the voltage supplied to the motor and the motor speeds up & slows down based on what you set the voltage to. Most home built stir plates are based on this design because it's cheap and easy to build. We have 3 issues with this design.

The stirplate won't self start at slow speeds and is easy to stall at slow speeds.
On the ones we build, only about 2/3 of the adjustment range was useable - the lower 1/3 of the speed setting would not even spin the motor.
The LM317 regulator can produce a lot of heat, so much that you will need a heat sink inside the stir plate box & the last thing you need is an additional head source sitting under your yeast culture.

Rheostat Based

These designs use a rheostat, basically a large variable resistor, to vary the motor speed. These designs are also extremely simple to build - you just wire the rheostat in series with the motor. Of all the designs we tested, this one seemed the least reliable.

Just like the LM317 regulator design, the rheostat based design won't self start at slow speeds and is easy to stall at slow speeds.
Only about 1/2 of the adjustment range is useable - the lower 1/2 of the speed setting won't even spin the motor.
The one we tried seemed to stall at slow speed after the yeast culture ran for a while.

Model Train Transformer Based

These designs use a model train transformer to supply power to the motor and the varying the voltage changes the motor speed. These actually make decent stirplate power supplies, assuming you to have a train transformer laying around somewhere. The other advantage is that any heat generated is outside and away from the box - the transformer gets hot, not the box.

Just like the LM317 design, the train transformer based design won't self start at slow speeds and is easy to stall at slow speeds.
Only about 2/3 of the adjustment range is useable - the lower 1/3 of the speed setting won't even spin the motor.

Our overall observations? None of these designs start well at slow speeds and all stall at slow speeds, the speed you need to run at to grow your yeast culture. A PWM based unit does not exhibit these symptoms because a PWM regulated motor still has its full starting torque even at slow speeds. This is why we chose a PWM design even though we could have designed a stirplate around any of these other technologies for less money.

Now here is PWM much like servos in the RC industry and ESC's I do have several plans here at the store or i could e-mail them to anyone that wants them....i can also make them for someone.....the parts are cheap. about $6 and easy to solder up on a board..


PWM Technology - PWM (Pulse Width Modulation) technology is a better solution than a regulator based controller - PWM allows better motor speed control with less wasted energy. This means no heat from the box that could raise your yeast culture temperature higher than expected. PWM also translates into better speed regulation and a product that starts better and is less likely to stall at slow speeds.

Low Power Consumption - PWM also means less power consumption. Regulator based designs waste a lot of energy - if the speed control set to half, 1/2 the energy is used to drive the motor while 1/2 the energy is turned into waste heat. And if the speed control set to one quarter, 1/4 the energy is used to drive the motor while 3/4 the energy is turned into waste heat. With a PWM system, power is fed to the motor in varying widths of full-on - full-off pulses. For 1/2 speed, the pulses are 1/2 on & 1/2 off. For quarter speed, the pulses are 1/4 on & 3/4 off. And because power is always all the way on or all the way off with PWM, there is no waste heat.
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i had 3 fans given to me, they are identical to the fan i used for my stir plate. Jeff k. has spoken for one, Tyler spoke for the other. so there is one left at Jeff’s store, first come first serve. i gave him some earth magnets as well. and to save money on an ac/dc adaptor for a plug in, go to seeds of hope they have a hundred of them for 1 dollar each! they had other electronic stuff too didn’t look to hard but you may find your rheostat or potentiometer there too.