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.
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.
6/10/2010 - We just finished the design for our latest stir plate and this one has no problem spinning 5 liter and larger starters. The new stir plate is built in a larger high impact high strength polystyrene plastic housing to give a more stable base for larger starters while retaining the ability to spin smaller starters. At the same time we are designed a better stir plate controller. Our new stir plate - Stir-Plate 3000 measures 8" across by 7" front to back and features a much higher torque motor and stronger rare earth magnets.
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.