What happened to my stirplate?

[kanzimonson]

I had a DIY stirplate that wasn't great, but it worked. Now I seem to be having problems with the magnets' polarity matching up. Am I imagining things?

It used to be that the stir bar and the magnet would line up perfectly, now they're a little off-set. I can't even start the stirplate because the bar instantly gets thrown.

I'm pulling my hair out over this.

 

[TANSTAAFB]

did you epoxy the magnet down or can you adjust it? I have to make minor adjustments to my DIY plate just about every brew. I epoxied the washer but not the magnet and have to f%#k with it for a few minutes moving the magnet mm at a time till it is quiet and doesn't walk across the counter

 

[bovineblitz]

Try doubling up on the magnets, place additional ones on top

 

[kanzimonson]

I did glue it down so it hasn't shifted since I made it.

I really hate my stirplate... every single starter I have to play with the adjustable voltage, then adjust the potentiometer, and even still I'll come back and it will have stopped or thrown the stirbar.

I'm seriously thinking of just spending the $100 for a premade.

 

[KCBrewer]

Why spend $100 when you could just buy this lab quality one for $29.99 shipped?

http://cgi.ebay.com/VWR-Model-200-M...644?pt=LH_DefaultDomain_0&hash=item1c19ce9a74

I just had the same one given to me by a friend that works in a lab so I searched for one to see what they cost. Couldn't believe they could be had that cheap for professional stuff, not the cheap stuff most HBS sell.

 

[bovineblitz]

Idk man it shouldn't be that hard to get it to work. I made mine from nothing but 2 hard drive magnets, a small cardboard box, a 5 volt cell phone charger, 4 screws, and a computer case fan, I didn't pay a dime for it. Just snapped the blades off the fan, placed the screws in the corners of the fan to hold the top of the box/flask up, glued the fan inside the box, threw the magnets on the fan, and wired up the fan covering the connections with electrical tape.

I had issues getting it adjusted at first, it worked but I had to use a very small stir bar (an x shaped one worked best)... but then I added a second magnet and can now use up to a 1 inch bar. I never adjusted the voltage or anything.

Before giving up, try doubling up the magnets and even possibly trading out the multiple magnets for a hard drive magnet or possibly two stacked. It sounds like you have it all figured out, it's just the magnets are giving you problems.

 

[kanzimonson]

I'll work on some of this. I am using a hard drive magnet right now, and I do have another one.

Ever since I built this thing, I've always had to give it a jump start to get it going. So for example, I'll make a 2L starter, set the 12V adapter to 7.5V, set the potentiometer to about halfway, and then I'll have to reach under the plexiglass surface with a knife and use the knife to get it spinning. I have to do this every time.

If I set it to a speed that's high enough it can start by itself, it instantly throws the stirbar. I've been fighting friction and speed ever since I built it. HATE!

 

[FishFace]

Does the stirbar stick to both poles of the magnet. Does it lie flat or stand on end. You should be able to put stirbar right on magnet, start the thing up. If it flies of, not enough gauss (magnetic pull). The more material between magnet and bar, the harder it can be.

Are you using the same stir bar. Different stirbars will react differently. I have to use some spacers on my DIY plate to use some of the larger ones. The pull is so strong it won't spin(too much friction).

Good Luck

 

[FishFace]

Spacer after reading again. Friction is killing your spin. Stack stuff, so you have a 1/4 gap or 1/2.

I have the same problem with my larger stirbars. Either try a smaller one, or use spacers.

 

[kanzimonson]

I'm using a 2" stirbar so maybe that's it. I just assumed bigger was better because it'd have more magnetic attraction.

I think I need to get a new fan - this one just isn't powerful enough, hence the jumpstart every time.

 

[bovineblitz]

I had a lot of issues with large stirbars

 

[Catt22]

I've had zero issues using the larger 2" stir bars. The key is to use strong, well aligned and balanced magnets. There should be almost no vibration detectable when running the fan at high speed with no load (ie without a flask and stir bar in place). Wobbble or excessive vibration at high rpm's is indicative of balance problems and will usually result in a thrown stir bar.

 

[TANSTAAFB]

Had no problem with my 1" bar for months. Upgraded to a 2000ml flask, figured I needed to upgrade to a 2" bar as well...no go. Threw the bar at more than the lowest speed. Went back to the 1" stir bar and I got a full on vortex immediately!!! Bigger is not always better...

 

[Catt22]

Had no problem with my 1" bar for months. Upgraded to a 2000ml flask, figured I needed to upgrade to a 2" bar as well...no go. Threw the bar at more than the lowest speed. Went back to the 1" stir bar and I got a full on vortex immediately!!! Bigger is not always better...

I disagree. IMO, bigger is better in this case. Also, slowly stirring the starter will be less damaging to the yeast than thrashing the hell out of the little critters with a "full on vortex". A well designed and properly constructed stir plate should have no problem handling a 2" stir bar at any reasonable speed. Mostly, from what I have seen, stirring at high speed on a DIY stir plate using the tiny stir bars is done because they can't be run at lower speeds for whatever reason. IOW, there is usually no alternative.