Questions and Answers
Does your product come with a warranty?
Our stir plates 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.
The warranty does not extent to the stir bars themselves as we are not in
control of how you handle your stir bars. Something as simple as dropping a
stir bar on the floor can reduce it's magnetism enough to cause issues.
- Does your stir plate have a weight limit?
Our stir plate housings are made of high impact high strength polystyrene
plastic and there is no known weight limit. I've actually stood on one of
the assembled housings we use to see if it would hold up to my weight and it
did.
Does your stir plate have a size limit?
We have set-up a starter in a 5 liter flask just to see what would
happen and the starter spun fine, even though the 5 liter flask overlapped the sides
of the stir plate by quite a bit. And even though the flask seemed to sit on
the plate fine, the overlap worried me. I would not recommend trying a larger
container without coming up with some type of outside support.
We are designing a stir plate for 5 liter and larger starters. The new
stir plate will be based on a larger high impact high strength polystyrene
plastic housing to give a more stable base for larger starters while still
being able to spin smaller starters. At the same time we are designing a
better stir plate controller. There is nothing wrong with our existing
controller but there is also nothing wrong with continuously improving
either. We have
a prototype running but we aren't happy with it yet.
Do your stirplates come with Speedsafe?
Speedsafe is a term used by a competitor to show that their stir plates
will not over-rev and destroy themselves. Although we can't use their term
in our product, our stir plates are also RPM limited and will not over-rev
and it is perfectly safe to remove a flask from one of our stir plates, even
at full RPM.
Does your stirplate make noise?
All stir plates make noise depending on the RPM you run them at, the type
of stir bar you choose, the type of flask or jar you use and how well the
flask is centered on the stir plate. The noise is caused by the stir bar
wobbling inside the flask. The noise can also be caused by a stir bar that's
too long. Our stir plate is no exception, but we carefully chose the correct
length stir bar and other components to minimize this effect.
Our stir plate does make a humming noise that you can hear when you don't
have a stirbar spinning. It's inherent in the design of a PWM stirplate. But
we chose a PWM frequency and components to minimize the hum and the volume
is low enough that you can't hear it over the stir bar.
I built a stir plate using one of the LM317 regulator plans on the net.
The stir plate spins the stir bar fine at slow speeds but when I try to speed it
up the stir bar throws off every time. Did I do something wrong?
Probably not - there are issues with the simple LM-317 design that's
floating around the net. The biggest issue is that at anything remotely approaching full
speed, the motor is spinning way too fast. A LM-317 regulator based design
will work but you need to build a smarter regulator circuit that limits the voltage to the
motor to about 6 VDC. Also, no-one discusses magnet spacing in detail and
the type of magnets you really need to be using. One of the worse magnets to
use is a used hard drive magnet because a used hard drive magnet does not
provide the two concentrated magnetic poles you need to keep the stir bar
captured at all speeds. To keep your stir bar captured at all speeds, you
need two opposing magnets with a flux density of at least 2500 Gauss, the
poles must be under or just outside the ends of the stir bar and the magnets
need to be very close to the ends of the stir bar.
Note: Some people try to play down these design flaws by stating
something like "you don't need to spin your stir plate at high speed
anyway, just a dimple on top will do". This does little to explain away
an obvious defect in their design!
Not seeing your stir plate I really cant tell what's going on but maybe I
can help anyway.
I'd suggest placing the stir bar in a flask full of water and then lower
the flask towards the top of the stir plate. If the magnets don't grab onto
and center the stir bar within 1/4" of the top of your stir plate with
some force then I can
say for certain that your magnets are mounted too far from the top of the
box or they are not strong enough.
If the magnets do center but you can't run full speed then start slow and slowly
turn the speed up. If you can generate a vortex that reaches at least 1/2
way down the flask but the stir bar is thrown at faster speeds then the regulator is driving
the motor too fast.
If you can't generate much of a vortex before throwing the stir bar then
it's a magnet problem. The drive magnets aren't strong enough, you are using
a used hard drive magnet, the spacing
isn't correct (this could be center to center spacing or distance from the
top of the box) or the stir bar is bad (not likely).
With any well designed stir plate, you should be able to place your flask
on the box, set the speed to high and turn the stir plate on. The stir plate
should spin up to full speed and pull a strong vortex without throwing the
stir bar.
| 
