Look around the net and you'll find plans for hundreds of
magnetic stir plate plans, from units stuffed in cheap plastic food
containers to others built in extravagant cabinets. You can also
find low cost stirplates for sale on the net very cheap, less than
$50.00 cheap! But look a little closer and you'll discover that all
of these are based on someone's "home built project". Now, I'm the
first to say "save money wherever you can" and the homebrew
community can get quite creative when it comes to saving a few
dollars. But, why buy someone else's home built project when you can
build your own?
You won't see ours for sale for $50.00! But why are our magnetic
stir plates more expensive than those cheap ones you see on the net?
The greatest cost difference between our unit and the theirs is the
commercial quality housings we chose for ours. The housings we use
are sturdy enough to support any size starter you dare place on our
stirplate! The next greatest cost difference is the PWM circuit we
designed and produce ourselves. PWM provides superior speed
regulation over any other circuit, even a speed controller based on
a LM317 regulator.
Also, a note on warranties. There is no such thing as a
lifetime warranty. A company who offers a lifetime warranty is
doing so for marketing purposes. They understand that once a
product gets through it's early life failure stage they will see
very few failures and even less returns. And the "lifetime
warranties" offered by individuals? Those are usually only good
until the individual has decided to move on to something else -
usually in one to three years.
Our units ship with a 1 year, 3 month warranty against
workmanship defects and the warranty extends from the
manufacture date of the product. This loosely translates into a
1 year warranty with up to 3 months buffer for time the stir
plate to sit on our shelves or our distributor's shelves. Why
did we settle on this time period? Because we understand that
almost all consumer products fail during the first three months
and after that period, most customers will enjoy many years of
trouble free service from their stirplate. In other words, a one
year warranty will cover any failure that may be our fault.
Now, watch us on
YouTube!
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.
And What Did We Do Different with our design?
Our magnetic stirplates feature:
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.
External DC Power Supply Included - By using a UL
approved external plug-in DC power supply, we moved one more
potential source of heat away from your yeast starter. This also
makes the power supply user replaceable in the unlikely case
that it should fail.
Professionally Designed - All of our controller cards
are professionally designed using state of the art PCB design
and layout software.
Professionally Manufactured - Built on commercial
quality double sided 0.062" FR4 PCB's with 1 ounce copper and
full solder mask on both sides. The same quality construction
you will find in any high-end electronics equipment. 100% Tested
Product with a 10% sample subjected to a 24 hour run-in. As of
12/18/09, we've had zero run-in test failures. All of our units
are tested with 2000 ML Borosilicate Glass Erlenmeyer Flasks of
water before shipping.
Tough, High Impact Polystyrene Housing - No cheap
Radio Shack project box or food container here. We designed our
stir plate to fit inside a commercial quality polystyrene
housing that's strong enough to support any flask that will sit
on the box.
Designed around Neodymium Rare Earth Magnets - No used
or surplus hard drive magnets are used in our designs!
All stir plates include two correctly sized stir bars.
Some competitors ship with one & some competitors ship with
none. You need two stir bars, one to hold against the outside of
the flask to hold the inside stir bar in place while pouring out
your starter.
Bright, large power indicator - We did not skimp on
the power-on light - large and bright enough to see from across
the room.
Linear speed Control & Control Range that you can Use
- We designed the speed control in such a way that the entire
adjustment range is useable. Most home built projects are set-up
so that only 1/2 to 2/3 of the adjustment range is useable. Our
design gives the user full adjustment range for increased
sensitivity. Note: Even with our adjustment range, some settings
will be too fast or too slow for some starters.
