Tight Arse Stir Plate

[merrick]

Hi All,

Catastrophe! Made my stir plate a couple of years with the same rare earth magnets used by Jye and Ross. Works brilliantly. Problem is the stir bar magnet has gone walkabout and I'm stuffed without it. I originally bought the magnets from Jaycar but they no longer stock this type.


View attachment 36795

Can anybody help with a replacement or point me in the right direction? Many thanks.

Merrick

Managed to find my magnets at Jaycar, Brookvale. They were described as 'Rattlesnake Sound Eggs' and found amongst the toys. Still had a few packets in stock at $4.99. They work brilliantly in a stir plate as one magnet becomes the stir bar while the other is glued to the motor.

Just thought I'd pass on the info.

Merrick

 

[Elbow]

Alrighty then,

Just assembling a few bits and bobs salvaged from work:

1 x 12v computer fan
1 x power supply 9v
1 x HDD rare earth magnet

Although I've read all the pages, brain bad and can't remember stuff good no more.

So, a couple of questions:

1. I've got the fan spinning no problem connected to a 9v p/s (i got a small paperclip spinning and vortexing inside a coffee plunger jar). I can probably get a 12v p/s if need be. Should I use this instead?
2. Do I need more than one rare earth hdd magnet? I've extracted one ok (minus a bit of the metallic covering), the other one I managed to break in half. I can probably get more.

Cheers

 

[leiothrix]

HD magnets tend to be a bit crap.

I got some from aussiemagnets, pretty sure they're 20x5mm. I got a couple of different sizes and had a play.

For the power - get a 12V power supply and a PWM controller for it. PWM gives the fan full power, it just turns it on and off really quick to vary the speed.

If you use a linear speed controller (i.e. reducing the voltage) it means that the motor will spin slower, but will have absolutely no torque at the same time.

Rob.

 

[Wolfy]

1. I've got the fan spinning no problem connected to a 9v p/s (i got a small paperclip spinning and vortexing inside a coffee plunger jar). I can probably get a 12v p/s if need be. Should I use this instead?
2. Do I need more than one rare earth hdd magnet? I've extracted one ok (minus a bit of the metallic covering), the other one I managed to break in half. I can probably get more.

If 9V is sufficient to turn your fan when you're using it as a stir-plate then thats all you need, but you'll need to test it and see how it goes.
You only need 1 HDD magnet, using 2 will not help. Again test it and see how you go, my first stir-plate used a HDD magnet, but now I find the small round magnets easier and better to use.

 

[BjornJ]

Hi,
my homemade stir plate burns out, is that common?

The potentiometer seems to actually burn out with use.
After a while I had to turn it more and more "on" to get the fan spinning.
Eventually I noticed a burning smell and opened the project box (after working for several days).
Inside the potentiometer there was an orange spark like if the resistance or whatever is in there to reduce the voltage was being burned by the power supply.

I went back to Jaycar and asked for some help. The guy I talked with said I probably had a too weak potentiometer and gave me what I think was called a 1M strenght one.
Came home, replaced the potentiometer and straight away the same thing happened.
A slight smell of electics burning (not what I want on at night..) and a spark in the potentiometer.
So I turned it off and haven't looked at it since.

Is there a way to fix this?
Can it be the power supply is too powerful?
Can't remember what electric appliance I cut it from, but it is a "normal" small one, a little square thing that consists of a plug that sits in the power socket, not like a laptop power supply where you have a bigger "box" and I assume higher output.
It is definetly 12V but can't remember the Amp.

Would it help if I go back to Jaycar and ask about the pulse somethingorother changer in stead like mentioned here on the thread? The guy said this was another way of controlling the fan speed, and maybe this would mean no sparks

Any advice will be appreciated,

thanks
Bjorn

 

[leiothrix]

You need a speed controller of some sort. The easiest way of doing it is with a linear voltage regulator. That may work, but the fan will have stuff all torque, esp at lower speeds.

PWM is better because you still get some torque at lower speeds, but is a bit more complicated to make. You can also get fan speed controllers made for controlling fans in a computer.

Since you're using a computer fan, i'd imagine that would be perfect

Rob.

 

[crozdog]

Bjorn, read back through this thread - as it contains several circuits to do what you need

See you on Sat, Croz.

Hi,
my homemade stir plate burns out, is that common?

The potentiometer seems to actually burn out with use.
After a while I had to turn it more and more "on" to get the fan spinning.
Eventually I noticed a burning smell and opened the project box (after working for several days).
Inside the potentiometer there was an orange spark like if the resistance or whatever is in there to reduce the voltage was being burned by the power supply.

I went back to Jaycar and asked for some help. The guy I talked with said I probably had a too weak potentiometer and gave me what I think was called a 1M strenght one.
Came home, replaced the potentiometer and straight away the same thing happened.
A slight smell of electics burning (not what I want on at night..) and a spark in the potentiometer.
So I turned it off and haven't looked at it since.

Is there a way to fix this?
Can it be the power supply is too powerful?
Can't remember what electric appliance I cut it from, but it is a "normal" small one, a little square thing that consists of a plug that sits in the power socket, not like a laptop power supply where you have a bigger "box" and I assume higher output.
It is definetly 12V but can't remember the Amp.

Would it help if I go back to Jaycar and ask about the pulse somethingorother changer in stead like mentioned here on the thread? The guy said this was another way of controlling the fan speed, and maybe this would mean no sparks

Any advice will be appreciated,

thanks
Bjorn

 

[BjornJ]

thanks, will look it up at Jaycar.

Bjorn

 

[haysie]

Bjorn, read back through this thread - as it contains several circuits to do what you need

See you on Sat, Croz.

When you read all 607 posts, Bjorn please add you knowledge.

 

[crozdog]

When you read all 607 posts, Bjorn please add you knowledge.

start with LC's post #422 here http://www.aussiehomebrewer.com/forum//ind...5191&st=420

 

[Elbow]

updated diagram to make it a bit neater and include the new values.
Jaycar parts:
LM317T - ZV1615
5k linear pot - RP3508 or RP7508
knob to suit - pick one. HK7707
680ohm resistor - RR0568
switch - pick one. ST0355
10u cap - RE6070
100n cap - RC5360

I got all the parts as listed above. I got a mate to wire and solder it up as per the diagram. It turns on fine, but the speed does not deviate at all, slow or fast. Any ideas?

 

[MaestroMatt]

I got all the parts as listed above. I got a mate to wire and solder it up as per the diagram. It turns on fine, but the speed does not deviate at all, slow or fast. Any ideas?

This happened to me at first as well......check to see if the wiring to the pot is going into the center connection and one of the outside connections.......if they are going into both outside connections then it is effectively bypassing the pot - you'll only get one speed....on

 

[Elbow]

No It was definitely a centre and a side one. Maybe it's the Pot. Might take it back to Jaycar.

 

[BjornJ]

start with LC's post #422 here http://www.aussiehomebrewer.com/forum//ind...5191&st=420

Crozdog,
thanks for the link.
That looks a bit complicated for me :lol:

Maybe I will have to take Barls up on the offer of giving it to him and he will get someone at work to have a look at it. It seems my version without the resistors or whatever it is on the curcuit is giving the potentiometer too much power for its own good.

thanks
Bjorn

 

[Elbow]

This happened to me at first as well......check to see if the wiring to the pot is going into the center connection and one of the outside connections.......if they are going into both outside connections then it is effectively bypassing the pot - you'll only get one speed....on

I think it's now the LM317T thingo. I got a voltage metre on the two outside pins of the LM317T and they are going up and down as the pot is turned, but the centre output is staying constant.

I'll grab another one from JC tomorrow and have another crack.

 

[leiothrix]

That's pretty much what the LM317T is supposed to do. It is an adjustable voltage regulator. Basically you have in, out and ground/adjust.

Rob.

 

[LethalCorpse]

If you're measuring between the left pin and the centre, it's supposed to stay constant, at 1.25V. To measure the output voltage, you put the black probe of the meter on the negative wire from the power supply, and the red probe on the centre pin of the LM317.

not sure why you're getting no speed change, perhaps the fan is connected to the input instead of the output. Can't diagnose anything without photos, though - take lots of photos with a decent camera (ie, not your phone camera). Then pick the ones which best show the overall circuit and what's connected where and post them here. We should be able to see what's gone wrong.

 

[Elbow]

If you're measuring between the left pin and the centre, it's supposed to stay constant, at 1.25V. To measure the output voltage, you put the black probe of the meter on the negative wire from the power supply, and the red probe on the centre pin of the LM317.

not sure why you're getting no speed change, perhaps the fan is connected to the input instead of the output. Can't diagnose anything without photos, though - take lots of photos with a decent camera (ie, not your phone camera). Then pick the ones which best show the overall circuit and what's connected where and post them here. We should be able to see what's gone wrong.

I did the voltage thing again and it seemed to fluctuate a fair bit and closer to 2.5v. Apologies for the piss poor soldering job and mess of tangled wires shown.



The black wire on the left is the negative for the power supply




If I can't figure it out, i'll start again and hand over to a sparky who knows what they are doing. In the words of Homer "if it first you don't succeed, destroy all evidence you ever tried!"

 

[LethalCorpse]

You've got the fan backwards - swap the red and black wires. Also, with the switch turned off, check the polarity of your power supply wires. Red probe on the wire at the switch, black probe on the other wire. If it reads a negative voltage, you've got them backwards too. This would make sense - you said the fan is spinning, which it would not do if the supply wires were right, but the fan wires were backwards. This will also mean your lm317 has blown up. While you're at jaycar buying a new one, buy some veroboard and get them to show you how to use it.

 

[Elbow]

:icon_cheers: Now were talking!

Got another LM317T and some veroboard and I started again. When I say "I", I actually mean the 2 guys I work with who kindly agreed to wire it up for me. When I say "kindly agreed", I actually mean I locked them in a cell with no food and water until they fixed it.....thanks guys!

Works a treat this time, got it housed in cast off plastic box that was going to get scrapped. I've got my flask today, so I'm gonna fire that sucker up shortly and see how she goes. I'll post some photos to.

Thanks to Lethal and everyone else for input and advice. :chug: